VIEWING QUORUM SENSING IN A GLOBAL NETWORK: STUDIES ON SDIA-DEPENDENT SYSTEM 1AND AUTOINDUCER-2 MEDIATED SYSTEM-2 OF NON-PATHOGENIC ESCHERICHIA COLI K-12
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Quorum sensing is a process by which bacteria send out and perceive signal molecules that enumerate their population density. When a threshold signal level is achieved, these bacteria coordinate their behavior and exhibit multicellularity. This can be viewed as a sort of sociological behavior, wherein bacteria communicate with each other resulting in altered societal structure. Studies on the quorum sensing of common laboratory strains of E. coli K-12 have been independently directed on two mainly recognized systems, each associated with an autoinducer family (AI-1 and AI-2). This study has specifically addressed a question of the functionality of a sensor associated with system 1 (a LuxR type sensor, SdiA). Interestingly, this sensor, which is also a transcriptional regulator, was found to positively regulate the uptake of the quorum system 2 signaling molecule (AI-2). An sdiA mutant showed altered mRNA levels for motility genes, purine de novo synthesis and rRNAs, which are likely to link to phenotypic changes such as decreased motility and increased aggregation and stress resistance. This study also describes the regulatory effects of major molecular chaperones, DnaJKE and GroESL, on AI-2 level found in conditioned medium, suggesting a linkage between the well-characterized heat shock stress response and quorum sensing. The finding that there is cross-regulation between E. coli quorum system 1 and 2, and the interplay with global regulatory networks such as the heat shock response, will contribute to the development of "engineered" quorum systems in E. coli that serve industrial purposes and also to the potential control of pathogenic bacteria.