Assessing the Potential of an Induced-Mutation Strategy for Avermectin Overproducers

Abstract

Mutant libraries of avermectin-producing Streptomyces avermitilis strains were constructed by different mutagenesis strategies. A metric was applied to assess the mutation spectrum by calculating the distribution of average phenotypic distance of each population. The results showed for the first time that a microgravity environment could introduce larger phenotype distribution and diversity than UV and N-methyl-N-nitro-Nnitrosoguanidine (NTG) could.Induced mutagenesis is a classical and successful method for improving strains to increase the productivity of commercially significant microbial metabolites. To evaluate different induced-mutagenesis approaches, Klein-Marcuschamer and Stephanopoulos presented a metric based on the quantification of phenotypic diversity to evaluate strain improvement approaches (14).New approaches of inducing mutagenesis emerged with the development of biotechnology, and of these new approaches, spaceflight-induced mutagenesis has led to great progress in strain improvement (6,15,26). In outer space, cosmic rays, high vacuum, intense magnetic field, and microgravity induced chromosomal aberrations, which lead to genetic mutations in microorganisms (13). However, it is difficult to carry out spaceflight-induced mutagenesis extensively owing to the limitations of high cost and few chances to board spaceships. Therefore, ground-based simulated experiments have greater practical significance, and high-magnetogravity experiments are a good choice to simulate the space environment (16).Avermectins and its analogues, produced by Streptomyces avermitilis, are major commercial antiparasitic agents for animal health, agriculture, and human infections (7). A variety of mutagenesis methods have been developed to increase the productivity of S. avermitilis (18,19,(21)(22)(23)25). Though most of them can produce higher mutation rates, the potential of their success in strain improvement is different.In this study, mutant libraries of S. avermitilis strains were constructed by three mutagenesis-inducing strategies: UV, Nmethyl-N-nitro-N-nitrosoguanidine (NTG), and high-magnetogravitational environment (HMGE). For each population, the distribution of average phenotypic distance was calculated on the basis of the modified version (15) of the metric of Klein-Marcuschamer and Stephanopoulos (14). The mutation rate was also calculated. A good correlation between the distribution of average phenotypic distance and the percent improvement was found and analyzed. In this way, the potential to produce mutations among different induced-mutagenesis approaches was evaluated to find the most effective one for S. avermitilis.The industrial avermectin-producing S. avermitilis 3-115 strain and the mutants derived from strain 3-115 were grown on YMG agar medium (10). For diversity quantification and preliminary screening, fermentation was carried out in highthroughput format at 28°C. For confirmation of results and secondary screening, mutants that exhibited a higher yield than the wild-type strain were inoculated i...

Secondary metabolism in simulated microgravity and space flight

“…Therefore, our lab chose Streptomyces avermitilis grown on solid media to study secondary metabolism in simulated microgravity . S. avermitilis is used for the industrial production of the important anthelmintic agent avermectin, and has already been proven to be a highly efficient producer of several secondary metabolites (Gao et al, 2010). Of the eight major avermectin compounds, B1a is the most efficient component against a broad range of nematodes and arthropod parasites of domestic animals (Gao et al, 2009).…”

Interrogation of Streptomyces avermitilis for efficient production of avermectins

“…Gao et al. 24 assessed a potential induced mutation strategy called high-magnet gravitational environment (HMGE), a space flight-simulated mutation strategy. HMGE was compared with two other conventional strategies, UV and NTG.…”

Spaceflight-induced enhancement of 2-keto-L-gulonic acid production by a mixed culture of Ketogulonigenium vulgare and Bacillus thuringiensis

“…; Gao et al . ). Although the underlying mechanisms are not yet fully understood, the suggestion that spaceflight may be an effective way to obtain mutated strains for improved productivity has been strongly supported by accumulated information from fermentation industries, such as those concerned with microbial productions of actinomycin D (Lam et al .…”