Whole-Genome Sequencing Analysis of Quorum Quenching Bacterial Strain Acinetobacter lactucae QL-1 Identifies the FadY Enzyme for Degradation of the Diffusible Signal Factor.

Tian Ye,Shaohua Chen,Xinghui Fan,Xiaofan Zhou,Wenping Zhang,Tian Zhou,Lianhui Zhang,Xudan Xu,Sandhya Mishra

doi:10.3390/ijms21186729

Abstract

The diffusible signal factor (DSF) is a fatty acid signal molecule and is widely conserved in various Gram-negative bacteria. DSF is involved in the regulation of pathogenic virulence in many bacterial pathogens, including Xanthomonas campestris pv. campestris (Xcc). Quorum quenching (QQ) is a potential approach for preventing and controlling DSF-mediated bacterial infections by the degradation of the DSF signal. Acinetobacter lactucae strain QL-1 possesses a superb DSF degradation ability and effectively attenuates Xcc virulence through QQ. However, the QQ mechanisms in strain QL-1 are still unknown. In the present study, whole-genome sequencing and comparative genomics analysis were conducted to identify the molecular mechanisms of QQ in strain QL-1. We found that the fadY gene of QL-1 is an ortholog of Xcc rpfB, a known DSF degradation gene, suggesting that strain QL-1 is capable of inactivating DSF by QQ enzymes. The results of site-directed mutagenesis indicated that fadY is required for strain QL-1 to degrade DSF. The determination of FadY activity in vitro revealed that the fatty acyl-CoA synthetase FadY had remarkable catalytic activity. Furthermore, the expression of fadY in transformed Xcc strain XC1 was investigated and shown to significantly attenuate bacterial pathogenicity on host plants, such as Chinese cabbage and radish. This is the first report demonstrating a DSF degradation enzyme from A. lactucae. Taken together, these findings shed light on the QQ mechanisms of A. lactucae strain QL-1, and provide useful enzymes and related genes for the biocontrol of infectious diseases caused by DSF-dependent bacterial pathogens.

Highlights

Xanthomonas campestris pv. campestris (Xcc) a causal agent of black rot, the most important and harmful plant disease known to cruciferous plants
The present study first reported the genomic characteristics and diffusible signal factor (DSF) degradation mechanism of A. lactucae strain QL-1 isolated from agricultural soil
The results demonstrated that strain QL-1 was different from the type strain A. lactucae NRRL B-41902 and another DSF-degrading strain Pseudomonas aeruginosa PAO1

Summary

Introduction

Xanthomonas campestris pv. campestris (Xcc) a causal agent of black rot, the most important and harmful plant disease known to cruciferous plants. Campestris (Xcc) a causal agent of black rot, the most important and harmful plant disease known to cruciferous plants. It can infect all cultivable varieties of Brassica vegetables, crops, and ornamental and weed plants worldwide [1]. DSF exists in all Xanthomonas sp., and widely exists in a variety of Burkholderia sp., Pseudomonas aeruginosa, and marine bacteria [4]. For the treatment and control of black rot caused by Xcc, chemical pesticides and antibiotics are largely used, leading to critical environmental pollution; destruction of the ecological balance; and a series of serious problems, such as food safety. There is a need to find a novel and effective prevention strategy for the control of plant diseases caused by pathogens

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Conclusion