Screening of plant growth promoting attributes and arsenic remediation efficacy of bacteria isolated from agricultural soils of Chhattisgarh

Arsenic (As) resistant indigenous bacteria with discrete minimum inhibitory concentration values for arsenate [As(V)] and arsenite [As(III)] were isolated from the paddy fields of different regions of Chhattisgarh, India, following enrichment culture technique. Evaluation of the plant growth promoting (PGP) properties of the isolates revealed that two rod-shaped Gram-positive bacteria viz., ARP2 and ART2 acquired various PGP traits, including phosphate solubilization, production of siderophore, indole acetic acid, ammonia, and exopolysaccharide. Both the isolates significantly increased (40-80%) the root length of Oryza sativa L. even under As-exposure. Sequencing of 16S rRNA gene identified these isolates as Bacillus nealsonii strain ARP2 and Bacillus tequilensis strain ART2, respectively. Isolate ARP2 exhibited arsenate reductase activity thereby rapidly reduced As(V) into As(III), achieving a reduction rate of 37.5 mu M min(-1). Alike, strain ART2 was capable of oxidizing As(III) into As(V) via arsenite oxidase enzyme, and revealed the oxidation rate of 21.8 mu M min(-1). Quantitative estimation of As through atomic absorption spectrophotometer revealed that the isolates ARP2 and ART2 removed 93 +/- 0.2% and 77 +/- 0.14% of As(V) and As(III), respectively, from As-containing culture media. The FTIR analysis showed the interaction of As with the cell membrane and was further confirmed by SEM and TEM techniques, which marked the increase in cell volume owing to successive accumulation of As. The As-resistant and PGP properties of above two isolates demonstrates their potentiality for sustainable bioremediation of As, and establishment of flora in As-rich environment.