A comparison of DNA profiling techniques for monitoring nutrient impact on microbial community composition during bioremediation of petroleum-contaminated soils

Amplicon length heterogeneity PCR (LH-PCR) and terminal restriction fragment length polymorphisms (TRFLP) were used to monitor the impact that nutrient amendments had on microbial community dynamics and structural diversity during bioremediation of petroleum-contaminated soils. Slurried soils contaminated with petroleum hydrocarbons were treated in airlift bench-scale bioreactors and were either amended with optimal inorganic nutrients or left unamended. Direct DNA extraction and PCR amplification of whole eubacterial community DNA were performed with universal primers that bracketed the first two or three hypervariable regions of the 16S rDNA gene sequences. The LH-PCR method profiled a more diverse microbial community than did the TRFLP method. The LH-PCR method also tracked differences between the communities due to nutrient amendments. An in silico database search for bacterial genera with amplicon lengths represented in the community fingerprints was performed. It was possible to qualitatively identify different groups in the microbial community based on the amplicon length variations. A similar "virtual" search was performed for the TRFLP fragments using the web-based TAP-TRFLP program. Cloning and sequencing of the PCR products confirmed the in silico database matches. The application of the LH-PCR method as a monitoring tool for bioremediation could greatly enhance and extend the current understanding of the microbial community dynamics during the biodegradation of environmental contaminants.     

Bacterial community evaluation during establishment of tall fescue (Festuca arundinacea) in soil contaminated with pyrene

A greenhouse study was conducted to monitor microbial community dynamics related to contaminant concentration and plant growth during the phytoremediation of pyrene. Soil microbial communities in both bulk and rhizosphere soils were assessed using a polymerase chain reaction--denaturing gradient gel electrophoresis (PCR-DGGE). However, no correlation between pyrene concentration and bacterial community shifts was observed. Even though plants significantly enhanced pyrene degradation (undetectable after 91 d for planted treatments compared with 82 mg/kg for unplanted treatments after 147 d with initial concentration of 758 mg/kg), biodegradation may have been accomplished by the pre-existing microbial community. It is also possible that the method was unable to pick up subtle community shifts, considering that the carbon source from pyrene was only 3.7% of the existing soil organic matter. This research suggests that plants significantly enhance degradation and mineralization of pyrene in soil, although there was no conclusive evidence supporting any specific bacterial activity responsible for this enhancement.     

Robust hydrocarbon degradation and dynamics of bacterial communities during nutrient-enhanced oil spill bioremediation

Degradation of oil on beaches is, in general, limited by the supply of inorganic nutrients. In order to obtain a more systematic understanding of the effects of nutrient addition on oil spill bioremediation, beach sediment microcosms contaminated with oil were treated with different levels of inorganic nutrients. Oil biodegradation was assessed respirometrically and on the basis of changes in oil composition. Bacterial communities were compared by numerical analysis of denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rRNA genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Nutrient amendment over a wide range of concentrations significantly improved oil degradation, confirming that N and P limited degradation over the concentration range tested. However, the extent and rate of oil degradation were similar for all microcosms, indicating that, in this experiment, it was the addition of inorganic nutrients rather than the precise amount that was most important operationally. Very different microbial communities were selected in all of the microcosms. Similarities between DGGE profiles of replicate samples from a single microcosm were high (95% +/- 5%), but similarities between DGGE profiles from replicate microcosms receiving the same level of inorganic nutrients (68% +/- 5%) were not significantly higher than those between microcosms subjected to different nutrient amendments (63% +/- 7%). Therefore, it is apparent that the different communities selected cannot be attributed to the level of inorganic nutrients present in different microcosms. Bioremediation treatments dramatically reduced the diversity of the bacterial community. The decrease in diversity could be accounted for by a strong selection for bacteria belonging to the alkane-degrading Alcanivorax/Fundibacter group. On the basis of Shannon-Weaver indices, rapid recovery of the bacterial community diversity to preoiling levels of diversity occurred. However, although the overall diversity was similar, there were considerable qualitative differences in the community structure before and after the bioremediation treatments.     

