Burkholderia pseudomallei (Bps) is a facultative intracellular bacterial pathogen endemic to tropical regions, and is the aetiologic agent of melioidosis. Bps is inherently resistant to many commonly employed antibiotics, and its treatment requires a lengthy antibiotic course involving both intravenous and oral administration. Despite the treatment available, melioidosis still causes an estimated 165,000 cases resulting in 89,000 deaths per annum, globally. This highlights the urgency for the development of novel antibiotics that are more effective for combatting this severe disease.
Folate metabolism has been a long-standing target of successful antibiotics. Humans are unable to synthesise folate, making the bacterial folate biosynthesis enzymes a prime target for antibiotics, as there will be limited cross-reactivity with human enzymes. The folate molecule comprises three linked moieties; a pterin ring, para-aminobenzoic acid (PABA), and glutamate. Their synthesis has been well-studied in many pathogenic microorganisms, but in Bps, the PABA biosynthesis pathway is yet to be fully characterised. PABA biosynthesis is generally well-conserved in bacteria, and involves three enzymes: PabA, PabB, and PabC. A study by Pilatz et al. (2006) using environmental Bps isolate E8, showed through a transposon deletion mutant of bpsl2825 (pabB), that this gene was involved in PABA metabolism, and important for infection in a murine model.
In this study, through computational and bioinformatic characterisation, bpsl2825 is shown to, in fact, encode an additional C-terminal domain with strong homology to PabC. This suggests that BPSL2825 is a dual-function enzyme containing both PabB and PabC, which although unusual, can similarly be seen in Lactococcus lactis. Interestingly, PabA does not appear to be present in Bps. To confirm the findings of Pilatz et al. in a clinically relevant strain, the full-length bpsl2825 gene was deleted from Bps K96243, and the mutant strain was shown to be auxotrophic for PABA. Additionally, a murine macrophage infection model validated that bpsl2825 plays an important role in infection. This data confirms the role of bpsl2825 in metabolism and infection in Bps K96243. Further enzymatic and structural characterisation will evaluate the predicted dual-function activity of BPSL2825, and its potential as a novel target for antibiotic development can be assessed.