2,3-Butanediol pathway links metabolism and virulence under the control of FNR and ArcA in Klebsiella pneumoniae

Klebsiella pneumoniae is a clinically significant human pathogen. Previously, we identified K. pneumoniae as a high-alcohol producer, implicating it as a novel etiological agent in non-alcoholic fatty liver disease (NAFLD). However, the molecular basis underlying its high-alcohol production remained unclear. By comparing its alcohol biosynthetic capacity with that of Escherichia coli, we uncovered that the 2,3-butanediol (2,3-BD) pathway plays a critical role in high-alcohol production through the regulation of the phosphotransferase system (PTS) and the alcohol dehydrogenase gene adhE. Notably, we found that the presence of the 2,3-BD pathway is strongly associated with high-alcohol production across Enterobacteriaceae species, suggesting a conserved metabolic mechanism among high-alcohol enteric bacteria. Moreover, activation of the 2,3-BD pathway significantly promotes the expression of multiple virulence determinants, including capsular polysaccharides, lipopolysaccharides, type 1 fimbriae, and type 3 fimbriae, thereby markedly influencing virulence phenotypes in a murine pneumonia model. Intriguingly, we further demonstrate that the global transcriptional regulator FNR enhances alcohol production in K. pneumoniae by upregulating both the 2,3-BD pathway and adhE. In parallel, we reveal that ArcA regulates the 2,3-BD pathway in an ArcB-independent manner, indicating a non-canonical signaling mechanism that contributes to metabolic adaptation and pathogenicity in this organism. These findings provide new insights into how the 2,3-BD pathway, regulated by FNR and ArcA, bridges metabolism and virulence in K. pneumoniae, offering potential targets for therapeutic strategies against this pathogen.