Robust Hydrocarbon Degradation and Dynamics of Bacterial Communities during Nutrient-Enhanced Oil Spill Bioremediation

Degradation of oil on beaches is, in general, limited by the supply of inorganic nutrients. In order to obtain a more systematic understanding of the effects of nutrient addition on oil spill bioremediation, beach sediment microcosms contaminated with oil were treated with different levels of inorganic nutrients. Oil biodegradation was assessed respirometrically and on the basis of changes in oil composition. Bacterial communities were compared by numerical analysis of denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rRNA genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Nutrient amendment over a wide range of concentrations significantly improved oil degradation, confirming that N and P limited degradation over the concentration range tested. However, the extent and rate of oil degradation were similar for all microcosms, indicating that, in this experiment, it was the addition of inorganic nutrients rather than the precise amount that was most important operationally. Very different microbial communities were selected in all of the microcosms. Similarities between DGGE profiles of replicate samples from a single microcosm were high (95% ± 5%), but similarities between DGGE profiles from replicate microcosms receiving the same level of inorganic nutrients (68% ± 5%) were not significantly higher than those between microcosms subjected to different nutrient amendments (63% ± 7%). Therefore, it is apparent that the different communities selected cannot be attributed to the level of inorganic nutrients present in different microcosms. Bioremediation treatments dramatically reduced the diversity of the bacterial community. The decrease in diversity could be accounted for by a strong selection for bacteria belonging to the alkane-degrading Alcanivorax/Fundibacter group. On the basis of Shannon-Weaver indices, rapid recovery of the bacterial community diversity to preoiling levels of diversity occurred. However, although the overall diversity was similar, there were considerable qualitative differences in the community structure before and after the bioremediation treatments.     

Enhanced Microbial Removal of Pyrene in Soils in the Presence of Earthworms

Microbial degradation of pyrene was studied in soils in the presence and absence of earthworms (Eisenia foetida) to demonstrate an integrated innovative strategy for bioremediation of sites lightly polluted by polycyclic aromatic hydrocarbons. Desorption of pyrene and soil microbial respiration were measured to elucidate the mechanism of enhanced microbial degradation. The results showed that both soil properties and contact time could influence pyrene biodegradation. The introduction of E. foetida enhanced pyrene removal significantly both in freshly spiked and aged soils. The percentage pyrene removal in the presence of E. foetida was 45.5–91.0% after 14 d of incubation, which were 2.1 to 2.8 times greater than those without the worms. The enhanced pyrene removal is attributed to both enhanced microbial degradation and uptake by the worms. Microbial degradation of pyrene increased by 1.2 to 1.6 times in the presence of the worms. Overall, the introduction of live worms could improve both pyrene bioavailability and microbial activity, which leads to enhanced microbial degradation of pyrene.     

Effect of salinity on the bioremediation of petroleum hydrocarbons in a saline-alkaline soil

Aims: The aim of this paper is to check the effect of salinity on the bioremediation process of petroleum hydrocarbons in the saline‐alkaline soil. Methods and Results: In this study, soil salinity was adjusted to different levels by water leaching method and the bioremediation process was conducted for 28 days. Soil pH increased after leaching and decreased during bioremediation process. At initial time, moderate salinity enhanced the biodegradation and addition of microbial consortium was not effective in enhancing degradation rate of petroleum hydrocarbons. At day of 28 days, higher degradation rate was found in treatments with more leaching times with a maximum value of 42·36%. Dehydrogenase activity increased with the progress of bioremediation and positive correlation was found between dehydrogenase activity and degradation rate of petroleum hydrocarbons. Denaturing gradient gel electrophoresis analysis result showed decreased microbial community diversity with increased salt content. Conclusions: The result suggested that salinity had great impact on bioremediation, and leaching and addition of inoculated consortium were effective in enhancing biodegradation of petroleum hydrocarbons in the saline‐alkaline soil. Significance and Impact of the Study: The result of this study is important for understanding the bioremediation process of petroleum in contaminated soil. New remediation method of petroleum contaminated soil can be developed based on this study.     

Effects of community-accessible biochar and compost on diesel-contaminated soil

Petroleum pollution is a global problem that requires effective and accessible remediation strategies that takes ecosystem functioning into serious consideration. Bioremediation can be an effective tool to address the challenge. In this study, we used a mesocosm experiment to evaluate the effects of locally sourced and community produced biochar and compost amendments on diesel-contaminated soil. At the end of the 90-day experiment, we quantified the effects of the amendments on total petroleum hydrocarbons (C9-C40) (TPH) and soil pH, organic matter, aggregate stability, soil respiration, extractable phosphorus, extractable potassium, and micronutrients (Mg, Fe, Mn, and Zn). We observed significantly higher TPH degradation in compost-amended soils than in controls and soils amended with biochar. We propose that the addition of compost improved TPH biodegradation by augmenting soil nutrient content and microbial activity. Our results suggest that community-accessible compost can improve TPH biodegradation, and that implementation is possible at the community level.     

