Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.     

Culturable populations of Sporomusa spp. and Desulfovibrio spp. in the anoxic bulk soil of flooded rice microcosms.

Most-probable-number (MPN) counts were made of homoacetogenic and other bacteria present in the anoxic flooded bulk soil of laboratory microcosms containing 90- to 95-day-old rice plants. MPN counts with substrates known to be useful for the selective enrichment or the cultivation of homoacetogenic bacteria (betaine, ethylene glycol, 2, 3-butanediol, and 3,4,5-trimethoxybenzoate) gave counts of 2.3 x 10(3) to 2.8 x 10(5) cells per g of dry soil. Homoacetogens isolated from the terminal positive steps of these dilution cultures belonged to the genus Sporomusa. Counts with succinate, ethanol, and lactate gave much higher MPNs of 5.9 x 10(5) to 3.4 x 10(7) cells per g of dry soil and led to the isolation of Desulfovibrio spp. Counting experiments on lactate and ethanol which included Methanospirillum hungatei in the medium gave MPNs of 2.3 x 10(6) to 7.5 x 10(8) cells per g of dry soil and led to the isolation of Sporomusa spp. The latter strains could grow with betaine, ethylene glycol, 2, 3-butanediol, and/or 3,4,5-trimethoxybenzoate, but apparently most cells of Sporomusa spp. did not initiate growth in counting experiments with those substrates. Spores apparently accounted for 2. 2% or less of the culturable bacteria. It appears that culturable Desulfovibrio spp. and Sporomusa spp. were present in approximately equal numbers in the bulk soil. Multiple, phylogenetically-distinct, phenotypically-different, strains of each genus were found in the same soil system.     

Bacterial population dynamics in a meromictic lake.

Polyclonal antibodies against nine different bacteria isolated from Lake Saelenvannet in western Norway were produced, and the population dynamics of these strains in the lake were monitored through two spring seasons by immunofluorescence staining. The total counts of bacteria varied over time and space from 1.5 x 10(6) to 1.5 x 10(7) cells ml-1. The counts of specific bacteria were in the range of 10(3) to 10(4) cells ml-1 or less; in sum, they generally made up less than 1% of the bacterial community. Some populations showed significant changes in abundance, with blooms lasting 1 to 3 weeks. The rate of change (increase and decrease) in abundance during blooms was estimated to be 0.2 to 0.6 day-1. The average virus-to-bacteria ratio was 50, and there was a significant correlation between the abundances of virus and bacteria. Both protozoan grazing and lytic virus infection were assessed as possible mechanisms driving the variations in bacterial population density.     

Soil microbial counts and identification of culturable bacteria in an extreme by arid zone

Sixteen samples of two soil cores (about 550 and 180 cm in depth) were drilled at intervals in the lower reach of Heihe river basin (northwest of China) in order to illustrate soil microbial characteristics and diversity of culturable bacteria in an extreme by arid environment. Soil water content, organic matter, total nitrogen, pH, direct cell counts, and culturable microorganism counts were evaluated. The total cell concentration was 19-1120/microg (i.e. 0.19-11.2 x 10(8) per g) soil, the culturable bacteria count being 0.2-10.9 per microg (i.e. 2 x 10(5)-10.9 x 10(6) CFU/g) soil. The number of direct cell counts obtained by 4',6-diamidino-2-phenylindole-staining or the cound of culturable microbes after enrichment with different media were statistically significantly correlated with soil organic matters, total nitrogen content, soil water content and surface vegetation; this partly explained the larger number in the deeper first core than in the shallower one. As part of identification of 228 colonies isolated from the two cores, thirty-two were selected for 16S rDNA amplification, sequencing and molecular identification. These 32 isolates were affiliated to 5 major groups of bacteria: alpha-Proteobacteria, 5-Proteobacteria, gamma-Proteobacteria, the high-G+C G+-bacteria, the low-G+C G- -bacteria, and the Cytophaga-Flexibacter-Bacteroides group. Twenty-eight were rod- or short-rod shaped, which accounted for >87.5% of all species; only 4 of 32 species were cocci (<12.5%).     

