Seasonal patterns of viruses, bacteria and dissolved organic carbon in a riverine wetland

SUMMARY 1. Viral and bacterial abundances were studied in relation to environmental attributes over an annual period, for both planktonic and attached (sediment, aquatic macrophyte and submerged wood) habitats, in a riverine wetland.
2. Annual mean abundance of planktonic viruses ranged from 2.3 × 10⁵−3.8 × 10⁵ particles mL⁻¹ and varied according to sampling site. Significant seasonal patterns in viral abundance were evident and appeared to be linked to variations in bacterial abundance, dissolved organic carbon and inorganic nutrients.
3. Annual mean abundance of viruses associated with surfaces ranged from 1.3 × 10⁶ particles cm⁻² on aquatic macrophytes to 1.1 × 10⁷ particles cm⁻² on wood and also showed seasonal patterns. The difference in viral dynamics among the different sites emphasizes the importance of considering habitat diversity within wetlands when examining microbial communities.     

CELL ASSOCIATION PATTERN IN AGGREGATES CONTROLLED BY MULTIPLE CELL-CELL ADHESION MECHANISMS

We have previously assumed the presence of two mechanisms for the aggregation of Chinese hamster V79 cells, the Ca²⁺-dependent one and the Ca²⁺-independent one. In order to examine if each of these mechanisms contributed differently to the various aspects of cell aggregation, the morphology of V79 cell aggregates, pretreated so that they were provided with only one of the two adhesion mechanisms, was compared by light and electron microscopy. The adhesion among cells with only the Ca²⁺-dependent mechanism was very tight, with the formation of gap and intermediate junctions. Cells were arranged in a rod or dendric shape in aggregates. In aggregates of cells with only the Ca²⁺-independent mechanism, cells were loosely attached to each other without the formation of specialized junctions and the aggregates were of globular shape. In aggregates of cells with both mechanisms, both characteristics of the above two aggregates were found. Four clones of V79 cells, which formed colonies with different morphology when they were grown in soft agar, were isolated. It was found that such differences were due to the different activity of the Ca²⁺-independent mechanism among these clones. These results suggested that the two adhesion mechanisms play different roles in the cell arrangement in aggregates.     

8 Grazing by heterotrophic nanoflagellates on virus- and bacteria-sized particles in two lakes of different trophy

Although viruses are now widely recognized to infect aquatic bacteria as well as prokaryotic and eukaryotic phytoplankton, our understanding of how they fit into aquatic foodwebs remains still deficient. The present study examined the potential nutritional food source that viral particles represent for natural assemblages of heterotrophic nanoflagellates (HNF). We determined the seasonal and depth-related variability in the grazing activity of HNF on virus- and bacteria-sized particles in the oligomesotrophic Lake Pavin and the eutrophic Lake Aydat. Ingestion rates were determined using 50 and 500 nm diameter fluorescent microspheres. Estimated ingestion rates ranged from 0.01 to 1.7 viruses cell⁻¹·h⁻¹ (Aydat) and from 0.01 to 2 viruses cell⁻¹·h⁻¹ (Pavin). Derived clearance rates for viruses represented 3–5% (Aydat) and 10–12% (Pavin) of those for bacteria. In general, HNF grazing on both viruses and bacteria showed a similar pattern characterized by an apparent decrease in summer followed by autumnal peaks, with lowest values always being recorded in the hypolimnion. Viral production, estimated from the frequency of visibly infected cells (using transmission electronic microscopy), was consumed by HNF at rates averaging 2% (Aydat) and 10% (Pavin). This study suggests that, viruses, which are assumed to correspond to 1×10⁻⁷ ng C/particle, are likely to be of low nutritive value for HNF in both lakes. However, these results imply that HNF grazing may contribute significantly to the removal of viruses in freshwaters, especially in low productive systems.     

The use of direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) to assess microbial populations on food contact surfaces

Two rapid methods, direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) on swab resuspension fluids, were compared with the traditional total viable count (TVC) on swab resuspension fluids for their ability to enumerate surface populations of attached bacteria. The degree of error in estimating surface populations was shown to be significantly less with DEM than DEFT followed by TVC. DEM estimated populations in the range 3 times 10³ to 5 times 10⁷ colonies/cm² whilst DEFT enumerated populations above 3 times 10⁴ colonies/cm² and TVC above 3 times 10⁵ colonies/cm² (as measured by DEM). Swabbing was shown to remove a constant proportion of organisms from the surface populations tested, although below 3 times 10⁵ colonies/cm² most of the organisms remained in the cotton matrix and were difficult to resuspend. DEFT was more able to enumerate swab resuspension fluids obtained from surface populations below 3 times 10⁵ colonies/cm² than was TVC.     

