Verification of a benthic boxcosm system with potential for extrapolating experimental results to the field

A marine mesocosm system (boxcosm system) was developed for ecological and/or ecotoxicological studies of sediment community function and structure. The system consists of continuous flow-through incubations of intact sediment samples, each with a surface area of 0.25 m². The experimental setup enables repeated non-destructive measurements of benthic fluxes, such as of nutrients, oxygen and dissolved inorganic carbon, over the sediment-water interface. The benthic fluxes reflect the function of the sediment community, integrating over the chemical, biological and physical activities in the sediment. The suitability of the boxcosm system for controlled, highly ecologically relevant studies of intact sediment communities was evaluated in two experiments of six weeks and five months duration respectively, where the functional and structural development over time was compared to the development of the sampling site. The function of the sediment was measured as nutrient and oxygen fluxes, and the structural component consisted of microbial functional diversity and meio- and macrofauna composition. Differences between the boxcosm and the sampling site were detected especially in nitrate fluxes and meiofauna diversity and abundance, but all differences fell within seasonal and inter-annual variability at the sampling site. The cause of the differences could be referred to differences in oxygen availability, supply of organic matter particles, and recruitment of larvae. These factors can however be compensated for within the present setup. The study shows that the boxcosms are suitable tools for ecologically relevant studies generating comparable conditions to the natural environment.     

Microbial Activity at the Sediment-Water Interface in Halifax Harbor, Canada

The sediment-water interface in Halifax Harbor supports a microbial population of 6.95 × 10⁹ cells per g (dry weight). As determined by the standard technique of suspending subsamples in filtered seawater, the uptake of added glutamic acid by this population is 113.5 ng g (dry weight)⁻¹ h⁻¹. An alternate technique was developed to measure the heterotrophic activity of the interface over longer periods of time, using undisturbed cores with the sediment-water interface intact. Under these conditions, the microbes in the water column and the interface increased exponentially in number, with mean doubling times of 9.6 and 4.5 days, respectively. The uptake of glutamic acid by the microbial population of the interface was determined to be 12.7 ng g (dry weight)⁻¹ h⁻¹, almost an order of magnitude less than the uptake determined by the previous method. This indicates that substrate diffusion and competition for substrate by the microbes in the water column are important factors when considering the heterotrophic activity of the sediment microbial population. After 48 h of incubation, uptake and respiration ceased, probably due to the exhaustion of labeled substrate. Additional substrate added after 48 h of incubation was taken up at a rate similar to that measured after the first addition. It appears that the microbial population of the interface is able to respond quickly and repeatedly to relatively large nutrient additions. After 10 days of incubation, the number of “viable” cells as determined by autoradiography was much smaller than the increase in numbers as determined by direct counts. Apparently a large part of the viable population is unaffected by nutrient addition.     

Influence of Deep Ocean Sewage Outfalls on the Microbial Activity of the Surrounding Sediment

The microbial activity near two deep ocean sewage outfalls off the coast of the island of Oahu, Hawaii, was characterized. Water samples and sediment samples to a depth of 4.5 cm were analyzed from an area of approximately 4.5 × 10⁴ m² surrounding the outfalls. Although the effluent water at both sites exhibited heterotrophic activity that was 2 orders of magnitude greater than water from a control site, ambient water samples taken within 1 m of the discharge ports exhibited activity only twice that of the control water. The heterotrophic activity of the outfall sediment was only elevated above that of the control site for surface samples collected within 10 m of the outfall. Likewise, the rates of microbial nucleic acid synthesis and carbon production in the sediment were only elevated immediately adjacent to the outfalls. Total microbial biomass, as determined by the ATP content of the sediment, varied spatially but was generally elevated at the outfall sites. The specific growth rates calculated for the sediment microbial populations, however, were not greater at the outfall sites. At one site the rocks surrounding the diffuser pipe were covered with copious amounts of slime that appeared to be composed entirely of microbial cells and filaments. This microbial mat was extremely active with respect to heterotrophic activity and biomass production. Overall, it appears that the impact of the sewage discharge on the ambient seawater microbiota is slight and that the effect on the sediment microbiota is confined to an area immediately adjacent to the diffuser ports. In the sand itself, the effect is limited to the upper 2 cm at most.     

