Groundwater arsenic pollution causes many deaths worldwide. Arsenic levels in ground water are increasing day by day due to human activities, leading to higher threats of arsenic exposure. Arsenic release in drinking water resources causes major health problems.
Researchers at SPPU Pune, NCMR-NCCS Pune and NCL Pune collaboratively attempted to bio-prospect the microorganisms causing arsenic transformation. They used culture-dependent and independent approaches to study the microorganisms from Lonar Lake. Growth and Arsenic oxidation potential of microorganisms at increasing concentration was studied. The study also tried to understand possible pathway of Arsenic oxidation by studying the genes, transcripts and proteins involved.
Soil samples were collected from alkaline Lonar Crater Lake in Maharashtra. DNA was extracted from soil sample using soil DNA extraction kit. Unculturable and culturable diversity of soil sample was studied. Hyper-tolerance towards arsenic was studied. Growth and As(III) oxidation profile, ArsB amplification, enzyme inhibitor assay, As (III) oxidase assay, resting cells assay, Liquid chromatography mass spectrometry analysis , relative quantification of transcripts, microcosm studies and statistical analysis was done.
Bacterial community in the sample set comprised of total 21 phyla. Proteobacteria was predominantly found in the samples followed by Bacteroidetes. The bacterial member Pelagibacteraceae was detected predominantly in the sample followed by Microbacteriaceae, Flavobacteriaceae, Flammeovirgaceae, Vibrionaceae and Rhodobacteraceae with more than 5% abundance in all the samples. The bacterial diversity from Lonar Lake soil exhibited the presence of 10 As(III) oxidizing, 2 As(V) reducing, and 5 arsenic tolerant bacteria. Total 10 different genera were obtained viz. Bacillus, Lysinibacillus, Halomonas, Noviherbaspirillum, Roseomonas, Zobellela, Allidiomarina, Indibacter, Nocardioides, and Oceanimonas.
Arsenic hyper-tolerant Firmicute Bacillus firmus L-148 was isolated from arsenic limiting Lonar lake soil, which tolerated more than 3 M arsenic and could oxidize 75 mM arsenite [As (III)] in 14 days. It oxidized As (III) in presence of heavy metals. B. firmus L-148 was studied at the biochemical, protein, genomic and transcript level for understanding its arsenic oxidizing machinery. This study can be explored for bioremediation of arsenic contaminated water.
The tolerance towards arsenic in bacteria may be due to many reasons like expression of certain genes to combat the deleterious toxic effect. Expression of ArsA can contribute to high tolerance apart from the presence of more than one arsenic transforming operons. Once it gets delivered, arsenic shows actual level of oxidation . The means of transport of Arsenic was through water pipes and oxidation of samples in the waste water.
Though the potential cultures in this study were isolated from trivial arsenic content environment, they tolerated moderate to high concentration of As(III) and As(V). These findings clearly demonstrated that arsenic tolerance level of bacteria is not correlated to the arsenic content of the environment in which they thrive.