Effects of small scale fluid motion on bacterial growth and respiration

1. Laboratory experiments were conducted to investigate the effect of small‐scale turbulent motion on the growth and respiration of bacteria in an oscillating grid apparatus. The experiments were performed under a range of energy dissipation levels similar to those occurring in freshwater systems. 2. The results showed that small‐scale turbulent motion does have an effect on bacterial growth and respiration. A higher gradient in the dissolved oxygen time series, higher 5‐day biochemical oxygen demand values, increased bacterial abundance, increased bacterial specific respiration, higher bacterial growth rate and increased nutrient uptake were all observed when the energy dissipation rate in the water column was increased. 3. This has implications for traditional laboratory procedures that are used to characterise bacterial metabolic rates under stagnant fluid‐flow conditions, such as biochemical oxygen demand (BOD), which would be influenced by the effects of the small‐scale fluid motion inherent in aquatic environments. According to our results, BOD values in natural systems experiencing fluid motion would be higher than traditional bottle‐derived rates.     

The growth and respiration of bacterial colonies

Young colonies of two swarming organisms, Bacillus subtilis and Proteus vulgaris, grew about as quickly on solid media as in liquid culture whilst four non-swarming organisms, Bacillus cereus, Enterobacter cloacae, Escherichia coli and Staphylococcus albus, all grew slower on solid than in liquid media. Oxygen uptake by young colonies of B. subtilis, followed manometrically, increased exponentially at about the same rate as unrestricted aerobic growth. All other colonies demonstrated accelerating respiration which was either not strictly exponential or, in the case of S. albus, definitely biphasic, with a fast then a slow exponential rate of increase. Actual and potential respiration was determined for each species by measuring oxygen uptake before and after resuspending the colony in liquid medium. The ratio of actual to potential respiration was largest in the flat, spreading B. subtilis and smallest in the small, hemispherical S. albus. Calculations suggest that oxygen penetrates between 31 and 41 micron into colonies of B. cereus, Ent. cloacae and E. coli and only 9 micron into colonies of S. albus.     

Toxicity of 2-mercaptobenzothiazole towards bacterial growth and respiration

Active sludge systems containing benzothiazoles may be intoxicated by 2-mercaptobenzothiazole (MBT). This toxicity towards several bacteria is now confirmed and is situated at around 100 mg MBT l^–1. Octanol-water partition coefficients indicated that MBT might interact with membrane-bound systems. This was confirmed through experiments showing that bacterial cell respiration was inhibited using lactate or succinate as substrates. Using these substrates and also NADH, it was found that their oxidation was also inhibited using isolated membrane fragments of Escherichia coli and Paracoccus denitrificans. Methylene blue reduction was also found to be inhibited. The oxidation of ascorbate was not inhibited in P. denitrificans. From these results it is suggested that MBT might interact with the respiratorychain at the level of flavoproteins or quinones and Fe-S clusters.     

Comparison of temperature effects on soil respiration and bacterial and fungal growth rates

Temperature is an important factor regulating microbial activity and shaping the soil microbial community. Little is known, however, on how temperature affects the most important groups of the soil microorganisms, the bacteria and the fungi, in situ. We have therefore measured the instantaneous total activity (respiration rate), bacterial activity (growth rate as thymidine incorporation rate) and fungal activity (growth rate as acetate-in-ergosterol incorporation rate) in soil at different temperatures (0-45 degrees C). Two soils were compared: one was an agricultural soil low in organic matter and with high pH, and the other was a forest humus soil with high organic matter content and low pH. Fungal and bacterial growth rates had optimum temperatures around 25-30 degrees C, while at higher temperatures lower values were found. This decrease was more drastic for fungi than for bacteria, resulting in an increase in the ratio of bacterial to fungal growth rate at higher temperatures. A tendency towards the opposite effect was observed at low temperatures, indicating that fungi were more adapted to low-temperature conditions than bacteria. The temperature dependence of all three activities was well modelled by the square root (Ratkowsky) model below the optimum temperature for fungal and bacterial growth. The respiration rate increased over almost the whole temperature range, showing the highest value at around 45 degrees C. Thus, at temperatures above 30 degrees C there was an uncoupling between the instantaneous respiration rate and bacterial and fungal activity. At these high temperatures, the respiration rate closely followed the Arrhenius temperature relationship.     