Response of sediment microbial community structure in a freshwater reservoir to manipulations in oxygen availability

Hypolimnetic oxygenation systems (HOx) are being increasingly used in freshwater reservoirs to elevate dissolved oxygen levels in the hypolimnion and suppress sediment-water fluxes of soluble metals (e.g. Fe and Mn) which are often microbially mediated. We assessed changes in sediment microbial community structure and corresponding biogeochemical cycling on a reservoir-wide scale as a function of HOx operations. Sediment microbial biomass as quantified by DNA concentration was increased in regions most influenced by the HOx. Following an initial decrease in biomass in the upper sediment while oxygen concentrations were low, biomass typically increased at all depths as the 4-month-long oxygenation season progressed. A distinct shift in microbial community structure was only observed at the end of the season in the upper sediment near the HOx. While this shift was correlated to HOx-enhanced oxygen availability, increased TOC levels and precipitation of Fe- and Mn-oxides, abiotic controls on Fe and Mn cycling, and/or the adaptability of many bacteria to variations in prevailing electron acceptors may explain the delayed response and the comparatively limited changes at other locations. While the sediment microbial community proved remarkably resistant to relatively short-term changes in HOx operations, HOx-induced variation in microbial structure, biomass, and activity was observed after a full season of oxygenation.     

Dynamics of microbial biomass and activity in five habitats of the Okefenokee Swamp ecosystem

A variety of freshwater marsh and swamp habitats are found interspersed in a mosaic pattern throughout the Okefenokee Swamp, Georgia, USA. We examined spatial and temporal patterns in standing stocks and activity in the microbial community of five habitats within this heterogeneous ecosystem. Standing stock dynamics were studied by measuring microbial biomass (ATP) and bacterial numbers (AODC) in both water and sediments over a 14 month period. Abundance varied temporally, being generally lower in winter months than in spring and summer months. However, a large proportion of the measured variability was not correlated with temporal patterns in temperature or with bulk nutrient levels. Spatial variability was characteristic of the Okefenokee at a variety of large and small scales. Habitat-level heterogeneity was evident when microbial standing stocks and activity (measured as [¹⁴C]lignocellulose mineralization) were compared across the five communities, although abundance differences among sites were restricted to nonwinter months when microbial biomass was high. Spatial variation within habitats was also found; patches of surface sediment with differing microbial activity or abundance were measured at scales from 30 cm to 150 m.     

Heterotrophic Activity Throughout a Vertical Profile of Seawater and Sediment in Halifax Harbor, Canada

The relative heterotrophic activity of marine microorganisms was determined at two sites by the heterotrophic uptake technique throughout the water column, the sediment-water interface, and the surface layer of sediment. In the water column, uptake was greatest at the surface and steadily decreased with depth. The percentage of the substrate that was respired also decreased with depth from 69 to 56%. The activity of the sediment-water interface was several orders of magnitude greater than that of the overlying water and twice that of the sediment immediately below. Hand-collected water samples carefully taken as close as 1 cm from the sediment-water interface had the same characteristically low activity as the bottom few meters of water. Microautoradiography with ³H-labeled glucose, glutamic acid, or thymidine revealed a general decrease in the percentage of active cells with depth from 35 to <1%. The number of active cells in the interface and sediment averaged <10% of the total population. The data indicate that the sediment-water interface is the most active region in this system due to an increased number of active cells rather than an increased percentage of active cells or increased per-cell activity.     

Virio- and Bacterioplankton Microscale Distributions at the Sediment-Water Interface

