| 總結: | Quorum sensing (QS) is bacterial communication that allows bacteria to respond to
stimuli in population density-dependent manner. In this work, seawater sampling site
was Morib Beach, Malaysia. This work has successfully isolated 60 bacterial strains.
Five of them namely T01, T08, T14, T33 and T47 showed N-acyl homoserine lactones
(AHLs) production screened by QS biosensor. These QS bacteria were identified using
MALDI-TOF mass spectrometry and analyses of 16S rRNA gene sequence which
showed that all of them are members of Vibrio genus. Profiling of the AHLs produced
by these isolates revealed production of both short-chain and long-chain AHL
production by all of the strains. The AHLs profiles are as follows; T01 produced Nhexanoyl-
L-homoserine lactone (C6-HSL), N-(3-oxo-decanoyl)-L-homoserine lactone
(OC10 HSL) and N-dodecanoyl homoserine-L-lactone (C12-HSL), T08 produced Nbutanoyl-
L-homoserine lactone (C4-HSL) and C6-HSL, T14 produced C6-HSL, T33
produced C6-HSL and OC10-HSL and T47 produced C4-HSL. Next, draft genomes of
all five strains were obtained using MiSeq platform followed by bioinformatics
analyses. Of these, V. variabilis strain T01 showed the presence of a QS synthase gene
vanM (contig 16, 1203 bp) in V. variabilis strain T01 vanM was heterologously
expressed in Escherichia coli BL21 (DE3) pLysS. From the overexpression analyses,
vanM is responsible for the production of three AHL which are C6-HSL, OC10 HSL
and C12-HSL. Using a known anti-QS compound, gallic acid, biofilm assay was
performed on V. variabilis strain T01 and treatment of gallic acid significantly reduced
its biofilm production. To further study the mode of action of gallic acid on V. variabilis strain T01,
transcriptomic analyses were carried out. From the RNA-sequencing data, most of the
V. variabilis strain T01 genes were affected upon gallic acid treatment involved in
transport and metabolism (inorganic ions, amino acids, carbohydrates and lipids). Genes
related to QS such as cell motility (fliS, fliT and fliL) were down-regulated and cell
wall/membrane/envelope biogenesis (tonB) were notably up-regulated
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