Role of the Genes of Type VI Secretion System in Virulence of Rice Bacterial Brown Stripe Pathogen Acidovorax avenae subsp. avenae Strain RS-2.

Md Masum,Bin Li,Wen Qiu,Yingzi Yang,Yushi Fang,Guochang Sun,Jie Chen,Ogunyemi Olaitan,Yanli Wang,Yang Zhang

doi:10.3390/ijms18102024

Abstract

The Type VI secretion system (T6SS) is a class of macromolecular machine that is required for the virulence of gram-negative bacteria. However, it is still not clear what the role of T6SS in the virulence of rice bacterial brown stripe pathogen Acidovorax avenae subsp. avenae (Aaa) is. The aim of the current study was to investigate the contribution of T6SS in Aaa strain RS2 virulence using insertional deletion mutation and complementation approaches. This strain produced weak virulence but contains a complete T6SS gene cluster based on a genome-wide analysis. Here we compared the virulence-related phenotypes between the wild-type (RS-2) and 25 T6SS mutants, which were constructed using homologous recombination methods. The mutation of 15 T6SS genes significantly reduced bacterial virulence and the secretion of Hcp protein. Additionally, the complemented 7 mutations ΔpppA, ΔclpB, Δhcp, ΔdotU, ΔicmF, ΔimpJ, and ΔimpM caused similar virulence characteristics as RS-2. Moreover, the mutant ΔpppA, ΔclpB, ΔicmF, ΔimpJ and ΔimpM genes caused by a 38.3~56.4% reduction in biofilm formation while the mutants ΔpppA, ΔclpB, ΔicmF and Δhcp resulted in a 37.5~44.6% reduction in motility. All together, these results demonstrate that T6SS play vital roles in the virulence of strain RS-2, which may be partially attributed to the reductions in Hcp secretion, biofilm formation and motility. However, differences in virulence between strain RS-1 and RS-2 suggest that other factors may also be involved in the virulence of Aaa.

Highlights

The gram-negative bacteria Acidovorax avenae subsp. avenae (Aaa) causes diseases in a wide range of economically important plants such as rice, corn, oats, sugarcane, millet, and foxtail [1]
In this-isolated from rice-has been sequenced by our laboratory, which avenae is a useful resource study, we found 25 Type VI secretion system genes in the A. avenae subsp
The current study revealed the diversity of T6SS genes in the pathogenicity of the Aaa strain RS-2 to rice seedlings

Summary

Introduction

The gram-negative bacteria Acidovorax avenae subsp. avenae (Aaa) causes diseases in a wide range of economically important plants such as rice, corn, oats, sugarcane, millet, and foxtail [1]. Avenae (Aaa) causes diseases in a wide range of economically important plants such as rice, corn, oats, sugarcane, millet, and foxtail [1]. This well-known seed-borne bacterium [1,2] causes bacterial brown stripe (BBS) in rice, which leads to heavy economic losses. It has been reported in many rice-growing countries such as Asia, Africa, North America and Europe [3,4]. The contaminated seeds represent the most important primary source.

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