Protozoan predation of bacterial cells in soil aggregates

Abstract The development and survival of Aerobacter aerogenes IAM11022 in the inner and outer zones of soil aggregates (1–2 mm) was investigated in relation to a protozoan ( Colpoda sp.). With different dilutions of the bacterial cell suspension, a constant partition ratio of these cells was observed between outer and inner zones of the aggregates. Protozoa inoculated in the same manner were generally recovered only from the outer zone of the aggregates.
In the presence of protozoa, prey cell numbers of the outer zone were reduced from more than 10⁸ to approx. 10⁴ cells · g soil⁻¹ in 12 days. In contrast, 10⁸ cells · g soil⁻¹ remained in the inner zone of the aggregates, even after 12 days.
The increase in predator cell number was proportional to initial prey densities in the outer zone of the aggregates. At a constant initial prey density (1.8 × 10⁷ cells · g soil⁻¹), Colpoda sp. multiplied in proportion to the initial number of predators. When the initial density of the predator was low more prey cells survived in the outer zone.
Prey persistence was associated with 3 different types of protection: (1) small pore necks of the inner zone space of the aggregates; (2) the division of the outer zone space into compartments; and (3) the distribution of protozoan cells among soil aggregates. The latter two were closely related to the moisture condition of the soil.     

Calcification in aquatic plants

Abstract. The CaCO₃ deposits of aquatic plants may be intra-, inter- and extracellular. Calcification is mainly the result of photosynthetic CO₂ or HCO⁻₃ assimilation. This raises the local pH and CO²⁻₃ concentration resulting from shifts in the dissolved inorganic carbon equilibrium, due to either net CO₂ depletion as in Halimeda or localized OH⁻ efflux (or H⁺ influx) as in Chara. The plant cell wall may be important in CaCO₃ nucleation by acting as an epitaxial substratum or template, or by creating a microenvironment enriched in Ca²⁺ compared to Mg²⁺. Hypotheses on the reason for the lack of calcification in many aquatic plants are presented.     

Viruses in soils: morphological diversity and abundance in the rhizosphere

Soil viruses are potentially of great importance as they may influence the ecology and evolution of soil biological communities through both an ability to transfer genes from host to host and as a potential cause of microbial mortality. Despite this importance, the area of soil virology is understudied. Here, we report the isolation and preliminary characterisation of viruses from soils in the Dundee area of Scotland. Different virus morphotypes including tailed, polyhedral (spherical), rod shaped, filamentous and bacilliform particles were detected in the soil samples. An apparent predominance of small spherical and filamentous bacteriophages was observed, whereas tailed bacteriophages were significantly less abundant. In this report, we also present observations and characterisation of viruses from different soil functional domains surrounding wheat roots: rhizosheath, rhizosphere and bulk soil. In spite of the differences in abundance of bacterial communities in these domains, no significant variations in viral population structure in terms of morphology and abundance were found. Typically, there were approximately 1.1–1.2 × 10⁹ virions g⁻¹ dry weight, implicating remarkable differences in virus-to-bacteria ratios in domains close to roots, rhizosphere and rhizosheath (approximately 0.27) and in bulk soil (approximately 4.68).     

Acid resistance of attached organisms and its implications for the pathogenicity of plasmid-bearing Escherichia coli

Organisms of Escherichia coli attached to glass beads in a model attachment system were more resistant to acid than were unattached organisms and this applied to cultures exposed to either pH 2·5 or 3·5. Attached organisms of both Col^- and Col V, I-K94⁺ strains showed the effect but with prolonged exposure to pH 2·5, the attached Col V⁺ organisms appeared more resistant than the attached Col^- ones, possibly because they formed a thicker surface layer. It is proposed that the increased resistance of attached organisms to pH 2·5 might allow the survival, in gastric acid, of organisms attached to food particles. This would be more significant for the Col V⁺ strains because the plasmid enhances enterobacterial attachment properties. The increased resistance of attached organisms to pH 3·5 might be significant for survival of particle- or surface-bound organisms in the acidic environment of the phagocyte especially since lactate (which occurs in phagocytes) enhanced the effect of exposure to pH 3·5.     

