Adaptation of Aquatic Microbial Communities to Quaternary Ammonium Compounds

The effects of long-chain (C₁₂ to C₁₈) quaternary ammonium compounds (QACs) on the density, heterotrophic activity, and biodegradation capabilities of heterotrophic bacteria were examined in situ in a lake ecosystem. Monoalkyl and dialkyl substituted QACs were tested over a range of concentrations (0.001 to 10 mg/liter) in both acute (3 h) and chronic (21 day) exposures. In general, none of the QACs tested had significant adverse effects on bacterial densities in either acute or chronic studies. However, significant decreases in bacterial heterotrophic activity were noted in acute studies at QAC concentrations from 0.1 to 10 mg/liter. Chronic exposure of lake microbial communities to a specific monoalkyl QAC resulted in an adaptive response and recovery of heterotrophic activity. No-observable-effect level in the adapted populations was >10 mg/liter. Chronic exposure also resulted in significant increases in the number and activity of bacteria capable of biodegrading the material. The increase in biodegradation capability was observed at low (microgram per liter) concentrations which are approximately the same as realistic environmental levels. In general, our studies indicated that exposure of lake microbial communities to QACs results in the development of adapted communities which are less sensitive to potential toxic effects and more active in the biodegradation of these materials.     

Degradation of Phenol Compounds by Microbial Communities of the Amur Estuary

The microbiological transformation of various phenol compounds and their origin in the mixing zone of the Amur Estuary is considered. The results of the model experiments on the decomposition and transformation of phenol compounds by microbial communities and bacteria are reported. Self-depuration of the Amur Estuary depends on the mechanisms of the transformation of aromatic compounds in the presence of cosubstrates, the enzymatic activity of microbial communities, and the temperature. In winter, the ecological risk of pollution by aromatic compounds increases.     

Second-Order Model to Predict Microbial Degradation of Organic Compounds in Natural Waters

The reliability of second-order rate constants for assessing microbial degradation kinetics in natural waters was examined by using three compounds that undergo hydrolytic degradation. The butoxyethyl ester of 2,4-dichlorophenoxyacetic acid was studied in water samples from 31 sites, malathion was examined in water from 14 sites, and chlorpropham was studied in samples from 11 sites. The coefficient of variation for rate constants for each compound was less than 65% over all sites. Additional studies indicated that the rate conformed to second-order kinetics; that is, the rate was proportional to both bacterial and xenobiotic concentrations.     

Effects of Endogenous Substrates on Adaptation of Anaerobic Microbial Communities to 3-Chlorobenzoate

Lengthy adaptation periods in laboratory studies evaluating the potential for contaminant biodegradation in natural or engineered environments may indicate that the native microbial communities are not metabolizing the contaminants in situ. In this study, we characterized the adaptation period preceding the biodegradation of 3-chlorobenzoate in anaerobic communities derived from lake sediment and wastewater sludge digesters. The importance of alternative mechanisms of adaptation of the anaerobic communities to 3-chlorobenzoate was evaluated by monitoring the concentrations of metabolic substrates and products as well as the levels of total small subunit (SSU) rRNA and SSU rRNA from populations thought to be important in 3-chlorobenzoate mineralization. The anaerobic environments from which the 3-chlorobenzoate-degrading communities were derived contained different levels of endogenous substrates. Increasing methane levels in the digester and sediment communities and decreasing chemical oxygen demand concentrations in the sediment community during the adaptation periods revealed that endogenous substrates were preferentially utilized relative to 3-chlorobenzoate. Methane and chemical oxygen demand concentrations leveled off concomitantly with the onset of 3-chlorobenzoate biodegradation, suggesting that depletion of the preferentially degraded endogenous substrates stimulated 3-chlorobenzoate metabolism. Consistent with these observations, adaptation to 3-chlorobenzoate occurred more rapidly in digester samples that were depleted of endogenous substrates compared to samples that contained high levels of these biodegradable compounds. Other potential adaptation mechanisms, e.g., genetic change or selective population enrichment, appeared to be less important based on the reproducibility and relative lengths of the adaptation events, trends in the SSU rRNA levels, and/or amplification of SSU rRNA genes from key populations.     

