Microbial Community Changes in Response to Ethanol or Methanol Amendments for U(VI) Reduction

Abstract

Microbial community responses to ethanol, methanol, and methanol plus humics amendments in relationship to U(VI) bioreduction were studied in laboratory microcosm experiments using sediments and ground water from a uranium-contaminated site in Oak Ridge, TN. The type of carbon source added, the duration of incubation, and the sampling site influenced the bacterial community structure upon incubation. Analysis of 16S rRNA gene clone libraries indicated that (i) bacterial communities found in ethanol-and methanolamended samples with U(VI) reduction were similar due to the presence of Deltaproteobacteria and Betaproteobacteria (members of the families Burkholderiaceae, Comamonadaceae, Oxalobacteraceae, and Rhodocyclaceae); (ii) methanol-amended samples without U(VI) reduction exhibited the lowest diversity and the bacterial community contained 69.2 to 92.8% of the family Methylophilaceae; and (iii) the addition of humics resulted in an increase of phylogenetic diversity of Betaproteobacteria (Rodoferax, Polaromonas, Janthinobacterium, Methylophilales, and unclassified) and Firmicutes (Desulfosporosinus and Clostridium).The use of uranium in nuclear research, fuel production, and weapons manufacturing has resulted in environmental contamination at production, manufacturing, and storage sites throughout the United States. Although all of the common isotopes of uranium ( The U.S. Department of Energy (DOE) has ongoing efforts to identify and remediate contaminated areas under its control. Stimulating the in situ metabolism of microorganisms capable of reduction of U(VI) to U(IV), producing the insoluble mineral uraninite which precipitates and renders uranium immobile in ground water, has been proposed as an environmentally safe and a potentially cost-effective remediation method (37). Typically, an organic substrate is added to stimulate microbial growth and promote the development of anaerobic conditions, under which the reduction of U(VI) is favored (67). Various substrates (e.g., acetate, ethanol, glucose, and methanol) have been used either in the field or in microcosm studies, and most were capable of stimulating microbial U(VI) reduction (1,8,42,43,47,60); however, the addition of methanol did not always result in U(VI) reduction (49). Many microorganisms are known to reduce U(VI) in pure culture, including a hyperthermophilic archaeon (28), a thermophilic bacterium Thermoterrabacterium ferrireducens (29), the mesophilic dissimilatory metal-reducing bacteria Geobacter and Shewanella (67) and Anaeromyxobacter dehalogenans (71), the sulfate-reducing bacterium Desulfovibrio sp. (61), and fermentative bacteria such as Clostridium spp. (20). These data suggest that U(VI) can be reduced by many microorganisms once suitable electron donors are available.The purpose of this study was to analyze the ability of various amendments to stimulate the reduction of U(VI) by the indigenous microbial communities found in subsurface sediments collected from a uranium-contaminated site. A previous publication from this project (42...

16S rRNA Gene Microarray Analysis of Microbial Communities in Ethanol-Stimulated Subsurface Sediment

“…Array signals for Rhodocyclaceae and Geobacteraceae were not responsive when the relative abundance of these taxa in the clone libraries exceeded 15%; the reason for this lack of response is unknown. A recent 16S rRNA gene clone library-based study (36) of microbial community development in suspensions of ethanol-amended U(VI)-contaminated sediment (similar to the sediment used in this study) revealed the proliferation of Deltaproteobacteria and Betaproteobacteria taxa analogous to those detected in this study.…”

Methylotrophy in a Lake: from Metagenomics to Single-Organism Physiology

“…(11,14,41,48), pointing to the environmental importance of this group. Four formally described genera within Methylophilaceae are now recognized: Methylophilus, Methylobacillus, Methylovorus (1,33), and more recently Methylotenera (20,21).…”

Iron Cycling Potentials of Arsenic Contaminated Groundwater in Bangladesh as Revealed by Enrichment Cultivation

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