The marine sediment-water interface is an important location for microbially controlled nutrient and gas exchange processes. While microbial distributions on the sediment side of the interface are well established in many locations, the distributions of microbes on the water side of the interface are less well known. Here, we measured that distribution for marine virio- and bacterioplankton with a new two-dimensional technique. Our results revealed higher heterogeneity in sediment-water interface biomass distributions than previously reported with a greater than 45– and 2500-fold change cm⁻¹ found within bacterial and viral subpopulations compared to previous maxima of 1.5- and 1.4-fold cm⁻¹ in bacteria and viruses in the same environments. The 45-fold and 2500-fold changes were due to patches of elevated and patches of reduced viral and bacterial abundance. The bacterial and viral hotspots were found over single and multiple sample points and the two groups often coincided whilst the coldspots only occurred over single sample points and the bacterial and viral abundances showed no correlation. The total mean abundances of viruses strongly correlated with bacteria (r = 0.90, p<0.0001, n = 12) for all three microplates (n = 1350). Spatial autocorrelation analysis via Moran’s I and Geary’s C revealed non-random distributions in bacterial subpopulations and random distributions in viral subpopulations. The variable distributions of viral and bacterial abundance over centimetre-scale distances suggest that competition and the likelihood of viral infection are higher in the small volumes important for individual cell encounters than bulk measurements indicate. We conclude that large scale measurements are not an accurate measurement of the conditions under which microbial dynamics exist. The high variability we report indicates that few microbes experience the ‘average’ concentrations that are frequently measured.     

Sedimentary microbial community dynamics in a regulated stream: East Fork of the Little Miami River,Ohio

A field study was conducted in the Lower East Fork of the Little Miami River, a regulated stream in Clermont county, Ohio, to determine how changes in streamflow, water temperature and photo-period affect sediment microbial community structure. Surface sediment cores were collected from sampling stations spanning 60 river kilometers three to four times per year between October 1996 and October 1999. During the final year of the field study, water temperature, water depth, conductivity, total suspended solids, dissolved organic carbon, instantaneous streamflow velocity, sediment grain size and sediment organic matter were determined. Total microbial biomass was measured using the phospholipid phosphate technique (PLP) and ranged between 2 and 134 nmol PLP * g(-1) dry weight sediment with a mean of 25 nmol PLP * g(-1). Microbial community structure was determined using the phospholipid fatty acid analysis and indicated seasonal shifts in sedimentary microbial community composition. January to June sedimentary microbial biomass was predominately prokaryotic (60% +/- 2), whereas microeukaryotes dominated samples collected during the late summer (55% +/- 2.4) and fall (60% +/- 2). These changes were correlated with stream discharge and water temperature. Microbial community structure varied spatially about a reservoir with prokaryotic biomass dominant at upstream stations and eukaryotic biomass dominant at downstream stations. These findings reveal that sedimentary microbial communities in streams are dynamic responding to the seasonal variation of environmental factors.     

Microbial community structure and biomass estimates of a methanogenic Antarctic Lake ecosystem as determined by phospholipid analyses

Phospholipid analyses were performed on water column particulate and sediment samples from Ace Lake, a meromictic lake in the Vestfold Hills, Antarctica, to estimate the viable microbial biomass and community structure in the lake. In the water column, methanogenic bacterial phospholipids were present below 17 m in depth at concentrations which converted to a biomass of between 1 and 7×10⁸ cells/liter. Methanogenic biomass in the sediment ranged from 17.7×10⁹ cells/g dry weight of sediment at the surface to 0.1×10⁹ cells/g dry weight at 2 m in depth. This relatively high methanogenic biomass implies that current microbial degradation of organic carbon in Ace Lake sediments may occur at extremely slow rates. Total microbial biomass increased from 4.4×10⁸ cells/ liter at 2 m in depth to 19.4×10⁸ cells/liter at 23 m, near the bottom of the water column. Total nonarchaebacterial biomass decreased from 4.2 ×10⁹ cells/g dry weight in the surface sediment (1/4 the biomass of methanogens) to 0.06×10⁸ cells/g dry weight at 2 m in depth in the sediment. Phospholipid fatty acid profiles showed that microeukaryotes were the major microbial group present in the oxylimnion of the lake, while bacteria dominated the lower, anoxic zone. Sulfate-reducing bacteria (SRB) comprised 25% of the microbial population at 23 m in depth in the water column particulates and were present in the surface sediment but to a lesser extent. Biomass estimates and community structure of the Ace Lake eco-system are discussed in relation to previously measured metabolic rates for this and other antarctic and temperate ecosystems. This is the first instance, to our knowledge, in which the viable biomass of methanogenic and SRB have been estimated for an antarctic microbial community.     

