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1.
Growth of Escherichia coli in Model Distribution System Biofilms Exposed to Hypochlorous Acid or Monochloramine 总被引:2,自引:0,他引:2
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Bacteria indigenous to water distribution systems were used to grow multispecies biofilms within continuous-flow slide chambers. Six flow chambers were also inoculated with an Escherichia coli isolate obtained from potable water. The effect of disinfectants on bacterial populations was determined after exposure of established biofilms to 1 ppm of hypochlorous acid (ClOH) for 67 min or 4 ppm of monochloramine (NH2Cl) for 155 min. To test the ability of bacterial populations to initiate biofilm formation in the presence of disinfectants, we assessed the biofilms after 2 weeks of exposure to residual concentrations of 0.2 ppm of ClOH or 4 ppm of NH2Cl. Lastly, to determine the effect of recommended residual concentrations on newly established biofilms, we treated systems with 0.2 ppm of ClOH after 5 days of growth in the absence of disinfectant. Whole-cell in situ hybridizations using fluorescently tagged, 16S rRNA-targeted oligonucleotide probes performed on cryosectioned biofilms permitted the direct observation of metabolically active bacterial populations, including certain phylogenetic groups and species. The results of these studies confirmed the resistance of established bacterial biofilms to treatment with recommended levels of disinfectants. Specifically, Legionella pneumophila, E. coli, and β and δ proteobacteria were identified within biofilms both before and after treatment. Furthermore, although it was undetected using routine monitoring techniques, the observation of rRNA-containing E. coli within biofilms demonstrated not only survival but also metabolic activity of this organism within the model distribution systems. The persistence of diverse bacterial species within disinfectant-treated biofilms suggests that current testing practices underestimate the risk to immunocompromised individuals of contracting waterborne disease. 相似文献
2.
Incubation of excised cucumber cotyledons (Cucumis sativus L.) with NH4Cl solutions exceeding 0.001 M inhibited their greening, fresh weight increases, and incorporation of 14C-leucine into insoluble N compounds. The absorption of 14C-leucine during incubation and retention of moisture by the excised cotyledons after incubation were greatly diminished by the NH4Cl treatments. Treatment with KCl solutions of the same concentrations as the NH4Cl stimulated the greening, fresh weight increases, and the absorption and incorporation of 14C-leucine. Desiccation of cotyledons stored at 5°C for 10 days was inhibited by dilute KCl solutions. The toxicity of NH4Cl was alleviated by KCl solutions at low concentrations. 相似文献
3.
A simulation model was developed for the carbon (C), nitrogen (N), and phosphorus (P) content of bacteria and their medium in a chemostat. Cell components distinguished included the structural component, synthetic machinery, building blocks and intermediates, C reserves, ammonium (NH4), orthophosphate (PO4), and polyphosphate. Growth, incorporation of substrates, and production of waste products were related to physiological status, as indicated by the amounts of various cell components. The model was fitted to data from chemostats on the chemical composition of bacteria growing in C-, N-, and P-limiting media and was used to explore the consequences of predation on bacterial populations. In C-limiting media predation (without the return of nutrients to the medium by the predator) increased NH4 uptake in spite of a decrease in bacterial biomass. In N-limiting media predation decreased both biomass and the rate of N uptake. These results were accounted for by the effect of growth rate on bacterial N demand. In C-limiting media the return of NH4 and PO4 by the predator did not change the effect of predation on bacteria. But in N-limiting media the return of nutrients decreased the effect of predation on biomass, and stimulated respiration and NH4 uptake by the bacteria. The effect of growth rate on the chemical composition of bacteria was proposed as a possible explanation of the stimulatory effect of predators on bacteria. 相似文献
4.
Ammonium influence on nitrogen assimilating enzymes and protein accumulation in suspension cultures of Paul's Scarlet rose 总被引:2,自引:0,他引:2
The influence of NH4+ on protein accumulation was examined by growing suspension cultures of Rosa cv. Paul's Scarlet on two defined media. Both contained 1920 μmol of NO3? but only one contained 72.8 μmol of NH4+. At the conclusion of a 14-day growth period, cultures grown with NH4+ possessed twice as much protein as cultures grown without NH4+. The influence of NH4+ did not appear to be a substrate effect, since the amount of NH4+ provided accounted for only 10% of the nitrogen recovered in protein. The provision of NH4+ in the starting medium increased the activity (μmol substrate. h?1· g?1 fr wt) of glutamate dehydrogenase and glutamate synthase, and reduced the activity of glutamine synthetase. A comparison of the total activity per culture for each of these enzymes with the rate of nitrogen incorporation into protein showed that the enzymatic potential of glutamine synthetase and glutamate dehydrogenase greatly exceeded the actual in vivo rate of nitrogen assimilation through the respective pathways. Thus it was concluded that the availability of either of these enzymes does not limit nitrogen assimilation in rose cells and the fluctuations in their level brought about by NH4+ was of no physiological importance. The activity of glutamate synthase per culture approximated the rate of nitrogen incorporation into protein during early stages of growth, and for that reason may have limited nitrogen assimilation or caused a diversion of nitrogen through the alternative pathway to glutamate catalyzed by glutamate dehydrogenase. 相似文献
5.
