Characterisation of vietnamycin: a novel Burkholderia antibiotic targeting mupirocin-resistant methicillin-resistant Staphylococcus aureus (MRSA)

Gram-negative Burkholderia bacteria are an untapped source of new antibiotics with multiple bioactive compounds currently under investigation1. An antimicrobial activity produced by Burkholderia vietnamiensis has been identified and designated vietnamycin. The compound has potent activity against methicillin-resistant, mupirocin-resistant Staphylococcus aureus (MRSA), but the chemical structure of vietnamycin and its biosynthetic pathway are not known. To bring vietnamycin from discovery towards pre-clinical testing, an efficient extraction method based on solvent extraction of growth media followed by FLASH chromatography has been developed. A thin layer chromatography (TLC) bioassay of the resulting crude extract demonstrated the presence of two bioactive fractions, with vietnamycin (Rf 0.43) separating from a bioactive fraction with a mobility (Rf 0.90) characteristic of the 4-hydroxy-3-methyl-2-alkylquinoline (HMAQ) Burkholderia signalling molecules1. In tandem with chemical characterisation of vietnamycin, a genome mining approach is being undertaken to identify the gene cluster responsible for its biosynthesis. The genome sequence of producer strain B. vietnamiensis BCC0268 (6.77 Mb) has been determined by single molecule real time sequencing, and is composed of 3 chromosomal replicons (3.28, 2.22, and 1.26 Mb). Prediction of secondary metabolite biosynthesis clusters was performed using the Antibiotics and Secondary Metabolite Analysis Shell2 (antiSMASH), and demonstrated presence of 32 clusters including a nonribosomal peptide synthase (NRPS) and NRPS-type I polyketide synthase (PKS) locus. Deletion of the smallest replicon had no impact on vietnamycin biosynthesis, eliminating the NRPS-type I PKS encoded on this replicon as the pathway responsible for its biosynthesis. In summary, an interdisciplinary approach combining microbiology, chemistry, and genome mining is being used to identify vietnamycin and progress it as a novel Burkholderia antibiotic.