Microbial Response of a Freshwater Benthic Community to a Simulated Diatom Sedimentation Event: Interactive Effects of Benthic Fauna

Abstract The response of a sediment microbial assemblage to a pulse of diatoms was studied over 36 days by measuring bacterial activity and biomass, ATP concentration, and overall community respiration in laboratory microcosms. Also, the contribution of macrofaunal chironomids to the decomposition of settling diatoms in benthic communities, and the relative importance of benthic meiofauna in community metabolism, were determined. The addition of diatoms resulted in an immediate response by sediment bacteria, with higher bacterial production recorded after only 2 h, and a more than tenfold increase within one day. The rapid response by sediment bacteria was accompanied by relatively high initial concentrations of dissolved organic carbon. In treatments receiving diatoms, higher bacterial production was sustained throughout the experiment. Surprisingly, neither these elevated production estimates, nor the starvation of controls affected bacterial abundance. Mean bacterial cell volume, however, was markedly affected by the addition of diatoms. Combining community respiration measurements and bacterial production estimates showed that growth efficiencies for sediment bacteria ranged from 14.6 to 34.5%. The contribution of ambient meiozoobenthos to carbon metabolism was less than 1%. Carbon budgets showed that 1.3 mg C was cooxidized along with 4.3 mg added diatom C. Sediment reworking by Chironomus larvae initially enhanced bacterial production, but the presence of Chironomus resulted in lower bacterial production estimates after 16 and 36 days. This was interpreted as a result of faster decomposition of diatoms in treatments with chironomids, which was validated by a faster decline of ATP and chlorophyll a in the sediment. Our results indicate that Chironomus larvae compete with sediment bacteria for available organic substrates. Received: 11 June 1996; Accepted: 13 August 1996     

Determination of the sedimentary microbial biomass by extractible lipid phosphate

Summary The measurement of lipid phosphate is proposed as an indicator of microbial biomass in marine and estuarine sediments. This relatively simple assay can be performed on fresh, frozen or frozen-lyophilized sediment samples with chloroform methanol extraction and subsequent phosphate determination. The sedimentary lipid phosphate recovery correlates with the extractible ATP and the rate of DNA synthesis. Pulse-chase experiments show active metabolism of the sedimentary phospholipids. The recovery of added ¹⁴C-labeled bacterial lipids from sediments is quantitative. Replicate analyses from a single sediment sample gave a standard deviation of 11%. The lipid extract can be fractionated by relatively simple procedures and the plasmalogen, diacyl phospholipid, phosphonolipid and non-hydrolyzable phospholipid content determined. The relative fatty acid composition can be readily determined by gas-liquid chromatography.The lipid composition can be used to define the microbial community structure. For example, the absence of polyenoic fatty acids indicates minimal contamination with benthic micro-eukaryotes. Therefore the high content of plasmalogen phospholipids in these sediments suggests that the anaerobic prokaryotic Clostridia are found in the aerobic sedimentary horizon. This would require anaerobic microhabitats in the aerated zones.     

Shifts in Microbial Community Composition Following Surface Application of Dredged River Sediments

Sediment input to the Illinois River has drastically decreased river depth and reduced habitats for aquatic organisms. Dredging is being used to remove sediment from the Illinois River, and the dredged sediment is being applied to the surface of a brownfield site in Chicago with the goal of revegetating the site. In order to determine the effects of this drastic habitat change on sediment microbial communities, we examined sediment physical, chemical, and microbial characteristics at the time of sediment application to the soil surface as well as 1 and 2 years after application. Microbial community biomass was determined by measurement of lipid phosphate. Microbial community composition was assessed using phospholipid fatty acid (PLFA) analysis, terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes, and clone library sequencing of 16S rRNA genes. Results indicated that the moisture content, organic carbon, and total nitrogen content of the sediment all decreased over time. Total microbial biomass did not change over the course of the study, but there were significant changes in the composition of the microbial communities. PLFA analysis revealed relative increases in fungi, actinomycetes, and Gram positive bacteria. T-RFLP analysis indicated a significant shift in bacterial community composition within 1 year of application, and clone library analysis revealed relative increases in Proteobacteria, Gemmatimonadetes, and Bacteriodetes and relative decreases in Acidobacteria, Spirochaetes, and Planctomycetes. These results provide insight into microbial community shifts following land application of dredged sediment.     

