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Category: Food Microbiology; Applied and Industrial Microbiology
Quorum Sensing and Signal Transduction in Biofilms: the Impacts of Bacterial Social Behavior on Biofilm Ecology, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815479/9781555814052_Chap07-1.gif /docserver/preview/fulltext/10.1128/9781555815479/9781555814052_Chap07-2.gifAbstract:
The advances from at least two major research areas, biofilms and bacterial quorum sensing, have led us to begin to appreciate the concept that bacteria can organize into groups, form well-organized communities, and communicate with each other for coordinated activities or social life that was once believed to be restricted to multicellular organisms. Bacteria with altered physiological activities (biofilm phenotypes) are known to result largely from bacterial social behaviors controlled by quorum sensing or other mechanisms when they are living in biofilms. Understanding bacterial social behaviors and their molecular mechanisms in the development of biofilms will greatly facilitate the development of novel strategies in the prevention and treatment of biofilm infections. In 1998, researchers first described the role of las quorum sensing in biofilm formation of Pseudomonas aeruginosa. The biofilms formed by the mutant were also dispersed by the addition of the detergent sodium dodecyl sulfate. This finding suggests that quorum sensing plays an important role in the development of bacterial biofilms. More importantly, this study suggests an inextricable connection between two bacterial social behaviors, quorum sensing and biofilm formation. In P. aeruginosa organism, quorum sensing is highly complex and consists of two interlinked N-acyl-homoserine lactone (AHL) dependent regulatory circuits, which are modulated by numerous regulators acting at both the transcriptional and posttranscriptional levels. The chapter discusses how might quorum sensing signal molecules function in biofilms. Quorum sensing is emerging as an integral component of bacterial global gene regulatory networks responsible for bacterial adaptation in biofilms.
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LuxI/LuxR-type quorum sensing in gram-negative bacteria. The LuxI-like protein is an autoinducer synthase that catalyzes the formation of a specific AHL. The AHL freely diffuses through the cell membrane at high cell density. LuxR is a transcriptional regulator protein that binds to the diffusing AHL and, in turn, activates the transcription of its target genes.
Oligopeptide–two-component-type quorum sensing in gram-positive bacteria. Here is a hypothetical model of a quorum sensing system and its controlled phenotypes in Streptococcus mutans. ComD is the histidine kinase protein to sense CSP. ComE is the cognate response regulator to control the transcription of its target genes with the promoter containing a conserved 9-bp repeat element of accgttnag-12 bpaccgttnag (ComE binding site). ComX is an alternative sigma factor that is presumably regulated by ComE and directs RNA polymerase to drive transcription of the late competence genes, such as cinA, recA, and coiA, which contain the consensus sequence of tacgaata (cin-box). nlmAB and bip are the genes encoding CSP-dependent bacteriocin and bacteriocin immunity protein.
luxS-encoded AI-2 quorum sensing in both gram-negative and -positive bacteria. AI-2 is synthesized by the enzyme LuxS and chemically is a furanone. Many gram-negative and -positive bacteria have been found to harbor LuxS homologues in their genomes, but their cognate receptors are unknown with the exception of that in Vibrio harveyi, which uses the LuxPQ two-component-like system to sense and respond to AI-2 for bioluminescence emission. AI-2′ and AI-2″ stand for AI-2 homologues from different species, and they can be sensed by LuxPQ of V. harveyi.