Bacterial chromosomal painting for in situ monitoring of cultured marine bacteria

We previously described a new method, bacterial chromosomal painting (BCP), for the in situ identification of bacterial cells. Here, we describe the application of this technique to study the ecology and physiology of cultured marine pelagic bacteria from the western Sargasso Sea (WSS). A total of 86 bacteria were isolated from seawater collected from near the surface, at a depth of 250 m and from nutrient-amended seawater incubations. The 10 bacterial isolates that were best represented in environmental genomic DNA from the WSS were selected using reverse genome probing. BCP hybridization cell counts were used to determine the depth-specific distribution of one of the alpha proteobacterial isolates, B5-6, in the WSS during two thermal stratification regimes: stratified and partially mixed. The maximum cell count measured for B5-6 at the summer deep chlorophyll maximum was approximately 4% of the total cell count. This study is the first application of BCP to natural environments .     

Butyric acid bacteria of the genus Clostridium in the bottom sediments of inland basins of different types

The cell numbers and ecological characteristics of the distribution of certain species of butyric acid bacteria (BAB) of the genus Clostridium in the bottom sediments of inland basins of different types were studied using the optimal nutrient media. The seasonal dynamics of clostridial vegetative cells and spores in sediments with different ecological conditions were revealed. The cell numbers of the dominant BAB species were shown to depend on the redox potential of the sediments, the amount and composition of C(org), and the trophic state of the basin in general. C. pasteurianum was found to predominate in eutrophic lakes and reservoirs (5-11 x 10(6) cells/cm3), C. butyricum and C. felsineum predominated in mesotrophic ones (2-11 x 10(6) cells/cm3), and C. acetobutylicum was predominant in acidic chthionoeutrophic lakes and reservoirs (0.1-0.5 x 10(6) cells/cm3). The lowest cell numbers of BAB were found in river sediments, whereas the highest numbers were recorded in the sediments of polysaprobic zones (0.1-1.0 x 10(3) and 0.5-2.0 x 10(7) cells/cm3 respectively).     

Unexpected diversity of bacteria capable of carbon monoxide oxidation in a coastal marine environment, and contribution of the Roseobacter-associated clade to total CO oxidation

The species diversity, phylogenetic affiliations, and physiological activity rates of carbon monoxide-oxidizing microorganisms were investigated, using new isolates from surface waters collected from the coast of New England and type strains from established collections. A direct isolation method allowed the simultaneous recovery of organisms with different growth rates and nutritional requirements and the identification of marine microorganisms that oxidize CO at an environmentally relevant concentration (42 nM CO). Isolates that oxidized CO at environmentally relevant rates (>4.5x10(-11) nmol CO oxidized cell-1 h-1) were taxonomically diverse, with representatives in the alpha and gamma subclasses of the Proteobacteria and the phylum Bacteroidetes, and represent a hitherto unreported metabolic function for several diverse microbial types. Isolates and type strains having the greatest specific rates of CO metabolism (1.1x10(-10) to 2.3x10(-10) nmol CO oxidized cell-1 h-1) belonged to the Roseobacter-associated clade (RAC) of the alpha subclass of the Proteobacteria. By using triple-labeled slide preparations, differential counts of active CO-oxidizing RAC cells, total RAC cells, and total bacterial cell counts in environmental samples were obtained. RAC organisms were a major component of total cell numbers (36%). Based on the density of active CO-oxidizing RAC cells in natural samples and RAC-specific metabolic activities determined for pure cultures, active CO-oxidizing RAC cells may contribute up to 15% of the total CO oxidation occurring in coastal waters.     

