RESUMEN
γ-Polyglutamic acid (γ-PGA) is a biodegradable polymer naturally produced by Bacillus spp. that has wide applications. Fermentation of γ-PGA using Bacillus species often requires the supplementation of L-glutamic acid, which greatly increases the overall cost. Here, we report a metabolically engineered Corynebacterium glutamicum capable of producing γ-PGA from glucose. The genes encoding γ-PGA synthase complex from B. subtilis (pgsB, C, and A) or B. licheniformis (capB, C, and A) were expressed under inducible promoter Ptac in a L-glutamic acid producer C. glutamicum ATCC 13032, which led to low levels of γ-PGA production. Subsequently, C. glutamicum F343 with a strong L-glutamic acid production capability was tested. C. glutamicum F343 carrying capBCA produced γ-PGA up to 11.4â¯g/L, showing a higher titer compared with C. glutamicum F343 expressing pgsBCA. By introducing B. subtilis glutamate racemase gene racE under Ptac promoter mutants with different expression strength, the percentage of L-glutamic acid units in γ-PGA could be adjusted from 97.1% to 36.9%, and stayed constant during the fermentation process, while the γ-PGA titer reached 21.3â¯g/L under optimal initial glucose concentrations. The molecular weight (Mw) of γ-PGA in the engineered strains ranged from 2000 to 4000â¯kDa. This work provides a foundation for the development of sustainable and cost-effective de novo production of γ-PGA from glucose with customized ratios of L-glutamic acid in C. glutamicum.
Asunto(s)
Corynebacterium glutamicum , Ingeniería Metabólica , Ácido Poliglutámico , Bacillus licheniformis/genética , Bacillus licheniformis/metabolismo , Bacillus subtilis/genética , Bacillus subtilis/metabolismo , Proteínas Bacterianas/biosíntesis , Proteínas Bacterianas/genética , Corynebacterium glutamicum/genética , Corynebacterium glutamicum/metabolismo , Ácido Poliglutámico/biosíntesis , Ácido Poliglutámico/genéticaRESUMEN
Metabolic engineering strives to develop microbial strains that are capable of producing a target chemical in a biological organism. There are still many challenges to overcome in order to achieve titers, yields, and productivities necessary for industrial production. The use of recombinant microorganisms to meet these needs is the next step for metabolic engineers. In this chapter, we aim to provide insight on both the applications of metabolic engineering for natural product biosynthesis as well as optimization methods.