Recent evidence for multifactorial biofilm regulation by heme sensor proteins NosP and H-NOX

Antibacterial effects and microarray-based molecular mechanisms of trans-cinnamaldehyde against Porphyromonas gingivalis

Porphyromonas gingivalis (P. gingivalis) is one of the keystone pathogenic bacteria of periodontitis and peri-implantitis. This study aimed to investigate the antibacterial effects and molecular mechanisms of trans-cinnamaldehyde (TC), a safe extract from natural plants, on P. gingivalis. Minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) of TC were determined, and scanning and transmission electron microscopies were used to assess the morphological changes. The overall biomass was estimated, and the metabolic activity of biofilms was determined at different TC concentrations. A microarray-based bioinformatics analysis was performed to elucidate the underlying molecular mechanisms of TC-inhibited P. gingivalis, and significant differences among groups were determined. TC showed an inhibitory effect on the proliferation and survival of planktonic P. gingivalis, of which the MIC and MBC were 39.07 μg/mL and 78.13 μg/mL, respectively. TC also significantly suppressed the formation and metabolic activity of P. gingivalis biofilm. The results of the significant pathways and gene ontology (GO) analyses revealed that TC treatment inhibited two metabolic pathways, accompanied by the downregulation of relative genes of nitrogen metabolism (NrfA, NrfH, and PG_2213) and starch and sucrose metabolism (PG_1681, PG_1682, and PG_1683). Thus, this study confirmed TC to be a natural antimicrobial agent against P. gingivalis and further demonstrated that TC suppressed the microbial activity on P. gingivalis through the disruption of physiological metabolism, which might inhibit the growth and the biofilm formation of P. gingivalis.

NosP Detection of Heme Modulates Burkholderia thailandensis Biofilm Formation

Aggregated bacteria embedded within self-secreted extracellular polymeric substances, or biofilms, are resistant to antibiotics and cause chronic infections. As such, they are a significant public health threat. Heme is an abundant iron source for pathogenic bacteria during infection; many bacteria have systems to detect heme assimilated from host cells, which is correlated with the transition between acute and chronic infection states. Here, we investigate the heme-sensing function of a newly discovered multifactorial sensory hemoprotein called NosP and its role in biofilm regulation in the soil-dwelling bacterium Burkholderia thailandensis, the close surrogate of Bio-Safety-Level-3 pathogen Burkholderia pseudomallei. The NosP family protein has previously been shown to exhibit both nitric oxide (NO)- and heme-sensing functions and to regulate biofilms through NosP-associated histidine kinases and two-component systems. Our in vitro studies suggest that BtNosP exhibits heme-binding kinetics and thermodynamics consistent with a labile heme-responsive protein and that the holo-form of BtNosP acts as an inhibitor of its associated histidine kinase BtNahK. Furthermore, our in vivo studies suggest that increasing the concentration of extracellular heme decreases B. thailandensis biofilm formation, and deletion of nosP and nahK abolishes this phenotype, consistent with a model that BtNosP detects heme and exerts an inhibitory effect on BtNahK to decrease the biofilm.