L-Tryptophan is an important aromatic amino acid that is used widely in the food, chemical, and pharmaceutical industries. Compared with the traditional synthetic methods, production of l-tryptophan by microbes is environmentally friendly and has low production costs, and feed stocks are renewable. With the development of metabolic engineering, highly efficient production of l-tryptophan in Escherichia coli has been achieved by eliminating negative regulation factors, improving the intracellular level of precursors, engineering of transport systems and overexpression of rate-limiting enzymes. However, challenges remain for l-tryptophan biosynthesis to be cost-competitive. In this review, successful and applicable strategies derived from metabolic engineering for increasing l-tryptophan accumulation in E. coli are summarized. In addition, perspectives for further efficient production of l-tryptophan are discussed.

Change in pH in growth conditions is the primary stress for most neutralophilic bacteria, including model microorganism Escherichia coli. However, different survival capacities under acid stress in different bacteria are ubiquitous. Research on different acid-tolerance mechanisms in microorganisms is important for the field of combating harmful gut bacteria and promoting fermentation performance of industrial strains. Therefore, this study aimed to carry out a narrative review of acid-stress response mechanism of E. coli discovered so far, including six AR systems, cell membrane protection, and macromolecular repair. In addition, the application of acid-tolerant E. coli in industry was illustrated, such as production of industrial organic acid and developing bioprocessing for industrial wastes. Identifying these aspects will open the opportunity for discussing development aspects for subsequent research of acid-tolerant mechanisms and application in E. coli.

As natural parasites of bacteria, phages have greatly contributed to bacterial evolution owing to their persistent threat. Diverse phage resistance systems have been developed in bacteria during the coevolutionary process with phages. Conversely, phage contamination has a devastating effect on microbial fermentation, resulting in fermentation failure and substantial economic loss. Accordingly, natural defense systems derived from bacteria can be employed to obtain robust phage-resistant host cells that can overcome the threats posed by bacteriophages during industrial bacterial processes. In this review, diverse phage resistance mechanisms, including the remarkable research progress and potential applications, are systematically summarized. In addition, the development prospects and challenges of phage-resistant bacteria are discussed. This review provides a useful reference for developing phage-resistant bacteria.

Shikimate is an important intermediate in the aromatic amino acid pathway, which can be used as a promising building block for the synthesis of biological compounds, such as neuraminidase inhibitor Oseltamivir (Tamiflu®). Compared with traditional methods, microbial production of shikimate has the advantages of environmental friendliness, low cost, feed stock renewability, and product selectivity and diversity, thus receiving more and more attentions. The development of metabolic engineering allows for high-efficiency production of shikimate of Escherichia coli by improving the intracellular level of precursors, blocking downstream pathway, releasing negative regulation factors, and overexpressing rate-limiting enzymes. In addition, novel technologies derived from systems and synthetic biology have opened a new avenue towards construction of shikimate-producing strains. This review summarized successful and applicable strategies derived from traditional metabolic engineering and novel technologies for increasing accumulation of shikimate in E. coli.