HigB Reciprocally Controls Biofilm Formation and the Expression of Type III Secretion System Genes through Influencing the Intracellular c-di-GMP Level in Pseudomonas aeruginosa.

Yueying Zhang,Bin Xia,Weihui Wu,Fang Bai,Shouguang Jin,Yuqing Long,Mei Li,Zhihui Cheng,Jing Shi,Yongxin Jin

doi:10.3390/toxins10110424

Abstract

Toxin-antitoxin (TA) systems play important roles in bacteria persister formation. Increasing evidence demonstrate the roles of TA systems in regulating virulence factors in pathogenic bacteria. The toxin HigB in Pseudomonas aeruginosa contributes to persister formation and regulates the expression of multiple virulence factors and biofilm formation. However, the regulatory mechanism remains elusive. In this study, we explored the HigB mediated regulatory pathways. We demonstrate that HigB decreases the intracellular level of c-di-GMP, which is responsible for the increased expression of the type III secretion system (T3SS) genes and repression of biofilm formation. By analyzing the expression levels of the known c-di-GMP metabolism genes, we find that three c-di-GMP hydrolysis genes are up regulated by HigB, namely PA2133, PA2200 and PA3825. Deletion of the three genes individually or simultaneously diminishes the HigB mediated regulation on the expression of T3SS genes and biofilm formation. Therefore, our results reveal novel functions of HigB in P. aeruginosa.

Highlights

Toxin-antitoxin (TA) systems have been found in almost all bacterial species [1]
We previously demonstrated that the higB/higA operon is induced by treatment with ciprofloxacin and HigB contributes to persister formation and controls the expression of T3SS genes [3]
Upon overexpressing higB, the triple mutant displayed similar levels of biofilm formation, expression of cdrA and the T3SS genes as those in wild type PA14 (Figure 7). These results suggest that the up regulation of PA2133, PA2200 and PA3825 are involved in the HigB mediated reduction of intracellular level of c-di-GMP and the reciprocal regulation of the T3SS genes and biofilm formation

Summary

Introduction

Toxin-antitoxin (TA) systems have been found in almost all bacterial species [1]. Degradation of an antitoxin results in the activation of its cognate toxin, which inhibits bacterial growth by interfering with biosynthesis of macromolecules, cell division or reducing membrane potential [2]. The type II TA systems are widely distributed in bacteria and archaea, and are composed of two proteins that are encoded in a bicistronic operon. Most type II toxins are endonucleases, the activities of which are repressed by the cognate antitoxins through direct interactions. Some type II TA systems have been found to influence virulence gene expression and biofilm formation [6,7,8,9,10]

Methods

Results

Conclusion