INHIBITION OF QUORUM SENSING BY BACTERIA FROM MARINE MICROALGAE

Quorum sensing (QS) is a bacterial cell-to-cell communication, resulted in behavioural regulations such as luminescence, biofilm, motility etc. Virulence factors productions by pathogens in aquaculture have also been to be regulated by QS. Thus, QS inhibition (QSI) is proposed as an alternative way to control diseases among aquatic organisms. We focus to evaluate the effects of live and dead (autoclaved cells) bacterial QS inhibitors to interfere QS system in pathogenic bacteria Vibrio campbellii BB120 using gnotobiotic Artemia as a model organism. Bacteria were isolated from microalgae and were screened for their anti-QS activity using Chromobacterium violaceum CV026. The selected QSIs were characterized and identified using 16S rRNA analysis. Their anti-QS activity were then quantified through acylhomoserine lactones (AHL) degradation assay, in comparison with positive and negative control strains, Pseudomonas sp. P3/pME6863 and Pseudomonas sp. P3/pME6000, respectively. The effects of QS inhibitors toward Artemia survival in challenge test were observed. Data were statistically analysed using students t-test (p=0.05), through SAS software version 9.4.

Three bacteria isolated from microalgae inhibited purple production of C. violaceum CV026. Analysis of 16S rRNA sequence revealed that those species belong to the genus Bacillus, and were deposited into GenBank database respectively under accession number KX356688 for BpChlAY, KX644098 (BpNofAY) and KX356689 (BpSpiAY). Degradation of AHL showed that BpNofAY was able to degrade the QS signal molecules within 6h, while BpChlAY and BpSpiAY within 9h. In Artemia challenged test, the highest Artemia survival was observed with live BpChlAY (P<0.05) (Figure 1). In contrast, dead BpChlAY, live and dead BpNofAY resulted to low Artemia survival (P<0.05) while there were no significant effect when fed with both live and dead BpSpiAY. In unchallenged group, dead BpNofAY, live and dead BpSpiAY showed low Artemia survival (P<0.05).

There were no significant effect when fed with both live and dead BpChlAY and live BpNofAY.

Live and dead bacterial QSIs showed different effects on Artemia survival to BB120. The probiotic effect of BpChlAY could serve as a biocontrol agent and has beneficial effect towards Artemia sp.