ABSTRACT
The bacterium Burkholderia thailandensis produces an arsenal of secondary metabolites that have diverse structures and roles in the ecology of this soil-dwelling bacterium. In liquid co-culture experiments, B. thailandensis secretes a previously unstudied antimicrobial that nearly eliminates another soil bacterium, Bacillus subtilis. To identify the antimicrobial, we used a transposon mutagenesis approach. This screen identified antimicrobial-defective mutants with insertions in the hmqA, C and F genes involved in biosynthesis of a family of quinolones called 3-methyl-4-hydroxy-2-alkenylquinolines (HMAQs), which are related to the Pseudomonas aeruginosa 4-hydroxy-2-alkylquinolines (HAQs). Insertions also occurred in a previously uncharacterized gene BTH_II1576. We confirm that BTH_II1576 is involved in generating N-oxide HMAQ (HMAQ-NO) in B. thailandensis and that HMAQ-NOs are sufficient to eliminate B. subtilis in co-cultures. Moreover, synthetic HMAQ-NO is ~50-fold more active than HMAQ. Both the methyl group and the length of the carbon side chain account for high activity of HMAQ-NO against B. subtilis. The results provide new information on the biosynthesis and activities of HMAQs and reveal new insight into how these molecules might be important for the ecology of B. thailandensis.
IMPORTANCE The soil bacterium Burkholderia thailandensis produces methylated alkylquinolones, which are a family of relatively unstudied molecules related to the alkylquinolones of Pseudomonas aeruginosa. Several of the methylated alkylquinolones have antimicrobial activity against other species. We show N-oxidated methyl-alkenylquinolone is particularly antimicrobial and is sufficient to kill Bacillus subtilis in co-cultures, and requires a previously unstudied protein HmqL for biosynthesis. These results also provide new information about the biology of alkyl-quinolones, particularly the methylated alkylquinolones, which are unique to B. thailandensis. This study also has importance for understanding B. thailandensis secondary metabolites and has implications for potential therapeutic development.
Competing Interest Statement
The authors have declared no competing interest.