Dissimilatory nitrite-reductase provides a competitive advantage to Pseudomonas sp. RTC01 to colonise the centre of soil aggregates

Abstract: The effect of soil aggregation on denitrification has been studied in different ways: artificial or natural aggregates individually analysed or comparison of denitrifying activity of different size classes of aggregates. However, until now, no work has been conducted to evaluate the role of denitrification in the microbial colonisation of soil aggregates. Over a one-month period, we examined on remoulded nonsterile soil aggregates the survival of inoculated wild-type Pseudomonas strain and of its corresponding isogenic Tn5 mutant (Nir⁻) lacking the ability to synthesize the dissimilative nitrite-reductase. Simultaneously, the evolution of the O₂ repartition inside the soil aggregates was assessed by the use of microelectrodes. The inner and outer portions were roughly anoxic and oxic, respectively, during the entire experiment while the intermediate portion showed fluctuating aeration conditions. The values of the Nir⁻ to wild-type + Nir⁻ ratio were found in the following order: inner < intermediate < outer portion, demonstrating that the nitrite-reductase may provide a competitive advantage to the Pseudomonas strain to colonise the centre of soil aggregates. However, a clear differentiation between inner and outer aggregates portions was not observed with the indigenous microflora (denitrifiers-to-total heterotrophs, biomass or physiological abilities).     

Annual changes of bacterial mortality due to viruses and protists in an oligotrophic coastal environment (NW Mediterranean)

The impact of viruses and protists on bacterioplankton mortality was examined monthly during 2 years (May 2005–April 2007) in an oligotrophic coastal environment (NW Mediterranean Sea). We expected that in such type of system, (i) bacterial losses would be caused mainly by protists, and (ii) lysogeny would be an important type of virus–host interaction. During the study period, viruses and grazers together were responsible for 50.6 ± 40.1% day⁻¹ of bacterial standing stock losses (BSS) and 59.7 ± 44.0% day⁻¹ of bacterial production losses (BP). Over the first year (May 2005–April 2006), protists were the principal cause of bacterial mortality, removing 29.9 ± 20.4% day⁻¹ of BSS and 33.9 ± 24.3% day⁻¹ of BP, whereas viral lysis removed 13.5 ± 17.0% day⁻¹ of BSS and 12.3 ± 12.3% day⁻¹ of BP. During the second year (May 2006–April 2007), viruses caused comparable bacterial losses (29.2 ± 14.8% day⁻¹ of BSS and 40.9 ± 20.7% day⁻¹ of BP) to protists (28.6 ± 25.5% day⁻¹ of BSS and 32.4 ± 20.0% day⁻¹ of BP). In 37% of cases higher losses of BP due to viruses than due to protists were found. Lysogenic infection was detected in 11 of 24 samplings. Contrary to our expectations, lytic infections dominated over the two years, and viruses resulted to be a significant source of bacterial mortality in this oligotrophic site.     

Quantitative PCR reveals transient and persistent algal viruses in Lake Ontario, Canada

To determine if different algal viruses ( Phycodnaviridae ) share common patterns of seasonal abundance, quantitative PCR methods were developed and applied to monitor the abundances of three different viruses in Lake Ontario, Canada over 13 months. Throughout the year, the abundances of two different phycodnavirus polB gene fragments (LO1b-49 and LO1a-68) varied by more than two orders of magnitude, peaked during the autumn months, and were lowest during the summer. The seasonal abundance patterns of these two virus genes were similar and both were detected in almost every sample, but LO1b-49 was consistently an order of magnitude more abundant than LO1a-68. LO1b-49 reached a maximum abundance of 5413 ± 312 genes ml⁻¹, whereas LO1a-68's abundance peaked at only 881 ± 113 genes ml⁻¹. Another phycodnavirus polB fragment that was monitored (LO1b-16) was detected in only a few samples, but reached a higher maximum concentration (6771 ± 879 genes ml⁻¹) than either LO1b-49 or LO1a-68. The results of this year-long investigation of virus gene abundances suggests that Lake Ontario's phycodnavirus community is composed of persistent viruses detectable throughout the year and transient viruses present in only a few sporadic samples. The results also suggest that some persistent algal viruses are able to survive at relatively low abundances through several seasons.     

