Abstract

Background: Microbes are a rich source of antibacterial and anti-insect molecules. Due to rising antibiotic and anti-insect resistance in various sectors of the society, it is important to identify new compounds that may address these issues.

Aims and Objective: This study aimed to explore the bacteria isolated from soil to identify new molecules with antibacterial and anti-insect activity. Further, the current study is aimed at testing and characterizing antimicrobial and insecticidal properties of methanolic extracts from four different soil bacteria

Methods: This study reports the isolation and characterization of soil bacteria by morphological, biochemical, and molecular analysis. The antibacterial and insecticidal potential of methanolic extracts of four bacterial strains were tested using an agar well diffusion assay, along with the development and survival of Spodoptera litura. Fractionation of the methanolic extract was performed by chromatography, and the separated fractions were tested for their antibacterial activity.

Results: The bacteria belong to Bacillus, Exiguobacterium, and Microbacterium species. The extract of Bacillus licheniformis SKS7 exhibited maximum antibacterial activity against all tested microbes, including human pathogens. Extract from the same microbe also showed maximum anti-insect activity against Spodoptera litura by significantly increasing the pupal period by as much as 80% and hence extending the time to adult emergence. Morphological abnormalities like deformed wings, deformed pupae, and failure to emerge from pupae were also observed. Purification of the extract by HPLC and gel permeation chromatography helped us to observe a low molecular weight protein that may be responsible for its antibacterial activity.

Conclusion: Methanolic extract of Bacillus licheniformis SKS7 contains bioactive molecules with antibacterial and anti-insect activities. Further characterization and identification of these molecules may form the basis for the development of novel antibacterial drugs and insecticidal molecules in the future.

Keywords: Antibacterial activity, insecticidal activity, agar well diffusion assay, bacillus sp., chromatography, spodoptera litura