Genome_wide_identification_of_Klebsiella_pneumoniae_capsule_regulators

Klebsiella pneumoniae infections affect infants and the immunocompromised, and the recent emergence of hypervirulent and multi-drug resistant K. pneumoniae lineages is a significant healthcare concern. Hypervirulence in K. pneumoniae is mediated by several factors, including the overproduction of extracellular capsule. However, the full details of how K. pneumoniae capsule biosynthesis is achieved or regulated are not known. Here, we have developed a robust and sensitive procedure to identify genes influencing capsule production, which combines the physical enrichment of non-capsulated cells with transposon-insertion sequencing. We have used this method to explore capsule regulation in two clinically-relevant Klebsiella strains; K. pneumoniae NTUH-K2044 (hyper-capsulated, capsule type K1), and K. pneumoniae ATCC43816 (capsule type K2). We identified multiple genes required for full capsule production in K. pneumoniae, as well as putative suppressors of capsule in NTUH-K2044, and have validated the results of our screen with targeted knockout mutants. We show that capsule production in K. pneumoniae is at the centre of a complex regulatory network involving multiple global regulators and environmental cues, and that the majority of capsule regulatory genes are located on the core genome of K. pneumoniae. We have also confirmed the activity of several of the novel K. pneumoniae capsule regulators identified in our screen. Our findings expand our understanding of how capsule is regulated in this medically-important pathogen, and provide a technology that can be easily implemented to study capsule regulation in other bacterial species.