Transcriptome profiling of a novel Enterobacter aerogenes mutant with mannose-rich exopolysaccharide phenotype...

Mannose, a common monosaccharide with primary functions in protein glycosylation and immune regulation, has been widely used in medicine, cosmetics, and food additives, increasing its economic value. In our study, the ppc gene was knocked out in Enterobacter aerogenes IAM1183 to regulate phosphoenolpyruvate carboxylase activity, thereby optimizing hydrogen-producing metabolism. Unexpectedly, the mutant strain exhibited successful production of a substantial amount of polysaccharides with a yield of 6.75 ± 0.20 g∙L^-1, a feature not observed in the original strain. Notably, the four main monosaccharides of the detected polysaccharide were mannose, glucuronic acid, glucose, and galactose, with proportions of 50.28%, 24.15%, 18.35%, and 7.2%, respectively. According to the transcriptional analysis, 481 genes were significantly differentially expressed, 47% of which were metabolism-related, encoding key enzymes of amino acid and carbohydrate metabolism, phosphotransferase system, and exopolysaccharide synthesis. It was speculated that the deletion of ppc not only enhanced the extracellular polysaccharide synthesis pathway but also affected the transport and phosphorylation of carbohydrates in cells, resulting in a distinct polysaccharide production phenotype. In this study, the production of mannose-rich exopolysaccharide (EPS) in E. aerogenes was realized for the first time. The high-mannose content of this EPS endows the mutant strain with significant potential as a candidate for downstream mannose extraction and utilization. Concurrently, this work delineates a pathway to mannose-rich EPS production in E. aerogenes, thereby enhancing the understanding of its metabolic network in this non-model microorganism.

Mannose is a crucial monosaccharide with diverse applications in multiple industries, yet current production methods have limitations. Our study is of great importance as it represents the first instance of mannose-rich polysaccharides being identified in Enterobacter aerogenes when hydrogen production metabolism is optimized by knocking out the ppc gene. Transcriptomic analysis suggested that the ppc gene knockout affected numerous genes related to metabolism, which is crucial for further exploring the metabolic regulation mechanism of Enterobacter aerogenes. This study reports a novel genetically engineered strain and a systematic methodology for mannose biosynthesis, thereby identifying candidate regulatory nodes within its metabolic network in this non-model microorganism.