Effect of Concentration of Organic Chemicals on Their Biodegradation by Natural Microbial Communities

The effect of concentration on the biodegradation of synthetic organic chemicals by natural microbial communities was investigated by adding individual ¹⁴C-labeled organic compounds to stream water at various initial concentrations and measuring the formation of ¹⁴CO₂. The rate of degradation of p-chlorobenzoate and chloroacetate at initial concentrations of 47 pg/ml to 47 μg/ml fell markedly with lower initial concentrations, although half or more of the compound was converted to CO₂ in 8 days or less. On the other hand, little mineralization of 2,4-dichlorophenoxyacetate and 1-naphthyl-N-methylcarbamate, or the naphthol formed from the latter, occurred when these compounds were present at initial concentrations of 2 to 3 ng/ml or less, although 60% or more of the chemical initially present at higher concentrations was converted to CO₂ in 6 days. It is concluded that laboratory tests of biodegradation involving chemical concentrations greater than those in nature may not correctly assess the rate of biodegradation in natural ecosystems and that low substrate concentration may be important in limiting biodegradation in natural waters.     

Adaptation of Aquatic Microbial Communities to Hg2+ Stress

The mechanism of adaptation to Hg²⁺ in four aquatic habitats was studied by correlating microbially mediated Hg²⁺ volatilization with the adaptive state of the exposed communities. Community diversity, heterotrophic activity, and Hg²⁺ resistance measurements indicated that adaptation of all four communities was stimulated by preexposure to Hg²⁺. In saline water communities, adaptation was associated with rapid volatilization after an initial lag period. This mechanism, however, did not promote adaptation in a freshwater sample, in which Hg²⁺ was volatilized slowly, regardless of the resistance level of the microbial community. Distribution of the mer operon among representative colonies of the communities was not related to adaptation to Hg²⁺. Thus, although volatilization enabled some microbial communities to sustain their functions in Hg²⁺-stressed environments, it was not mediated by the genes that serve as a model system in molecular studies of bacterial resistance to mercurials.     

Effects of Environmental Toxicants on Metabolic Activity of Natural Microbial Communities

Two methods of measuring microbial activity were used to study the effects of toxicants on natural microbial communities. The methods were compared for suitability for toxicity testing, sensitivity, and adaptability to field applications. This study included measurements of the incorporation of ¹⁴C-labeled acetate into microbial lipids and microbial glucosidase activity. Activities were measured per unit biomass, determined as lipid phosphate. The effects of various organic and inorganic toxicants on various natural microbial communities were studied. Both methods were useful in detecting toxicity, and their comparative sensitivities varied with the system studied. In one system, the methods showed approximately the same sensitivities in testing the effects of metals, but the acetate incorporation method was more sensitive in detecting the toxicity of organic compounds. The incorporation method was used to study the effects of a point source of pollution on the microbiota of a receiving stream. Toxic doses were found to be two orders of magnitude higher in sediments than in water taken from the same site, indicating chelation or adsorption of the toxicant by the sediment. The microbiota taken from below a point source outfall was 2 to 100 times more resistant to the toxicants tested than was that taken from above the outfall. Downstream filtrates in most cases had an inhibitory effect on the natural microbiota taken from above the pollution source. The microbial methods were compared with commonly used bioassay methods, using higher organisms, and were found to be similar in ability to detect comparative toxicities of compounds, but were less sensitive than methods which use standard media because of the influences of environmental factors.     

Nutrient Limitation and Adaptation of Microbial Populations to Chemical Transformations

Using field-collected periphyton and bacterial isolates, we determined adaptation lag periods for microbial transformation of p-cresol. Lag periods were longer for periphyton samples collected from field sites that were low in dissolved inorganic nitrogen and phosphorus. Moreover, lag periods decreased in samples amended with N or P. Our data suggest that adaptation lag periods for microbial transformation of low concentrations of chemicals may correlate with limiting nutrient concentrations, and this correlation may provide a basis for predictive mathematical modeling of lag periods.     

Dissolved Organic Matter Concentration and Quality Influences upon Structure and Function of Freshwater Microbial Communities