Diversity of cultivable Azotobacter in the semi-arid alfisol receiving long-term organic and inorganic nutrient amendments

Monitoring the biological processes and microbial diversity is essential for sustaining the soil health for long-term productivity. In the present study, the impact of long-term nutrient management systems on changes in Azotobacter diversity of Indian semi-arid alfisol was assessed. Three soils, i.e., unfertilized control, soils amended with organic manures (OM), and with inorganic chemical fertilizers (IC) from century-old experimental fields were evaluated for Azotobacter diversity by Amplified Ribosomal DNA Restriction Analysis (ARDRA). Bray–Curtis’s similarity index of the ARDRA data of the isolates was analyzed by non-metric multi-dimensional scaling and hierarchical cluster analysis. The results revealed that the long-term organically managed soil recorded significantly higher soil organic carbon, microbial biomass carbon, and total culturable bacterial counts, whereas the chemical fertilized and control soils remained unaffected. Though the Azotobacter population was significantly higher in OM soil than IC and control soils, the genetic diversity was unaffected due to long-term addition of either organic manures or inorganic chemical fertilizers. This result implies the importance of continuous addition of organic manures and also the optimal use of inorganic chemical fertilizers without disturbing the biological properties of the soil.     

Nutrient-limited biodegradation of PAH in various soil strata at a creosote contaminated site

The effects of nutrient addition on the in situ biodegradation of polycyclic aromatic hydrocarbons in creosote contaminated soil were studied in soil columns taken from various soil strata at a wood preserving plant in Norway. Three samples were used: one from the topsoil (0–0.5 m), one from an organic rich layer (2–2.5 m) and one from the sandy aquifer (4.5–5 m). The addition of inorganic nitrogen and phosphorous stimulated the degradation of polycyclic aromatic hydrocarbons (PAHs) in the top soil and the aquifer sand. These two soils, which differed strongly in contamination levels, responded similarly to nutrient addition with the corresponding degradation of 4-ring PAHs. The ratio between available nitrogen (N) and phosphorous (P) might explain the degree of degradation observed for the 4-ring PAHs. However, the degree of degradation of 3-ring PAHs did not significantly increase after nutrient addition. An increase in the respiration rate, after nutrient addition, could only be observed in the topsoil. In the aquifer sand, 4-ring PAH degradation was not accompanied by an increase in the respiration rate or the number of heterotrophic micro-organisms. PAH degradation in the organic layer did not respond to nutrient addition. This was probably due to the low availability of the contaminants for micro-organisms, as a result of sorption to the soil organic matter. Our data illustrate the need for a better understanding of the role of nutrients in the degradation of high molecular weight hydrocarbons for the successful application of bioremediation at PAH contaminated sites.     

A Correlation to Estimate the Bioventing Degradation Rate Constant

Estimating the biodegradation rate is essential when designing a bioremediation strategy for petroleum-contaminated sites, and when evaluating assessment guidelines. However, estimating the biodegradation rate is difficult as the rate constant varies from site to site due to changing site conditions, which include soil type, biological activity, and type of contaminant. Accordingly, bench-scale biodegradation studies were completed using respirometers to measure first-order biodegradation rate constants for gasoline in several soils over 30 days of incubation. A total of seven soils were tested at various gasoline concentrations with constant nutrient ratios and water content. No microbial inhibition was observed for the range of gasoline concentrations studied. Analysis showed that the statistically significant parameters were the initial population of petroleum-degrading microorganisms and the organic matter content. The developed empirical correlation is a simple tool that practioners can use to estimate the biodegradation rate without conducting lengthy and expensive experiments.     

