Growth on mannitol-rich media elicits a genome-wide transcriptional response in Burkholderia multivorans that impacts on multiple virulence traits in an exopolysaccharide-independent manner

Abstract

In common with other members of the Burkholderia cepacia complex (BCC), Burkholderia multivorans is capable of producing exopolysaccharide (EPS) when grown on certain mannitolrich media. The significance of the resulting mucoid phenotype and the genome-wide response to mannitol has never been characterized despite its clinical relevance following the approval of a dried-powder preparation of mannitol as an inhaled osmolyte therapy for cystic fibrosis (CF) patients. In the present study we defined the transcriptional response of B. multivorans ATCC 17616, a model genome-sequenced strain of environmental origin, to growth on mannitol-rich yeast extract media (MYEM). EPS-dependent and -independent impact of MYEM on virulenceassociated traits was assessed in both strain ATCC 17616 and the CF isolate B. multivorans C1576. Our studies revealed a significant transcriptional response to MYEM encompassing approximately 23 % of predicted genes within the genome. Strikingly, this transcriptional response identified that EPS induction occurs in ATCC 17616 without the upregulation of the bce-I and bce-II EPS gene clusters, despite their pivotal role in EPS biosynthesis. Of approximately 20 differentially expressed putative virulence factors, 16 exhibited upregulation including flagella, ornibactin, oxidative stress proteins and phospholipases. MYEM-grown B. multivorans also exhibited enhanced motility, biofilm formation and epithelial cell invasion. In contrast to these potential virulence enhancements, MYEM-grown B. multivorans C1576 showed attenuated virulence in the Galleria mellonella infection model. All of the observed phenotypic responses occurred independently of EPS production, highlighting the profound impact that mannitol-based growth has on the physiology and virulence of B. multivorans.

Antibiotics Disrupt Coordination between Transcriptional and Phenotypic Stress Responses in Pathogenic Bacteria

“…Moreover, upon transitioning to MCDM, the clusters of fitness or expression changes expand, but they almost never merge (Figure 3b). Our data on S. pneumoniae thus confirms that phenotypically (PIGs) and transcriptionally (TIGs) important stress response genes are distinct, which may indeed be a general phenomenon across different (microbial) species (Birrell et al , 2002; Smith et al , 2006; Deutschbauer et al , 2011; Denman et al , 2014; Turner et al , 2014; Keren et al , 2016). …”

“…are differentially expressed genes also phenotypically important during stress? Previous studies have shown poor correlation between phenotypic and transcriptional profiles in several bacterial and yeast species (Birrell et al , 2002; Giaever et al , 2002; Smith et al , 2006; Deutschbauer et al , 2011; Price et al , 2013; Denman et al , 2014; Turner et al , 2014; Xie et al , 2015; Keren et al , 2016). However, in these studies Tn-Seq or RNA-Seq profiles were scarcely validated and analyses did not consider (network-)relationships between genes.…”

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies

“…To date, species known to produce ornibactin under iron starvation include Burkholderia cepacia, Burkholderia cenocepacia, Burkholderia vietnamiensis and Burkholderia ambifaria (Meyer et al, 1995;Thomas, 2007;Asghar et al, 2011). More recently, ornibactin gene expression has been reported for the first time in Burkholderia multivorans (Denman et al, 2014). There are three known species of this linear hydroxamate siderophore: ornibactin-C4, ornibactin-C6 and ornibactin-C8 produced by Bcc strains (Stephan et al, 1993), and ferrated ornibactin is transported across the outer membrane by a ferric-ornibactin receptor, OrbA.…”

Biofilms produced by Burkholderia cenocepacia: influence of media and solid supports on composition of matrix exopolysaccharides

“…However, YEM is a peculiar medium, containing 2 % mannitol and only 0.2 % yeast extract, and may be unsuitable for full biofilm growth. At the same time, mannitol is the carbon source associated with cepacian production (Denman et al, 2014), but how and why it promotes its biosynthesis still needs to be clarified. It is also very interesting that, even when bacteria lacked the mucoid appearance, as in the growth developed on KA, LBG, MH and SCFM media, EPOLs were produced, even if to a lesser extent than in YEM.…”