The Role of Cycle Inhibiting Factor in Burkholderia pseudomallei Neuroinfections: Structural and Functional Insights

Burkholderia pseudomallei, the causative agent of melioidosis, can lead to severe brain infections with high mortality risk. The cycle inhibiting factor (Cif) plays a crucial role in neuronal cell invasion. This study investigates Cif's role in B. pseudomallei virulence using the Galleria mellonella model. Analysis of the cif gene (bpss1385) in 1,294 clinical isolates revealed 57.7% carried the gene, with 18 distinct variant types (VT) identified. The wild-type (WT) (bpss1385) was the most common form, showing close similarities in its amino acid sequence to most other variants with a small number of exceptions (VT4, VT6, and VT15). Three-dimensional structural analysis showed significant similarities among 18 variants, except for VT4. Functional studies demonstrated enhanced neuronal plaque formation in variants VT1, VT2, VT5, and VT15. Interestingly, no significant differences were observed between bpss1385 WT and VT3, VT4, VT6, or VT9, despite structural divergences in VT4. This suggests a complex relationship between Cif structure and B. pseudomallei pathogenesis. We further gained insights into the role of Cif in neuronal cells by proteomic analysis, identified 52 SH-SY5Y proteins with significant expression changes when comparing cif knockout mutant infection to parental strain (K96243) infection. These proteins, mainly involved in mRNA metabolism and cellular structure, indicate the involvement of Cif in disrupting host processes for bacterial survival. These findings emphasize the importance of Cif in B. pseudomallei pathogenesis, particularly in manipulating host neuronal pathways, potentially contributing to enhanced virulence in certain variants within neuronal environments.