Characterization of a Starch Hydrolysing Bacillus flexus U8 Isolated from Rhizospheric Soil of the Paddy Plants

Abstract

One bacterial strain U8 having starch hydrolysing activity was isolated from the rhizospheric soil of rice fields of Purba Bardhaman district in West Bengal, India. This bacterial sample was screened on nutrient agar plates (NA) and checked for starch hydrolysing activity in starch agar media. Colonies of this bacterial isolate were white and opaque with rough margins. Various tests were performed on this isolate including catalase, methyl red test, voges–proskauer, indole, citrate utilization and nitrate reduction test. Positive results were obtained for the former two tests and negative results for the latter tests. The presence of exoenzymes like gelatinase, amylase, oxidase and lipase was observed in the isolate; however, no urease was found. 16S rRNA sequencing and phylogenetic tree analyses indicated the present bacterial strain U8, was Bacillus flexus. Sugar fermentation tests revealed that Bacillus flexus U8 utilized fructose, xylose, lactose, cellobiose, dextrose and mannose as carbon sources. Antibiotic susceptibility tests showed that Bacillus flexus U8 was resistant to penicillin (10 µg/disc) and ampicillin (10 µg/disc). No haemolysis was observed on the blood agar media containing the bacterial isolate, indicating its non-pathogenic nature. The GC content of the isolate was 55% and AT content was 45%. Restriction mapping of the Bacillus flexus U8 16S rRNA gene sequence was also performed. Due to the abundance of Bacillus flexus U8 in the soil, its starch hydrolysing properties can be explored on agricultural land to potentially improve the health of the soil and plants.