Microbial synthesis of serotonin and melatonin

Serotonin is a widely distributed monoamine neurotransmitter that plays a critical role in emotion regulation and management in animals. It also serves as a key intermediate in the melatonin biosynthesis pathway. Melatonin is crucial for circadian rhythm regulation, antioxidant defense, and plant growth as well as stress resistance. Both serotonin and melatonin are involved in signaling transduction pathways that modulate various nervous system activities. Currently, serotonin is primarily obtained through natural extraction and chemical synthesis. However, these methods are time-consuming, low-yielding, and environmentally unfriendly. In recent years, environmentally friendly bio-fabrication has garnered significant attention. Microbial synthesis, characterized by short growth cycles and eco-friendly production processes, has emerged as a promising platform for the synthesis of serotonin and melatonin. Nevertheless, the production yield of serotonin and melatonin in microorganisms remains insufficient to meet industrial production demands. This review provides a comprehensive overview of the fundamental properties and physiological functions of serotonin and melatonin with a focus on their biosynthesis. In addition, it examines recent advancements in microbial biosynthesis of serotonin and melatonin, identifies key bottlenecks limiting production efficiency, and proposes metabolic engineering strategies to enhance microbial synthesis efficiency, aiming for scalable industrial applications.