Bacteriocins and survival in the biofilm environment

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Biofilms represent the predominant form of bacterial life. When presented with a surface or an interface and conditions advantageous for growth, bacteria almost always will assemble as a group of cells encapsulated within a self-produced protective extracellular matrix. Biofilms allow survival of bacteria in hostile environments, such as UV exposure, dehydration, salinity, and several disinfectants and biocidal agents. When bacteria are growing within biofilms, they secrete signaling molecules that increase in concentration as a function of cell density. In a process called quorum sensing, bacteria communicate with one another by using signaling molecules to regulate their gene expression in response to fluctuations in the cell population density. A wide array of phenotypes is controlled by quorum sensing including biofilm formation, bacteriocin production, and genetic competence for acquisition of exogenous DNA. Thus, quorum sensing allows bacteria to display a unified response that benefits the bacteria during adaptation to environment, colonization, and defense against competitors. Bacteriocins are ribosomally synthesized proteinaceous antibacterial peptides. They selectively interfere with the growth of other bacteria, and regulation of bacteriocin production plays an important role in the competitive interactions in bacterial biofilms. Extensive work done by my group showed that quorum sensing can also function as a stress-inducible system by triggering the signaling to the bacterial population to initiate an adaptive response that results in different outcomes. Biofilms are very complex and a fundamental property of bacteria is their ability to regulate cell growth when faced with a fluctuating environment. The production and secretion of bacteriocins in response to environmental stressors could confer a distinct ecological advantage to the producer in competing against other bacteria that are present in the same ecological niche or as a possible mechanism for the acquisition of DNA from other species during the genetic competence state. Using Streptococcus mutans as a model chosen because of its relevance of a biofilm lifestyle, my overall goal is to answer the following question: Do microbial growth modulators such as bacteriocins play a role in competition, biodiversity and ecological fitness of the biofilm? Research (past and ongoing) from my lab suggests a complex interplay between quorum sensing (signal), bacteriocin activation (response), and biofilm persistence (phenotype) as a reaction to the environmental perturbations. Using state-of-the-art technology to elucidate the physiology and gene activities of biofilms, my research has the potential to contribute to the development of cost-effective biocidal strategies for the control and/or eradication of microbial biofilms. **