Sulfate-reducing bacteria (SRB) are anaerobic prokaryotes found ubiquitously in nature. SRB were the first nonphotosynthetic, anaerobic bacteria shown to generate energy (ATP) through electron transfer-coupled phosphorylation. For this process, the SRB typically use sulfate as the terminal electron acceptor for respiration of hydrogen or various organic acids, which results in the production of sulfide, a highly reactive and toxic end-product. Beyond their obvious function in the sulfur cycle, SRB play an important role in global cycling of numerous other elements 1 . For example, in the carbon cycle, the SRB form part of microbial consortia that completely mineralize organic carbon in anaerobic environments; polymeric materials (e.g., cellulose) are first depolymerized and metabolized by fermentative microorganisms, and the resulting organic acid and reduced gas (that is, CO and H 2 ) end-products are further fermented or oxidized by other microbes, including SRB. The latter are particularly active in sulfate-rich (e.g., marine) environments, where they effectively link the global sulfur and carbon cycles 1,2 .Beyond these ecological roles, SRB also have a major economic impact because of their involvement in biocorrosion of ferrous metals in anaerobic environments 3 , described as "industrial venereal disease-it's expensive, everybody has it, and nobody wants to talk about it" 4 . For example, because SRB are abundant in oil fields, their metabolism has many negative consequences for the petroleum industry (e.g., corrosion of drilling and pumping machinery and storage tanks, souring of oil by sulfide production, plugging of machinery and rock pores with biomass and sulfide precipitates). The SRB also contribute to bioremediation of toxic metal ions 5,6 . Their metabolism increases the pH, causing toxic metal ions like copper (II), nickel (II) and cadmium (II) to precipitate as metal sulfides in acidic aquatic environments (e.g., mine effluents). Additionally, SRB can deliver electrons directly to oxidized toxic metal ions, including uranium (VI), technetium (VII), and chromium (VI), converting these into less soluble, reduced forms. Hence, SRB-mediated reduction represents a potentially useful mechanism for the bioremediation of metal ion contaminants from anaerobic sediments 6 .Most research on the metabolism and biochemistry of SRB has been done on the genus Desulfovibrio, a member of the δ-proteobacteria The genome sequence of the anaerobic, sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough Desulfovibrio vulgaris Hildenborough is a model organism for studying the energy metabolism of sulfate-reducing bacteria (SRB) and for understanding the economic impacts of SRB, including biocorrosion of metal infrastructure and bioremediation of toxic metal ions. The 3,570,858 base pair (bp) genome sequence reveals a network of novel c-type cytochromes, connecting multiple periplasmic hydrogenases and formate dehydrogenases, as a key feature of its energy metabolism. The relative arrangement of genes encod...

Understanding adaptation of biological communities to environmental change is a central issue in ecology and evolution. Metagenomic analysis of a stressed groundwater microbial community reveals that prolonged exposure to high concentrations of heavy metals, nitric acid and organic solvents (B50 years) has resulted in a massive decrease in species and allelic diversity as well as a significant loss of metabolic diversity. Although the surviving microbial community possesses all metabolic pathways necessary for survival and growth in such an extreme environment, its structure is very simple, primarily composed of clonal denitrifying c-and b-proteobacterial populations. The resulting community is overabundant in key genes conferring resistance to specific stresses including nitrate, heavy metals and acetone. Evolutionary analysis indicates that lateral gene transfer could have a key function in rapid response and adaptation to environmental contamination. The results presented in this study have important implications in understanding, assessing and predicting the impacts of human-induced activities on microbial communities ranging from human health to agriculture to environmental management, and their responses to environmental changes.

A new generation of functional gene arrays (FGAs; GeoChip 3.0) has been developed, with ∼28 000 probes covering approximately 57 000 gene variants from 292 functional gene families involved in carbon, nitrogen, phosphorus and sulfur cycles, energy metabolism, antibiotic resistance, metal resistance and organic contaminant degradation. GeoChip 3.0 also has several other distinct features, such as a common oligo reference standard (CORS) for data normalization and comparison, a software package for data management and future updating and the gyrB gene for phylogenetic analysis. Computational evaluation of probe specificity indicated that all designed probes would have a high specificity to their corresponding targets. Experimental analysis with synthesized oligonucleotides and genomic DNAs showed that only 0.0036–0.025% false-positive rates were observed, suggesting that the designed probes are highly specific under the experimental conditions examined. In addition, GeoChip 3.0 was applied to analyze soil microbial communities in a multifactor grassland ecosystem in Minnesota, USA, which showed that the structure, composition and potential activity of soil microbial communities significantly changed with the plant species diversity. As expected, GeoChip 3.0 is a high-throughput powerful tool for studying microbial community functional structure, and linking microbial communities to ecosystem processes and functioning.

Micro-organisms play critical roles in many important biogeochemical processes in the Earth's biosphere. However, understanding and characterizing the functional capacity of microbial communities are still difficult due to the extremely diverse and often uncultivable nature of most micro-organisms. In this study, we developed a new functional gene array, GeoChip 4, for analysing the functional diversity, composition, structure, metabolic potential/activity and dynamics of microbial communities. GeoChip 4 contained approximately 82 000 probes covering 141 995 coding sequences from 410 functional gene families related to microbial carbon (C), nitrogen (N), sulphur (S), and phosphorus (P) cycling, energy metabolism, antibiotic resistance, metal resistance/reduction, organic remediation, stress responses, bacteriophage and virulence. A total of 173 archaeal, 4138 bacterial, 404 eukaryotic and 252 viral strains were targeted, providing the ability to analyse targeted functional gene families of micro-organisms included in all four domains. Experimental assessment using different amounts of DNA suggested that as little as 500 ng environmental DNA was required for good hybridization, and the signal intensities detected were well correlated with the DNA amount used. GeoChip 4 was then applied to study the effect of long-term warming on soil microbial communities at a Central Oklahoma site, with results indicating that microbial communities respond to long-term warming by enriching carbon degradation, nutrient cycling (nitrogen and phosphorous) and stress response gene families. To the best of our knowledge, GeoChip 4 is the most comprehensive functional gene array for microbial community analysis.