| Summary: | 碩士 === 國立臺灣大學 === 醫事技術學研究所 === 91 === Bacteria show complex multicellular behaviors to cope with the rapid changes when cell population reaches a threshold. Swarming is a specialized form of bacterial surface translocation when bacteria culture on solid growth media. Serratia marcescens CH-1 swarms on 0.8% LB agar at 30℃, but these characters are inhibited at 37℃. In order to understand the underlying mechanism of temperature-dependent swarming behavior, transposon mutagenesis was performed to screen for the mutants that swarm at 37℃. One super-swarming mutant (named O6 / CH-1DC) was found to bear a defective gene rssC (for repression / regulation of Serratia swarming), and was predicted to encode a 364 amino-acid polypeptide. It shows in the GenBank sequence identity to members of trans-acylase protein family whose function is related to lipid metabolism. There is no difference in growth rate compared with CH-1. In order to unravel the role of RssC, the total cellular fatty-acid profiles were determined by gas-chromatography analysis, the acyl chains composition of CH-1 and CH-1DC were indeed different. Under TEM, SEM, and AFM observation, surface morphology of CH-1DC is found to be significantly altered. In addition, there was more filamentous material being observed. This suggested that RssC is closed related to maintain the structure of cell membrane. Factors already identified to be essential for or involved in the regulation of swarming process were examined. The swimming motility, flagellum production and biosurfactant production of CH-1DC is significantly increased, while the cell length of CH-1DC is shortened, which might be related to regulation of flhDC master operon. Further study showed that the biofilm formation in CH-1DC is less finer than CH-1. The production of hemolysin was also elevated in CH-1DC. Taken together, it is suggested that the super swarming phenotype of CH-1DC at 37℃ might be due to rssC mutated and cell wall stress driving some stress-sensing apparatus situated in the bacterial cell wall, and subsequently either directly or indirectly affects global physiological changes including swarming behavior.
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