A note on the attachment rate of suspended bacteria to submerged aquatic plants in a calcareous stream

The density of epiphytic bacteria on leaflets of laboratory-grown Apium nodiflorum , immersed in calcareous stream water, increased linearly with time over 10 h, both in the laboratory and in the field. This increase was probably due to attachment of suspended bacteria. The rate of attachment to leaflets of plants, immersed in a stream at different concentrations of suspended bacteria, was linearly related to the concentration of suspended bacteria. The attachment rate, relative to concentration, was 1.7 × 10⁴ bacteria/cm²/h for each 10⁵ bacteria/ml in the surrounding water.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

Protein aggregation in neurons following OGD: a role for Na+ and Ca2+ ionic dysregulation

In this study, we investigated whether disruption of Na⁺ and Ca²⁺ homeostasis via activation of Na⁺-K⁺-Cl⁻ cotransporter isoform 1 (NKCC1) and reversal of Na⁺/Ca²⁺ exchange (NCX_rev) affects protein aggregation and degradation following oxygen–glucose deprivation (OGD). Cultured cortical neurons were subjected to 2 h OGD and 1–24 h reoxygenation (REOX). Redistribution of ubiquitin and formation of ubiquitin-conjugated protein aggregates occurred in neurons as early as 2 h REOX. The protein aggregation progressed further by 8 h REOX. There was no significant recovery at 24 h REOX. Moreover, the proteasome activity in neurons was inhibited by 80–90% during 2–8 h REOX and recovered partially at 24 h REOX. Interestingly, pharmacological inhibition or genetic ablation of NKCC1 activity significantly decreased accumulation of ubiquitin-conjugated protein aggregates and improved proteasome activity. A similar protective effect was obtained by blocking NCX_rev activity. Inhibition of NKCC1 activity also preserved intracellular ATP and Na⁺ homeostasis during 0–24 h REOX. In a positive control study, disruption of endoplasmic reticulum Ca²⁺ with thapsigargin triggered redistribution of free ubiquitin and protein aggregation. We conclude that overstimulation of NKCC1 and NCX_rev following OGD/REOX partially contributes to protein aggregation and proteasome dysfunction as a result of ionic dysregulation.     

Calcium and plant action potentials

Abstract. Under normal conditions the action potential in Characeae is dependent on the presence of both Cl⁻ and Ca²⁺. Cl⁻ seems to play a straightforward part as a transient depolarizing flow. The role of Ca²⁺, however, is emerging as an increasingly complex one: there are Ca²⁺ concentration changes in the cytoplasm, as well as transient Ca²⁺ currents across the plasmalemma and possibly the tonoplast. In most Characeae Ca²⁺ is necessary for the Cl⁻ channel to function, and it is also involved in the cessation of the cytoplasmic streaming observed at the time of excitation.
The function of Ca²⁺ at the time of the action potential is being revealed by experimental techniques of increasing sophistication. The development of these methods and possible associated artefacts are considered.     

Detection of potato leafroll and potato mop-top viruses by immunosorbent electron microscopy

Attachment of virus particles to antiserum-coated electron microscope grids (immunosorbent electron microscopy) provided a test that was at least a thousand times more sensitive than conventional electron microscopy for detecting potato leafroll (PLRV) and potato mop-top (PMTV) viruses. The identity of the attached virus particles was confirmed by exposing them to additional virus antibody, which coated the particles.
PLRV particles (up to 50/μm² of grid area) were detected in extracts of infected potato leaves and tubers, infected Physalis floridana leaves, and single virus-carrying aphids. On average, Myzus persicae yielded 10–30 times more PLRV particles than did Macrosiphum euphorbiae .
PMTV particles (up to 10/μm² of grid area) were detected in extracts of inoculated tobacco leaves, and of infected Arran Pilot potato tubers with symptoms of primary infection. Particles from tobacco leaves were of two predominant lengths, about 125 nm or about 290 nm, and fewer particles of other lengths were found than in previous work, in which partially purified or purified preparations of virus particles were examined, using grids not coated with antiserum.     

