The afc antifungal activity cluster, which is under tight regulatory control of ShvR, is essential for transition from intracellular persistence of Burkholderia cenocepacia to acute pro-inflammatory infection

PLoS Pathog. 2018 Dec 4;14(12):e1007473. doi: 10.1371/journal.ppat.1007473. eCollection 2018 Dec.

Abstract

The opportunistic pathogen Burkholderia cenocepacia is particularly life-threatening for cystic fibrosis (CF) patients. Chronic lung infections with these bacteria can rapidly develop into fatal pulmonary necrosis and septicaemia. We have recently shown that macrophages are a critical site for replication of B. cenocepacia K56-2 and the induction of fatal pro-inflammatory responses using a zebrafish infection model. Here, we show that ShvR, a LysR-type transcriptional regulator that is important for biofilm formation, rough colony morphotype and inflammation in a rat lung infection model, is also required for the induction of fatal pro-inflammatory responses in zebrafish larvae. ShvR was not essential, however, for bacterial survival and replication in macrophages. Temporal, rhamnose-induced restoration of shvR expression in the shvR mutant during intramacrophage stages unequivocally demonstrated a key role for ShvR in transition from intracellular persistence to acute fatal pro-inflammatory disease. ShvR has been previously shown to tightly control the expression of the adjacent afc gene cluster, which specifies the synthesis of a lipopeptide with antifungal activity. Mutation of afcE, encoding an acyl-CoA dehydrogenase, has been shown to give similar phenotypes as the shvR mutant. We found that, like shvR, afcE is also critical for the switch from intracellular persistence to fatal infection in zebrafish. The closely related B. cenocepacia H111 has been shown to be less virulent than K56-2 in several infection models, including Galleria mellonella and rats. Interestingly, constitutive expression of shvR in H111 increased virulence in zebrafish larvae to almost K56-2 levels in a manner that absolutely required afc. These data confirm a critical role for afc in acute virulence caused by B. cenocepacia that depends on strain-specific regulatory control by ShvR. We propose that ShvR and AFC are important virulence factors of the more virulent Bcc species, either through pro-inflammatory effects of the lipopeptide AFC, or through AFC-dependent membrane properties.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Burkholderia Infections / microbiology*
  • Burkholderia cenocepacia / pathogenicity*
  • Macrophages / microbiology*
  • Virulence / physiology*
  • Zebrafish

Grants and funding

This study was supported by l'Institut National de la Santé et de la Recherche Médicale INSERM and Université de Montpellier. MCG was supported by a doctoral grant from the French Ministry of Higher Education and Research, YT was supported by “Vaincre la Mucoviscidose” and co-financed by l’Association Gregory Lemarchal, JRF was recipient of a doctoral grant from Fundação Ciência e Tecnologia (FCT), Portugal. KA and LE were financed by the Swiss National Science Foundation (SNSF) (Project 31003A_169307). Work in the group of ACV was also supported by the Marie-Curie Initial Training Network FishForPharma (PITN-GA-2011-289209). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.