Error bars indicate the variation between triplicate samples within the real-time RT-PCR. The relative cDNA abundance of the WT sample was assigned a value of 1. (A) Relative transcript levels of icaA of WT (RN6390B), ΔluxS and ΔluxS complemented with 3.9 nM DPD
under aerobic conditions. (B) Relative transcript levels of icaR of WT (RN6390B), ΔluxS and ΔluxS complemented with 3.9 nM DPD under aerobic conditions. It was reported that IcaR is a negative regulator of the icaA locus , and that icaR could be regulated by Rbf, SarA and SigB [56, 57]. However, few studies indicate that the signalling molecule AI-2 could be an activator of icaR. We ZD1839 mw therefore investigated whether repression of icaA by AI-2 was mediated by IcaR by examining the icaR transcription in the biofilm bacteria of the WT strain, the ΔluxS strain and the ΔluxS strain complemented with 3.9 nM DPD. We found that the ΔluxS strain displayed decreased transcription of icaR compared to WT, and DPD supplementation could complement the effect of luxS mutation (Figure 4B). These data indicate selleck that the repression of icaADBC transcription by AI-2 is through the activation of icaR. These results allow us to conclude that AI-2 activates icaR, which results in decreased icaADBC transcription and subsequently decreased biofilm formation.
AI-2 inhibits biofilm formation and represses the transcription of icaA under anaerobic conditions Hypoxia or anaerobic conditions is a common hostile environment that the biofilm bacteria suffer in vivo[3, 58, 59]. To determine
whether or not AI-2 could also affect biofilm formation under anaerobic conditions, the microtitre plate assay was used to examine Dichloromethane dehalogenase the biofilm growth. After incubation of the plate for 4 h under anaerobic conditions, we found that the ΔluxS strain displayed increased biofilm formation compared to the WT strain, and AI-2 supplementation restored the WT phenotype (Figure 5A). Consistently, AI-2 repressed the transcription of icaA under anaerobic conditions (Figure 5B). Figure 5 Analysis of biofilm formation and the icaA transcription under anaerobic conditions. (A) Biofilm formation of WT (RN6390B), ΔluxS and ΔluxS complemented with 3.9 nM DPD under anaerobic conditions. (B) Relative transcript levels of icaA of WT (RN6390B), ΔluxS and ΔluxS complemented with 3.9 nM DPD under anaerobic conditions. The LuxS/AI-2 QS system and the agr-mediated QS system have a cumulative effect on the regulation of biofilm formation It was reported that the agr QS system mediates biofilm dispersal in S. aureus. To determine whether the LuxS/AI-2 QS system and the agr-mediated QS system have a cumulative or complementary effect on the regulation of biofilm formation, we constructed a Δagr ΔluxS strain and compared the biofilm formation among the WT strain and the mutants using different assays, including the microtitre plate assay, flow cell, anaerobic jar and SEM.