对虾综合养殖生态系底泥细菌的数量动态

1997年5～9月于山东海阳市黄海集团公司养虾场,用5个实验围隔研究了对虾综合养殖生态系底泥细菌的数量动态.结果表明,底泥细菌数量波动在4.10×108～12.36×108cells·g-1之间,平均为8.09×108±2.17×108cells·g-1.随着养殖时间的推移,底泥细菌数量逐渐增加.底泥细菌数量最大值出现在表层1cm之内,2～3cm以下泥层,细菌数量明显减小     

The effect of sewage sludge composting on the quantitative state of some groups of bacteria and fungi

Analysis of the quantitative state of disease causing bacteria and of other microbic groups were done on the sewage sludge from a sewage treatment plant. The results of the analysis include the ammonifying bacteria, nitrifying and denitrifying bacteria. The general quantity of bacteria and fungi in a secondary dehydrated sludge, fermented secondary dehydrated sludge, and in composted secondary dehydrated sludge was deterinated. Composts were prepared from dehydrated secondary sludge with the addition of sawdust. Microbiological analysis of sewage sludge showed, that the quantities of the fecal coli bacteria were 6500; 220 and 150 cells per cm3 of the secondary dehydrated sludge, fermented secondary dehydrated sludge and composted dehydrated secondary sludge, respectively. The numbers of Salmonella were respectively 67.80; 6.48 and 6.60 cells per cm3. The general numbers of bacteria were 2.98 x 10(7); 2.79 x 10(7); 2.15 x 10(7) cells per cm3 of sludge. The cell numbers of fungi were: 6.20x 10(2); 19.60 x 10(2); 7.80 x 10(2) per cm3 of sludge. In the three types of sludge, the results show great numbers of the ammonifying, nitrifying and denitrifying bacteria. Of the analysed groups of bacteria, the highest numbers of cells were found for general bacteria; ammonifying and nitrifying bacteria were next in abundance; still fewer were the denitrifying bacteria. Fungi and pathogenic bacteria were the least numerous.     

Application of a rapid direct viable count method to deep-sea sediment bacteria

For the first time, a Live/Dead (L/D) Bacterial Viability Kit (BacLight ) protocol was adapted to marine sediments and applied to deep-sea sediment samples to assess the viability (based on membrane integrity) of benthic bacterial communities. Following a transect of nine stations in the Fram Strait (Arctic Ocean), we observed a decrease of both bacterial viability and abundance with increasing water (1250-5600 m) and sediment depth (0-5 cm). Percentage of viable (and thus potentially active) cells ranged between 20-60% within the first and 10-40% within the fifth centimetre of sediment throughout the transect, esterase activity estimations (FDA) similarly varied from highest (13.3+/-5.4 nmol cm(-3) h(-1)) to lowest values below detection limit down the sediment column. Allowing for different bottom depths and vertical sediment sections, bacterial viability was significantly correlated with FDA estimations (p<0.001), indicating that viability assessed by BacLight staining is a good indicator for bacterial activity in deep-sea sediments. Comparisons between total L/D and DAPI counts not only indicated a complete bacterial cell coverage, but a better ability of BacLight staining to detect cells under low activity conditions. Time course experiments confirmed the need of a rapid method for viability measurements of deep-sea sediment bacteria, since changes in pressure and temperature conditions caused a decrease in bacterial viability of up to 50% within the first 48 h after sample retrieval. The Bacterial Viability Kit proved to be easy to handle and to provide rapid and reliable information. It's application to deep-sea samples in absence of pressure-retaining gears is very promising, as short staining exposure time is assumed to lessen profound adverse effects on bacterial metabolism due to decompression.     

Enumeration of anaerobic bacterial microflora of the equine gastrointestinal tract

