Balancing Redox Homeostasis to Improve <scp>l</scp>-Cysteine Production in <i>Corynebacterium glutamicum</i>

Abstract

l-Cysteine is a valuable sulfur-containing amino acid with applications across a wide range of fields. Recently, microbial fermentation has emerged as a method to produce l-cysteine. However, cellular redox stress from high levels of l-cysteine is a bottleneck for achieving efficient production. In this study, we aimed to facilitate l-cysteine biosynthesis by modulating cellular redox homeostasis through the introduction of the natural antioxidant astaxanthin in <i>Corynebacterium glutamicum</i>. To achieve this, we first introduced an exogenous astaxanthin synthesis module in <i>C. glutamicum</i>. Then, an l-cysteine-dependent autonomous bifunctional genetic switch was developed to dynamically regulate the l-cysteine and astaxanthin biosynthesis pathway to maintain cellular redox homeostasis. This regulation system achieved high biosynthesis of astaxanthin, which significantly facilitated l-cysteine production. Finally, engineered strain Cg-10 produced 8.45 g/L l-cysteine and 95 mg/L astaxanthin in a 5 L bioreactor, both of which are the highest reported levels in <i>C. glutamicum</i>.