The flhDC master operon regulates nuclease synthesis and cell differentiation in Serratia marcescens

• Main Authors: LIU, JIA-HURNG, 劉家宏
• Other Authors: LAI HSIN-CHIH
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/64513518306879946641

碩士 === 國立臺灣大學 === 醫事技術學系研究所 === 86 === Abstract Serratia marcescens shows interesting cell differentiation and populationsur face migration (swarming) phenomena. The underlying regulatory mechanismof cel l differentiation/swarming is being studied. In order to investigatewhether th e regulation of flagellar synthesis, together with celldifferentiation,and nuc expression were under the control of flhDC, the flhDoperon was cloned from S. marcescens and sequenced. In this study, it isdemonstrated that flhD operon i n S. marcescens has additional function besidesthe flagellar regulon. This fun ction is the involvement in the regulationof swarming and nuc expression. It is hypothesized that cell differentiation is a part of t he cell cycle andenvironmental factors are to stimulate instead of initiating the celldifferentiation in S. marcescens. To test this, cells were first monit oredin minimal growth medium (MGM) broth cultures to see whether there is anyd ifferentiated characteristics. With the construction of an isogenic strainF-3 (flhDP2::luxAB) to monitor cell differentiation via intensity of bioluminescen ce, it is shown that cells with differentiated characteristics are observed in the liquid rich broth culture, occur in a growth-phase dependent way and are regulated by different environmental factors. The environmental glucose concentration was reported to be involved in theprocess of bacterial flagellar synthesis. Since the observation that glucoseprevents the synthesis of flagella in E. coli was first reported in 1967(glucose catabolite repressio n), many studies addressed the underlyingmechanism. Currently, it is thought t hat an increase in glucose concentrationdecreases the intracellular CRP/cAMP c oncentration, which leads to aninhibitory effect on the expression of the flh D operon. From my studyon cell differentiationof S. marcescens, it was found t hat glucose cataboliterepression on flhDC expression was not observed. My resu lts also showed thatsurface contact and nutrients might not be necessary for c ell differentiationin MGM broth and it might be possible to uncouple cell diff erentiationfrom its surface dependence by controlling the expression of flhDC inS. marcescens.