Genotypic and Phenotypic Responses of a Riverine Microbial Community to Polycyclic Aromatic Hydrocarbon Contamination

The phenotypic and genotypic adaptation of a freshwater sedimentary microbial community to elevated (22 to 217 μg g [dry weight] of sediment⁻¹) levels of polycyclic aromatic hydrocarbons (PAHs) was determined by using an integrated biomolecular approach. Central to the approach was the use of phospholipid fatty acid (PLFA) profiles to characterize the microbial community structure and nucleic acid analysis to quantify the frequency of degradative genes. The study site was the Little Scioto River, a highly impacted, channelized riverine system located in central Ohio. This study site is a unique lotic system, with all sampling stations having similar flow and sediment characteristics both upstream and downstream from the source of contamination. These characteristics allowed for the specific analysis of PAH impact on the microbial community. PAH concentrations in impacted sediments ranged from 22 to 217 μg g (dry weight) of sediment⁻¹, while PAH concentrations in ambient sediments ranged from below detection levels to 1.5 μg g (dry weight) of sediment⁻¹. Total microbial biomass measured by phospholipid phosphate (PLP) analysis ranged from 95 to 345 nmol of PLP g (dry weight) of sediment⁻¹. Nucleic acid analysis showed the presence of PAH-degradative genes at all sites, although observed frequencies were typically higher at contaminated sites. Principal component analysis of PLFA profiles indicated that moderate to high PAH concentrations altered microbial community structure and that seasonal changes were comparable in magnitude to the effects of PAH pollution. These data indicate that this community responded to PAH contamination at both the phenotypic and the genotypic level.     

Ecosystem properties and microbial community changes in primary succession on a glacier forefront

We studied microbial community composition in a primary successional chronosequence on the forefront of Lyman Glacier, Washington, United States. We sampled microbial communities in soil from nonvegetated areas and under the canopies of mycorrhizal and nonmycorrhizal plants from 20- to 80-year-old zones along the successional gradient. Three independent measures of microbial biomass were used: substrate-induced respiration (SIR), phospholipid fatty acid (PLFA) analysis, and direct microscopic counts. All methods indicated that biomass increased over successional time in the nonvegetated soil. PLFA analysis indicated that the microbial biomass was greater under the plant canopies than in the nonvegetated soils; the microbial community composition was clearly different between these two types of soils. Over the successional gradient, the microbial community shifted from bacterial-dominated to fungal-dominated. Microbial respiration increased while specific activity (respiration per unit biomass) decreased in nonvegetated soils over the successional gradient. We proposed and evaluated new parameters for estimating the C use efficiency of the soil microbial community: “Max” indicates the maximal respiration rate and “Acc” the total C released from the sample after a standard amount of substrate is added. These, as well as the corresponding specific activities (calculated as Max and Acc per unit biomass), decreased sharply over the successional gradient. Our study suggests that during the early stages of succession the microbial community cannot incorporate all the added substrate into its biomass, but rapidly increases its respiration. The later-stage microbial community cannot reach as high a rate of respiration per unit biomass but remains in an “energy-saving state,” accumulating C to its biomass. Received: 4 June 1998 / Accepted: 11 January 1999     

Fluorometric Determination of Adenosine Nucleotide Derivatives as Measures of the Microfouling, Detrital, and Sedimentary Microbial Biomass and Physiological Status

