Biotin synthesis and assimilation are vital for pathobiology of the insect pathogenic fungus Beauveria bassiana

Biotin is essential for metabolic processes. Bioinformatics analysis revealed that there was a gene cluster consisting of three biotin synthesis genes (BbBIOB, D, and F) in the insect pathogenic fungus Beauveria bassiana. When the cluster was ablated, the protein biotinylation was significantly decreased, and the disruptant displayed phenotypic defects in radial growth, conidial germination, development, and virulence. However, exogenous biotin could restore the protein biotinylation and phenotypic defects. Notably, B. bassiana growth on asparagine (as nitrogen source) was independent of the biotin synthesis. Comparative transcriptomic analysis was conducted between the wild-type and ΔBbbiob which were cultured on plates with and without biotin, which resulted in a group of potential transporter genes involved in biotin uptake. Gene function analyses demonstrated that three transporters (BbTrp1, BbTrp2, and BbTrp4) contributed to the assimilation of biotin at low biotin concentrations but only BbTrp1 and BbTrp2 were required for B. bassiana virulence. This research deepens our understanding of the physiological roles of vitamin metabolism in the insect pathogenic fungi, and highlights the biotin transporters firstly identified in filamentous fungi.