Co-regulation of root hair tip growth by ROP GTPases and nitrogen source modulated pH fluctuations 总被引:1,自引:0,他引:1
Daria Bloch Gabriele Monshausen Simon Gilroy Shau Yalovsky 《Plant signaling & behavior》2011,6(3):426-429
Growth of plant cells involves tight regulation of the cytoskeleton and vesicle trafficking by processes including the action of the ROP small G proteins together with pH-modulated cell wall modifications. Yet, little is known on how these systems are coordinated. In a paper recently published in Plant Cell and Environment1 we show that ROPs/RACs function synergistically with NH4NO3-modulated pH fluctuations to regulate root hair growth. Root hairs expand exclusively at their apical end in a strictly polarized manner by a process known as tip growth. The highly polarized secretion at the apex is maintained by a complex network of factors including the spatial organization of the actin cytoskeleton, tip-focused ion gradients and by small G proteins. Expression of constitutively active ROP mutants disrupts polar growth, inducing the formation of swollen root hairs. Root hairs are also known to elongate in an oscillating manner, which is correlated with oscillatory H+ fluxes at the tip. Our analysis shows that root hair elongation in wild type plants and swelling in transgenic plants expressing a constitutively active ROP11 (rop11CA) is sensitive to the presence of NH4+ at concentrations higher than 1 mM and on NO3−. The NH4+ and NO3− ions did not affect the localization of ROP in the membrane but modulated pH fluctuations at the root hair tip. Actin organization and reactive oxygen species distribution were abnormal in rop11CA root hairs but were similar to wild-type root hairs when seedlings were grown on medium lacking NH4+ and/or NO3−. These observations suggest that the nitrogen source-modulated pH fluctuations may function synergistically with ROP regulated signaling during root hair tip growth. Interestingly, under certain growth conditions, expression of rop11CA suppressed ammonium toxicity, similar to auxin resistant mutants. In this short review we discuss these findings and their implications.Key words: ROP, RAC, nitrogen, root hair, cell polarity, ammoniumIn Arabidopsis, root hairs grow out at the basal, rootward region (closer to root tip) of specialized root epidermal cells and expand exclusively at their apical end in a strictly polarized manner by a process known as tip growth. Tip growth is facilitated by Rho of Plants (ROP)-regulated processes such as maintenance of longitudinally-oriented actin cables in the shank of the root hair that are required for myosin-mediated organelle transport through the cytoplasm. ROPs also play a role in sustaining fine F-actin structures at the root hair tip, which promote the transport of secretory vesicles to sites of their fusion with the plasma membrane.2,3 In addition, the polar growth of root hairs involves an oscillatory tip-focused Ca2+ gradient4 and tip-localized reactive oxygen species (ROS).5 Tip growth is also associated with oscillatory fluxes of H+ at the apex that correlate with the periodicity of growth.6,7 These oscillations in extracellular pH and ROS have been shown to modulate tip growth and are predicted to act in a coordinated and complementary mode to regulate root hair elongation. Growth accelerates following reduction of apoplastic pH and slows upon apoplastic ROS increase and a coincident pH increase.7ROPs are small G proteins that localize to the plasma membrane at the apex of growing root hairs, where they activate a range of downstream pathways required for tip growth.8,9 ROP activity is regulated by its cycling between a GTP-bound, active and GDP-bound, inactive state. Ectopic expression of constitutively active mutants of ROPs (dominant mutations in conserved residues that abolish the GTPase activity) depolarizes the growth of root hairs.8–10 Downstream pathways activated by such ROP GTPases include the regulation of cytoskeletal dynamics and vesicular trafficking, production of ROS, maintenance of intracellular Ca2+ gradients and accumulation of signaling lipids, features all related to the regulation of apical growth.11,12 For example, ectopic expression of constitutively active ROP11 (Atrop11CA) depolarizes root hair growth, leading to the formation of swollen root hairs. This bulging root hair phenotype was associated with altered actin organization and inhibition of endocytosis.10It is well known that root hair development is highly plastic and regulated by environmental signals.13,14 Yet, despite the known function of ROP GTPases and their regulatory proteins in root hair growth there is no data in the literature describing the relationship between ROP signaling and environmental factors in this process. Our results1 show that induction of root hair swelling by rop11CA occurs only under specific growth conditions, indicating that there is an interplay between ROP activity and the external environment, particularly nitrogen supply. We demonstrated that high external concentrations of ammonium are essential for the induction of depolarized root hair growth and activation of downstream pathways by rop11CA. Depletion of ammonium did not affect the membrane localization and expression of GFP-rop11CA, implying that NH4+ was required in addition to ROP activity to cause root hair swelling. In agreement with this idea, normal actin organization and ROS localization were detected in rop11CA root hairs when NH4+ was