Furthermore, the present gingipain mutants lacked proteinase domains as well as C-terminal flanking segments coding for hemaglutinin/adhesin (HA) domains [36]. Higher concentrations of iron in the cultivation media can have a positive effect on the stability of the biofilms [37], thus decreased hemin uptake due to the lack of HA domains might modulate the biofilm structures in dTSB. Autoaggregation driven by nonspecific hydrophobic mechanisms
is thought to contribute to hetero- and homo-typic biofilm formation [24]. Indeed, the significant change of autoaggregation efficiencies in KDP129, KDP150, MPG67 and MPG4167 were found to be positively associated with alteration of biofilm structures under the non-proliferation condition. However, such an association was not observed in Rgp-null
mutant strains, KDP133 and KDP136, and was not significant under the proliferation condition. Our present results suggested MDV3100 that a biofilm-regulatory molecule Rgp does not function through autoaggregation but rather through other mechanisms mediating intimate contact among P. gingivalis cells. Recently Kato et al. found that autoaggregation ability correlated poorly with the hydrophobicity ZD1839 solubility dmso in FimA-substituted mutants [38]. In addition, the hydrophobicity was reported not to depend on the presence or absence of FimA on the bacterial surface [39]. In-depth mathematical and physical examinations may be needed to explain the complicated roles of hydrophobicity, autoaggregation and cell surface structure on biofilm development. Besides fimbria and proteinases, our Selleckchem PR-171 findings indicate that other molecules of P. gingivalis, which are not processed by gingipains, mediate homotypic biofilm formation. P-type ATPase Indeed several factors, including a putative glycosyltransferase
(PG_0106), UDP-galactose 4-epimerase (GalE), internalin J protein (InlJ), a universal stress protein (UpsA), and a low molecular weight tyrosine phosphatase (Ltp1), have been reported to be required for homotypic biofilm formation by P. gingivalis [10, 19, 40–42]. Autoinducer-2, which regulates proteinase and hemagglutinin activities, hemin and iron acquisition pathways, and stress gene expression, is also considered to be involved in homotypic biofilm formation [43–46]. It is possible that these molecules also have effects in regard to biofilm structure alterations, in addition to fimbriae and gingipains. Further work is necessary to understand the complete process of the biofilm formation by P. gingivalis. Conclusion The present results suggest distinct roles of long/short fimbriae and gingipains in homotypic biofilm development by P. gingivalis. Long fimbriae are initial positive mediators of biofilm formation, and thereafter they decrease the expression of exopolysaccharide to regulate adhesive properties. Short fimbriae as well as Kgp are negative regulators of microcolony formation.
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