Effects of Insect Cuticular Compounds on Appressorium Formation and Metabolic Activity in Beauveria bassiana

The rate of appressoria formation following conidial germination in <i>Beauveria bassiana</i> is closely associated with its pathogenicity. This study investigated the effects of insect cuticular compounds on the formation and metabolism in <i>B. bassiana</i> through the addition of insect cuticle analogues. Results indicate that both the fatty acid compound carnitine C3:0 and the organic acid compound Thiamine Pyrophosphate (TPP) exert dose-dependent bell-shaped effects on <i>B. bassiana</i> spore germination and appressorium formation at different concentrations. Both low and high concentrations inhibit spore germination and appendage formation. At a concentration of 0.10 mg/mL, spore germination and appendage formation rates peaked at all time points, being significantly higher than the control (<i>p</i> ≤ 0.05). Compounds in the benzene and its derivatives class, such as enilconazole and disulfide bis(2-hydroxy-3-methylpropan-2-yl) (DSBA), significantly reduced spore germination and appressorium formation in <i>B. bassiana</i> (<i>p</i> ≤ 0.05), with stronger inhibition becoming more pronounced at higher concentrations. In contrast, amino acids and their metabolites (e.g., glycylmethionine) and glycerophospholipid compounds like 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC) had no significant effects on spore germination or appressorium formation at any tested concentration (<i>p</i> > 0.05). LC-MS analysis revealed that the insect cuticular fatty acyl compound carnitine C3:0 broadly modulated the secondary metabolism of <i>B. bassiana</i>. Following appressorium formation, 146 metabolites with significant changes in abundance were identified. Before appressorium formation, carnitine C3:0 promoted the activation of <i>B. bassiana</i> signaling pathways, such as Rap1, and stimulated antibiotic biosynthesis (penicillin and cephalosporin), thereby suppressing competing microorganisms and facilitating initial attachment. After appressorium formation, carnitine C3:0 activated pathways related to metabolite synthesis (e.g., arginine and nucleotides biosynthesis) and population regulation (ferroptosis), thereby enhancing appressorium function and structural stability. Thus, carnitine C3:0 enhances <i>B. bassiana</i>'s ability to establish infection sites before appressorium formation through antibiotic clearance and signal activation, and maintain infection structures after formation via metabolic reinforcement and population regulation. This study lays a theoretical foundation for further investigations into <i>B. bassiana</i> infection mechanisms, pathogenicity, and the role of its conidiophores.