A novel <i>klebsiella pneumoniae</i> diguanylate cyclase contributes to intestinal cell adhesion, biofilm formation, iron utilization, and <i>in vivo</i> virulence by gastrointestinal infection

<i>Klebsiella pneumoniae</i> is responsible for various infections such as bacteraemia, urinary tract infections, pneumonia, and liver abscesses. Multidrug-resistant <i>K. pneumoniae</i> infections pose a critical public health threat, often associated with high mortality rates. The emergence of hypervirulent <i>K. pneumoniae</i> has also raised global health concerns due to its invasive disease potential. Clinical studies suggest intestinal colonization by <i>K. pneumoniae</i> as a risk factor for subsequent infections but underlying mechanisms remain unclear. Cyclic di-GMP (c-di-GMP), a bacterial signalling molecule synthesized by diguanylate cyclases (DGCs), controls various cellular processes and is absent in higher organisms, making it an attractive target for antimicrobial development. In this study, we identified a novel DGC, designated as DgcG, in <i>K. pneumoniae</i>, which plays a pivotal role in gastrointestinal colonization and pathogenesis. Using genetic deletion and complementation analyses in a bacteraemia and liver abscesses-inducing strain Ca0437, we observed that DgcG promoted intestinal adherence, biofilm formation, iron utilization, and <i>in vivo</i> virulence. RT-qPCR showed that DgcG regulated genes involved in type 3 fimbrial expression and iron transport. In a gastrointestinal infection model of female BALB/cByl mice, <i>dgcG</i> deletion significantly reduced host mortality and bacterial load in the liver, spleen, and intestines, underscoring its role in enhancing bacterial survival and dissemination. Additionally, <i>dgcG</i> gene was found highly conserved and prevalent among diverse <i>K. pneumoniae</i> isolates. These findings provide new insights into c-di-GMP-mediated virulence regulation in <i>K. pneumoniae</i> and highlight DgcG as a potential therapeutic target for controlling <i>K. pneumoniae</i> infections, especially amidst the growing global antimicrobial resistance crisis.