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PubMed2006

The influence of different temperature programmes on the bioremediation of polycyclic aromatic hydrocarbons (PAHs) in a coal-tar contaminated soil by in-vessel composting.

The biodegradation of 16 US. EPA-listed polycyclic aromatic hydrocarbons (sigma PAHs), with accompanying humification and microbial community structure changes during simulated in-vessel composting-bioremediation of an aged coal-tar-contaminated soil amended with green waste were studied over 56 days. The experimental design compared one constant temperature profile (TC=38 degrees C) with three variable temperature profiles (TP1, TP2 and TP3), including treatment at 70 degrees C to comply with regulatory requirements. Greatest sigma PAHs removal (75.4+/-0.1%; k(1)=0.026 day(-1), R(2)=0.98) occurred at TC=38 degrees C compared to all variable temperature profiles TP1 (62.1+/-11.0%; k(1)=0.016 day(-1), R(2)=0.93), TP2 (71.8+/-8.2%; k(1)=0.021 day(-1), R(2)=0.95) and TP3 (45.3+/-9.7%; k(1)=0.010 day(-1), R(2)=0.91). This study proved that using thermophilic temperatures (70 degrees C) towards the end of in-vessel composting processes (TP2) resulted in greater sigma PAHs removal than using other variable temperature profiles (TP1, TP3), as long as the increase was stepwise via an intermediate temperature (55 degrees C). Phospholipid fatty acid (PLFA) signatures indicated that use of thermophilic temperatures towards the end of the in-vessel composting-bioremediation (TP2) resulted in a higher fungal to bacterial PLFA ratio and a lower Gram-positive to Gram-negative (G(+)/G(-)) bacterial ratio. Fluorescence excitation-emission matrix (EEM) showed the presence of peaks typical of humic-like (Ex/Em wavelength pair approximately 340/460 nm) and fulvic-acid-like (Ex/Em wavelength pair approximately 245/460 nm) substances, indicating mineralization and/or maturation of the compost. Varying the temperature during in-vessel composting to comply with regulatory requirements for pathogen control, promoted contaminant biodegradation, microbial activity and compost maturation.

Bacteria↗

PubMed2007

Inhibitory effects of nitrogen oxides on a mixed methanogenic culture.

The effect of nitrate, nitrite, nitric oxide (NO), and nitrous oxide on a mixed, mesophilic (35 degrees C) methanogenic culture was investigated. Short-term inhibition assays were conducted at a concentration range of 10-350 mg N/L nitrate, 17-500 mg N/L nitrite, 0.02-0.8 mg N/L aqueous NO, and 19-191 mg N/L aqueous nitrous oxide. Simultaneous methane production and N-oxide reduction was observed in 10 and 30 mg N/L nitrate and 0.02 mg N/L aqueous NO-amended cultures. However, addition of N-oxide resulted in immediate cessation of methanogenesis in all other cultures. Methanogenesis completely recovered subsequent to the complete reduction of N-oxides to nitrogen gas in all N-oxide-amended cultures, with the exception of the 500 mg N/L nitrite- and 0.8 mg N/L aqueous NO-amended cultures. Partial recovery of methanogenesis was observed in the 500 mg N/L nitrite-amended culture in contrast to complete inhibition of methanogenesis in the 0.8 mg N/L aqueous NO-amended culture. Accumulation of volatile fatty acids was observed in both cultures at the end of the incubation period. Among all N-oxides, NO exerted the most and nitrate exerted the least inhibitory effect on the fermentative/methanogenic consortia. The effect of multiple additions of nitrate (300 mg N/L) on the same methanogenic culture was also investigated. Long-term exposure of the methanogenic culture to nitrate resulted in an increase of N-oxide reduction rates and decrease of methane production rates, which was attributed to changes in the microbial community structure due to nitrate addition.

Bioreactors↗

PubMed2006

Proteomics for the analysis of the Candida albicans biofilm lifestyle.

Candida albicans is an opportunistic pathogenic fungus capable of causing infections in immunocompromised patients. Candidiasis is often associated with the formation of biofilms on the surface of inert or biological materials. Biofilms are structured microbial communities attached to a surface and encased within a matrix of exopolymeric substance (EPS). At present, very little is known about the changes in protein profiles that occur during the transition from the planktonic to the biofilm mode of growth. Here, we report the use of proteomics for the comparative analysis of subcellular fractions obtained from C. albicans biofilm and planktonic cultures, including cell surface-associated proteins and secreted components present in liquid culture supernatants (for planktonic cultures) and EPS (for biofilms). The analysis revealed a high degree of similarity between the protein profiles associated with the planktonic and biofilm extracts, and led to the identification of several differentially expressed protein spots. Among the differentially expressed proteins, there was a preponderance of metabolic enzymes that have been described as cell surface proteins and immunodominant antigens. Proteins found in the biofilm matrix included a few predicted to form part of the secretome, and also many secretion-signal-less proteins. These observations contribute to our understanding of the C. albicans biofilm lifestyle.