Samples from the duodenum, jejunum, and ileum, as well as from the cecum and colon, were obtained from 11 mature grass-fed horses. Viable counts of total culturable and proteolytic bacteria were made on habitat-simulating media containing 40% clarified ruminal fluid. The mean pHs in the duodenum, jejunum, and ileum were 6.32, 7.10, and 7.47, respectively; the mean pH decreased to 6.7 in the hindgut. The acetate concentration increased along the length of the small intestine and was the only volatile fatty acid present in this gut segment. Molar proportions of acetate, propionate, and butyrate in the hindgut were 85:10:3. Differences in bacterial counts on habitat-simulating media containing equine cecal fluid or clarified ruminal fluid were negligible. Bacterial counts showed a substantial population in the duodenum (ca. 2.9 x 10(6) per g [wet weight] of sample), and this increased to 29.0 x 10(6) in the jejunum and 38.4 x 10(6) in the ileum. Proteolytic bacteria formed a high proportion of the total culturable bacteria, especially in duodenal samples. Counts of proteolytic bacteria per gram (wet weight) of sample were 3.0 x 10(6), 15.6 x 10(6), and 22.0 x 10(6) in the duodenum, jejunum, and ileum, respectively. There was a close relationship between lumenal and mucosal bacterial counts, although actual values were lower in mucosal samples. The mucosal bacterial population in the duodenum was high relative to the lumenal population. Although the comparison of bacterial populations in the hindgut of the horse and white rhino was limited to a single animal, the results were of interest. Counts were higher in the cecum than in the colon for both the horse and the white rhino.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enumeration of anaerobic bacterial microflora of the equine gastrointestinal tract.

Samples from the duodenum, jejunum, and ileum, as well as from the cecum and colon, were obtained from 11 mature grass-fed horses. Viable counts of total culturable and proteolytic bacteria were made on habitat-simulating media containing 40% clarified ruminal fluid. The mean pHs in the duodenum, jejunum, and ileum were 6.32, 7.10, and 7.47, respectively; the mean pH decreased to 6.7 in the hindgut. The acetate concentration increased along the length of the small intestine and was the only volatile fatty acid present in this gut segment. Molar proportions of acetate, propionate, and butyrate in the hindgut were 85:10:3. Differences in bacterial counts on habitat-simulating media containing equine cecal fluid or clarified ruminal fluid were negligible. Bacterial counts showed a substantial population in the duodenum (ca. 2.9 x 10(6) per g [wet weight] of sample), and this increased to 29.0 x 10(6) in the jejunum and 38.4 x 10(6) in the ileum. Proteolytic bacteria formed a high proportion of the total culturable bacteria, especially in duodenal samples. Counts of proteolytic bacteria per gram (wet weight) of sample were 3.0 x 10(6), 15.6 x 10(6), and 22.0 x 10(6) in the duodenum, jejunum, and ileum, respectively. There was a close relationship between lumenal and mucosal bacterial counts, although actual values were lower in mucosal samples. The mucosal bacterial population in the duodenum was high relative to the lumenal population. Although the comparison of bacterial populations in the hindgut of the horse and white rhino was limited to a single animal, the results were of interest. Counts were higher in the cecum than in the colon for both the horse and the white rhino.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microbial processes of the carbon and sulfur cycles in the Chukchi Sea

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 x 10(3) cells ml(-1) in the northern and eastern parts to 245 x 10(3) cells ml(-1) in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH4 l(-1) in the eastern part of the sea to 31 nmol CH4 l(-1) in the northern part of the Herald Canyon. Active microbial processes occurred in the upper 0-3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH4 dm(-3) day(-1). The rates of methane oxidation varied from 1.61 to 14.7 nmol CH4 dm(-3) day(-1). The rates of sulfate reduction varied from 1.35 to 16.2 micromol SO4(2-) dm(-3) day(-1). The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 micromol SO4(2-) dm(-3) day(-1)). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 micromol CH4 m(-2) day(-1).     

Study on the pathophysiology of experimental Burkholderia pseudomallei infection in mice

