Exploring Hyper- Tolerant Arsenic Resistant Bacillus Species from nepalese Agriculture Soil and their Plant Growth promoting efficacy

Abstract

Both surface and ground water is significantly used for irrigation and drinking purpose in which deposited arsenic on top of agriculture soil. Nepal Arsenic contamination in agricultural soils possess a significant threat to crop productivity and human health. The main aim of this study is to isolate and characterize hyper tolerant arsenic-resistant bacteria from contaminated agricultural soil of terai region of Nepal and evaluate their potential plant growth-promoting efficacy. For the isolation of arsenic resistant Bacillus, sixteen soil samples were collected from cultivable agricultural fields of Terai region of Nepal and isolated bacteria were screeened based on tolerance to high levels of arsenic through minimal inhibitory concentration assays. Only two S1 and M1 bacterial isolates with high arsenic tolerant arsenic resistant were selected and were characterized. Both bacterial isolates S1 and M1 showed maximum resistance against arsenic; up to 5,500 ppm of As (V) and 1000 ppm of As (III). In addition, both isolates showed heavy metal resistant against cobalt, copper, and zinc (200 ppm) and lead (400 ppm) which make its hyper tolerance in nature. Both S1 and M1 exhibited plant growth-promoting activities such as auxin and hydrogen cyanide production, phosphate and zinc solubilization, nitrogen fixation, biofilm production, heavy metal resistant, organic acid production, phosphatse production, amylase, HCN, protease, Laccase and lipase producers. Bio control activities were also observed against F. oxisporum, R. solani, A. solani etc. Based on 16S rRNA gene sequencing, isolates S1 and M1 showed highest similarity with Bacillus cereus (99.77%) and Bacillus weidmanii (99.69%) respectively. Pot experiment in green house condition was performed using isolates S1 and M1 to confirm their effect of on growth of Brassica juncea L. Czern, in both presence and absence of arsenic. Both the isolates significantly enhanced the growth of Brassica juncea such as increase in shoot length, root lengths, leaf area, water content, chlorophyll a & b, total chlorophyll, soluble protein in leaf were observed as compared to uninoculated control in the presence and absence of arsenic. These findings suggest that isolates S1 and M1 are first hyper tolerant arsenic resistant bacteria ever reported in Nepal and could be best promising candidate as plant growth promoters and biocontrol agent in arsenic contaminated soil. Keywords: Soil, Arsenic resistant Bacillus, Plant growth promotion, Bioremediation, biofilm, Biocontrol