3.9 Influence of rex and sigB on surfactin production and biofilm formation
We further deleted the genes for globally regulating anti-oxidation reactions such as rex and sigB in WH1 (Fig. S3 in supplementary materials). The colony morphology and biofilm in Δrex and ΔsigB were both similar to WH1 (Fig. 7A). The growth of ΔsigB was also similar to WH1, but the growth of Δrex was obviously weaker than WH1 (Fig. 7B).
Deletion of rex resulted in a significant decrease of surfactin production when compared to WH1 at all time points. At 12 h, the biomass of Δrex was similar to WH1, but the surfactin production was significantly lower than WH1 (Fig. 7C). Knockout of sigB also led to a significant decrease of surfactin production at 36 and 48 h when compared to WH1 (Fig. 7C). The transcription of perR was significantly increased in Δrex , while the transcription ofsrfAB and perR were both significantly increased and the transcription of spx was significantly decreased in ΔsigBcompared to WH1 (Fig. 7D). Western blot analysis also showed that the protein PerR was slightly increased in Δrex and ΔsigB when compared to WH1 (Fig. 7D).
We constructed the rex complementary strain C-Δrex (Fig. S3 in supplementary materials), and found it could form a robuster biofilm than Δrex and WH1 (Fig. 7A), but unfortunately the surfactin production was not well restored in C-Δrex when compared to WH1 (Fig. 7C). This result also confirmed that the signal to trigger biofilm formation is not always dependent on surfactin inB. amyloliquefaciens .