SR5AL serves as a key regulatory gene in lycopene biosynthesis by Blakeslea trispora.

BACKGROUND: Trisporic acids are considered to be key regulators of carotenoid biosynthesis and sexual reproduction in zygomycetes, but the mechanisms underlying this regulation have not been fully elucidated. RESULTS: In this study, the relationships between trisporic acids and lycopene synthesis were investigated in Blakeslea trispora. The lycopene concentration in single fermentation by the (-) strain with the addition of 24 µg/L trisporic acids was slightly higher than that observed in mated fermentation. After transcriptomic analysis, a steroid 5α-reductase-like gene, known as SR5AL in B. trispora, was first reported. 5α-Reductase inhibitors reduced lycopene biosynthesis and downregulated the expression of sex determination and carotenoid biosynthesis genes. Overexpression of the SR5AL gene upregulated these genes, regardless of whether trisporic acids were added. CONCLUSION: These findings indicated that the SR5AL gene is a key gene associated with the response to trisporic acids.

Effect of inoculation process on lycopene production by Blakeslea trispora in a stirred-tank reactor.

Lycopene biosynthesis by Blakeslea trispora was greatly enhanced in a stirred-tank reactor when a nonsynchronous inoculation process, in which the (+) mating type was inoculated after the (-) mating type has been grown for a certain period of time, was applied. The lycopene concentration with nonsynchronous inoculation in a 24-h inoculation interval was 33 % higher than that with synchronous inoculation. The optimum inoculation ratio was 1:2 (+/-) at the 36 and 48 h inoculum age of mating types (+) and (-), respectively. Fermentation time for the individual strains and mated conditions showed that the (+) mating type grows faster than the (-) mating type. Morphological observation showed that the mycelium ratio of B. trispora (-) in mating culture with nonsynchronous inoculation was higher than that with synchronous inoculation. The results indicated that nonsynchronous inoculation process increased the dominance of B. trispora (-) in joint cultivation and hence stimulated lycopene biosynthesis.

Enhanced lycopene content in Blakeslea trispora by effective mutation-screening method.

The zygomycete fungus Blakeslea trispora is usually used as a natural source of lycopene and ß-carotene. In this study, the B. trispora (-) strain, a major mating type for lycopene production, was treated with N(+) ion implantation and N-methyl-N'-nitro-N-nitrosoguanidine (NTG), and further isolated on the screening plates supplemented with lovastatin and crude extracts of trisporic acid (CTA). After several rounds of screening, four mutants with higher yield of lycopene and biomass were isolated. Among these mutants, I5 obtained with N(+) ion implantation showed a maximum lycopene yield (28.8 mg/g), which was 64 % higher than the parent strain (17.5 mg/g) in the production of lycopene. The results indicated that N(+) ion implantation is more suitable for B. trispora (-) than NTG treatment, and the addition of lovastatin promoted the generation of positive mutant and CTA amplified the color differences between colonies.