Enhanced bioremediation of n-alkane in petroleum sludge using bacterial consortium amended with rhamnolipid and micronutrients

The purpose of the present study was to investigate possible methods to enhance the rate of biodegradation of oil sludge from crude oil tank bottom, thus reducing the time usually required for bioremediation. Enhancement of biodegradation was achieved through bioaugmentation and biostimulation. About 10% and 20% sludge contaminated sterile and non-sterile soil samples were treated with bacterial consortium (BC), rhamnolipid biosurfactant (RL) and nitrogen, phosphorus and potassium (NPK) solution. Maximum n-alkane degradation occurred in the 10% sludge contaminated soil samples. The effects of treatment carried out with the non-sterile soil samples were more pronounced than in the sterile soils. Maximum degradation was achieved after the 56th day of treatment. n-Alkanes in the range of nC8-nC11 were degraded completely followed by nC12-nC21, nC22-nC31 and nC32-nC40 with percentage degradations of 100%, 83-98%, 80-85% and 57-73% respectively. Statistical analysis using analysis of variance and Duncan's multiple range test revealed that the level of amendments, incubation time and combination of amendments significantly influenced bacterial growth, protein concentration and surface tension at a 1% probability level. All tested additives BC, NPK and RL had significant positive effects on the bioremediation of n-alkane in petroleum sludge.     

Effect of various amendments on heavy mineral oil bioremediation and soil microbial activity

To examine the effects of amendments on the degradation of heavy mineral oil, we conducted a pilot-scale experiment in the field for 105 days. During the experiment, soil samples were collected and analyzed periodically to determine the amount of residual hydrocarbons and evaluate the effects of the amendments on microbial activity. After 105 days, the initial level of contamination (7490+/-480 mg hydrocarbon kg(-1) soil) was reduced by 18-40% in amended soils, whereas it was only reduced by 9% in nonamended soil. Heavy mineral oil degradation was much faster and more complete in compost-amended soil than in hay-, sawdust-, and mineral nutrient-amended soils. The enhanced degradation of heavy mineral oil in compost-amended soil may be a result of the significantly higher microbial activity in this soil. Among the studied microbial parameters, soil dehydrogenase, lipase, and urease activities were strongly and negatively correlated with heavy mineral oil biodegradation (P<0.01) in compost-amended soil.     

土壤中多环芳烃的微生物降解及土壤细菌种群多样性

利用室内模拟方法,研究中、低浓度多环芳烃(PAHs)污染土壤的微生物修复效果,阐明土壤微生物（接种和土著）与PAHs降解的关系.结果表明:投加PAHs高效降解菌可以促进土壤中PAHs的降解,2周内效果显著;典型PAHs降解的难易程度依据为：菲<蒽<芘<苯并(a)芘和屈;细菌种群丰度和多样性均与PAHs降解呈负相关关系,同一处理细菌种群结构随时间变化不大.对于中、低浓度PAHs原位污染土壤,增强土著菌的活性是提高土壤PAHs降解率的有效途径之一.     

Bacterial community dynamics and polycyclic aromatic hydrocarbon degradation during bioremediation of heavily creosote-contaminated soil

Bacterial community dynamics and biodegradation processes were examined in a highly creosote-contaminated soil undergoing a range of laboratory-based bioremediation treatments. The dynamics of the eubacterial community, the number of heterotrophs and polycyclic aromatic hydrocarbon (PAH) degraders, and the total petroleum hydrocarbon (TPH) and PAH concentrations were monitored during the bioremediation process. TPH and PAHs were significantly degraded in all treatments (72 to 79% and 83 to 87%, respectively), and the biodegradation values were higher when nutrients were not added, especially for benzo(a)anthracene and chrysene. The moisture content and aeration were determined to be the key factors associated with PAH bioremediation. Neither biosurfactant addition, bioaugmentation, nor ferric octate addition led to differences in PAH or TPH biodegradation compared to biodegradation with nutrient treatment. All treatments resulted in a high first-order degradation rate during the first 45 days, which was markedly reduced after 90 days. A sharp increase in the size of the heterotrophic and PAH-degrading microbial populations was observed, which coincided with the highest rates of TPH and PAH biodegradation. At the end of the incubation period, PAH degraders were more prevalent in samples to which nutrients had not been added. Denaturing gradient gel electrophoresis analysis and principal-component analysis confirmed that there was a remarkable shift in the composition of the bacterial community due to both the biodegradation process and the addition of nutrients. At early stages of biodegradation, the alpha-Proteobacteria group (genera Sphingomonas and Azospirillum) was the dominant group in all treatments. At later stages, the gamma-Proteobacteria group (genus Xanthomonas), the alpha-Proteobacteria group (genus Sphingomonas), and the Cytophaga-Flexibacter-Bacteroides group (Bacteroidetes) were the dominant groups in the nonnutrient treatment, while the gamma-Proteobacteria group (genus Xathomonas), the beta-Proteobacteria group (genera Alcaligenes and Achromobacter), and the alpha-Proteobacteria group (genus Sphingomonas) were the dominant groups in the nutrient treatment. This study shows that specific bacterial phylotypes are associated both with different phases of PAH degradation and with nutrient addition in a preadapted PAH-contaminated soil. Our findings also suggest that there are complex interactions between bacterial species and medium conditions that influence the biodegradation capacity of the microbial communities involved in bioremediation processes.     

