## 3 Results
### Effect of Growth Conditions on the Culture Morphology of B. bassimata Strains  
The dimorphic fungus _B. bassimata_ can develop yeast-like cells on MacConkey agar medium [29]. Fungal conidia (\(10^{6}\)) of the AS5 and AI2 strains were inoculated into the culture medium, and the yeast forms were observed after 48 h of growth. Otherwise, the abundance of conidia differed between the strains, with the numbers of conidia reaching a maximum at 120 h in AI2. In contrast, there was no significant increase in counted conidia or the number of yeast-like cells in AS5 under similar assay conditions (Figure 2A,B). The AS5 strain showed a slow development on the MacConkey agar medium, and the yeast phase prevailed throughout 144 h of growth (Figure 2B). As expected, other growing conditions modified the fungal morphology. In the case of the PDB culture medium, all conidia germinated as filamentous growths (Figure 3A,B). Meanwhile, on YPG-2%, conidial germination decreased by 20%, but the hyphae were longer than those observed on PDB. An increase in the carbon source concentration in YPG-6% and YNB culture media negatively affected conidial germination and hyphal growth. Furthermore, the anaerobic conditions negatively affected conidial germination and conidial germ tube length (Figure 3C). The effect of pH on colonial morphology was also determined. The results showed that pH 6 was optimal for conidial germination and mycelial growth (Figure 4A,B). A pH of 3 significantly decreases conidial germination and limits hyphal growth, whereas a pH of 9 stimulates hyphal branching under aerobic conditions. Under anaerobic conditions, conidial germination and the morphology of mycelium were affected at pH 6 because the hyphae were more branched than those under aerobic conditions (Figure 4C). In addition, the fungal growth in a more acidic culture medium allowed for hyphal elongation, whereas under alkaline conditions, the hyphae were scarce and poorly branched. Figure 1: Survival rate of C. elegans reared in the presence of the secretome of _B. bassimata_. The fungal strains AI2 and AS5 were grown on PDB culture medium, and the cell-free media were used to perform the assays. A total of 15 nematodes were used per experiment and incubated at 18 \({}^{\circ}\)C for 72 h. n = 3, with three independent repetitions. Data were statistically analyzed using the Mantel–Cox test; \({}^{**}\), \(p<0.01\). Figure 2: Development of _B. bassiana_ AI2 (**A**) and AS5 (**B**) strains inoculated on MacConkey agar medium and exposed to 3-methylbutanol (3 MB). The inoculum size was \(10^{6}\) spores. The experiment was conducted in triplicate. Data are presented as mean \(\pm\) standard error. Asterisks indicate means that differed significantly at * \(p<0.05\), ** \(p<0.01\), *** \(p<0.001\) based on one-way ANOVA and [PERSON]’s LSD test. Means within columns with different letter indicate statistically significant differences using one-way ANOVA and [PERSON]’s test (\(p\leq 0.05\)). Figure 4: Effect of pH on the morphology of the strain AS5 from _B. basisana_. Conidia were germinated in PDB at pH 3, 6, and 9 for 24 h at 28 \({}^{\circ}\)C (anaerobiosis) and 150 rpm (aerobiosis). (**A**) Germination kinetics under aerobiosis conditions. Representative photographs at 100\(\times\) of the morphology during (**B**) aerobiosis and (**C**) anaerobiosis at 24 h. White arrowheads indicate germinated conidia and white arrows indicate ungeminated conidia. Scale bar, 20 \(\upmu\)m. Data were analyzed with one-way ANOVA and [PERSON] post hoc test (***, \(p<0.001\)). Figure 3: Effect of the carbon and nitrogen sources and oxygen on the morphology of the strain AS5 of _B. basisana_ at 24 h of fungal growth. Conidia were germinated in PDB, YPG-2%, YPG-6% and YNB for 24 h at 28 \({}^{\circ}\)C (anaerobiosis) and 150 rpm (aerobiosis). (**A**) Germination kinetics under aerobiosis conditions.