depleted, suggesting that ammonium functions downstream of, or in parallel to ROP signaling (Fig. 1).Open in a separate windowFigure 1A model for regulation of root hair tip growth by ROP GTPases and pH oscillations dependent on nitrogen supply. GTP bound ROPs activate downstream effectors which directly affect actin organization, vesicular trafficking and localized ROS production as well as indirectly affecting the localization of membrane proteins involved in ion/proton fluxes. High concentrations of nitrogen ions in the growth medium increase pH oscillations at the apex of growing root hairs. In turn downstream ROP effectors sense the changes in pH and adjust their function accordingly. pH oscillations affect tip growth independent of ROPs via changes of wall pH and possibly through additional unknown factors. Dashed lines indicate that these effects were not confirmed experimentally.Plants can absorb and use various forms of nitrogen from soils, primarily the inorganic ions ammonium and nitrate. The concentrations of these ions are highly heterogeneous around the plant and can vary across several orders of magnitude among different soils and as a result of seasonal changes.15 Thus, plants would be expected to display highly plastic, N-regulated developmental responses and to employ a range of nitrogen uptake transport systems to optimize exploitation of local N resources. Transport systems that mediate NH4 fluxes across the plasma membrane of root cells are divided into two categories: high affinity transport systems (HATS) that mediate uptake from relatively dilute solutions at relatively low rates and low affinity transport systems (LATS) that operate at high rates and higher external concentrations.16 The HATS are plasma membrane localized NH4+-specific transporters (AMTs) that are most likely proton-coupled and their expression and function are repressed at external ammonium concentrations of 1 mM or higher.17–19 In contrast, ammonium uptake by LATS is believed to take place through non-specific cation channels.17,20 The NH4+ concentration in the 0.5× Murashige Skoog (MS) medium is 10.3 mM, exceeding by an order of magnitude the concentration at which the high affinity NH4+ uptake system is repressed. The root hair swelling in Atrop11CA plants and inhibition of root hair elongation in wild type plants occurred primarily at external ammonium concentrations greater than 1 mM, and thus is most likely associated with uptake by the LATS.As noted above, root hair elongation is associated with oscillations of cytoplasmic and apoplastic pH that have been linked to growth control. Simultaneous fluorescence ratio imaging of internal and external pH revealed that application of 10 mM NH4NO3 enhanced the amplitude of these pH oscillations at the extreme apex of wild type root hairs1 and Figure 2. These oscillations are thought to modulate tip growth through altering the extensibility of the wall.4 Additional measurements (Fig. 2) show that similar to the effects of NH4NO3, addition of NH4Cl induced increase in the apoplastic pH fluctuations and reduced the pH. However, the effects of NH4Cl on cytoplasmic pH fluctuations seem subtler compared to the effects of NH4NO3. Thus, one possible explanation for the observed swelling of the root hair apex in rop11CA expressing plants in media containing NH4NO3 is that rop11CA root hairs are affected in their ability to re-establish the normal proton gradient across the plasma membrane in response to ammonium transport. The altered proton gradient would then prevent the normal localized oscillatory changes in pH-dependent wall properties required to restrict expansion to the very tip of the elongating root hair.Open in a separate windowFigure 2Changes in apoplastic and cytoplasmic pH fluctuations, following application of NH4NO3, NH4Cl or KNO3. (A) Apolplastic pH (pHex) following treatments with either NH4NO3, NH4Cl or KNO3. Note the increase pH fluctuations induced by either NH4NO3 and NH4Cl but not by KNO3. (B) Cytoplasmic pH (pHcyt) following treatments as above. Note the changes in pH fluctuations induced by NH4NO3 and the subtler effects of NH4Cl.Concurrent absorption of NH4+ and NO3−- maintains the cation-anion balance within both the rooting medium and the root, and thus potentially has an important function in maintaining intracellular and extracellular pH.21,22 In agreement, application of these ions affected the amplitude of pH oscillations1 and Figure 2. Interestingly, treatments of WT seedlings with 10 mM NH4NO3 causes increase in root hair pH oscillations and often tip bursting. Yet, prolonged exposure of WT root hairs to NH4NO3 is accompanied by adaptation (our unpublished data). This adaptation does not occur in rop11CA mutants, suggesting that cycling of ROPs between active and inactive states maybe important in adaptation to changing environment. These data strongly suggest that NH4+-dependent root hair swelling in the plants expressing activated ROP resulted from physiological changes in ion balance rather than a direct effect of ammonium on enzymatic activities required for root hair growth (Fig. 1). Application of NH4+ and NO3−, in the absence of other ions, induced formation of additional growth tips, in which the membrane localized GFP-rop11CA was concentrated. This observation suggests that interplay between the regulation of ROP localization and activity and the regulation of nitrogen fluxes may have an important function in the maintenance of unidirectional