Burkholderia pseudomallei is the etiological agent of melioidosis, a potentially fatal disease occurring in man and animals. The aim of this study was to investigate the pathophysiological course of experimental melioidosis, and to identify the target organs, in an animal model. For this purpose SWISS mice were infected intraperitoneally with the virulent strain B. pseudomallei 6068. The bacterial load of various organs was quantified daily by bacteriological analysis and by an enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody specific to B. pseudomallei exopolysaccharide (EPS). Electron microscopic investigation of the spleen was performed to locate the bacteria at the cellular level. In this model of acute melioidosis, B. pseudomallei had a marked organ tropism for liver and spleen, and showed evidence of in vivo growth with a bacterial burden of 1.6x10(9) colony forming units (CFU) per gram of spleen 5 days after infection with 200 CFU. The highest bacterial loads were detected in the spleen at all time points, in a range from 2x10(6) to 2x10(9) CFU g(-1). They were still 50-80 times greater than the load of the liver at the time of peak burden. Other investigated organs such as lungs, kidneys, and bone marrow were 10(2)-10(4)-fold less infected than the spleen, with loads ranging from 3x10(2) to 3x10(6) CFU g(-1). The heart and the brain were sites of a delayed infection, with counts in a range from 10(3) to 10(7) times lower than bacterial counts in the spleen. The EPS-specific ELISA proved to be highly sensitive, particularly at the level of those tissues in which colony counting on agar revealed low contamination. In the blood, EPS was detected at concentrations corresponding to bacterial loads ranging from 8x10(3) to 6x10(4) CFU ml(-1). Electron microscopic examination of the spleen revealed figures of phagocytosis, and the presence of large numbers of intact bacteria, which occurred either as single cells or densely packed into vacuoles. Sparse figures suggesting bacterial replication were also observed. In addition, some bacteria could be seen in vacuoles that seemed to have lost their membrane. These observations provide a basis for further investigations on the pathogenesis of the disease.     

Comparison of bacteria from deep subsurface sediment and adjacent groundwater

Samples of groundwater and the enclosing sediments were compared for densities of bacteria using direct (acridine orange direct staining) and viable (growth on 1% PTYG medium) count methodology. Sediments to a depth of 550 m were collected from boreholes at three sites on the Savannah River Site near Aiken, South Carolina, using techniques to insure a minimum of surface contamination. Clusters of wells screened at discreet intervals were established at each site. Bacterial densities in sediment were higher, by both direct and viable count, than in groundwater samples. Differences between direct and viable counts were much greater for groundwater samples than for sediment samples. Densities of bacteria in sediment ranged from less than 1.00×10⁶ bacteria/g dry weight (gdw) up to 5.01 ×10⁸ bacteria/gdw for direct counts, while viable counts were less than 1.00×10³ CFU/gdw to 4.07×10⁷ CFU/gdw. Bacteria densities in groundwater were 1.00×10³–6.31×10⁴ bacteria/ml and 5.75–4.57×10² CFU/ml for direct and viable counts, respectively. Isolates from sediment were also found to assimilate a wider variety of carbon compounds than groundwater bacteria. The data suggest that oligotrophic aquifer sediments have unique and dense bacterial communities that are attached and not reflected in groundwater found in the strata. Effective in situ bioremediation of contaimination in these aquifers may require sampling and characterization of sediment communities.     

Persistence and multiplication of obligate anaerobe bacteria in amebae under aerobic conditions

After co-cultivation of Mobiluncus curtisii, an obligate non-sporeforming anaerobe, with free living amebae from the Acanthamoeba spp. under aerobic conditions, internalization, multiplication and persistence of bacterial cells were established for at least 4-6 weeks. Under the same conditions and media without viable amebae, the cells of M. curtisii did not replicate and died in 4-7 days. The infection of amebae occurred with 10 to 100 bacteria per ml of co-cultivation media. In 7-14 days the amount of bacterial cells increased to 1x10(5)-1x10(6) CFU/mL. Electron microscopic examinations revealed bacteria within vacuoles in the amebae and intracellular replication. These results suggest a previously undescribed mechanism for spread, replication and persistence of obligately anaerobe bacteria in the environment and new possible sources, reservoirs and transfer mechanisms of infections caused by obligate anaerobe bacteria.     

Psychrotrophic bacteria from a coastal station in the Ross sea (Terra Nova Bay, Antarctica).

