Flagellin (FliC) phosphorylation affects Type 2 protease secretion and biofilm dispersal in Pseudomonas aeruginosa PAO1

Protein phosphorylation has a major role in controlling the life-cycle and infection stages of bacteria. Proteome-wide occurrence of S/T/Y phosphorylation has been reported for many prokaryotic systems. Previously, we reported the phosphoproteome of Pseudomonas aeruginosa and Pseudomonas putida. In this study, we show the role of S/T phosphorylation of one motility protein, FliC, in regulating multiple surface-associated phenomena of Pseudomonas aeruginosa PAO1. The absence of phosphorylation in the conserved T27 and S28 residues of flagellin FliC, interestingly, did not affect swimming motility, but affected the secretome of type 2 secretion system (T2SS) and biofilm formation of PAO1. Flagellin phosphomutants had increased levels and activities of type 2 secretome proteins. This occurs by a possible mechanism affecting the secretion efficiency of T2SS machinery. Flagellin phosphomutants also formed reduced biofilm at 24h and had delayed biofilm dispersal under static and dynamic flow conditions, respectively. The levels of type 2 secretome and biofilm formation under static conditions had an inverse correlation. Hence, increase in the levels of type 2 secretome was accompanied by reduced biofilm formation in the flagellin phosphomutants. Altogether, we found a system of phosphorylation that co-ordinately regulates surface related processes such as proteases secretion by T2SS, biofilm formation and dispersal.