growth. As root hair elongation is coupled to spatially distinct regulation of extracellular pH oscillations and ROS production,7 it seems likely that there is a mechanism that can adjust the fluxes of nitrogen ions relative to these pH fluxes. This system would then maintain the oscillations in pH such that polarized growth is continued. One possible mechanism for this coordination is through the highly localized ROP cycling between active and inactive states that has an important role in the spatial activation of cell polarization machinery.23–27 Due to the function of ROP GTPases in vesicle trafficking, actin organization and maintenance of ROS and Ca2+ gradients,2,8,9,23,24,28–33 expression of activated ROP11 may indirectly influence cell wall properties by altering the localization and/or recycling of cation and anion transporters/channels or plasma membrane H+-ATPases delivered to the growing tip of the hair and in this way affect the maintenance of the proton gradients. In agreement with a possible effect of activated ROPs on localization and/or recycling of membrane transporters we discovered that rop11CA plants were resistant to ammonium toxicity when grown in the presence of NH4NO3 and several micronutrients.1We propose a model (Fig. 1) in which spatial regulation of ROP activity creates a positive feedback loop with pH oscillations around the growing apex of root hairs. According to this model ROP cycling between active and inactive states spatially and temporally activates the downstream signaling cascades essential for the tip-growth of root hairs. At the same time, localization of membrane proteins involved in maintenance of normal nitrogen fluxes across the plasma membrane is indirectly affected by ROP signaling. Alternatively, ROP signaling is modulated to adapt to altered nitrogen fluxes. NH4+ fluxes increase the amplitude of pH oscillations at the root hair apex and in turn affect cell-wall properties. Thus, when the ROP activity is upregulated by dominant mutations, the synergistic effects of pH changes and constant activation of ROP downstream effectors result in the uncontrolled cell expansion seen as root hair bulging. Previous studies have suggested that feedback between oscillatory pH change and ROS distribution is required to support tip growth.7 However, the factors that may integrate these processes are unknown. Our results suggest that spatial regulation of ROP activity in response to changing environments is one of the key elements that may coordinate the pH and ROS oscillations during the root hair tip growth.It will be interesting to examine whether ROP function is coordinated with apoplastic pH fluctuation in other cell types. Recently, it has been suggested that the effects of auxin on pavement cell structure in leaf epidermis require Auxin Binding Protein 1 (ABP1) dependent ROP activation.34 It is well known that auxin induces changes in apoplastic pH. Possibly, like nitrogen source in root hairs, auxin dependent apolplastic pH fluctuations in the leaf epidermis may function coordinately with ROP in the regulation of cell growth. Consistent with this idea, it has been shown that auxin inhibits clathrin-dependent endocytosis through ABP1 reinforcing a possible role in modulating membrane flux/membrane properties.35 Some auxin resistant mutants also display resistance to ammonium toxicity36 further suggesting a link between auxin and membrane transport. Hence, auxin and ROPs may indeed function synergistically to modulate plasma membrane properties, in turn affecting ion balance in the apoplast and so modulating cell wall properties and growth. 相似文献
6.
Abstract
To determine if spatial variation in soluble carbon sources along the root coincides with different trophic groups of bacteria,
copiotrophic and oligotrophic bacteria were enumerated from bulk soil and rhizosphere samples at 2 cm intervals along wheat
roots 2, 3, and 4 weeks after planting. There was a moderate rhizosphere effect in one experiment with soil rich in fresh
plant debris, and a very pronounced rhizosphere effect in the second experiment with soil low in organic matter. We obtained
wavelike patterns of both trophic groups of bacteria as well as water-soluble total organic carbon (TOC) along the whole root
length (60 or 90 cm). TOC concentrations were maximal at the root tip and base and minimal in the middle part of the roots.
Oscillations in populations of copiotrophic and oligotrophic bacteria had two maxima close to the root tip and at the root
base, or three maxima close to the tip, in the middle section, and at the root base. The location and pattern of the waves
in bacterial populations changed progressively from week to week and was not consistently correlated with TOC concentrations
or the location of lateral root formation. Thus, the traditional view that patterns in bacterial numbers along the root directly
reflect patterns in exudation and rhizodeposition from several fixed sources along the root may not be true. We attributed
the observed wavelike patterns in bacterial populations to bacterial growth and death cycles (due to autolysis or grazing
by predators). Considering the root tip as a moving nutrient source, temporal oscillations in bacterial populations at any
location where the root tip passed would result in moving waves along the root. This change in concept about bacterial populations
in the rhizosphere could have significant implications for plant growth promotion and bioremediation.