Biofilms↗

PubMed2005

Temperature-dependent shift from labile to recalcitrant carbon sources of arctic heterotrophs.

Soils of high latitudes store approximately one-third of the global soil carbon pool. Decomposition of soil organic matter (SOM) is expected to increase in response to global warming, which is most pronounced in northern latitudes. It is, however, unclear if microorganisms are able to utilize more stable, recalcitrant C pools, when labile soil carbon pools will be depleted due to increasing temperatures. Here we report on an incubation experiment with intact soil cores of a frost-boil tundra ecosystem at three different temperatures (2 degrees C, 12 degrees C and 24 degrees C). In order to assess which fractions of the SOM are available for decomposition at various temperatures, we analyzed the isotopic signature of respired CO2 and of different SOM fractions. The delta13C values of CO2 respired were negatively correlated with temperature, indicating the utilization of SOM fractions that were depleted in 13C at higher temperatures. Chemical fractionation of SOM showed that the water-soluble fraction (presumably the most easily available substrates for microbial respiration) was most enriched in 13C, while the acid-insoluble pool (recalcitrant substrates) was most depleted in 13C. Our results therefore suggest that, at higher temperatures, recalcitrant compounds are preferentially respired by arctic microbes. When the isotopic signatures of respired CO2 of soils which had been incubated at 24 degrees C were measured at 12 degrees C, the delta13C values shifted to values found in soils incubated at 12 degrees C, indicating the reversible use of more easily available substrates. Analysis of phospholipid fatty acid profiles showed significant differences in microbial community structure at various incubation temperatures indicating that microorganisms with preference for more recalcitrant compounds establish as temperatures increase. In summary our results demonstrate that a large portion of tundra SOM is potentially mineralizable.

Arctic Regions↗

PubMed2002

Responses of microbial activity and decomposer organisms to contamination in microcosms containing coniferous forest soil.

Soil respiration from microcosms contaminated with pentachlorophenol, 2-ethanolhexanoate, creosote, CuSO4, and benomyl was measured in order to evaluate usefulness of soil microcosms and microbial respiration rate monitoring as a toxicity test in soils with high organic matter content. Coniferous forest soil and its organisms were used as test objects. In addition, how a short-term low temperature period including frost affects respiration dynamics in stressed soils was studied, i.e., whether contaminants reduce resistance of the community to other (also natural) stresses. In addition, at the end of the experiment, effects of contaminants on faunal and microbial community structures were analyzed. Soil respiration measurements from the microcosms appeared to be a sensitive parameter for testing community-level effects of chemicals in the soil with high organic matter content. An 84-day exposure had acute effects, long-term effects, delaying effects, and total recovery of community respiration. Direct negative and indirect positive effects of chemical contamination on the community of soil organisms were found. Responses to contamination of soil respiration rate and structure of the soil community were parallel. Addition of pentachlorophenol, 2-ethanolhexane, and Cu into the soil reduced frost resistance of the decomposer community. It was concluded that soil respiration monitoring of artificially contaminated soil microcosms seems to be a useful tool for testing community-level toxic effects of chemicals.

Antidotes↗

PubMed1999

Microbial methods for assessing contaminant effects in sediments.

Contaminated sediments influence drastically the long-term toxicological and ecological properties of aquatic ecosystems. During the past three decades, scientific knowledge about sediment-water exchange processes and the deposition and distribution of pollutants in water and sediment phases has been supplemented by extensive research on the effects of sediment-associated pollutants on aquatic organisms. Basic research in microbiology, ecology, and toxicology has uncovered the crucial role of sediment microorganisms for the biodegradation of organic matter and for the cycling of nutrients, as well as the susceptibility of these processes to toxic pollution events. Microorganisms have been extensively applied in aquatic toxicology, and various microbial toxicity tests are today available that successfully couple microbial toxicity endpoints to the specificity of the sediment matrix. Sediment-associated toxicants can be brought in contact with test bacteria using sediment pore waters, elutriates, extracts, or whole-sediment material. Toxicity indication principles for microorganisms are versatile and comprise growth and biomass determinations, respiration or oxygen uptake, bacterial luminescence, the activity of a variety of enzymes, and a compendium of genotoxicity assays. The border between toxicological and ecological contaminant effect evaluations in sediments is flexible, and long-term ecological predictions should also include an assessment of pollutant degradation capacities and of key reactions in element cycling. Evaluating microbial community structure and function in environmental systems makes use of modern molecular techniques and bioindicators that could trigger a new quality in the assessment of contaminated sediments in terms of indication of subtoxic effects and early-warning requirements.

