Cellobiose-specific phosphotransferase system of Klebsiella pneumoniae and its importance in biofilm formation and virulence

Klebsiella pneumoniae is a Gram-negative bacillus belonging to the family Enterobacteriaceae. In the past 20 years, K. pneumoniae has become the predominant pathogen causing community-acquired pyogenic liver abscess (PLA). The formation of biofilm facilitates bacterial colonization and has been implicated in reduced susceptibility to the host immune response. To investigate genes related to biofilm formation in a PLA-associated K. pneumoniae strain, a transposon mutant library was screened by microtiter plate assay to identify isolates impaired for biofilm formation. One of the mutants was disrupted in celB, encoding the putative cellobiose-specific subunit IIC of enzyme II (EIIC) of a carbohydrate phosphotransferase system (PTS). This transmembrane protein is responsible for recognizing and binding specific sugars and transporting them across the cell membrane into the cytoplasm. Deletion and chromosomal complementation of celB confirmed, by microtiter plate and slide culture assays, that celB was indeed responsible for biofilm formation. Cellobiose-specific PTS activities of deletion mutants grown in LB broth and 0.005% cellobiose minimal medium were markedly lower than that of the wild-type strain grown under the same conditions, thereby confirming the involvement of celB in cellobiose transport. In 0.005% cellobiose minimal medium, the celB mutant showed a delay in growth compared to the wild-type strain. In a mouse model of intragastric infection, deletion of the celB gene increased the survival rate from 12.5% to 87.5%, which suggests that the celB deletion mutant also exhibited reduced virulence. Thus, the celB locus of K. pneumoniae may contribute to biofilm formation and virulence through the metabolism of cellobiose.