Past studies have suggested that the concentration and quality of dissolved organic matter (DOM) may influence microbial community structure. In this study, we cross-inoculated the bacterial communities from two streams and a dystrophic lake that varied in DOM concentration and chemistry, to yield nine fully crossed treatments. We measured dissolved organic carbon (DOC) concentration and heterotrophic microbial community productivity throughout a 72-h incubation period, characterized DOM quality by molecular weight, and determined microbial community structure at the initial and final time points. Our results indicate that all bacterial inoculate sources had similar effects upon DOC concentration and DOM quality, regardless of the DOM source. These effects included an overall decrease in DOM M _W and an initial period of DOC concentration variability between 0-24h. In contrast, microbial communities and their metabolic rates converged to profiles that reflected the DOM source upon which they were growing, regardless of the initial bacterial inoculation. The one exception was that the bacterial community from the low-concentration and low-molecular-weight DOM source exhibited a greater denaturing gradient gel electrophoresis (DGGE) band richness when grown in its own DOM source than when grown in the highest concentration and molecular weight DOM source. This treatment also exhibited a higher rate of productivity. In general, our data suggest that microbial communities are selected by the DOM sources to which they are exposed. A microbial community will utilize the low-molecular-weight (or labile) DOM sources as well as parts of the high-molecular-weight (refractory) DOM, until a community develops that can efficiently metabolize the more abundant high-molecular-weight source. This experiment examines some of the complex interactions between microbial community selection and the combined factors of DOM quality and concentration. Our data suggest that the roles of aerobic aquatic heterotrophic bacteria in carbon cycling, as well as the importance of high-molecular-weight DOM as a carbon source, may be more complex than is conventionally recognized.     

Effects of Concentration and Time of Exposure on the Phytotoxicity of Linuron

When seedlings of lettuce and turnip were grown in nutrientsolutions containing different concentrations of linuron, theconcentration in the shoot at the time when toxicity symptomsappeared was related to the solution concentration. With lettuce,for example, symptoms were recorded after 7 d at 0.15 µg/mland the shoot concentration was 2.7 µg/g fresh wt. At0.06 µg/ml, symptoms appeared after 10 d and the shootconcentration was then 1.1 µg/g fresh wt. If grown fordifferent periods in solutions containing linuron and then transferredto fresh nutrient solutions containing no herbicide, turnipor lettuce seedlings which had accumulated 0.7–0.8 µglinuron/g fresh wt developed toxicity symptoms 4 to 6 d later.Seedlings were also treated with linuron after they had grownfor different periods in control nutrient solutions. The shootconcentrations attained before toxicity symptoms appeared werehigher in those seedlings which were larger when herbicide treatmentbegan. These results show that the herbicide concentration insolution, time of exposure, and age of seedling are interrelatedin determining linuron phytotoxicity.     

Oxygen and the Spatial Structure of Microbial Communities

Oxygen has two faces. On one side it is the terminal electron acceptor of aerobic respiration – the most efficient engine of energy metabolism. On the other hand, oxygen is toxic because the reduction of molecular O₂ creates reactive oxygen species such as the superoxide anion, peroxide, and the hydroxyl radical. Probably most prokaryotes, and virtually all eukaryotes, depend on oxygen respiration, and we show that the ambiguous relation to oxygen is both an evolutionary force and a dominating factor driving functional interactions and the spatial structure of microbial communities.We focus on microbial communities that are specialised for life in concentration gradients of oxygen, where they acquire the full panoply of specific requirements from limited ranges of PO₂ , which also support the spatial organisation of microbial communities. Marine and lake sediments provide examples of steep O₂ gradients, which arise because consumption or production of oxygen exceeds transport rates of molecular diffusion. Deep lakes undergo thermal stratification in warm waters, resulting in seasonal anaerobiosis below the thermocline, and lakes with a permanent pycnocline often have permanent anoxic deep water. The oxycline is here biologically similar to sediments, and it harbours similar microbial biota, the main difference being the spatial scale. In sediments, transport is dominated by molecular diffusion, and in the water column, turbulent mixing dominates vertical transport.Cell size determines the minimum requirement of aerobic organisms. For bacteria (and mitochondria), the half‐saturation constant for oxygen uptake ranges within 0.05 – 0.1% atmospheric saturation; for the amoeba Acanthamoeba castellanii it is 0.2%, and for two ciliate species measuring around 150 μm, it is 1‐2 % atmospheric saturation. Protection against O₂ toxicity has an energetic cost that increases with increasing ambient O₂ tension. Oxygen sensing seems universal in aquatic organisms. Many aspects of oxygen sensing are incompletely understood, but the mechanisms seem to be evolutionarily conserved. A simple method of studying oxygen preference in microbes is to identify the preferred oxygen tension accumulating in O₂ gradients. Microorganisms cannot sense the direction of a chemical gradient directly, so they use other devices to orient themselves. Different mechanisms in different prokaryotic and eukaryotic microbes are described. In O₂ gradients, many bacteria and protozoa are vertically distributed according to oxygen tension and they show a very limited range of preferred PO₂. In some pigmented protists the required PO₂ is contingent on light due to photochemically generated reactive oxygen species. In protists that harbour endosymbiotic phototrophs, orientation towards light is mediated through the oxygen production of their photosynthetic symbionts. Oxygen plays a similar role for the distribution of small metazoans (meiofauna) in sediments, but there is little experimental evidence for this. Thus the oxygenated sediments surrounding ventilated animal burrows provide a special habitat for metazoan meiofauna as well as unicellular organisms.     

