Studies on the multi-cellular behaviours in Bacillus thuringiensis KPWP1

Jha, Sushmita (2022) Studies on the multi-cellular behaviours in Bacillus thuringiensis KPWP1. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Sushmita Jha (14RS008)) 14RS008.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

A paramount survival system of microorganisms is their robustness and flexibility to adapt to various environmental conditions. Bacillus thuringiensis is one of the most important bacterial species due to its wide range of applications. Previously it was reported that glucose at higher concentrations in semi solid growth media imposed restricted motility and pattern formation in the growing colonies Bacillus thuringiensis KPWP1. It is therefore important to further explore the behavioural changes in KPWP1 strain in details. The present study investigated the behavioural changes of salt, pH and arsenate tolerant Bacillus thuringiensis isolate KPWP1 when grown under different conditions. Microscopic studies including confocal-, scanning electron- and transmission electron microscopy uncovered modifications in behaviour in terms of pattern formation, movement and multicellular association in growing colonies of KPWP1 under different growth conditions. Interestingly, it was also observed that restricted colony movement due to the presence of 1% glucose or 3 mM arsenate in growth media triggered cell elongation and differential expression of ftsA, ftsZ, minC,minD (genes which are involved in cell division) and mreB (gene regulates the cell shape) which are involved in cell elongation. Differential expression of genes associated with sporulation (spoOA), chemotaxis (cheY), flagellation (CodY) and quorum sensing (nprB) was also found to be correlated with the observed behavioural changes. As Bacillus thuringiensis KPWP1 has evolved with the ability to exhibit multicellular behavior, the present study also investigated whether the observed restricted motility imposed by the presence of higher concentrations of glucose in growth media can induce biofilm formation by KPWP1 or not? It was observed that increased glucose concentrations in growth media resulted in a significant increase in biofilm formation by KPWP1 and the response was found to be glucose specific. The glucose induced biofilm formation by KPWP1 was found to be associated with increased production of exopolymeric substances, increased presence of densely packed micro-colonies, and greater hydrophobicity and adherence properties in KPWP1 cells. The understanding of multicellular behaviours and the differential expressions of genes, observed in this study, will be helpful in engineering and use of Bacillus thuringiensis for better regulation of biofilm formation and bioremediation.

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