Dissertation > Excellent graduate degree dissertation topics show

Study on Synthesis and Degradation of Bacterial Quorum Sensing Signal Auto-inducer 2

Author: KongXiangFei
Tutor: PengHuaSong
School: Shanghai Jiaotong University
Course: Biochemical Engineering
Keywords: quorum sensing DPD chemically synthesis biodegradation
CLC: Q936
Type: Master's thesis
Year: 2009
Downloads: 158
Quote: 0
Read: Download Dissertation

Abstract

Quorum sensing (QS) is a physiological phenomenon of cell-density-dependent gene expression. Many bacteria can secret signal molecules called autoinducers, which increase simultaneously with the increasing of cell density. When autoinducers accumulate to a necessary threshold value, it activates transcription of certain genes, including those for inducer synthesis, symbiosis, virulence expression, antibiotics biosynthesis, mobility, spore and biofilm formation. Autoinducer-2 is a kind of metabolite of methionine cycle in some bacteria and can be used a signal molecule in cell to cell communication. The study of biosynthesis and biodegradation of AI-2 will not only be helpful to understand the relationship among bacteria, but also benefit to control bacteria behaviors by interfering with QS system.Firstly the 4,5-dihydroxy-2,3-pentanedione (DPD), which is the precursor of AI-2, was chemically synthesis by the Baylis–Hillman/ozonolysis route between 2-(tert-butyldimethylsilyloxy) ethanal and 3-buten-2-one. Intermediate products were purified by organic extraction and column chromatography and the structure were identified by NMR instrument. DPD could be analyzed by HPLC after derivatization with O-phenylenediamine. The DPD sample could be bioassay in ABT media using the indictor bacterium, Vibrio harveyi BB170. The appropriate detection time of biofluorescence was 3~4h after incubation. There was no linear relationship between fluorescence intensity and DPD concentration. The concentration of DPD between 0.01μM ~1000μM could be detected by bioassay. Then the concentrations of DPD were determined in the supernatant of several common bacteria and some bio-control Pseudomonas strains which were separated in our lab. The results indicated that there were AI-2 bioactivity in E. coli K12 and S. aureus and little bioactivity in B. subtilis、Pseudomonas aeruginosa PAO1 and Pseudomonas sp P76, while no bioactivity in Pseudomonas sp M18、Pseudomonas sp P26 and E. coli DH5α. The DPD was biosynthesis in the early stage of logarithmic phase but biodegraded quickly in the late stage of logarithmic phase. All of these bacteria can grow in inorganic salt medium with DPD using as sole carbon source. The strains of S. aureus、B. subtilis、E. coli K12 and E. coli DH5αcan utilize DPD relatively quickly than three Pseudomonas strains. It seems that there was the luxS gene in the four strains, which did not exist in the three strains and there was the degradation gene of DPD in the four strains correspondingly. Comparative studies showed that glucose can be consumed in inorganic salt medium quickly by S. aureus、E. coli K12 and E. coli DH5α, and then the xylose. The consumption rate of DPD was the lowest. Similar to the above, the final OD600 of strains in DPD medium was the lowest. Perhaps that degradation pathway of DPD was distinct from the other two carbohydrates.

Study on Synthesis and Degradation of Bacterial Quorum Sensing Signal Auto-inducer 2

Abstract

Related Dissertations