Investigation of destruxin A and B from 80 Metarhizium strains in China, and the optimization of cultural conditions for the strain MaQ10

The production levels of destruxin A and B (DA and DB) of 80 Metarhizium strains from China were investigated. The average yields of DA and DB were 14.87±2.30 and 3.65±0.58 μg/mL, respectively. The strains isolated from soil had significantly (p<0.05) lower production of DA and DB than the strains isolated from insect cadavers. Also, there was a positive correlation in the yields of DA and DB, and the regressive equations were established. Of the 80 strains, MaQ10 had the highest yields of DA and DB, amounted to 106.78±9.41 and 29.52±2.63 μg/mL, respectively, at 10 days fermentation period. Followed by the strains MaQ05, MaQ07 and MaQ12, their yields of DA were 79.72±5.36, 77.69±8.54 and 70.04±10.1 μg/mL, respectively, and DB were 16.81±1.51, 13.38±0.41 and 16.88±1.15 μg/mL, respectively. Furthermore, the cultural conditions of MaQ10 were optimized to produce DA and DB. The optimal inoculum, initial pH, temperature and rotary speed were 8%, pH 9.0, 27 °C and 240 r/min for DA, and 8%, pH 9.0, 25 °C and 220 r/min for DB. Under these optimal culture conditions, the predicted production of DA and DB was 193.87 and 39.85 μg/mL, and the actual production was 189.13 and 43.35 μg/mL, respectively.