Adenosine, adenine, cyclic adenosine monophosphate (AMP), AMP, nicotinamide adenine dinucleotide, adenosine diphosphate, and adenosine triphosphate (ATP) were recovered quantitatively from aqueous portions of lipid extracts of microfouling, detrital, and sedimentary microbial communities. These could be detected quantitatively in the picomolar range by forming their 1-N⁶-etheno derivatives and analyzing by high-pressure liquid chromatography with fluorescence detection. Lipid extraction and subsequent analysis allowed the simultaneous measurement of the microbial community structure, total microbial biomass with the quantitative recovery of the adenine-containing cellular components, which were protected from enzymatic destruction. This extraction and fluorescent derivatization method showed equivalency with the luciferin-luciferase method for bacterial ATP measurements. Quick-freezing samples in the field with dry ice-acetone preserved the ATP and energy charge (a ratio of adenosine nucleotides) for analysis at remote laboratories. The metabolic lability of ATP in estuarine detrital and microfouling communities, as well as bacterial monocultures of constant biomass, showed ATP to be a precarious measure of biomass under some conditions. Combinations of adenosine and adenine nucleotides gave better correlations with microbial biomass measured as extractable lipid phosphate in the detrital and microfouling microbial communities than did ATP alone. Stresses such as anoxia or filtration are reflected in the rapid accumulation of intracellular adenosine and the excretion of adenosine and AMP into the surrounding milieu. Increases in AMP and adenosine may prove to be more sensitive indicators of metabolic status than the energy charge.     

Effect of starvation length upon microbial activity in a biomass recycle reactor

The kinetics of substrate degradation and bacterial growth was determined in a microbial community from a biomass recycle reactor that had been deprived of substrate feed for 0–32 days. Starvation caused changes in bacterial numbers, community composition, and physiological state. Substrate starvation for less than 1 day resulted in modest (less than threefold) changes in endogenous respiration rate, ATP content, and biomass level. During a starvation period of 32 days, there were substantial changes in microbial community composition, as assessed by denaturing gradient gel electrophoresis (DGGE) fingerprinting of PCR amplicons of a portion of the 16S rDNA or by phospholipid fatty acid (PLFA) analysis. When the starved communities were stimulated with organic nutrients, the growth kinetics was a function of the length of the starvation period. For starvation periods of 2–8 days prior to nutrient addition, there was a phase of suboptimal exponential growth (S-phase) in which the exponential growth rate was about 30% of the ultimate unrestricted growth rate. S-phase lasted for 2–8 h and then unrestricted growth occurred at rates of 0.3–0.4 h⁻¹. At starvation times of 12 and 20 days, a lag phase preceded S-phase and the unrestricted growth phase. Received 04 January 2002/ Accepted in revised form 08 August 2002     

Distribution and Composition of Microbial Populations in a Landfill Leachate Contaminated Aquifer (Grindsted, Denmark)

Abstract To investigate whether landfill leachates affected the microbial biomass and/or community composition of the extant microbiota, 37 samples were collected along a 305-m transect of a shallow landfill-leachate polluted aquifer. The samples were analyzed for total numbers of bacteria by use of the acridine orange direct count method (AODC). Numbers of dominant, specific groups of bacteria and total numbers of protozoa were measured by use of the most probable number method (MPN). Viable biomass estimates were obtained from measures of ATP and ester-linked phospholipid fatty acid (PLFA) concentrations. The estimated numbers of total bacteria by direct counts were relatively constant throughout the aquifer, ranging from a low of 4.8 × 10⁶ cells/g dry weight (dw) to a high of 5.3 × 10⁷ cells/g dw. Viable biomass estimates based on PLFA concentrations were one to three orders of magnitude lower with the greatest concentrations (up to 4 × 10⁵ cells/g dw) occurring at the border of the landfill and in samples collected from thin lenses of clay and silt with sand streaks. Cell number estimates based on ATP concentrations were also found to be lower than the direct count measurements (<2.2 × 10⁶ cells/g dw), and with the greatest concentrations close to the landfill. Methanogens (Archaea) and reducers of sulfate, iron, manganese, and nitrate were all observed in the aquifer. Methanogens were found to be restricted to the most polluted and reduced part of the aquifer at a maximum cell number of 5.4 × 10⁴ cells/g dw. Populations of sulfate reducers decreased with an increase in horizontal distance from the landfill ranging from a high of 9.0 × 10³ cells/g dw to a low of 6 cells/g dw. Iron, manganese, and nitrate reducers were detected throughout the leachate plume all at maximum cell numbers of 10⁶ cells/g dw. Changes in PLFA profiles indicated that a shift in microbial community composition occurred with increasing horizontal distance from the landfill. The types and patterns of lipid biomarkers suggested that increased proportions of sulfate- and iron-reducing bacteria as well as certain microeukaryotes existed at the border of the landfill. The presence of these lipid biomarkers correlated with the MPN results. There was, however, no significant correlation between the abundances of the specific PLFA biomarkers and quantitative measurements of redox processes. The application of AODC, MPN, PLFA, and ATP analyses in the characterization of the extant microbiota within the Grindsted aquifer revealed that as distance increased from the leachate source, viable biomass decreased and community composition shifted. These results led to the conclusion that the landfill leachate induced an increase in microbial cell numbers by altering the subsurface aquifer so that it was conducive to the growth of methanogens and of iron-and sulfate-reducing bacteria and fungi. Received: 11 June 1998; Accepted: 10 December 1998     

