Novel N-Acyl Homoserine Lactone-Degrading Bacteria Isolated From Penicillin-Contaminated Environments and Their Quorum-Quenching Activities.

Hiroyuki Kusada,Yoichi Kamagata,Hideyuki Tamaki,Nobutada Kimura,Yu Zhang

doi:10.3389/fmicb.2019.00455

Abstract

N-Acyl homoserine lactones (AHLs) are signaling molecules used in the quorum sensing (QS) of Gram-negative bacteria. Some bacteria interfere with the QS system using AHL-inactivating enzymes, commonly known as quorum-quenching (QQ) enzymes. We have recently isolated a new QQ bacterium showing high resistance to multiple β-lactam antibiotics, and its QQ enzyme (MacQ) confers β-lactam antibiotic resistance and exhibits QQ activities. This observation suggests the possibility of isolating novel QQ bacteria from β-lactam antibiotic-resistant bacteria. In this direction, we attempted to isolate penicillin G (PENG)-resistant bacteria from penicillin-contaminated river sediments and activated sludge treating penicillin-containing wastewater and characterize their QQ activities. Of 19 PENG-resistant isolates, six isolates showed high QQ activity toward a broad range of AHLs, including AHLs with 3-oxo substituents. Five of the six AHL-degraders showed AHL-acylase activity and hydrolyzed the amide bond of AHLs, whereas the remaining one strain did not show AHL-acylase activity, suggesting that this isolate may likely possess alternative degradation mechanism such as AHL-lactonase activity hydrolyzing the lactone ring of AHLs. The 16S rRNA gene sequence analysis results categorized these six AHL-degrading isolates into at least five genera, namely, Sphingomonas (Alphaproteobacteria), Diaphorobacter (Betaproteobacteria), Acidovorax (Betaproteobacteria), Stenotrophomonas (Gammaproteobacteria), and Mycobacterium (Actinobacteria); of these, Mycobacterium sp. M1 has never been known as QQ bacteria. Moreover, multiple β-lactam antibiotics showed high minimum inhibitory concentrations (MICs) when tested against all of isolates. These results strongly demonstrate that a wide variety of β-lactam antibiotic-resistant bacteria possess QQ activities. Although the genetic and enzymatic elements are yet unclear, this study may infer the functional and evolutionary correlation between β-lactam antibiotic resistance and QQ activities.

Highlights

Bacteria communicate with one another using chemical signaling molecules
Diverse Acyl homoserine lactones (AHLs)-inactivating bacteria that belong to the phyla Proteobacteria, Bacteroidetes (Chryseobacterium, Flaviramulus, and Tenacibaculum), and Cyanobacteria (Nostoc) have been isolated and characterized as quorum quenching (QQ) bacteria (Leadbetter and Greenberg, 2000; Flagan et al, 2003; Hu et al, 2003; Huang et al, 2003; Lin et al, 2003; Park et al, 2003; Uroz et al, 2003; Sio et al, 2006; Yoon et al, 2006; Romero et al, 2008, 2010; Chan et al, 2011; Christiaen et al, 2011; Mahmoudi et al, 2011; Chen et al, 2012; Wang et al, 2012; Zhang et al, 2013; Torres et al, 2016; Kusada et al, 2017)
Our study revealed a novel AHL-acylase (MacQ) from MR-S7 that confers β-lactam antibiotic resistance and exhibits QQ activity (Kusada et al, 2017)

Summary

Introduction

The sensing of auto-inducers allows bacteria to distinguish between low and high cell population densities as well as to adjust the gene expression in response to changes in cell number. This process, termed as quorum sensing (QS), allows bacterial cells to coordinately control the gene expression in the community. Gram-positive bacteria within the phyla, Actinobacteria (Arthrobacter, Microbacterium, Nocardioides, Rhodococcus, Staphylococcus, and Streptomyces), Deinococcus-Thermus (Deinococcus), and Firmicutes (Bacillus and Solibacillus) have been found to exhibit QQ activities, indicating that phylogenetically diverse bacteria may quench the AHL-based QS (Dong et al, 2000; Lee et al, 2002; Park et al, 2003; Uroz et al, 2003; d’Angelo-Picard et al, 2005; Wang et al, 2010; Morohoshi et al, 2012; Koch et al, 2014; Chan et al, 2015)

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