Received: 11 May 1998; Accepted: 4 November 1998 相似文献
7.
Influence of Protein Synthesis on NO(3) Reduction, NH(4) Accumulation, and Amide Synthesis in Suspension Cultures of Paul's Scarlet Rose
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Changes in the concentrations of NH4+ and amides during the growth of suspension cultures of rose (Rosa cv. Paul's Scarlet) cells were examined. When cells were grown in medium possessing only NO3− as a nitrogen source, the concentrations of NH4+ and amides increased to 4.0 × 10−1 and 5.9 micromoles per gram fresh weight, respectively. The amounts of both constituents declined during the later stages of growth. When a trace amount of NH4+ was added to the NO3− base starting medium, the concentration of NH4+ in the cells was increased to 7.0 × 10−1 micromoles per gram fresh weight. 相似文献
8.
In experiments with isolated hepatocytes, Seglen [1] has shown that in the combined presence of NH4Cl and high concentrations of valine, incorporation of this amino acid into cell protein is inhibited. He has proposed that NH4Cl, in addition to inhibiting protein degradation in lysosomes, inhibits protein synthesis in these cells as part of a general toxic effect. To determine if NH4Cl inhibits protein synthesis in cultured cells we incubated rat embryo fibroblasts, prelabeled with [14C]leucine, in the presence of 10 mM NH4Cl and 15 mM leucine in both growth and serum-free media. We did not detect any effect of NH4+ on protein synthesis or cell growth over a 3-day period. A partial inhibition of protein degradation was observed, particularly during the first 24 h of the experiment. In pulse-labeling experiments, NH4Cl had no effect on the incorporation of [3H]leucine in the media. High concentrations of leucine, however, reduced re-utilization of endogenously derived leucine and inhibited the transport of valine into the cellular acid-soluble pool.These experiments show that at least in cultured fibroblasts 10 mM NH4Cl shows no significant toxicity beyond an inhibition of lysosomal function. In addition these data suggest the possibility that high chase concentrations of one amino acid in the medium may be saturating a common transport mechanism, in effect reducing the transport of other amino acids utilizing this mechanism. A combined blockade by both NH4Cl and a high concentration of a single amino acid may in certain sensitive cells result in a significant reduction in protein synthesis. 相似文献
9.
Constructed wetlands (CWs) have received increasing attentions for their N removal performances, especially regarding NH4+-N. Different influent NH4+-N concentration may influence N removal efficiency in practice, while the effects of different NH4+-N concentrations on microorganisms removing N in CWs are poorly understood. In this study, surface flow CWs planted with Myriophyllum (M). aquaticum were established to investigate the influences of different NH4+-N concentrations on the composition, structure, and interactions of microbial community. Our findings suggested 105 mg/L NH4+-N CWs achieved highest N removal rate, removing 89.30 % NH4+-N and 92.34 % TN from the influent. The results of real-time quantitative polymerase chain reactions (qPCR) indicated abundances of nitrifying genes (nxrA) and denitrifying genes (narG, nirS, nirK, and nosZ) were increased by increasing NH4+-N concentrations, and the strongest effects were observed in narG (8-fold) and nosZ genes (11-fold). Different NH4+-N concentrations was proved to alter composition and structure of microbial communities via high-throughput sequencing, e.g. denitrifiers including Brevendomonas.sp, Dokdonella.sp and Rhodococcus.sp were enriched obviously with increasing NH4+-N concentrations. In addition, network showed interactions among microbial populations and positive interactions were dramatically shifted and enhanced by increasing NH4+-N concentrations. 相似文献
10.
Papoyan A. R. Oganesyan S. P. Davtyan M. A. 《Applied Biochemistry and Microbiology》2001,37(3):257-259
Various populations of peroxisomes in cells of Aspergillus nigerR-3 were formed under growth in media containing 0.5% glucose and various sources of nitrogen (1/4 of the optimal concentrations of (NH4)2SO4, L-alanine, and L-methionine). Different levels of L-amino acid oxidase activity were found in these populations of peroxisomes. 相似文献
11.
The effects of inorganic nutrient (ammonium [NH4 + ] and nitrate [NO3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO3 − , or NH4 + did not affect short-term rates of N2 fixation. This may be an important factor that allows for continued N2 fixation in oligotrophic areas where recycling processes are active. N2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH4 + , NO3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO3 − , proportional increases in NO3 − uptake and decreases in N2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH4 + , NO3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH4 + , glu, or gln. Cells incubated with NH4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N2 and take up NH4 + and how natural populations continue to fix N2 once combined N concentrations increase within a bloom. 相似文献
12.
