The main objective of this study was to investigate the effects of a low cost minimal medium, developed by the UL Bioprocessing Lab, on the cultivation of Lipomyces starkeyi NRRL Y-11557 using repeated fed-batch and continuous fermentation strategies. The highest cell and lipid concentrations obtained were 22.7 g L-1 and 11.67 g L-1 under repeated fed-batch cultivation, respectively. Continuous cultivation with the dilution rate of 0.06 h-1 presented the highest cell (0.401 g g-1) and lipid yields (0.177g g-1). Exopolysaccharide production was observed when L. starkeyi was cultivated in the minimal media supplemented with 90 g L-1 glucose under repeated fed-batch fermentation. The produced exopolysaccharide is likely composed of 4-5 repeating sugar units, incorporating mannose and galactose and their respective uronic acids.

Microbial fermentation processes are of great importance for the production of many bioproducts. Even for established processes, improvements in product yield, productivity, and quality are always continually demanded. This is particularly true as the products mature from being novelty to high demand, even bulk, substances, as has been witnessed for several antimicrobial compounds. High-density cultivations have been found very useful in producing a large number of modern bioproducts. Selection of the mode of fermentation, operating conditions, and optimized media are important characteristic features for high cell density, productivity, as well as the commercial success of any microbial product. This contribution reviews some of the challenges and technologies investigated for high-density cultivation. Important aspects such as medium composition, reactor conditions, oxygen transfer, temperature, agitation, pH, modes of operation, and feeding strategies for high-density cultivation are summarized in this review.