Microbial Activity and Community Composition during Bioremediation of Diesel-Oil-Contaminated Soil: Effects of Hydrocarbon Concentration,Fertilizers, and Incubation Time

We investigated the influence of three factors—diesel oil concentration [2500, 5000, 10,000, 20,000 mg total petroleum hydrocarbons (TPH) kg⁻¹ soil], biostimulation (unfertilized, inorganic fertilization with NPK nutrients, or oleophilic fertilization with Inipol EAP22), and incubation time—on hydrocarbon removal, enzyme activity (lipase), and microbial community structure [phospholipid fatty acids (PLFA)] in a laboratory soil bioremediation treatment. Fertilization enhanced TPH removal and lipase activity significantly (P ≤ 0.001). The higher the initial contamination, the more marked was the effect of fertilization. Differences between the two fertilizers were not significant (P > 0.05). Microbial communities, as assessed by PLFA patterns, were primarily influenced by the TPH content, followed by fertilization, and the interaction of these two factors, whereas incubation time was of minor importance. This was demonstrated by three-factorial analysis of variance and multidimensional scaling analysis. Low TPH content had no significant effect on soil microbial community, independent of the treatment. High TPH content generally resulted in increased PLFA concentrations, whereby a significant increase in microbial biomass with time was only observed with inorganic fertilization, whereas oleophilic fertilization (Inipol EAP22) tended to inhibit microbial activity and to reduce PLFA contents with time. Among bacteria, PLFA indicative of the Gram-negative population were significantly (P ≤ 0.05) increased in soil samples containing high amounts of diesel oil and fertilized with NPK after 21–38 days of incubation at 20°C. The Gram-positive population was not significantly influenced by TPH content or biostimulation treatment.     

Degradation of Nucleic Acids and Related Compounds by Microbial Enzymes

The culture filtrate of a strain of Bacillus subtilis decomposed ribonucleic acid into 5′-nucleotides and into other intermediates which released orthophosphate by an arsenate-resistant phosphatase. Under the best conditions examined in these experiments, about 50 per cent of ribonucleic acid was converted into 5′-nucleotides.

The culture filtrate of a strain of Bacillus brevis showed slight activities of ribonuclease and/or phosphodiesterase which produced 5′-nucleotides from ribonucleic acid, but showed predominant activity of 5′-adenylic acid degrading phosphatase.     

Adaptation of Phytoplankton-Degrading Microbial Communities to Thermal Reactor Effluent in a New Cooling Reservoir

In water column and sediment inocula from a nuclear reactor cooling reservoir, natural phytoplankton substrate labeled with ¹⁴C was used to determine aerobic and anaerobic mineralization rates for a range of temperatures (25, 40, 55, and 70°C) expected during reactor operation. For experiments that were begun during reactor shutdown, aerobic decomposition occurred at temperatures of <55°C. After 2 months of reactor operation, aerobic rates increased substantially at 55 and 70°C, although maximum rates were observed at temperatures of ≤40°C. The temperature range for which maximum anaerobic mineralization (i.e., the sum of CH₄ and CO₂) was observed was 25 to 40°C when the reactor was off, expanding to 25 to 55°C during reactor operation. Increased rates at 55°C, but not 70°C, correlated with an increase in the ratio of cumulative methane to carbon dioxide produced over 21 days. When reduced reactor power lowered the maximum temperature of the reservoir to 42°C, aerobic decomposition at 70°C was negligible, but remained substantial at 55°C. Selection for thermophilic decomposers occurred rapidly in this system in both aerobic and anaerobic communities and did not require prolonged exposure to elevated temperatures.     

