Abstract
The cooling water systems are used to remove heat generated in the various industries. Biofouling of the cooling water systems causes blocking of condenser pipes and the heat exchanger tubes. In many Gram-negative bacteria, N-acylhomoserine lactone (AHL) are used as quorum-sensing signal molecule and associated with biofilm formation. To investigate the relationship between quorum sensing and biofouling in the cooling water system, we isolated a total of 192 bacterial strains from the five cooling water systems, and screened for AHL production. Seven isolates stimulated AHL-mediated purple pigment production in AHL reporter strain Chromobacterium violaceum CV026 or VIR07. Based on their 16S rRNA gene sequences, AHL-producing isolates were assigned to Aeromonas hydrophila, Lysobacter sp., Methylobacterium oryzae, and Bosea massiliensis. To the best of our knowledge, B. massiliensis and Lysobacter sp. have not been reported as AHL-producing species in the previous researches. AHLs extracted from the culture supernatants of B. massiliensis and Lysobacter sp. were identified by liquid chromatography-mass spectrometry. AHLs produced by B. massiliensis were assigned as N-hexanoyl-l-homoserine lactone (C6-HSL), N-(3-oxohexanoyl)-l-homoserine lactone (3-oxo-C6-HSL), and N-(3-oxooctanoyl)-l-homoserine lactone (3-oxo-C8-HSL). AHLs produced by Lysobacter sp. were assigned as N-decanoyl-l-homoserine lactone (C10-HSL) and N-(3-oxodecanoyl)-l-homoserine lactone (3-oxo-C10-HSL). This is the first report of identification of AHLs produced by B. massiliensis and Lysobacter sp. isolated from the cooling water system.
Highlights
Quorum sensing is one of the cell-cell communication systems depending on cell population density [1]
In many Gram-negative bacteria, several kinds of N-acylhomoserine lactone (AHL) have been identified as autoinducer signal compounds involved in this mechanism [2]
To identify the bacterial species of AHL-producing bacteria, the 16S rRNA gene-encoding regions were amplified by PCR with Blend Taq plus DNA polymerase (Toyobo, Osaka, Japan) and the previously described universal primers, 27f (51 -AGA GTT TGA TCM TGG CTC AG-31 ) and 1525r
Summary
Quorum sensing is one of the cell-cell communication systems depending on cell population density [1]. It is expected that disrupting or manipulating the AHL signals could inhibit the expression of quorum-sensing regulated phenotypes such as virulence and infection of host cells [4]. In the case of the membrane bioreactor (MBR) wastewater treatment systems, quorum sensing is associated with the formation of a biofouling layer on the membrane surface [6]. It was revealed that the majority of the bacterial community in an industrial cooling water system was Proteobacteria [5]. From these facts, there is a high possibility that AHL-mediated quorum sensing affects the development of biofouling in the cooling water system. We screened for AHL-producing bacteria from the industrial cooling water systems, and identified AHL structures produced by them
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