Effect of humic substance photodegradation on bacterial growth and respiration in lake water

This study addresses how humic substance (HS) chemical composition and photoreactivity affect bacterial growth, respiration, and growth efficiency (BGE) in lake water. Aqueous solutions of HSs from diverse aquatic environments representing different dissolved organic matter sources (autochthonous and allochthonous) were exposed to artificial solar UV radiation. These solutions were added to lake water passed through a 0.7-microm-pore-size filter (containing grazer-free lake bacteria) followed by dark incubation for 5, 43, and 65 h. For the 5-h incubation, several irradiated HSs inhibited bacterial carbon production (BCP) and this inhibition was highly correlated with H2O2 photoproduction. The H2O2 decayed in the dark, and after 43 h, nearly all irradiated HSs enhanced BCP (average 39% increase relative to nonirradiated controls, standard error = 7.5%, n = 16). UV exposure of HSs also increased bacterial respiration (by approximately 18%, standard error = 5%, n = 4), but less than BCP, resulting in an average increase in BGE of 32% (standard error = 10%, n = 4). Photoenhancement of BCP did not correlate to HS bulk properties (i.e., elemental and chemical composition). However, when the photoenhancement of BCP was normalized to absorbance, several trends with HS origin and extraction method emerged. Absorbance-normalized hydrophilic acid and humic acid samples showed greater enhancement of BCP than hydrophobic acid and fulvic acid samples. Furthermore, absorbance-normalized autochthonous samples showed approximately 10-fold greater enhancement of BCP than allochthonous-dominated samples, indicating that the former are more efficient photoproducers of biological substrates.     

Effects of organic carbon sources on growth, photosynthesis, and respiration of Phaeodactylum tricornutum

The growth, photosynthesis, and respiration of the marine diatom Phaeodactylum tricornutum were examined under photoautotrophic and mixotrophic conditions. 100 mM glycerol, acetate, and glucose significantly increased specific growth rate, and mixotrophic growth achieved higher biomass concentrations. Under mixotrophic conditions, respiration rate (R _d) and light compensation irradiance (I _c) were significantly higher, but net maximum photosynthetic O₂ evolution rate (P _m) and saturation irradiance (I _k) were depressed. Organic carbon sources decreased the cell photosynthetic pigment content and chlorophyll a to c ratio, but with a higher carotenoid to chlorophyll a ratio. Ratios of variable to maximum chlorophyll fluorescence (F _v/F _m) and 77 K fluorescence spectra of mixotrophic cells indicated a reduced photochemical efficiency of photosystem II. The results were accompanied by lower electron transport rate. Therefore, organic carbon sources reduced the photosynthesis efficiency, and the enhancement of biomass of P. tricornutum implied that organic carbon sources had more pronounced effects on respiration than on photosynthesis.     

Complete chloroform dechlorination by organochlorine respiration and fermentation

Chloroform (CF, CHCl(3)) is a recalcitrant and toxic environmental pollutant. In this communication we report for the first time a microbial community capable of complete CF dechlorination by metabolic processes. Cultures derived from subsurface soil (3.5 m) could sustain complete dechlorination of CF at levels of least 360 μM at a rate of 40 μM per day. Scrutiny of CF dechlorination revealed two metabolic processes at work. First, CF was respired to dichloromethane (DCM, CH(2) Cl(2)), which was then fermented to acetate, hydrogen and carbon dioxide. Elevated hydrogen partial pressures were found to inhibit the fermentation process. Interspecies hydrogen transfer was observed in the form of methanogenesis and acetogenesis. This suggests that the dechlorination process required syntrophic partners to maintain low hydrogen partial pressures. (13)C-labelled DCM was employed to help elucidate the chemistry of the process and identify bacterial community members involved. CF respiring cultures, where emulsified vegetable oil was supplied as the electron donor and DCM fermenting cultures, where DCM was supplied as the sole organic carbon source were studied separately. Pyrosequencing of these cultures revealed Dehalobacter lineages as a predominant community member in both. Subsequent growth experiments confirmed that the proliferation of Dehalobacter was linked directly to both the dehalorespiration and dehalofermentation processes.     

