Sucrose reduces biofilm formation by Klebsiella pneumoniae through the PTS components ScrA and Crr

The presence of sucrose at concentrations of 0.5-5% can either increase bacterial biofilms (Streptococcus mutans and Escherichia coli) or have no significant effect on biofilms (Pseudomonas aeruginosa and Staphylococcus aureus). However, our study revealed that 1 % sucrose reduced the biofilm formation by Klebsiella pneumoniae STU1. To explore the role of the phosphoenolpyruvate-dependent-carbohydrate: phosphotransferase system (PTS) in regulating this process, the scrA gene, which encodes the sucrose-specific EIIBC of the PTS, was deleted in K. pneumoniae to create a scrA mutant (Delta scrA). Thereafter, we observed that the biofilm formation and type 3 fimbriae production were not affected by sucrose in the Delta scrA while sucrose reduced these processes in the wild type. Furthermore, we discovered that Crr, the glucose-specific EIIA of PTS, was the primary but not the sole EIIA of ScrA in K. pneumoniae by sucrose fermentation test. In addition, deficiency of Crr reduced the biofilm formation in K. pneumoniae. Our proposed model suggests that, through the action of Crr in the absence of sucrose, the transcription of the mrk operon, which produces type 3 fimbriae, was increased, thereby influencing biofilm formation by K. pneumoniae and bacterial number in the gut of nematode. This observation differs from the regulation of polysaccharide and biofilm by sucrose in other bacteria. Our findings extend the understanding of the effects of sucrose on biofilm formation.