Induced mutation breeding of Brevibacillus brevis FJAT-0809-GLX for improving ethylparaben production and its application in the biocontrol of Lasiodiplodia theobromae

摘要

Ethylparaben is the main antimicrobial substance in the culture supernatant of Brevibacillus brevis FJAT-0809GLX. The present study aimed to obtain and partially characterize mutant strains with higher ethylparaben production through mutagenesis of B. brevis FJAT-0809-GLX by UV irradiation and LiCl treatment. The results showed that the positive mutant rates of the UV irradiation, LiCl treatment and combination of UV irradiation and LiCl treatment were 7.8%, 0% and 12%, respectively. There were no morphological and growth rate differences between the mutants and the wild type strain. However, the mutant strains Bb-M1, Bb-M2 and Bb-M3 were more stable than the wild type strain FJAT-0809-GLX against temperature and pH changes. Mutant strains Bb-M1, Bb-M2 and Bb-M3 produced 5 times, 3 times and one time as much ethylparaben, respectively, when compared with the wild type strain FJAT-0809-GLX. The inhibition zones of the mutant strains to different pathogens, such as Fusarium oxysporum, Colletotrichum orbiculare, Lasiodiplodia theobromae, Escherichia coll. and Salmonella typhimurium, were significantly larger than those of the wild type strain. The mutant strains and wild type strain showed antibacterial activities, with an inhibition zone of 13.2 mm, 13.3 mm, 13.8 mm and 11.1 mm against E. coll. K88, respectively. When the storage time was 4 d, the percentages of fruit decay in the Bb-M1-, Bb-M2- and Bb-M3-treated wax apple fruits were 8.3%, 5.0%, and 5.0%, respectively; These values were significantly lower than the control treatment, which was 25.0%. These results indicated that B. brevis FJAT-0809-GLX mutant strains with higher ethylparaben yields may be more suitable as a candidate biocontrol agent for the control of L. theobromae.