Abstract
Growth-dependent cell-cell communication termed quorum sensing is a key regulatory system in bacteria for controlling gene expression including virulence factors. In this study five potential bacterial pathogens including Bacillus sp. W2.2, Klebsiella sp. W4.2, Pseudomonas sp. W3 and W3.1 and Serratia sp. W2.3 were isolated from diseased Tilapia fish in Malaysia, supplied by the leading global fish supplier. Proteolytic activity assays confirmed that with the exception of Klebsiella sp. W4.2, all isolates showed distinct proteolytic activity. Furthermore Bacillus sp. W2.2 and Pseudomonas sp. strains W3 and W3.1 also displayed haemolytic activity. By using high resolution liquid chromatography mass spectrometry, we revealed the presence of unusually long-chain N-(3-oxohexadecanoyl)-homoserine lactone (3-oxo-C16-HSL) from Pseudomonas sp. W3.1 and N-dodecanoyl-homoserine lactone (C12-HSL) from Serratia sp. W2.3, respectively. Interestingly, Pseudomonas sp. W3.1 also produced a wide range of Pseudomonas quinolone signalling (PQS) molecules. Pseudomonas sp. W3 did not show any quorum sensing properties but possessed quorum quenching activity that inactivated AHLs. This study is the first documentation that shows unusual long-chain AHLs production in Serratia sp. and Pseudomonas sp. isolated from diseased fish and the latter also produce a wide range of PQS molecules.
Highlights
Tilapia (Oreochromis niloticus as majority) is an important commercial fish in freshwater aquaculture around the world
In 2009, a tilapia epidemic of unknown etiology broke out in Malaysia and according to the Malaysian agriculture authority, it resulted in an estimated death of about 50% of the tilapia stock in Malaysia
We describe five bacterial strains isolated from tilapia which died as a result of the 2009 epidemic outbreak in Malaysia
Summary
Tilapia (Oreochromis niloticus as majority) is an important commercial fish in freshwater aquaculture around the world. The global tilapia production reached 2.5 million tonnes worth 3.7 billion US dollars in 2009 (www.fao.org). Malaysia is one of the major tilapia production countries. In 2009, a tilapia epidemic of unknown etiology broke out in Malaysia and according to the Malaysian agriculture authority, it resulted in an estimated death of about 50% of the tilapia stock in Malaysia. Preliminary investigations suggested that the causal agent of the epidemic was of bacterial origin G. Chan, unpublished) which led to this work
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