Extrinsic and intrinsic factors governing bacterial biofilms
Bacteria in nature live in multicellular communities surrounded by self-secreted molecules that help survival in the ever changing and challenging environment. B. subtilis forms architecturally complex structures in biofilms. The aim of the thesis is to contribute to the present understanding of the factors that influence biofilm formation in bacteria. My work focused on extracellular factors such as medium growth components, affecting the structure of biofilms combined with the intrinsic factors like metabolic heterogeneity that shaped the microbial colonies. The study found that certain subtle differences in the genes (epsG) and regulators that confer biofilm formation in B. subtilis, influences the bacterial capability to form wrinkle structure. This makes few variants of laboratory strain B. subtilis 168 capable of forming biofilms on some rich media. Further, the presence of manganese in medium impacted the white chalky wrinkles of the colony and made them morphologically complex and robust. Next, it demonstrated the role of Calcium in restricting the colony movement mediated by secreted components. My study showed that it sequesters surfactin, the molecule aiding passive, collective expansion, thus, making it unavailable for the cells to spread. The competition between metabolic efficient and inefficient metabolizers in biofilms showed that initially, the later dominated the space due to faster growth rate. However, the conditions in biofilm allowed the emergence of efficient metabolizers and both strategists coexist. Overall, results indicate that the complexity of bacterial biofilms is influenced by the environmental factors and metabolic strategies. A small change in sugar sources or the ion concentrations affect the biofilm formation and the cellular behaviour such as colony expansion. The study also displays the spatial structures of biofilms favouring the emergence of cooperative strategies and curb competition by favouring metabolic strategies to coexist.