Characterization of arsenite-oxidizing bacteria isolated from arsenic-contaminated groundwater of West Bengal

Abstract

Nine arsenic (As)-resistant bacterial strains isolated from As-rich groundwater samples of West Bengal were characterized to elucidate their potential in geomicrobial transformation and bioremediation aspects. The 16S rRNA gene-based phylogenetic analysis revealed that the strains were affiliated with genera Actinobacteria, Microbacterium, Pseudomonas and Rhizobium. The strains exhibited high resistance to As [Minimum inhibitory concentration (MIC) ≥ 10 mM As³⁺ and MIC ≥ 450 mM As⁵⁺] and other heavy metals, e.g., Cu²⁺, Cr²⁺, Ni²⁺, etc. (MIC ≥ 2 mM) as well as As transformation (As³⁺ oxidation and As⁵⁺ reduction) capabilities. Their ability to utilize diverse carbon source(s) including hydrocarbons and different alternative electron acceptor(s) (As⁵⁺, SO₄²⁻, S₂O₃²⁻, etc.) during anaerobic growth was noted. Growth at wide range of pH, temperature and salinity, production of siderophore and biofilm were observed. Together with these, growth pattern and transformation kinetics indicated a high As³⁺ oxidation activity of the isolates Rhizobium sp. CAS934i, Microbacterium sp. CAS905i and Pseudomonas sp. CAS912i. A positive relation between high As³⁺ resistance and As³⁺ oxidation and the supportive role of As³⁺ in bacterial growth was noted. The results highlighted As³⁺ oxidation process and metabolic repertory of strains indigenous to contaminated groundwater and indicates their potential in As³⁺ detoxification. Thus, such metabolically well equipped bacterial strains with highest As³⁺ oxidation activities may be used for bioremediation of As contaminated water and effluents in the near future.

Keywords:

• Arsenic
• groundwater
• indigenous bacteria
• arsenate reduction
• arsenite oxidation

Additional information

Funding

The authors acknowledge Council of Scientific and Industrial Research (Scheme No. 38/1314/11/EMR II) and Department of Biotechnology, Govt. of India (RGYI Scheme No. BT/PR8933/GBD/27/41/2006) for financial support. Dhiraj Paul acknowledges the University Grants Commission (UGC), India, for providing a fellowship.