Effects of cultural conditions on fungal biomass, blastospore yields and toxicity of fungal secreted proteins in batch cultures of Metarhizium anisopliae (Ascomycota: Hypocreales).

BACKGROUND

Recently, two fungal proteins with apparent molecular masses of 11 and 15 kDa and insecticidal activity against Ceratitis capitata (Wied.) have been purified from the crude soluble protein extract (CSPE) secreted by the entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin (strain EAMa 01/58-Su) in Adamek's liquid medium. The feasibility of culturing this strain in fermentation facilities in order to harvest and formulate the insecticidal proteins for C. capitata control is mainly dependent on the ability to produce high concentrations of the active proteins at a reasonable cost.

RESULTS

These studies report that, in batch cultures of EAMa 01/58-Su strain, the carbon (C) and nitrogen (N) ratios and sources are important considerations with respect to fungal biomass production, blastospore yield and secretion of insecticidal proteins against C. capitata adults. The data indicate that the type and concentration of N source in the medium influence the production of insecticidal protein and thus the toxicity of the CSPEs. The electrophoretic analysis suggests that the monomer of 11 kDa plays an important role in the insecticidal effect described. Concerning biomass production, no clear differences were found between media with different C and N sources and C:N ratios in total biomass production at day 7. Conversely, important differences were found among the media in terms of blastospore yields.

CONCLUSIONS

By optimising the culture media, the insecticidal effect of the CSPE against C. capitata can be improved. In the CSPE from G(40):P(20) (40 g L(-1) glucose and 20 g L(-1) peptone in dH(2)O), the LC(50) and the LT(50) were 7 and 4.5 times lower than in the CSPE obtained from Adamek.