produces 2-alkylquinolone derivatives important for host virulence and competition with bacteria that employ naphthoquinones for aerobic respiration.

Melioidosis is caused by , an opportunistic Gram-negative pathogen that inhabits soil and water in tropical and subtropical regions. infections often occur following contact with contaminated water or soil or by inhalation of contaminated dust and water droplets. There is limited knowledge about how is able to survive in harsh environmental conditions and compete with the microbes that inhabit these niches. Previous research demonstrated that 3-methyl-2-alkylquinolones (MAQs), and their corresponding -oxides (MAQNOs), are produced by and provide a competitive advantage when grown in the presence of Gram-positive bacteria. In this study, 39 Gram-negative environmental bacteria in the and phyla were isolated and characterized. Intriguingly, inhibited 71% of bacteria in the phylum in zone of inhibition and coculture competition assays, but no isolates were similarly inhibited. Transposon mutagenesis was utilized to identify genes required for the inhibition of sp. ST4, a representative member of the . Three mutations mapped to , the locus encoding 2-alkylquinolone derivatives, and two mutations were identified in , a gene encoding a quorum-sensing controlled LysR-type transcriptional regulator. strains with deletion mutations in and were unable to produce 2-alkylquinolone derivatives or inhibit isolates in competition assays. RAW264.7 murine macrophage cells were infected with 1026b and 1026b and there was a 94-fold reduction in the number of intracellular 1026b bacteria relative to 1026b. The 50% lethal dose (LD) of 1026b and 1026b in BALB/c mice was determined to be 3 x 10 colony forming units (CFU) and > 1 x 10 CFU, respectively. Taken together, the results indicate that the products of the locus are important for intracellular replication in murine macrophages, virulence in a mouse model of melioidosis, and competition with bacteria that utilize naphthoquinones for aerobic respiration.