Regulation of bacterial abundance and production by substrate supply and bacterivory: A mesocosm study 总被引:3,自引:0,他引:3
Daily bacterial abundance and production, heterotrophic nanoflagellates (HNAN) abundance, chlorophyll, and NH4
+ concentrations were measured in four indoor 400-liter tanks over 13 days to study the role of heterotrophic bacterioplankton in NH4
- cycling and to identify the succession of top-down and bottom-up processes in regulating bacterial biomass and production. Ammonium (NH4
+) was added to these four tanks daily whenever its concentration in tanks was < 4 m. Tanks 3 and 4 (treatment tanks) also received 4 m of glucose daily till the end of experiment. Lower NH4
- concentrations and higher bacterial specific growth rate and production observed in the treatment tanks indicated that bacteria might take up NH4+ with the addition of labile organic carbon. Bacterial biomass was controlled by substrate supply and HNAN grazing from day 7 to day 13, when phytoplankton declined. Bacterial size distribution patterns were determined primarily by substrate supply, with HNAN grazing playing a less important role. Certain variabilities existed between the control (and the treatment) tanks. These inconsistencies could be due to differences in time of expression of given variables. However, the total amounts of bacterial biomass accumulated in the four tanks were very similar. The inconsistency in timing of expression of variables was probably due to different initial conditions in each tank. The ecological meanings of the inconsistency in timing and overall consistency were discussed.
Correspondence to: F.-K. Shiah 相似文献
13.
van Bruggen AH Semenov AM Zelenev VV Semenov AV Raaijmakers JM Sayler RJ de Vos O 《Microbial ecology》2008,55(3):466-475
Culturable rhizosphere bacterial communities had been shown to exhibit wave-like distribution patterns along wheat roots.
In the current work we show, for the first time, significant wave-like oscillations of an individual bacterial strain, the
biocontrol agent Pseudomonas fluorescens 32 marked with gfp, along 3-week-old wheat roots in a conventionally managed and an organically managed soil. Significant wave-like fluctuations
were observed for colony forming units (CFUs) on selective media and direct fluorescent counts under the microscope. Densities
of fluorescent cells and of CFUs fluctuated in a similar manner along wheat roots in the conventional soil. The frequencies
of the first, second, and third harmonics were similar for direct cell counts and CFUs. Survival of P. fluorescens 32-gfp introduced into organically managed soil was lower than that of the same strain added to conventionally managed soil. Thus,
when root tips reached a depth of 10–35 cm below soil level, the majority of the introduced cells may have died, so that no
cells or CFU”s were detected in this region at the time of sampling. As a result, significant waves in CFUs or direct counts
along roots were not found in organically managed soil, except when a sufficiently long series with detectable CFUs were obtained.
In this last case the wave-like fluctuation in CFUs was damped toward the root tip. In conclusion, when cells of a single
bacterial strain randomly mixed in soil survived until a root tip passed, growth and death cycles after passage of the root
tip resulted in oscillating patterns of population densities of this strain along 3-week-old wheat roots. 相似文献
14.
Anne Turi Amtoft Neubauer Kai Finster Andrew P. Donnelly Gianmarco Giordani Bente Aa Lomstein 《Journal of experimental marine biology and ecology》2004,313(1):105-124
The initial benthic decomposition of Zostera marina roots was studied in a controlled flow-through chamber experiment for 23 days. Sediment chambers without added roots served as controls. The inflowing and outflowing artificial seawater (ASW) was analyzed for O2, ΣCO2, urea-N, NH4+ and NO2−+NO3−. Sediment profiles of Eh, particulate organic carbon (POC) and nitrogen, dissolved organic nitrogen (DON), dissolved free amino acids (DFAA), urea-N, NH4+, DFAA and urea turnover rates, sulfate reduction and counts of total anaerobic heterotrophic bacteria and different functional groups were determined. Fluxes of O2, ΣCO2, urea-N and NH4+ were stimulated during root decomposition compared to the unamended control. There were indications of stimulated bacterial growth based on counts of total anaerobic heterotrophic bacteria, anaerobic phosphatase utilizers, ammonifyers and sulfate reducers. Independent estimates of nitrogen and carbon incorporation into bacterial biomass during root decomposition indicate that a major fraction of the nitrogen for microbial growth was mobilized from the indigenous particulate organic nitrogen (PON) pool, whereas the energy source for bacterial growth was mainly obtained from the added eelgrass roots. Most of the nitrogen mineralized during root decomposition was incorporated into the bacterial biomass resulting in a low efflux of urea-N and inorganic nitrogen from the sediment to the water column. 相似文献
15.