Effects of some organophosphate and carbamate insecticides on nitrification and legume growth

Summary Nine insecticides (six organophosphates and three carbamates) were tested for their effects on soil nitrification, growth of legume seedlings, and growth of four species of rhizobia bacteria. No inhibition of nitrification was found at normal field rates (5 ppm) of application. Some instances of inhibition were observed at 50 ppm and at 500 ppm. Similarly, 5 ppm applications did not inhibit growth of alfalfa or sweetclover seedlings ... with one exception. Disc inhibition tests of the rhizobia bacteria showed thatRhizobium leguminosarum andRhizobium trifolii were most sensitive to the pesticides.Rhizobium meliloti, and particularlyRhizobium japonicum, were resistant to the insecticides. No consistent correlation was observed between tests on the nodulating bacteria and the tests on legume growth.Published with the approval of the Director of the North Dakota Agricultural Experiment Station as Journal Article No.309. Portion of a thesis presented by the senior author in partial fulfillment of the requirements for the M.S. degree in bacteriology at North Dakota State University.     

Effects of salicylhydroxamate on respiration, seed germination and seedling growth in Avena fatua

The effects of inhibitors of alternative respiration [salicylhydroxamate (SHAM) and propyl gallate (PG)] on germination, seedling growth and O₂ uptake in Avena fatua L. (wild oats) were studied. SHAM did not inhibit germination or O₂ uptake prior to germination. SHAM-sensitive (alternative) respiration, therefore, cannot be a pre-requisite for germination. Following germination, both chemicals inhibited seedling growth with the root being more susceptible than the shoot. SHAM concentrations that inhibited root growth by 90 to 95%, inhibited O₂ uptake of 1 cm root apices by less than 15%. While sodium azide (a cytochrome-oxidase inhibitor; 1 m M ) alone inhibited O₂ uptake by only 40 to 50%, in the simultaneous presence of SHAM (or PG), O₂ uptake was inhibited by 90 to 99%. Thus: 1) respiration of wild oat seedling root apices is predominantly cytochrome-mediated and incomplete inhibition of O₂ uptake in the presence of azide alone is due to diversion of electrons to the alternative pathway and 2) even though these roots have little alternative respiration, they maintain the capacity to support a much greater flux of electrons via this path way. SHAM and PG at concentrations (0.05 to 0.4 m M ) which inhibited O₂ uptake significantly in the presence (but not in the absence) of azide had little effect on root growth suggesting that an effect(s) other than that on respiration is involved in the inhibition of root growth at higher concentrations. The effect of SHAM on wild oat root growth is not selective as it also inhibits growth of a number of crop species.     

Effects of kepone on growth and respiration of several estuarine bacteria

The toxicity of Kepone to mixed populations of estuarine microorganisms was determined by standard plate assays on Zobell marine medium containing 0.02, 0.20, and 2.0 mg of Kepone per liter. Under aerobic conditions, Kepone reduced the number of colony-forming units at all concentrations tested, but had no effect on the number of anaerobic microorganisms. Gram-positive organisms were more sensitive to Kepone than were gram-negative organisms. Growth of gram-negative isolates was not inhibited in nutrient broth, but was significantly inhibited in a minimal salts broth. Oxygen uptake by most isolates was reduced 25 to 100% by 20 ppm (20 mg/ml) of Kepone. Oxygen evolution was observed when several gram-positive isolates were exposed to Kepone concentrations of 20 ppm. Pentachlorophenol at concentrations above 28 ppm produced effects similar to those produced by Kepone. Inhibition of electron transport by Kepone was demonstrated by a significant reduction in the specific activities of NADH oxidases and succinooxidase.     