Bacteriological Techniques↗

PubMed1995

Characterization of microbial communities in anaerobic bioreactors using molecular probes.

The microbial community structure of twenty-one single-phase and one two-phase full-scale anaerobic sewage sludge digesters was evaluated using oligonucleotide probes complementary to conserved tracts of the 16S rRNAs of phylogenetically defined groups of methanogens and sulfate-reducing bacteria. These probe results were interpreted in combination with results from traditional chemical analyses and metabolic activity assays. It was determined that methanogens in "healthy" mesophilic, single-phase sewage sludge digesters accounted for approximately 8-12% of the total community and that Methanosarcinales and Methanomicrobiales constituted the majority of the total methanogen population. Methanobacteriales and Methanococcales played a relatively minor role in the digesters. Phylogenetic groups of mesophilic, Gram-negative sulfate-reducing bacteria were consistently present at significant levels: Desulfovibrio and Desulfobulbus spp. were the dominant sulfate-reducing populations, Desulfobacter and Desulfobacterium spp. were present at lower levels, and Desulfosarcina, Desulfococcus, and Desulfobotulus spp. were absent. Sulfate reduction by one or more of these populations played a significant role in all digesters evaluated in this study. In addition, sulfate-reducing bacteria played a role in favoring methanogenesis by providing their substrates. The analysis of the two-phase digester indicated that true phase separation was not accomplished: significant levels of active methanogens were present in the first phase. It was determined that the dominant populations in the second phase were different from those in the single-phase digesters.

Bacteria, Anaerobic↗

PubMed1995

Application of DNA amplification fingerprinting (DAF) to mixed culture bioreactors.

The use of DNA amplification fingerprinting (DAF) as a tool for monitoring mixed microbial populations in bioreactors was evaluated. Short (8-mer or 10-mer) oligonucleotides were used to prime DNA extracts from various biological reactors during polymerase chain reaction (PCR) amplification. The reactors examined in this study included two sets of anaerobic stirred tank continuous flow bioreactors. One set of anaerobic reactors was operated under methanogenic conditions and one set was operated under sulfate-reducing conditions. The anaerobic reactor communities in the methanol-fed reactors showed extensive DAF homology. DAF was also applied to a fixed-film azo dye degrading reactor to examine the degree of uniformity of colonization of the substratum in representative regions of the reactor. This method is a quick and relatively inexpensive means of monitoring microbial community structure during biological processes. Since no cultivation of the sample is involved, the genetic profile of the community is not biased by outgrowth conditions. DAF profiles may be useful for comparisons of population changes over time or of bench-scale vs pilot-scale reactors but not adequate for assessing community diversity.

DNA Fingerprinting↗

PubMed2001

Spatial Patterns of Soil Microbial Communities in a Norway Spruce (Picea abies) Plantation.

The phospholipid fatty acid (PLFA) profiles of soil microbial communities were determined in relation to the patterns of tree cover in a mature Norway spruce plantation. Replicate samples of the surface organic layers were taken close to the trunk, at 1 m and at 2 m (under the edge of the canopy) beneath five trees. Samples were analyzed for standard PLFAs to assess the initial composition of the microbial communities. Replicate samples were then incubated under constant or fluctuating moisture conditions for 30 d to test the hypothesis that the patterns of microbial community structure (or its physiological state) might be determined by biophysical conditions under the tree canopies. The PLFA profiles near the trunks and at 2 m were similar, but samples taken 1 m from the bases of the trees contained lower concentrations of polyunsaturated (fungal) and monounsaturated PLFAs, and higher concentrations of saturated PLFAs. These differences in PLFA profiles were maintained during laboratory incubation under a regime of drying and wetting cycles, but there was some evidence of convergence in community structure under constant moisture conditions resulting from significant increases and decreases in specific bacterial PLFA concentrations. There were no effects of either moisture treatment on fungal PLFA concentrations. It is concluded that variation in the soil biophysical environment beneath the tree canopies resulted in the differentiation of spatially defined bacterial communities that were tolerant of moisture stress. The anomaly that differences in community structure were largest at an intermediate position of 1 m between the trunk and below the canopy edge was not explained but may relate to tree root distribution.