The authors studied removal rates of bacteria and the regeneration of inorganic nutrients in coral reef cavities in the reef slope of Curaçao, Netherlands Antilles. We found that in cavities the hard substratum surface area (=ca 68% of cavity surface area) is 65% covered with sessile filter feeders. The cryptic cavity surface area exceeds the projected surface area of the reef by 1.5–8 times. Consequently, the organisms living in these cryptic habitats have potentially a large impact on pico- and nano-plankton densities and are important in reef water nutrient dynamics. We closed cavities (±70 l volume, 15 m depth) in seven experiments to study changes in bacterial densities and dissolved inorganic nutrients (DIN, DIP, and silicate) over time. Water samples were taken from the middle of the cavity at 5-min intervals, for 30 min, and analyzed for heterotrophic bacterial abundance and nutrient concentrations. After closure, bacterial abundance dropped rapidly. Of the initial bacterial concentration in the cavities, 50–60% had disappeared after 30 min, an average disappearance rate of 1.43×104 bacteria ml–1 min–1 (0.62 mg C l–1 d–1; or 30.1 mg C m–2 cavity surface area d–1). NOx concentrations increased significantly during the time of closure. Efflux rates varied between 1.02–9.77 mmol m–2 cavity surface area d–1. NH4+ and PO43– concentrations were variable and did not show a consistent change over time in the experiments. Comparison of bacterial organic nitrogen disappearance rates and DIN (NOx+NH4+) release rates suggests that on average only 30–40% of additional sources of N besides bacteria were required to balance the nitrogen budget. This highlights the importance of heterotrophic bacterioplankton as food for cryptic filter feeders on coral reefs. Silicate concentrations significantly decreased after closure with 0.50 mmol m–2 cavity surface area d–1, suggesting the net deposition of SiO42– in spicules of cryptic filter feeding sponges. We conclude that coral reef cavities are a major sink for heterotrophic bacteria, a sink for dissolved silicon (DSi), and a source for NOx. That reef cavities are a source for NOx suggests strong remineralization and nitrification in cavities with a potential role for sponge-symbiotic microbial nitrification.Communicated by K.S. Sealey 相似文献
16.
Toxic effects of high concentrations of ammonia were studied in the cucumber plant (Cucumis sativus cv. Suisei No. 2). When the cucumber plant was cultured with 200 mg/l NH3-N (as NH4Cl), some characteristic symptoms, probably due to ammonium toxicity, appeared in the leaves after about 1 week, while no such symptoms were observed in the plants cultured with 20 mg/1 NH3-N. The level of free sugars in 20 mg/l NH3-N treated plants decreased with time and was lower than that in plants treated with 200 mg/l NH3-N. Specially distinct differences were found as regards the levels of fructose and glucose. After 9 days' culture the content of glucose in 200 mg/l NH3-N plants was 17 times higher than that of 20 mg/l NH3-N plants. From the results of an incorporation of photosynthesized 14CO2 for 3 hours into newly synthesized glucose it is evident that this accumulation of glucose can not be the degradative product of a glucose polymer such as starch. The levels of starch were also studied, and it was found that the starch level decreased due to ammonium toxicity. These results suggest that the translocation of glucose after its synthesis is inhibited by ammonium toxicity, at least up to starch synthesis. 相似文献
17.
The seasonal dynamics of amino acids and other nutrients in Alaskan Arctic tundra soils 总被引:4,自引:0,他引:4
Past research strongly indicates the importance of amino acids in the N economy of the Arctic tundra, but little is known about the seasonal dynamics of amino acids in tundra soils. We repeatedly sampled soils from tussock, shrub, and wet sedge tundra communities in the summers of 2000 and 2001 and extracted them with water (H2O) and potassium sulfate (K2SO4) to determine the seasonal dynamics of soil amino acids, ammonium (NH4+), nitrate (NO3–), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and phosphate (PO42–). In the H2O extractions mean concentrations of total free amino acids (TFAA) were higher than NH4+ in all soils but shrub. TFAA and NH4+ were highest in wet sedge and tussock soils and lowest in shrub soil. The most predominant amino acids were alanine, arginine, glycine, serine, and threonine. None of the highest amino acids were significantly different than NH4+ in any soil but shrub, in which NH4+ was significantly higher than all of the highest individual amino acids. Mean NO3– concentrations were not significantly different from mean TFAA and NH4+ concentrations in any soil but tussock, where NO3– was significantly higher than NH4+. In all soils amino acid and NH4+ concentrations dropped to barely detectable levels in the middle of July, suggesting intense competition for N at the height of the growing season. In all soils but tussock, amino acid and NH4+ concentrations rebounded in August as the end of the Arctic growing season approached and plant N demand decreased. This pattern suggests that low N concentrations in tundra soils at the height of the growing season are likely the result of an increase in soil N uptake associated with the peak in plant growth, either directly by roots or indirectly by microbes fueled by increased root C inputs in mid-July. As N availability decreased in July, PO42– concentrations in the K2SO4 extractions increased dramatically in all soils but shrub, where there was a comparable increase in PO42– later in the growing season. Previous research suggests that these increases in PO42– concentrations are due to the mineralization of organic phosphorus by phosphatase enzymes associated with soil microbes and plant roots, and that they may have been caused by an increase in organic P availability. 相似文献
18.
