Genetic regulation of biosynthesis and resistance to redox-active phenazines in Burkholderia spp.

Burkholderia includes gram-negative saprophytes, nitrogen-fixers, and species associated with nosocomial infections. Numerous strains in the Burkholderia cepacia , Burkholderia pseudomallei , Burkholderia glumae , and Burkholderia gladioli clades carry genes for phenazine (Phz) biosynthesis. Phenazines are a large class of colored, structurally diverse microbial secondary compounds with a common nitrogen-containing tricyclic core. They act as molecular signals and extracellular electron shuttles, contributing to the competitiveness of producer organisms in their natural habitats. Phenazines also undergo redox cycling, generating reactive oxygen species that suppress the growth of other organisms. The study of phenazines has largely been confined to the model opportunistic pathogen Pseudomonas aeruginosa , and many aspects of their biology in other bacterial groups remain poorly understood. In this study, we identified genes involved in phenazine production, regulation, and resistance in Burkholderia lata 383, a member of the B. cepacia complex, which produces dimethyl 4,9-dihydroxy-1,6-phenazinedicarboxylate. We subjected this strain to a transposon mutagenesis screen and characterized the transcriptomes of phenazine and quorum-sensing (QS) mutants of B. lata 383. Our results indicate that QS regulates phenazine production in Burkholderia and confirm that this cell-cell communication also controls other phenotypic traits, including biofilm formation. Analysis of transcriptome responses to phenazine methosulfate in B. lata 383 and two closely related phenazine-non-producing Burkholderia strains revealed that these organisms cope with phenazine toxicity by upregulating pathways involved in the oxidative stress response, iron-sulfur cluster biogenesis, and multidrug efflux.