Journal Article↗

PubMed2006

Analysis of bacterial communities in seagrass bed sediments by double-gradient denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA genes.

Bacterial communities associated with seagrass bed sediments are not well studied. The work presented here investigated several factors and their impact on bacterial community diversity, including the presence or absence of vegetation, depth into sediment, and season. Double-gradient denaturing gradient gel electrophoresis (DG-DGGE) was used to generate banding patterns from the amplification products of 16S rRNA genes in 1-cm sediment depth fractions. Bioinformatics software and other statistical analyses were used to generate similarity scores between sections. Jackknife analyses of these similarity coefficients were used to group banding patterns by depth into sediment, presence or absence of vegetation, and by season. The effects of season and vegetation were strong and consistent, leading to correct grouping of banding patterns. The effects of depth were not consistent enough to correctly group banding patterns using this technique. While it is not argued that bacterial communities in sediment are not influenced by depth in sediment, this study suggests that the differences are too fine and inconsistent to be resolved using 1-cm depth fractions and DG-DGGE. The effects of vegetation and season on bacterial communities in sediment were more consistent than the effects of depth in sediment, suggesting they exert stronger controls on microbial community structure.

Bacteria↗

PubMed2000

Variation of Microbial Rhizosphere Communities in Response to Crop Species, Soil Origin, and Inoculation with Sinorhizobium meliloti L33.

A greenhouse study with soil-plant microcosms was conducted in order to compare the effect of crop species, soil origin, and a bacterial inoculant on the establishment of microbial communities colonizing plant roots. Two crop species, alfalfa (Medicago sativa) and rye (Secale cereale), were grown separately in two soils collected from agricultural fields at different locations and with differing histories of leguminous crop rotation. A subset of microcosms was inoculated at 10(6) cfu g(-1) soil with the luciferase marker gene-tagged Sinorhizobium meliloti strain L33, a symbiotic partner of M. sativa. Microbial consortia were collected from the rhizospheres of alfalfa after 10 weeks of incubation and from rye after 11 weeks. S. meliloti L33 populations were one to two orders of magnitude higher in the rhizospheres of alfalfa than of rye. In soil with previous alfalfa cultivation, 80% of the alfalfa nodules were colonized by indigenous bacteria, while in the other soil alfalfa was colonized almost exclusively (>90%) with S. meliloti L33. Three community-level targeting approaches were used to characterize the variation of the extracted microbial rhizosphere consortia: (1) Community level physiological profiles (CLPP), (2) fatty acid methyl ester analysis (FAME), and (3) diversity of PCR amplified 16S rRNA target sequences from directly extracted ribosomes, determined by temperature gradient gel electrophoresis (TGGE). All approaches identified the crop species as the major determinant of microbial community characteristics. Consistently, the influence of soil was of minor importance, while a modification of the alfalfa-associated microbial community structure after inoculation with S. meliloti L33 was only consistently observed by using TGGE.

Journal Article↗

PubMed2001

Influence of Initial C/N Ratio on Chemical and Microbial Composition during Long Term Composting of Straw.

Shredded straw of Miscanthus was composted in 800-L boxes with different amounts of pig slurry added as nitrogen source. The impact of the different initial C/N ratios (11, 35, 47, 50, and 54) on the composting process and the end product was evaluated by examining chemical and microbiological parameters during 12 months of composting. Low initial C/N ratios caused a fast degradation of fibers during the first three months of composting (hemicellulose: 50-80%, cellulose: 40-60%), while high initial C/N ratios resulted in 10-20% degradation of both hemicellulose and cellulose. These differences were reflected in the microbial biomass and respiration, which initially were higher in low C/N treatments than in high C/N treatments. After 12 months of composting, this situation was reversed. Composts with high initial C/N ratios had high microbial biomass (15-20 mg ATP g-1 OM) and respiration rates (200 mg CO2 h-1 g-1 OM) compared to treatments with low initial C/N ratios (less than 10 mg ATP g-1 OM and 25 mg CO2 h-1 g-1 OM). This could be explained by the microorganisms being nitrogen limited in the high C/N ratio treatments. In the low C/N ratio treatments, without nitrogen limitation, the high activity in the beginning decreased with time because of exhaustion of easily available carbon. Different nitrogen availability was also seen in the nitrification patterns, since nitrate was only measured in significant amounts in the treatments with initial C/N ratios of 11 and 35. The microbial community structure (measured as phospholipid fatty acid, PLFA, profile) was also affected by the initial C/N ratios, with lower fungal/bacterial ratios in the low compared to the high C/N treatments after 12 months of composting. However, in the low C/N treatments higher levels of PLFAs indicative of thermophilic gram-positive bacteria were found compared to the high C/N treatments. This was caused by the initial heating phase being longer in the low than in the high C/N treatments. The different fungal/bacterial ratios could also be explained by the initial heating phase, since a significant correlation between this ratio and heat generated during the initial composting phase was found.

