The OmpR Regulator of Burkholderia multivorans Controls Mucoid-to-Nonmucoid Transition and Other Cell Envelope Properties Associated with Persistence in the Cystic Fibrosis Lung

Abstract

Bacteria from the complex grow in different natural and man-made environments and are feared opportunistic pathogens that cause chronic respiratory infections in cystic fibrosis patients. Previous studies showed that mucoid clinical isolates grown under stress conditions give rise to nonmucoid variants devoid of the exopolysaccharide cepacian. Here, we determined that a major cause of the nonmucoid morphotype involves nonsynonymous mutations and small indels in the gene encoding a response regulator of a two-component regulatory system. In complementation of nonmucoid variants (NMVs) with the native gene restored exopolysaccharide production. The loss of functional OmpR had positive effects on growth, adhesion to lung epithelial cells, and biofilm formation in high-osmolarity medium, as well as an increase in swimming and swarming motilities. In contrast, phenotypes such as antibiotic resistance, biofilm formation at low osmolarity, and virulence in were compromised by the absence of functional OmpR. Transcriptomic studies indicated that loss of the gene affects the expression of 701 genes, many associated with outer membrane composition, motility, stress response, iron acquisition, and the uptake of nutrients, consistent with starvation tolerance. Since the stresses here imposed on may strongly resemble the ones found in the cystic fibrosis (CF) airways and mutations in the gene from longitudinally collected CF isolates have been found, this regulator might be important for the production of NMVs in the CF environment. Within the cystic fibrosis (CF) lung, bacteria experience high-osmolarity conditions due to an ion unbalance resulting from defects in CF transmembrane conductance regulator (CFTR) protein activity in epithelial cells. Understanding how bacterial CF pathogens thrive in this environment might help the development of new therapeutic interventions to prevent chronic respiratory infections. Here, we show that the OmpR response regulator of one of the species found in CF respiratory infections, , is involved in the emergence of nonmucoid colony variants and is important for osmoadaptation by regulating several cell envelope components. Specifically, genetic, phenotypic, genomic, and transcriptomic approaches uncover OmpR as a regulator of cell wall remodeling under stress conditions, with implications in several phenotypes such as exopolysaccharide production, motility, antibiotic resistance, adhesion, and virulence.

Antibiotics select for novel pathways of resistance in biofilms

“…We showed that the EnvZ R397H substitution alters the balance of porin production with down-regulation of the major outer membrane pore, OmpF and up-regulation of the narrow outer membrane pore, OmpC. EnvZ controls activity of OmpR, which is known to control the balance of porin production as well as biofilm formation under low medium osmolarity conditions (17,40). OmpF is well characterised as an entry point for β-lactams due to the molecules’ physiochemical properties, which makes entry possible through this porin which has a larger pore size than OmpC (41,42).…”

A genome-wide association analysis reveals a potential role for recombination in the evolution of antimicrobial resistance in Burkholderia multivorans

“…reported parallelism in an OmpR-like response regulator, which is involved in the mucoidy phenotype of B . multivorans , and later showed its association with persistence in the CF lungs [54, 60]. We found two related multi-mutated genes encoding an OmpR family-sensor histidine kinase (BMUL_3678) and an OmpR family response regulator (BMUL_0075).…”

The Exopolysaccharide Cepacian Plays a Role in the Establishment of the Paraburkholderia phymatum – Phaseolus vulgaris Symbiosis

“…Another important regulator of CEP biosynthesis is the response regulator OmpR. In the Bcc strain B. multivorans, OmpR was shown to be important for the mucoid to non-mucoid switch (Silva et al, 2018). Interestingly, several Bcc non-mucoid isolates produce large amounts of the polysaccharide CEP when tissue of the natural host plant onion was provided as nutrient source (Bartholdson et al, 2008).…”

“…In silico analysis of P. phymatum gene cluster (Bphy_1056–Bphy_1077) suggested that it is involved in the biosynthesis of CEP, a branched acetylated heptasaccharide also produced by many strains of the Burkholderia sensu latu , which are opportunistic pathogens ( Conway et al, 2004 ; Cescutti et al, 2010 ; Ferreira et al, 2010 ; Hallack et al, 2010 ; Cuzzi et al, 2012 ). The role of CEP and particularly the associated switch to mucoid colonies in Burkholderia virulence is controversially discussed in the literature ( Govan et al, 1993 ; Conway et al, 2004 ; Zlosnik et al, 2008 , 2011 ; Silva et al, 2018 ). Recent data suggest that CEP is important for chronic infections and appears to be rather counter-productive for acute virulent infections ( Silva et al, 2018 ).…”

“…The role of CEP and particularly the associated switch to mucoid colonies in Burkholderia virulence is controversially discussed in the literature ( Govan et al, 1993 ; Conway et al, 2004 ; Zlosnik et al, 2008 , 2011 ; Silva et al, 2018 ). Recent data suggest that CEP is important for chronic infections and appears to be rather counter-productive for acute virulent infections ( Silva et al, 2018 ). The fact that the B. cenocepacia ET12 epidemic CF isolates J2315, K56-2, and BC7 have lost their ability to produce CEP due to an 11 bp deletion in bceB ( Moreira et al, 2003 ; Bartholdson et al, 2008 ) also suggests that CEP may not be required for acute infections caused by pathogenic Burkholderia strains.…”