Figure 4. Loss of the Hypoxia Induced Transcriptional Regulator SrbB Results in a Significant Growth Defect and Red Pigmented Mycelia in Hypoxia.

(A). Growth of ΔsrbB in normoxia and hypoxia on solid media. Wild type, ΔsrbB, and srbB-reconstituted strains were incubated on GMM at 37°C for 3 days in normoxia or hypoxia. The number of conidia used for inoculation is illustrated by the plate image. Compared to wild type and the reconstituted strain, growth of ΔsrbB is restricted in hypoxia. (B). A biomass test with wild type, an srbB null mutant, and an srbB reconstituted strain in liquid cultures in normoxia or hypoxia. Mycelia of wild type, ΔsrbB and srbB-reconstituted (srbB-recon) strains in liquid cultures were harvested, dried and weighed for the biomass study. Data are presented as the mean and standard error of three biological replicates. No significant differences between wild type and srbB-recon biomass were observed in all conditions tested. When analyzed by two-way ANOVA followed by Bonferroni posttest, biomass of ΔsrbB was not different from wild type or srbB-recon in normoxia. However, biomass of ΔsrbB significantly decreases in hypoxia compared to wild type (p<0.001). (C). E-test strips were utilized to test susceptibility to VCZ. 10⁵ conidia were overlaid on RPMI media, cultured at 37°C for 2 days. Minimal inhibitory concentrations (MIC, marked as an arrow) were measured. In both normoxia and hypoxia, ΔsrbB is slightly more tolerant to VCZ compared to wild type and the srbB reconstituted strain. MIC ratios of ΔsrbB to wild type are 1.76 and 3.42 in normoxia and hypoxia, respectively. (D). Conidia of each strain were cultured in LGMM at 37°C, 200 rpm for 2 days in hypoxia. ΔsrbB produces reddish mycelia compared to the wild type and reconstituted strain.