Seawater samples were collected from a fixed, coastal station in the Terra Nova Bay at different depths during the Xth Oceanographic Cruise in the 1994-95 Antarctic summer. Picoplanktonic abundance, estimated by direct counts in epifluorescence microscopy, ranged from 2.2 x 10(7) to 1.6 x 10(8) cells.l-1. The heterotrophic bacterial densities, evaluated on Marine Agar 2216 (Difco) after incubation at +4 degrees C for 21 days, ranged from 2 x 10(3) to 4.5 x 10(6) CFU.l-1. The qualitative composition of the heterotrophic bacterial community was studied on 64 morphological and biochemical characters of the 125 strains isolated. Heterotrophic, psychrotrophic isolates were tentatively identified at genus level as Pseudomonas, Vibrio, Acinetobacter, and Flavobacterium/Cytophaga. In order to compare the characteristics of the isolates with those previously studied during 1989/90, the synthetical indices of the structure and the metabolic potentiality of the heterotrophic bacterial community were processed. Results showed that the bacterial community was metabolically more active and more homogenous than that previously studied.     

Large fraction of dead and inactive bacteria in coastal marine sediments: comparison of protocols for determination and ecological significance

It is now universally recognized that only a portion of aquatic bacteria is actively growing, but quantitative information on the fraction of living versus dormant or dead bacteria in marine sediments is completely lacking. We compared different protocols for the determination of the dead, dormant, and active bacterial fractions in two different marine sediments and at different depths into the sediment core. Bacterial counts ranged between (1.5 +/- 0.2) x 10(8) cells g(-1) and (53.1 +/- 16.0) x 10(8) cells g(-1) in sandy and muddy sediments, respectively. Bacteria displaying intact membrane (live bacterial cells) accounted for 26 to 30% of total bacterial counts, while dead cells represented the most abundant fraction (70 to 74%). Among living bacterial cells, nucleoid-containing cells represented only 4% of total bacterial counts, indicating that only a very limited fraction of bacterial assemblage was actively growing. Nucleoid-containing cells increased with increasing sediment organic content. The number of bacteria responsive to antibiotic treatment (direct viable count; range, 0.3 to 4.8% of the total bacterial number) was significantly lower than nucleoid-containing cell counts. An experiment of nutrient enrichment to stimulate a response of the dormant bacterial fraction determined a significant increase of nucleoid-containing cells. After nutrient enrichment, a large fraction of dormant bacteria (6 to 11% of the total bacterial number) was "reactivated." Bacterial turnover rates estimated ranged from 0.01 to 0.1 day(-1) but were 50 to 80 times higher when only the fraction of active bacteria was considered (on average 3.2 day(-1)). Our results suggest that the fraction of active bacteria in marine sediments is controlled by nutrient supply and availability and that their turnover rates are at least 1 order of magnitude higher than previously reported.     

Importance of unattached bacteria and bacteria attached to sediment in determining potentials for degradation of xenobiotic organic contaminants in an aerobic aquifer.

The bacterial abundance, distribution, and degradation potential (in terms of degradation versus lack of degradation) for four xenobiotic compounds in an aerobic aquifer sediment have been examined in laboratory and field experiments. The xenobiotic compounds studied were benzene, toluene, o-xylene, and naphthalene (all at concentrations of approximately 120 micrograms/liter). The aerobic degradation experiments ran for approximately 90 days at 10 degrees C, which corresponded to the groundwater temperature. At the end of the experiment, the major part of the microbial biomass, quantified as acridine orange direct counts, was attached to the groundwater sediment (18 x 10(6) to 25 x 10(6) cells per g [dry weight], and only a minor part was unattached in the groundwater (0.6 x 10(6) to 5.5 x 10(6) cells per ml). Experiments involving aquifer sediment suspensions showed identical degradation potentials in the laboratory and in the field. However, laboratory experiments involving only groundwater (excluding aquifer sediment) showed less degradation potential than in situ experiments involving only groundwater, indicating that the manipulation or approach of the laboratory experiments could affect the determination of the degradation potentials. No differences were observed between the groundwater-only and the sediment compartments in the in situ experiments in the ability to degrade the compounds, but the maximum degradation rates were substantially lower in the groundwater-only compartment. Preparations used in laboratory experiments for studying the degradation potential for xenobiotic organic contaminants should contain sediment to obtain the highest numbers of bacteria as well as the broadest and most stable degradation.(ABSTRACT TRUNCATED AT 250 WORDS)