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Bioremediation may restore contaminated soils through the broad biodegradative capabilities evolved by microorganisms towards undesirable organic compounds. Understanding bioremediation and its effectiveness is rapidly advancing, bringing available molecular approaches for examining the presence and expression of the key genes involved in microbial processes. These methods are continuously improving and require further development and validation of primer- and probe-based analyses and expansion of databases for alternative microbial markers. Phylogenetic marker approaches provide tools to determine which organisms are present or generally active in a community; functional gene markers provide only information concerning the distribution or transcript levels (deoxyribonucleic acid [DNA]- or messenger ribonucleic acid [mRNA]-based approaches) of specific gene populations across environmental gradients. Stable isotope probing methods offer great potential to identify microorganisms that metabolize and assimilate specific substrates in environmental samples, incorporating usually a rare isotope (i.e., (13)C) into their DNA and RNA. DNA and RNA in situ characterization allows the determination of the species actually involved in the processes being measured. DNA microarrays may analyze the expression of thousands of genes in a soil simultaneously. A global analysis of which genes are being expressed under various conditions in contaminated soils will reveal the metabolic status of microorganisms and indicate environmental modifications accelerating bioremediation.

Aims:  To analyse the arsenic‐resistant bacterial communities of two agricultural soils of Bangladesh, to isolate arsenic‐resistant bacteria, to study their potential role in arsenic transformation and to investigate the genetic determinants for arsenic resistance among the isolates. Methods and Results:  Enrichment cultures were performed in a minimal medium in the presence of As(III) and As(V) to isolate resistant bacteria. Twenty‐one arsenic‐resistant bacteria belonging to different genera of Gram‐positive and Gram‐negative bacteria were isolated. The isolates, with the exception of Oceanimonas doudoroffii Dhal Rw, reduced 2 mmol l−1 As(V) completely to As(III) in aerobic conditions. Putative gene fragments for arsenite efflux pumps were amplified in isolates from Dhal soil and a putative arsenate reductase gene fragment was amplified from a Bacillus sp. from Rice soil. Conclusions:  Phylogenetically diverse arsenic‐resistant bacteria present in agricultural soils of Bangladesh are capable of reducing arsenate to arsenite under aerobic conditions apparently for detoxification purpose. Significance and Impact of the Study:  This study provides results on identification, levels of arsenic resistance and reduction of arsenate by the bacterial isolates which could play an important role in arsenic cycling in the two arsenic‐contaminated soils in Bangladesh.

Arsenic is present in many environments and is released by various natural processes and anthropogenic actions. Although arsenic is recognized to cause a wide range of adverse health effects in humans, diverse bacteria can metabolize it by detoxification and energy conservation reactions. This review highlights the current understanding of the ecology, biochemistry and genomics of these bacteria, and their potential application in the treatment of arsenic-polluted water.