LytR Family Transcriptional Regulator EpsA Positively Regulates Exopolysaccharide Biosynthesis in Lacticaseibacillus casei

Exopolysaccharides (EPSs) produced by Lacticaseibacillus casei have great potential for application in the food industry. However, the transcriptional regulation of EPS biosynthesis in L. casei remains unclear. Here, the transcription profile of the eps gene cluster was characterized in L. casei. Co-transcriptional analysis suggested that EPSs harbor three operons controlled by promoters P2169-2170, P2185-2186, and P2189-2190, respectively. Electrophoretic mobility shift assay showed that EpsA, the sole transcriptional regulator in the eps gene cluster, directly binds promoters P2169-2170 and P2189-2190. Overexpression of epsA increased the EPS titer (243.60 mg/L) with significantly enhanced expression of three eps genes, suggesting EpsA as a transcriptional activator for EPS biosynthesis. Furthermore, RNA-seq analysis revealed that 67 genes were significantly changed with the epsA knockout, especially 16 genes associated with EPS biosynthesis. This indicated that EpsA may be a global/pleiotropic regulator. Collectively, our findings lay the foundation for elucidating the transcriptional regulation of EPS biosynthesis in L. casei.