ISOLATION, CHARACTERIZATION AND IDENTIFICATION OF AN As(V)-RESISTANT PLANT GROWTH PROMOTING RHIZOBACTERIUM ASSOCIATED WITH THE RHIZOSPHERE OF Azolla microphylla

Abstract

In the present study, bacterial strains were obtained from the rhizosphere of Azolla microphylla Kaulf. and their arsenic (As) tolerance was tested under in-vitro conditions. Out of the two bacteria screened for As(V) tolerance, strain R1 was found to have the highest As(V) tolerance level at 2000 mg/l and was found to retain up to 58.76% of As given in the medium solution within its cells, as revealed by inductively coupled plasma optical emission spectroscopy analysis. This efficient As(V)-resistant strain was identified using16S rRNA sequencing and fatty acid methyl ester profile analysis, and was found to be a strain of Bacillus cereus (GenBank accession number MH819519). Along with showing abundance of hallmark fatty acids of the Bacillus cereus group, some unique fatty acids were also detected in the bacterial strain R1, namely 15:1 ω5C, 17:1 iso ω10C, 17:1 ante isoA, 17:0, 18:0 iso, 18:1 ω9c, and 17:1 iso ω5C. At its maximum tolerable As(V) dose of 2000 mg/l, strain R1 showed 59.9% As(V) reduction, which was assessed through arsenate reductase enzyme activity. Not only this, under As(V) stress, strain R1 was found to produce 20.4% more cellular protein and display 30.3% antioxidant activity assayed as DPPH reduction. The bacterium is also capable of exhibiting plant growth promoting traits such as solubilisation of inorganic phosphate, production of siderophore and biosynthesis of the plant growth regulator indole acetic acid. Thus, this bacterium has the potential to remediate As(V) from environment and also assist the growth of plants growing in As-polluted ecosystems.