Acute toxicology to an estuarine teleost of mixtures of cadmium, copper and zinc salts

Effects of mixtures of chloride salts of cadmium, copper and zinc on survival, whole body residues, and histopathology of mummichog, Fundulus heteroclitus (L.), were investigated in synthetic sea water at 20‰ salinity and 20°C. Mixtures of Cu²⁺ and Zn²⁺ as indicated by 96 h bioassay studies produced more deaths than expected on the basis of toxicities of individual components. Concentrations of Cd²⁺ not ordinarily lethal exerted a negative effect on survival of fish intoxicated by salts of copper, zinc, or both.
Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals. Residues from survivors held in mixtures, especially Cd²⁺ and Zn²⁺ mixtures, did not conform to patterns observed for single elements. Whole body aggregates of Cd, Cu, and Zn from dead mummichogs were of limited worth owing to possible accumulation of these metals from the medium after death.
Renal and lateral line canal lesions were noted in all fish subjected to copper concentrations of 1 mg/1 and higher. Renal lesions observed in fish immersed in mixtures of Cu²⁺ and Cd²⁺ assumed a damage pattern characteristic of Cd²⁺; with mixtures of Cu²⁺ and Zn²⁺, lesion were typical of Cu²⁺-induced damage. Lesions induced in lateral line epithelium by Cu²⁺ were not affected by either Cd²⁺ or Zn²⁺. Epithelia lining the oral cavity were necrotized by the caustic action of high levels of Zn²⁺ (60 mg/1) and of Cu²⁺ (8 mg/1).     

Water velocity, growth-form and diffusion resistances to photosynthetic CO2 uptake in aquatic bryophytes

Abstract. Boundary-layer resistances of aquatic bryophytes for CO₂ diffusion in water were estimated from wind tunnel measurements of evaporation of aniline in air, using the principle of dynamic similarity. The results indicated resistances at water velocities between 0.02 and 0.2 m s ⁻¹ ranging from about 35 to 5 s mm⁻¹ and 70 to 9 s mm⁻¹, respectively, for the mat-forming liverworts Nardia compressa and Scapania undulata , measured on a projected area (canopy) basis. Over a range of velocities from 0.01 to 0.2 m s⁻¹ the estimated CO₂ boundary-layer resistance of the streamer-like shoots of the moss Fontinalis antipyretica is between about 180 and 15 s mm⁻¹. Comparison with experiments on photosynthetic ¹⁴CO₂-uptake at a range of water velocities suggests that boundary-layer resistance limits photosynthesis at velocities below about 0.01 m s^−l in Fontinalis and below about 0.1 m s⁻¹ in the mat-forming species. It is suggested that high leaf-area index allows the mat growth form more effectively to exploit the low boundary-layer resistance at high velocities while remaining relatively invulnerable to drag. By contrast, the streamer form allows Fontinalis to maximize surface area under conditions where boundary-layer resistance is limiting.     

Membrane inlet mass spectrometric analysis of N-isotope labelling for aquatic denitrification studies

Abstract: Techniques are described for measuring the isotope distribution in dissolved nitrate and N₂ using membrane inlet mass spectrometry, which allows several gases to be measured in a water sample without the need for any separation steps. The isotope distribution in dissolved nitrate was measured using denitrifying Pseudomonas nautica to reduce the nitrate to N₂ which was then measured by mass spectrometry. Pseudomonas nautica NCIMB 1967 was easily grown in nitrate-limited continuous culture minimising intra- or extracellular nitrate or nitrite pools, and the bioassay was tolerant of a range of salinities. The precision of the bioassay when measuring samples with high ¹⁵NO₃⁻ contents (0.5 μmol) was 0.05 atom%; with 0.1 μmol ¹⁵NO₃⁻, the precision was around 0.2 atom%. Differences in labelling of N₂ in preserved samples obtained from ¹⁵NO₃⁻ incubations of water-covered sediment cores were measured on parallel samples with membrane inlet MS and GC-MS. The membrane inlet technique was accurate but the precision on ratio measurements was lower than by GC-MS.     

Growth rate of the aquatic moss Rhynchostegium riparioidesin Northern England

SUMMARY 1. The rale of shoot growth in Rhynchostegium riparioides was measured at monthly intervals over a 12-month period at four upland sites in the Northern Pennines. Changes were recorded by observations attached pieces of cotton. Detectable growth was found in each month, with the maximum in spring (up to 2.31 mm week⁻¹) and minimum in winter (1.12 mm week⁻¹); there was a second smaller peak in the autumn.
2. Growth rate was related strongly to several environmental variables, including spot measurements of water temperature (positive) and mean monthly precipitation (negative). A regression equation based on these two variables accounted for 5% of the variation recorded.
3. Total shoot growth over the 12-month period ranged from 33.4 to 73.3 mm, corresponding to an increase in mass of 22.9 and 120.8 mg, respectively.