Recent advances in screening amino acid overproducers

Abstract

Microbial fermentation has contributed to 80% of global amino acid production. The key to microbial fermentation is to obtain fermentation strains with high performance to produce target amino acids with a high yield. These strains are primarily derived from screening enormous mutant libraries. Therefore, a high-throughput, rapid, accurate, and universal screening strategy for amino acid overproducers has become a guarantee for obtaining optional amino acid overproducers. In recent years, the rapid development of various novel screening strategies has been witnessed. However, proper analysis and discussion of these innovative technologies are lacking. Here we systematically reviewed recent advances in screening strategies: the auxotrophic-based strategy, the biosensor-based strategy, and the latest translation-based screening strategy. The design principle, application scope, working efficiency, screening accuracy, and universality of these strategies were discussed in detail. The potential for screening nonstandard amino acid overproducers was also analyzed. Guidance for the improvement of future screening strategies is provided in this review, which could expedite the reconstruction of amino acid overproducers and help promote the fermentation industry to reduce cost, increase yield, and improve quality.

Keywords: Biosensor; Microbial cell factory; Rare codon; tRNA.

Graphical abstract

Fig. 1

Auxotrophic strain-based strategy. Screening strategy based on the coculture of the production strain and the indicator strain. In the coculture process, it is necessary to maintain dominance of the indicator strain by using strategies such as cross-feeding to obtain a stable screening effect. (A) To screen the l-Trp overproducers while knocking out the l-Trp-synthesis pathway gene trpB of the indicator strain, knocking out the l-His-synthesis pathway gene hisD of the production strain makes it rely on the l-His produced by the indicator strain for survival. (B) Proposed screening strategy for identifying optimal enzyme variants in amino acid synthesis pathways.

Fig. 2

Biosensor-based strategy for amino acid overproducers.(A) l-Tyr biosensor based on a tyrosinase-coupled color reaction. (B) l-Lys biosensor based on substrate-binding domain-fused proteins. (C) Basic amino acid biosensor based on transcription factor LysG. (D) Circularly permuted protein-based biosensor. (E) l-Lys biosensor based on riboswitch. LAO, lysine-/arginine-/ornithine-binding protein; FP, fluorescent protein; cpFP, circularly permuted fluorescent protein; RBS, ribosome binding site.

Fig. 3

Mechanism of using amino acid analogs to identify overproducers.

Fig. 4

The rare codon-based strategy for screening amino acid overproducers.

Fig. 5

The aaRS-based strategy for screening amino acid overproducers.