Journal Article↗

PubMed2003

Molecular, biochemical and ecological characterisation of a bio-catalytic calcification reactor.

Bio-catalytic calcification (BCC) reactors utilise microbial urea hydrolysis by autochthonous bacteria for the precipitation-removal of calcium, as calcite, from industrial wastewater. Due to the limited knowledge available concerning natural ureolytic microbial calcium carbonate (CaCO(3)) precipitation, the microbial ecology of BCC reactors has remained a black box to date. This paper characterises BCC reactor evolution from initialisation to optimisation over a 6-week period. Three key parameters were studied: (1) microbial evolution, (2) the (bio)chemical CaCO(3) precipitation pathway, and (3) crystal nucleation site development. Six weeks were required to establish optimal reactor performance, which coincided with an increase in urease activity from an initial 7 mg urea l(-1) reactor h(-1) to about 100 mg urea l(-1) reactor h(-1). Urease activity in the optimal period was directly proportional to Ca(2+) removal, but urease gene diversity was seemingly limited to a single gene. Denaturing gradient gel electrophoresis of 16S rRNA genes revealed the dynamic evolution of the microbial community structure of the calcareous sludge, which was eventually dominated by a few species including Porphyromonas sp., Arcobacter sp. and Bacteroides sp. Epi-fluorescence and scanning electron microscopy showed that the calcareous sludge was colonised with living bacteria, as well as the calcified remains of organisms. It appears that the precipitation event is localised in a micro-environment, due to colonisation of crystal nucleation sites (calcareous sludge) by the precipitating organisms.

Base Sequence↗

PubMed2000

Comparison of the spatial homogeneity of physico-chemical parameters and bacterial 16S rRNA genes in sediment samples from a dumping site for dredging sludge.

The homogeneity of the microbial community structure of a sediment landfill was examined by a culture-independent method and compared with physico-chemical parameters, i.e. organic matter, CaCO3 content, pH, and texture. Total genomic DNA was extracted from samples derived from different places and depths. After amplification with two different primer sets of partial bacterial 16S rRNA genes, the products were separated by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints of different sediment samples taken in regular patterns at the same depth were similar, which indicates a spatial homogeneity in the numerically dominant bacterial populations in a landfill over 10,000 m2 in size. In a vertical column of approx. 10 m, only some differences in a few bands of the bacterial community structure were observed between samples taken from different depths. This DNA homogeneity coincided with a similar homogeneity of the physico-chemical parameters in the landfill at this site. Nevertheless, the DGGE technique revealed small differences in less prominent bacteria and was capable of separating the upper and lower samples of one column into two clusters. It therefore seems more sensitive than the physico-chemical approach for characterising the homogeneity of an environmental habitat.

Belgium↗

PubMed2004

Order-specific 16S rRNA-targeted oligonucleotide probes for (hyper)thermophilic archaea and bacteria.

New oligonucleotide probes were designed and evaluated for application in fluorescence in situ hybridization (FISH) studies on (hyper)thermophilic microbial communities--Arglo32, Tcoc164, and Aqui1197 target the 16S rRNA of Archaeoglobales, Thermococcales, and Aquificales, respectively. Both sequence information and experimental evaluation showed high coverage and specificity of all three probes. The signal intensity of Aqui1197 was improved by addition of a newly designed, unlabeled "helper" oligonucleotide, hAqui1045. It was shown that in addition to its function as a probe for Aquificales, Aqui1197 is suitable as a supplementary probe to extend the coverage of the domain-specific bacterial probe EUB338. In sediments from two hydrothermal seeps on Vulcano Island, Italy, the microbial community structure was analyzed by FISH with both established and the new oligonucleotide probes, showing the applicability of Arglo32, Tcoc164, and Aqui1197/hAqui1045 to natural samples. At both sites, all major groups of (hyper)thermophiles, except for methanogens, were detected: Crenarchaeota (19%, 16%), Thermococcales (14%, 22%), Archaeoglobales (14%, 12%), Aquificales (5%, 8%), Thermotoga/Thermosipho spp. (12%, 9%), Thermus sp. (12%, none), and thermophilic Bacillus sp. (12%, 8%).

