Cellular adaptation responses in a halotolerant Exiguobacterium exhibiting organic solvent tolerance with simultaneous protease production

Abstract

Solvent tolerance is a novel trait among halotolerant bacteria and their enzymes. However, the solvent response mechanisms in Gram-positive bacteria remain less investigated. The Exiguobacterium indicum (TBG-PICH-001) was isolated from the sediment of Pichavaram estuary. It possessed halotolerance and could prove to be a suitable candidate for solvent tolerance studies. The present study extensively explores possible cellular mechanisms in a Gram-positive bacterium when exposed to the organic solvents. The isolate was highly tolerant towards hydrophobic solvents with high log P value such as tetradecane, dodecane, decane compared to the other hydrophobic solvents having low log P value, viz. octane, heptane, isooctane, and hexane. The electron micrographs showed less conspicuous differences in the bacterial cell membrane exposed to highly hydrophobic organic solvents. In contrast, anomalous cell aggregation and cell membrane disorganization was observed in the presence of comparatively less hydrophobic solvents. The spectroscopic assay for cell permeability and viability advocated the toxic effects of the solvents on the cells and their corresponding adaptability. Additionally, the microbe produced a high yield of alkaline protease (900 U/mL) in the presence of hydrophobic solvents. Such solvent stable proteases could find applications in solvent-mediated biosynthesis of peptides, while the solvent stable bacterial isolate might be an efficient biosystem for such bioprocesses. The significant level of cell tolerance could provide the response mechanism insights, while stable protease yield offers the cost-effective development of bioprocesses through non-aqueous enzymology and whole-cell bio-transformations.