Predictable bacterial composition and hydrocarbon degradation in Arctic soils following diesel and nutrient disturbance

Increased exploration and exploitation of resources in the Arctic is leading to a higher risk of petroleum contamination. A number of Arctic microorganisms can use petroleum for growth-supporting carbon and energy, but traditional approaches for stimulating these microorganisms (for example, nutrient addition) have varied in effectiveness between sites. Consistent environmental controls on microbial community response to disturbance from petroleum contaminants and nutrient amendments across Arctic soils have not been identified, nor is it known whether specific taxa are universally associated with efficient bioremediation. In this study, we contaminated 18 Arctic soils with diesel and treated subsamples of each with monoammonium phosphate (MAP), which has successfully stimulated degradation in some contaminated Arctic soils. Bacterial community composition of uncontaminated, diesel-contaminated and diesel+MAP soils was assessed through multiplexed 16S (ribosomal RNA) rRNA gene sequencing on an Ion Torrent Personal Genome Machine, while hydrocarbon degradation was measured by gas chromatography analysis. Diversity of 16S rRNA gene sequences was reduced by diesel, and more so by the combination of diesel and MAP. Actinobacteria dominated uncontaminated soils with <10% organic matter, while Proteobacteria dominated higher-organic matter soils, and this pattern was exaggerated following disturbance. Degradation with and without MAP was predictable by initial bacterial diversity and the abundance of specific assemblages of Betaproteobacteria, respectively. High Betaproteobacteria abundance was positively correlated with high diesel degradation in MAP-treated soils, suggesting this may be an important group to stimulate. The predictability with which bacterial communities respond to these disturbances suggests that costly and time-consuming contaminated site assessments may not be necessary in the future.     

Nutrient Amendments of Inorganic Fertiliser and Oil Palm Empty Fruit Bunch and Their Influence on Bacterial Species Dominance and Degradation of the Associated Crude Oil Constituents

The effects of inorganic commercial fertiliser (N:P:K = 8:8:1) and oil palm empty fruit bunch (EFB) as nutrient amendments for crude oil degradation and microbial population shift by a microbial consortium [Pseudomonas sp. (UKMP-14T), Acinetobacter sp. (UKMP-12T), Trichoderma sp. (TriUKMP-1M and TriUKMP-2M)] were assessed. The bacterial populations present during crude oil degradation were analysed by spread plate method and 16S rRNA sequences, whereas the presence of fungi was assessed by growth on potato dextrose agar. Crude oil degradation analysed using gas chromatography-flame ionisation detection showed total petroleum hydrocarbon reduced between 70 and 100%, depending on the type of amendments compared to control (≈55%) after 30 days of incubation. Nutrient amendments using NPK fertiliser or EFB were found to influence the domination of different bacterial species, which in turn preferentially utilised different hydrocarbons. This study suggested different nutrient amendments could be used to preferentially select bacteria to degrade different components of crude oil, particularly pertaining to the recalcitrant phytane. This information is very useful for application of in situ bioremediation of soil hydrocarbon contamination.     

