Ammonium-regulated high-cell-density heterotrophic cultivation enhances cost-effective chrysolaminarin production in Poterioochromonas malhamensis.

Chrysolaminarin exhibits diverse bioactivities, including antioxidant and immunomodulatory, making it a promising candidate for applications in pharmaceuticals, nutraceuticals, functional foods, biomedicine, and bio-based industries. Heterotrophic cultivation of Poterioochromonas malhamensis has considerable potential for large-scale chrysolaminarin production; however, existing bioprocesses remain inadequate for scalable manufacturing and application. In this study, a high-cell-density heterotrophic cultivation strategy, integrating nitrogen source optimization and dynamic concentration regulation, was established for P. malhamensis to enhance chrysolaminarin production. Shake flask screening identified ammonium acetate as optimal inorganic nitrogen, effectively substituting expensive yeast extract and liver extract powder. Through systematic optimization of nutrients, we developed a chemically defined synthetic medium composed of glucose, ammonium acetate, inorganic salts, vitamins, etc., which was used for the heterotrophic cultivation of the P. malhamensis and the efficient production of chrysolaminarin. Batch cultivation determined the optimal temperature, pH, and suitable agitation speed range for P. malhamensis. In fed-batch cultivation with this medium under the optimal culture conditions, biomass concentration and chrysolaminarin yield reached 55.75 g L-1 and 34.58 g L-1, respectively. Further ammonium concentration regulation during fed-batch operation increased both biomass density and polysaccharide content, obtained a peak chrysolaminarin yield of 42.72 g L-1. Cost-effectiveness assessment revealed an 89.07% reduction in nutrient input costs per kilogram of chrysolaminarin for fed-batch cultivation. These findings demonstrate a cost-efficient strategy to enhance chrysolaminarin production, strengthening its potential for industrial-scale applications.