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 (<i>Streptococcus mutans</i> and <i>Escherichia coli</i>) or have no significant effect on biofilms (<i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i>). However, our study revealed that 1 % sucrose reduced the biofilm formation by <i>Klebsiella pneumoniae</i> STU1. To explore the role of the phosphoenolpyruvate-dependent-carbohydrate: phosphotransferase system (PTS) in regulating this process, the <i>scrA</i> gene, which encodes the sucrose-specific EIIBC of the PTS, was deleted in <i>K. pneumoniae</i> to create a <i>scrA</i> mutant (Δ<i>scrA</i>). Thereafter, we observed that the biofilm formation and type 3 fimbriae production were not affected by sucrose in the Δ<i>scrA</i> 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 <i>K. pneumoniae</i> by sucrose fermentation test. In addition, deficiency of Crr reduced the biofilm formation in <i>K. pneumoniae</i>. Our proposed model suggests that, through the action of Crr in the absence of sucrose, the transcription of the <i>mrk</i> operon, which produces type 3 fimbriae, was increased, thereby influencing biofilm formation by <i>K. pneumoniae</i> 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.