Inadequacy of the Eucaryote Inhibitor Cycloheximide in Studies of Protozoan Grazing on Bacteria at the Freshwater-Sediment Interface

Four guilds from a lake sediment-water interface microbial community were isolated and tested for sensitivity to cycloheximide (0.1 to 200 mg liter⁻¹). Field experiments were conducted to compare the inhibition, dilution, and filtration methods for determining grazing rates. Cycloheximide inhibited anaerobic bacteria at 50 mg liter⁻¹, and inhibition of bacterial growth was observed in the grazing experiments. The results show that the assumption of selective inhibition of heterotrophic eucaryotes was violated and preclude the use of cycloheximide in grazing experiments.     

Impact of Coal-Coking Effluent on Sediment Microbial Communities: a Multivariate Approach

The functional response to and recovery from coal-coking waste effluent was evaluated for sediment microbial communities. Twenty estimates of microbial population density, biomass, and activity were measured five times during a 15-month period. Significant effects on microbial communities were observed in response to both wastewater contamination and diversion of the wastewater. Multivariate analysis of variance and discriminant analysis indicated that accurate differentiation between uncontaminated and contaminated sediments required a minimum of nine estimates of community response. Total viable population density, ATP, alkaline phosphatase, naphthalene, and phenanthrene mineralization rates were found to be highly weighted variables in site discrimination. Lipid and glucose mineralization, nitrogen fixation, and sediment protein also contributed significantly to explaining variation among sites. Estimates of anaerobic population densities and rates of methane production contributed little to discrimination among sites in the environment examined. In general, total viable population density, ATP, and alkaline phosphatase activity were significantly depressed in contaminated sediments. However, after removal of this contamination, the previously affected sites demonstrated greater temporal variability but a closer approximation of the mean response at the control site. Naphthalene and phenanthrene mineralization did not follow the general trend and were elevated at the contaminated sites throughout the investigation. Results of the investigation supported the hypothesis that multiple functional measures of microbial community response are required to evaluate the effect of and recovery from environmental contamination. In addition, when long-term effects are evaluated, select physiological traits, i.e., polyaromatic hydrocarbon mineralization, may not reflect population and biomass estimates of community response.     

Vertical and temporal shifts in microbial communities in the water column and sediment of saline meromictic Lake Kaiike (Japan), as determined by a 16S rDNA-based analysis, and related to physicochemical gradients

The vertical and temporal changes in microbial communities were investigated throughout the water column and sediment of the saline meromictic Lake Kaiike by PCR-denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Marked depth-related changes in microbial communities were observed at the chemocline and the sediment-water interface. However, no major temporal changes in the microbial community below the chemocline were observed during the sampling period, suggesting that the ecosystem in the anoxic zone of Lake Kaiike was nearly stable. Although the sequence of the most conspicuous DGGE band throughout the anoxic water and in the top of the microbial mat was most similar to that of an anoxic, photosynthetic, green sulphur bacterium, Pelodyction luteolum DSM273 (97% similarity), it represented a new phylotype. A comparison of DGGE banding patterns of the water column and sediment samples demonstrated that specific bacteria accumulated on the bottom from the anoxic water layers, and that indigenous microbial populations were present in the sediment. The measurements of bicarbonate assimilation rates showed significant phototrophic assimilation in the chemocline and lithoautotrophic assimilation throughout the anoxic water, but were not clearly linked with net sulphide turnover rates, indicating that sulphur and carbon metabolisms were not directly correlated.