Making Time for Nature: Visual Exposure to Natural Environments Lengthens Subjective Time Perception and Reduces Impulsivity

Impulsivity in delay discounting is associated with maladaptive behaviors such as overeating and drug and alcohol abuse. Researchers have recently noted that delay discounting, even when measured by a brief laboratory task, may be the best predictor of human health related behaviors (e.g., exercise) currently available. Identifying techniques to decrease impulsivity in delay discounting, therefore, could help improve decision-making on a global scale. Visual exposure to natural environments is one recent approach shown to decrease impulsive decision-making in a delay discounting task, although the mechanism driving this result is currently unknown. The present experiment was thus designed to evaluate not only whether visual exposure to natural (mountains, lakes) relative to built (buildings, cities) environments resulted in less impulsivity, but also whether this exposure influenced time perception. Participants were randomly assigned to either a natural environment condition or a built environment condition. Participants viewed photographs of either natural scenes or built scenes before and during a delay discounting task in which they made choices about receiving immediate or delayed hypothetical monetary outcomes. Participants also completed an interval bisection task in which natural or built stimuli were judged as relatively longer or shorter presentation durations. Following the delay discounting and interval bisection tasks, additional measures of time perception were administered, including how many minutes participants thought had passed during the session and a scale measurement of whether time "flew" or "dragged" during the session. Participants exposed to natural as opposed to built scenes were less impulsive and also reported longer subjective session times, although no differences across groups were revealed with the interval bisection task. These results are the first to suggest that decreased impulsivity from exposure to natural as opposed to built environments may be related to lengthened time perception.     

Degradation of Nucleic Acids and their Related Compounds by Microbial Enzymes

The distribution in microorganisms of extracellular enzymes which degrade RNA into 5′-mononucleotides was studied. The degradation products of RNA were determined by using 5′-nucleotidase and adenosine deaminase.

It was found that the enzymes were produced by various microorganisms belonging to Streptomyces, Bacillus, Fungi imperfecta such as Fusarium, Helminthosporium, etc., and Ascomycetes such as Neurospora, Glomerella, Aspergillus, etc.     

Degradation of Nucleic Acids and their Related Compounds by Microbial Enzymes

Attempts were made to form 5′-mononucleotides from non-proliferating cells of various kinds of yeasts. It was found that yeasts were devided into four groups according to their ability to excrete compounds absorbing at 260 mμ, the first of which excreted UV-absorbing materials at the acid pH (I), the second at the alkaline pH (II), the third both at the acid and alkaline pHs (III), and the fourth showed weak ability to excrete UV-absorbing materials at both pHs (IV). In general, 3′-mononucleotides were excreted at the acid pH and 5′-mononucleotides at the alkaline pH. Rhodotorula pallida, however, excreted 5′-mononucleotides both at the acid and alkaline pHs.     

Degradation of Nucleic Acids and Their Related Compounds by Microbial Enzymes

The optimum pH of the DNA-depolymerase produced by Aspergillus quercinus was found to be about 8.5 and maximal formation of the enzyme in the culture medium was observed at the 96th hour. The culture filtrate of Aspergillus quercinus hydrolyzed DNA into 5′-deoxy-mononucleotides at a pH range higher than 6.0. Each deoxymononucleotide was isolated as crystals in good yield from an enzymatic digest of DNA and characterized spectfophotometri-cally, enzymatically and by determination of its nitrogen and phosphorus composition. 5′-Deoxyinosinic acid was obtained by hydrolysis of DNA with Streptomyces aureus. 5′-Deoxyribo-tides of hypoxanthine and guanine possessed an attractive taste very similar to that of 5′-ino-sinic and 5′-guanylic acids.     

Degradation of Nucleic Acids and their Related Compounds by Microbial Enzymes

Aspergillus quercinus (IFO 4363) was selected as the most suitable strain to produce 5′-mononucleotides from RNA among several species of Aspergillus which produced enzymes capable of degrading RNA into 5′-mononucleotides.

Aspergillus quercinus produced two kinds of RNA-depolymerases (designated as RNA-deploymerase I and II), phosphodiesterase, phosphomonoesterase and adenylic deaminase in the culture medium. The optimum pH of each enzyme was found to be about 4.5, 7.0, 5.0, 6.0 and 5.5, respectively. Maximal production of these enzymes in the culture medium occurred at 96, 96, 216, 168 and 264 hour culture, respectively. The culture filtrate of Aspergillus quercinus degraded RNA into 3′-mononucleotides at the pH lower than 6.0, into 5′-mono-nucleotides at the pH higher than 8.5 and into both mononucleotides at the pH range between 6.0 and 8.5. 5′-Inosinic acid was prepared from RNA by using the extra- and intracellular enzymes of Aspergillus quercinus.