Abstract
Hafnia alvei H4 is a bacterium subject to regulation by a N-acyl-l-homoserine lactone (AHL)-mediated quorum sensing system and is closely related to the corruption of instant sea cucumber. Studying the effect of Hafnia alvei H4 quorum sensing regulatory genes on AHLs is necessary for the quality and preservation of instant sea cucumber. In this study, the draft genome of H. alvei H4, which comprises a single chromosome of 4,687,151 bp, was sequenced and analyzed and the types of AHLs were analyzed employing thin-layer chromatography (TLC) and high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS). Then the wild-type strain of H. alvei H4 and the luxI/R double mutant (ΔluxIR) were compared by transcriptome sequencing (RNA-seq). The results indicate that the incomplete genome sequence revealed the presence of one quorum-sensing (QS) gene set, designated as lasI/expR. Three major AHLs, N-hexanoyl-l-homoserine lactone (C6-HSL), N-butyryl-l-homoserine lactone (C4-HSL), and N-(3-oxo-octanoyl)-l-homoserine lactone (3-oxo-C8-HSL) were found, with C6-HSL being the most abundant. C6-HSL was not detected in the culture of the luxI mutant (ΔluxI) and higher levels of C4-HSL was found in the culture of the luxR mutant (ΔluxR), which suggested that the luxR gene may have a positive effect on C4-HSL production. It was also found that AHL and QS genes are closely related in the absence of luxIR double deletion. The results of this study can further elucidate at the genetic level that luxI and luxR genes are involved in the regulation of AHL.
Highlights
IntroductionIt is widely accepted that bacteria (both planktonic and biofilm cells) communicate with each other by sensing and releasing signaling compounds in a process commonly known as quorum sensing (QS) (Miller and Bassler 2000)
It is widely accepted that bacteria communicate with each other by sensing and releasing signaling compounds in a process commonly known as quorum sensing (QS) (Miller and Bassler 2000)
Secretion of acyl-1-homoserine lactone (AHL) by H. alvei H4 wild type and mutants In order to comprehensively analyze the AHLs produced by the QS system of H. alvei H4, the AHLs extracted from the cultures of wild type and three mutants (ΔluxI, ΔluxR and ΔluxIR) at different time points were first subjected to thin-layer chromatography (TLC) analysis
Summary
It is widely accepted that bacteria (both planktonic and biofilm cells) communicate with each other by sensing and releasing signaling compounds in a process commonly known as quorum sensing (QS) (Miller and Bassler 2000). This process is composed of an N-acyl-1-homoserine lactone (AHL) synthase (a LuxI-type family protein) and an AHL reporter (a LuxR-type family transcription regulator) (Kumar et al 2016). H. alvei is considered to be the most common biological contaminant in vacuumpacked frozen meat (Bruhn et al 2004) This bacterium is known to produce N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL) (Viana et al 2009). H. alvei plays an important role either in the decay of meat or other vacuum-packed foods, little research has been carried out to determine the specific interaction mechanisms between AHLs and luxI/luxR genes in the H. alvei community
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