Effects of sieving, drying and rewetting upon soil bacterial community structure and respiration rates

Soil microcosm studies often require some form of soil homogenisation, such as sieving, to provide a representative sample. Frequently, soils are also homogenised following drying and are then rewetted, yet little research has been done to understand how these methods impact upon microbial communities. Here we compared the molecular diversity and functional responses of intact cores from a Scottish grassland soil with homogenised samples prepared by drying, sieving and rewetting or freshly sieving wet soils. Results showed that there was no significant difference in total soil CO₂-C efflux between the freshly sieved and intact core treatments, however, respiration was significantly higher in the dried and rewetted microcosms. Molecular fingerprinting (T-RFLP) of bacterial communities at two different time-points showed that both homogenisation methods significantly altered bacterial community structure with the largest differences being observed after drying and rewetting. Assessments of responsive taxa in each treatment showed that intact cores were dominated by Acidobacterial peaks whereas an increased relative abundance of Alphaproteobacterial terminal restriction fragments were apparent in both homogenised treatments. However, the shift in community structure was not as large in the freshly sieved soil. Our findings suggest that if soil homogenisation must be performed, then fresh sieving of wet soil is preferable to drying and rewetting in approximating the bacterial diversity and functioning of intact cores.     

Effects of abscisic Acid on growth, RNA metabolism, and respiration in germinating bean axes

The effect of abscisic acid on growth, respiration, the ATP pool, and rate and amount of RNA synthesis in aseptically cultured axes of Phaseolus vulgaris during the first 24 hours of germination has been measured in experiments where the duration of abscisic acid application and its concentration have been varied. At concentrations from 10(-7) to 10(-4)m, abscisic acid inhibits synthesis of RNA with maximal inhibition (80%) at 10(-5)m. RNA synthesis is inhibited by abscisic acid at all times examined (12, 18, and 24 hours), but the extent of inhibition is maximal at 18 hours. In 18-hour axes RNA synthesis is inhibited 42%, ATP pool size is reduced 3%, and O(2) consumption is decreased by 6% after 75 minutes of abscisic acid treatment. Inhibition of RNA synthesis is complete by 2 hours of treatment with abscisic acid, and recovery to near control levels occurs by the 3rd hour after removal from abscisic acid.     

Effects of three systemic insecticides on seed germination and growth ofPinus halepensis seedlings

Summary The systemic insecticides Acephate, Chlorpyrifos, and Oxamyl were variously toxic toPinus halepensis seeds and seedlings. When applied directly to seeds. Oxyamyl completely suppressed germination; Acetate and Chlorpyrifos greatly inhibited germination. The insecticides either prevented emergence or inhibited elongation of cotyledons and radicals. The insecticides were toxic to youngPinus halepensis seedlings whether applied to the soil or as shoot dips. Oxamyl was the most toxic of the three insecticidesResearch supported by the Council for International Exchange of Scholars and the College of Agricultural and Life Sciences, University of Wisonsin.     

Determination of organochlorine insecticides in human milk in Costa Rica

DDT and DDE were detected in the milk of 51 nursing mothers in Costa Rica. In the provinces of Puntarenas, Guanacaste and Limón, where a campaign against malaria took place during the last three decades and where crops are intensively sprayed, the amount of total DDT ranges from 0.12 to 2.60 ppm (mean 1.27 ppm), comparatively, the data of total DDT yielded an average of 0.11 ppm (range 0.01-1.22 ppm) in the provinces of San José, Heredia and Cartago, not so intensively exposed to pesticides. Higher concentrations of the metabolite DDE in 100% of the samples indicated chronic contaminations.     

Effects of kepone on growth and respiration of several estuarine bacteria.

The toxicity of Kepone to mixed populations of estuarine microorganisms was determined by standard plate assays on Zobell marine medium containing 0.02, 0.20, and 2.0 mg of Kepone per liter. Under aerobic conditions, Kepone reduced the number of colony-forming units at all concentrations tested, but had no effect on the number of anaerobic microorganisms. Gram-positive organisms were more sensitive to Kepone than were gram-negative organisms. Growth of gram-negative isolates was not inhibited in nutrient broth, but was significantly inhibited in a minimal salts broth. Oxygen uptake by most isolates was reduced 25 to 100% by 20 ppm (20 mg/ml) of Kepone. Oxygen evolution was observed when several gram-positive isolates were exposed to Kepone concentrations of 20 ppm. Pentachlorophenol at concentrations above 28 ppm produced effects similar to those produced by Kepone. Inhibition of electron transport by Kepone was demonstrated by a significant reduction in the specific activities of NADH oxidases and succinooxidase.