LytR Family Transcriptional Regulator EpsA Positively Regulates Exopolysaccharide Biosynthesis in <i>Lacticaseibacillus casei</i>

Exopolysaccharides (EPSs) produced by <i>Lacticaseibacillus casei</i> have great potential for application in the food industry. However, the transcriptional regulation of EPS biosynthesis in <i>L. casei</i> remains unclear. Here, the transcription profile of the <i>eps</i> gene cluster was characterized in <i>L. casei</i>. Co-transcriptional analysis suggested that EPSs harbor three operons controlled by promoters P_2169-2170, P_2185-2186, and P_2189-2190, respectively. Electrophoretic mobility shift assay showed that EpsA, the sole transcriptional regulator in the <i>eps</i> gene cluster, directly binds promoters P_2169-2170 and P_2189-2190. Overexpression of <i>epsA</i> increased the EPS titer (243.60 mg/L) with significantly enhanced expression of three <i>eps</i> genes, suggesting EpsA as a transcriptional activator for EPS biosynthesis. Furthermore, RNA-seq analysis revealed that 67 genes were significantly changed with the <i>epsA</i> 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 <i>L. casei</i>.