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Bacillus licheniformis DAS-1 and DAS-2 were found as potent tool for removal/uptake of arsenic [As(V) and As(III)] and reduction [(As(V) to As(III)] of arsenic from the liquid growth medium in our previous studies. Present work gives light on modulation of arsenic remediation (in terms of uptake and reduction) by two selected essential soil nutrients, phosphate (PO4)3− and nitrate (NO3)−. PO43− has structural analogy with arsenate [AsO43−/As(V)] that compete with cell uptake of As(V). It was found that enrichment of 0.75 mM of PO43− had significantly moderated the As(V) toxicity in liquid broth culture by retarding As(V) uptake. Lowering level of PO43− can lead to increase in As(V) removal from medium and vice versa. NO3− has strong oxidant properties which controls As(III) oxidation into As(V) in medium that resulted less toxicity favouring growth of bacteria and also more uptake via phosphate transporters. Hence, accelerated As(III) uptake has shown on enrichment of 0.5 mM of NO3− in medium. All the results of work give evidence that appropriate enrichment of PO43− and NO3− into liquid growth medium, can significantly contribute in alteration of efficiency for arsenic removal/uptake and reduction by bacteria from the medium.

Three arsenic hyper tolerant bacteria were isolated and identified as Acinetobacter calcoaceticus J1, Agrobacterium tumefaciens J2 and Bacillus cereus DAS3, with MICs (minimal inhibitory concentrations) were found 310, 300, 280 mM As(V) and 25, 3, 35 mM As(III), respectively. All the three isolates were found efficient in removing arsenic both As(V) as well as As(III) from the growth medium. Maximum removal of As(V) observed was 56.7% by DAS3 and of As(III) was 68% by J2. pH and nutrients strength of medium were found as factors to modulate the potential of As removal by bacteria. Maximum values of removal for As(V) was 64% by DAS3 on 20% dilution of medium and for As(III) was 76% by J2 at pH 8. Study of bacterial growth and chemical toxicity (DHA) had drawn picture of better arsenic [As(V) and As(III)] tolerance than other osmotic stress [NaCl or PEG 6000], indicating the existence of cross-protection between arsenic toxicity and arsenic generated osmotic stress.