Arsenic Reduction by Indigenous Bacteria in Shallow Aquifers from Ambikanagar, West Bengal, India

摘要

Possible biological mechanisms contributing towards the transformation of arsenic (As) in aquifer sediments was investigated in Ambikanagar. Enrichment cultures indicated several As tolerant species, which actively reduced As(V) under sub-oxic conditions. High As concentrations in the microcosms increased toxicity, and hence, bacterial types and the heterotrophic plate counts declined. Bacteria isolated from enrichment cultures were Acinetobacter johnsonii, Citrobacter freundii, Comamonas testosteroni, Enterobacter cloacae, and Sphingobium yanoikuyae. On inoculating the medium with these bacteria, different growth and As(V) reduction rates occurred. A zero-order model fits the As(V) reduction data. Initial As concentration seems to affect growth and As(V) reduction rates, and these values were highest in A. johnsonii. In contrast, C. testosteroni and S. yanoikuyae were almost unaffected by the initial As(V) concentrations. As(V) reduction in these bacteria occurs for detoxification or respiratory purposes (e.g., A. johnsonii). These experiments confirm that microorganisms may result in remobilization of As from sediments, and impact groundwater treatment.