Next, the ability of P. aeruginosa

Next, the ability of P. aeruginosa to form biofilms in the presence ofcalycopterin was evaluated. In contrast to other flavonoids [65,66],calycopterin showed a dose-dependent increase (17%, 47% and 256%,respectively) of biofilm formation (Fig. 4), in the conditions tested. Thisresult suggests that calycopterin's mechanism of action is different fromthe one proposed for naringenin and kaempferol (quorum sensing inhibition or inhibition of the expression of the QS-regulated genes)[45,65,66].The inverse effect of calycopterin on swarming motility and biofilmformation suggest that this compound might interfere with pathwaysrelated to c-di-GMP. High levels of this second messenger favour thesessile lifestyle, increasing biofilm formation and decreasing flagelladriven motility [67,68]. Pyocyanin production also correlates with c-diGMP: It decreases in cells with high levels of c-di-GMP and increaseswhen a EAL phosphodiesterase is overproduced [69]. This effect wasT.Q. Froes, et al. Microbial Pathogenesis 144 (2020) 1041423attributed to lower expression of QS genes in high c-di-GMP conditions,especially the pqs and rhl genes, through the regulator PqsR/MvfR,which also regulates the synthesis of rhamnolipids, required forswarming motility [69].