Genomic and Transcriptomic Insights into Exopolysaccharide Biosynthesis and Low-Temperature Fermentation Performance of Lactiplantibacillus plantarum L75 from the Alpine Region of the Qinghai-Tibetan Plateau

This study characterized the exopolysaccharide (EPS) of Lactiplantibacillus plantarum L75 and investigated its biosynthesis and the strain's cold adaptation mechanisms. Strain L75 produced 161.2 ± 13.75 mg/L of a heteropolysaccharide (358.24 kDa) at 37 °C, composed of glucose (32.68%), mannose (30.53%), galactose (17.75%), glucuronic acid (12.63%), and rhamnose (6.41%). Crucially, this EPS promoted L. plantarum L75 growth at 15 °C. Genomic analysis revealed two typical wzx/wzy-dependent EPS gene clusters and a versatile carbohydrate metabolism capacity. Transcriptomic profiling confirmed L75's multifaceted cold adaptation, involving the upregulation of cold shock proteins and molecular chaperones, enhanced reactive oxygen species (ROS) scavenging, accumulation of compatible solutes, and maintenance of membrane fluidity. By integrating physiological and transcriptional data, our findings elucidate the molecular basis for L75's high EPS production, the role of EPS in low-temperature growth, and its robust cold tolerance, supporting its potential as a functional silage inoculant for cold regions.