Soil labile C and N fractions can change rapidly in response to management practices compared to non-labile fractions. High variability in soil properties in the field, however, results in nonresponse to management practices on these parameters. We evaluated the effects of residue placement (surface application [or simulated no-tillage] and incorporation into the soil [or simulated conventional tillage]) and crop types (spring wheat [Triticum aestivum L.], pea [Pisum sativum L.], and fallow) on crop yields and soil C and N fractions at the 0–20 cm depth within a crop growing season in the greenhouse and the field. Soil C and N fractions were soil organic C (SOC), total N (STN), particulate organic C and N (POC and PON), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), NH4-N, and NO3-N concentrations. Yields of both wheat and pea varied with residue placement in the greenhouse as well as in the field. In the greenhouse, SOC, PCM, STN, MBN, and NH4-N concentrations were greater in surface placement than incorporation of residue and greater under wheat than pea or fallow. In the field, MBN and NH4-N concentrations were greater in no-tillage than conventional tillage, but the trend reversed for NO3-N. The PNM was greater under pea or fallow than wheat in the greenhouse and the field. Average SOC, POC, MBC, PON, PNM, MBN, and NO3-N concentrations across treatments were higher, but STN, PCM and NH4-N concentrations were lower in the greenhouse than the field. The coefficient of variation for soil parameters ranged from 2.6 to 15.9% in the greenhouse and 8.0 to 36.7% in the field. Although crop yields varied, most soil C and N fractions were greater in surface placement than incorporation of residue and greater under wheat than pea or fallow in the greenhouse than the field within a crop growing season. Short-term management effect on soil C and N fractions were readily obtained with reduced variability under controlled soil and environmental conditions in the greenhouse compared to the field. Changes occurred more in soil labile than non-labile C and N fractions in the greenhouse than the field. 相似文献
19.
V. Álvarez-López A. Prieto-Fernández J. Janssen R. Herzig J. Vangronsveld P.S. Kidd 《International journal of phytoremediation》2016,18(4):406-415
In this study different bacterial inoculation methods were tested for tobacco plants growing in a mine-soil contaminated with Pb, Zn, and Cd. The inoculation methods evaluated were: seed inoculation, soil inoculation, dual soil inoculation event, and seed+soil inoculation. Each inoculum was added at two bacterial densities (106 CFUs mL?1 and 108 CFUs mL?1). The objectives were to evaluate whether or not the mode of inoculation or the number of applied microorganisms influences plant response. The most pronounced bacterial-induced effect was found for biomass production, and the soil inoculation treatment (using 106 CFUs mL?1) led to the highest increase in shoot dry weight yield (up to 45%). Bacterial-induced effects on shoot metal concentrations were less pronounced; although a positive effect was found on shoot Pb concentration when using 108 CFUs mL?1 in the soil inoculation (29% increase) and in the seed+soil inoculation (34% increase). Also shoot Zn concentration increased by 24% after seed inoculation with 106 CFUs mL?1. The best effects on the total metal yield were not correlated with an increasing number of inoculated bacteria. In fact the best results were found after a single soil inoculation using the lower cellular density of 106 CFUs mL?1. 相似文献
20.
Shiro Higashi Akinori Nakashima Hideki Ozaki Mikiko Abe Toshiki Uchiumi 《Journal of plant research》1993,106(1):47-54
The process of digestion of captured feeds in a pitcher, an insect-trapping organ, ofNepenthes was studied. Changes in bacterial population, pH and NH4
+ concentrations in pitcher juice were examined. Strong activities of both acid- and alkaline phosphatase, phosphoamidase,
esterase C4 and esterase C8 were found in the pitcher juice. Optimum pH of proteases in the juice and those secreted from
bacteria showed pH 3.0 and pH 8.0–9.0, respectively. Twenty six strains of bacteria were isolated from 4 pitchers: 10 strains
were gram positive, 16 strains were gram negative (10 strains had casein hydrolase activity). A proton excretion was induced
by NH4
+ released from the added solutions, and accordingly, the pH of the solutions fell. As a simulation model of the digestion
process of feeds in pitcher juice and polypeptone solution was added into the washed pitcher. A good correlation was found
among the NH4
+ concentration, pH and bacterial cell titer. 相似文献