Archaea↗

PubMed2006

Identification and characterization of o-xylene-degrading Rhodococcus spp. which were dominant species in the remediation of o-xylene-contaminated soils.

Soils contaminated with o-xylene were more difficult to bioremediate than those contaminated with other BTEX hydrocarbons (benzene, toluene, ethylbenzene, m-xylene and p-xylene). In order to identify microorganisms responsible for o-xylene degradation in soil, microbial community structure analyses were carried out with two soil samples in the presence of o-xylene and mineral nutrients. In two different soil samples, Rhodococcus opacus became abundant. We were also able to isolate o-xylene degrading Rhodococcus species from these soil samples. A primer set was developed to specifically detect a cluster of this Rhodococcus group including isolated Rhodococcus strains, Rhodococcus opacus and Rhodococcus koreensis. The growth of this bacterial group in an o-xylene-contaminated soil was followed by competitive PCR (cPCR). The decrease in o-xylene clearly paralleled the growth of the Rhodococcus group.

Base Sequence↗

PubMed2005

Biotransformation of 2-benzoxazolinone to 2-amino-(3H)-phenoxazin-3-one and 2-acetylamino-(3H)-phenoxazin-3-one in soil.

An alternative to the use of synthetic pesticides is to exploit the natural defense chemicals produced by cereals. An important class of allelochemicals is cyclic hydroxamic acids and related benzoxazolinones. A prolonged degradation experiment of the allelochemical compound from rye 2-benzoxazolinone (BOA) was carried out for up to 90 d at 15 degrees C at three different concentration levels, 3, 3000, and 30,000 nmol BOA g soil(-1), respectively, in a sandy loam soil. Two main degradation products, 2-amino-(3H)-phenoxazin-3-one (APO) and 2-acetylamino-(3H)-phenoxazin-3-one (AAPO), were identified and quantified by LC-ESI-MS-MS. The half-life of BOA increased with higher levels of BOA added to the soil. Half-lives of BOA, APO, and AAPO were determined by fitting a single first-order model to the degradation data. Half-life of BOA was determined to be 0.6 d in the 3 nmol BOA g soil(-1) treatment. Half-lives of BOA, APO, and AAPO were 3.1, 2.7, and 2.1 d, respectively, in the 3000 nmol BOA g soil(-1) treatment. In the 30,000 nmol BOA g soil(-1) treatment, the half-lives were 31 d for BOA and 45 d for APO. The microbial community structure was not affected by addition of BOA to the soil as investigated by analysis of signature fatty acids. The results suggest that the exploitability of BOA for crop protection is dependent on the existing concentration of BOA in the soil and the timing of incorporation of hydroxamic acid synthesizing crops into the soil.

Agriculture↗

PubMed2003

Fatty acids of lipid fractions in extracellular polymeric substances of activated sludge flocs.

Phospholipid (PL), glycolipid (GL), and neutral lipid (NL) FA, and the lipopolysaccharide 2- and 3-hydroxy (LPS 2-OH and 3-OH) FA of activated sludges and extracted extracellular polymeric substances (EPS) were determined on samples collected from two wastewater treatment plants. EPS extracted from sludges by means of sonication and cation exchange contained proteins (43.4%), humic-like substances (11.5%), nucleic acids (10.9%), carbohydrates (9.9%), and lipid-bound FA (1.8%). The lipids associated with EPS were composed of GL, PL, NL, and LPS acids in proportions of 61, 21, 16, and 2%, respectively. The profiles of lipid-bound FA in activated sludges and EPS were similar (around 85 separate FA were identified). The FA signatures observed can be attributed to the likely presence of yeasts, fungi, sulfate-reducing bacteria, gram-positive and gram-negative bacteria, and, in lesser quantities, mycobacteria. Comparison of data from the dates of sampling (January and September) showed that there were more unsaturated PLFA in the EPS extracted from the activated sludges sampled in January. This observation could be partly related to microorganism adaptation to temperature variations. The comparison between two wastewater treatment plants showed that the FA profiles were similar, although differences in microbial community structure were also seen. Most of the FA in sludges had an even number of carbons.

Extracellular Fluid↗