Genome analysis of quorum sensing Cedecea neteri SSMD04 leads to identification of its novel signaling synthase (cneI), cognate receptor (cneR) and an orphan receptor.

Kian-Hin Tan,Wai-Fong Yin,Kok-Gan Chan,Jia-Yi Tan

doi:10.7717/peerj.1216

Abstract

Cedecea neteri is a very rare human pathogen. We have isolated a strain of C. neteri SSMD04 from pickled mackerel sashimi identified using molecular and phenotypics approaches. Using the biosensor Chromobacterium violaceum CV026, we have demonstrated the presence of short chain N-acyl-homoserine lactone (AHL) type quorum sensing (QS) activity in C. neteri SSMD04. Triple quadrupole LC/MS analysis revealed that C. neteri SSMD04 produced short chain N-butyryl-homoserine lactone (C4-HSL). With the available genome information of C. neteri SSMD04, we went on to analyse and identified a pair of luxI/R homologues in this genome that share the highest similarity with croI/R homologues from Citrobacter rodentium. The AHL synthase, which we named cneI(636 bp), was found in the genome sequences of C. neteri SSMD04. At a distance of 8bp from cneI is a sequence encoding a hypothetical protein, potentially the cognate receptor, a luxR homologue which we named it as cneR. Analysis of this protein amino acid sequence reveals two signature domains, the autoinducer-binding domain and the C-terminal effector which is typical characteristic of luxR. In addition, we found that this genome harboured an orphan luxR that is most closely related to easR in Enterobacter asburiae. To our knowledge, this is the first report on the AHL production activity in C. neteri, and the discovery of its luxI/R homologues, the orphan receptor and its whole genome sequence.

Highlights

Cedecea spp. are extremely rare Gram-negative bacteria that belong to the Enterobacteriaceae family (Berman, 2012)
We show for the first time that C. neteri possesses an acyl-homoserine lactone (AHL) quorum sensing (QS) system and identified a novel signaling synthase gene, its cognate receptor, and an orphan LuxR-type receptor gene
As was mentioned in the introduction, C. neteri SSMD04 was isolated from shime saba in an attempt to recover AHL-producing bacteria from food

Summary

Introduction

Cedecea spp. are extremely rare Gram-negative bacteria that belong to the Enterobacteriaceae family (Berman, 2012). The representative of the genus is lipase-positive and resistant to colistin and cephalothin. The name Cedecea was coined by Grimont and Grimont, from the abbreviation of the Centers for Disease Control (CDC) (Grimont et al, 1981). Recognized as Enteric group 15, this genus is comprised of five species, out of which only three are valid, C. neteri, C. lapagei, C. davisae, while the other two were not validly published and are known as Cedecea species 3 and Cedecea species 5 (Brenner et al, 2005). How to cite this article Tan et al (2015), Genome analysis of quorum sensing Cedecea neteri SSMD04 leads to identification of its novel signaling synthase (cneI), cognate receptor (cneR) and an orphan receptor.

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