Enhanced crude oil biodegradation in soil via biostimulation

Research on feasible methods for the enhancement of bioremediation in soil contaminated by crude oil is vital in oil-exporting countries such as Kuwait, where crude oil is a major pollutant and the environment is hostile to biodegradation. This study investigated the possibility of enhancing crude oil bioremediation by supplementing soil with cost-effective organic materials derived from two widespread locally grown trees, Conocarpus and Tamarix. Amendments in soils increased the counts of soil microbiota by up to 98% and enhanced their activity by up to 95.5%. The increase in the biodegradation of crude oil (75%) and high levels of alkB expression substantiated the efficiency of the proposed amendment technology for the bioremediation of hydrocarbon-contaminated sites. The identification of crude-oil-degrading bacteria revealed the dominance of the genus Microbacterium (39.6%), Sphingopyxis soli (19.3%), and Bordetella petrii (19.6%) in unamended, Conocarpus-amended, and Tamarix-amended contaminated soils, respectively. Although soil amendments favored the growth of Gram-negative bacteria and reduced bacterial diversity, the structures of bacterial communities were not significantly altered.     

Effects of soil amendment with different carbon sources and other factors on the bioremediation of an aged PAH-contaminated soil

Carbon supplementation, soil moisture and soil aeration are believed to enhance in situ bioremediation of PAH-contaminated soils by stimulating the growth of indigenous microorganisms. However, the effects of added carbon and nitrogen together with soil moisture and soil aeration on the dissipation of PAHs and on associated microbial counts have yet to be fully assessed. In this study the effects on bioremediation of carbon source, carbon-to-nitrogen ratio, soil moisture and aeration on an aged PAH-contaminated agricultural soil were studied in microcosms over a 90-day period. Additions of starch, glucose and sodium succinate increased soil bacterial and fungal counts and accelerated the dissipation of phenanthrene and benzo(a)pyrene in soil. Decreases in phenanthrene and benzo(a)pyrene concentrations were effective in soil supplemented with glucose and sodium succinate (both 0.2 g C kg⁻¹ dry soil) and starch (1.0 g C kg⁻¹ dry soil). The bioremediation effect at a C/N ratio of 10:1 was significantly higher (P < 0.05) than at a C/N of either 25:1 or 40:1. Soil microbial counts and PAH dissipation were lower in the submerged soil but soil aeration increased bacterial and fungal counts, enhanced indigenous microbial metabolic activities, and accelerated the natural degradation of phenanthrene and benzo(a)pyrene. The results suggest that optimizing carbon source, C/N ratio, soil moisture and aeration conditions may be a feasible remediation strategy in certain PAH contaminated soils with large active microbial populations.     

Comparison of the effects of poultry manure and its biochar on barley growth in petroleum-contaminated soils

This study was conducted to evaluate and compare the effectiveness of two organic amendments [poultry manure (PM) and poultry manure biochar (PMB)] for the degradation of petroleum hydrocarbons in contaminated soils by barley plant at three levels of total petroleum hydrocarbons (TPHs) during 5 months under greenhouse conditions. TPHs removal efficiency and microbial respiration were shown to be higher at soil-cultivated plant than at uncultivated soil and in lowest level of contamination rather than other levels of contamination and at organic amendment treatment than unamended soil. Soil microbial respiration and TPHs degradation in the rhizosphere of barley increased by 15.64 and 12.74% for PM-amended treatment and 28.07 and 26.83% for PMB-amended treatment, respectively, in the 4% TPHs level compared with unamended treatment. Comparison of two amendments showed that in PMB treatment soil, highest dry weight, microbial respiration, and TPHs degradation potential were observed.     

Succession of bacterial communities during early plant development: transition from seed to root and effect of compost amendment

Compost amendments to soils and potting mixes are routinely applied to improve soil fertility and plant growth and health. These amendments, which contain high levels of organic matter and microbial cells, can influence microbial communities associated with plants grown in such soils. The purpose of this study was to follow the bacterial community compositions of seed and subsequent root surfaces in the presence and absence of compost in the potting mix. The bacterial community compositions of potting mixes, seed, and root surfaces sampled at three stages of plant growth were analyzed via general and newly developed Bacteroidetes-specific, PCR-denaturing gradient gel electrophoresis methodologies. These analyses revealed that seed surfaces were colonized primarily by populations detected in the initial potting mixes, many of which were not detected in subsequent root analyses. The most persistent bacterial populations detected in this study belonged to the genus Chryseobacterium (Bacteroidetes) and the family Oxalobacteraceae (Betaproteobacteria). The patterns of colonization by populations within these taxa differed significantly and may reflect differences in the physiology of these organisms. Overall, analyses of bacterial community composition revealed a surprising prevalence and diversity of Bacteroidetes in all treatments.