| Summary: | 碩士 === 長庚大學 === 醫學生物技術暨檢驗學系 === 98 === Toxin-antitoxin (TA) modules are gene pairs specifying for a toxin and its cognate antitoxin and are found on the chromosomes of many bacteria including pathogens. It has been demonstrated that chromosomal TA systems influence bacterial multicellular behaviors such as biofilm formation and fruiting body formation. However, the role of TA systems in swarming behavior, another type of bacterial multicellular behavior, remains elusive. Swarming is a complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria from nonmotile vegetative cells into highly-motile swarmer cells. Here we demonstrated that approximately 90% of cells undergo cell death in vegetative cell population during swarming development in Serratia marcescens. A pair of chromosomal TA module named ccdAB(Sm) was identified. Deletion of ccdAB(Sm) caused dramatic reduction of dead cells during swarming development and showed precocious swarming motility. Interestingly, deletion of rssBA, a two-component system regulating swarming initiation, also reduced cell death during swarming. Furthermore, the transcription of ccdAB(Sm) and their upstream genes are negatively regulated by RssAB signaling which led to cell death in early swarming development. Taken together, these findings provide evidences that RssAB regulates cell death through a chromosomal TA module, CcdAB(Sm), in swarming development.
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