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Liquid submerged fermentation is an effective strategy to achieve large-scale production of active ingredients by macrofungi, and controlling mycelium morphology is a key factor restricting the development of this technology. Mining for superior morphological regulatory factors and elucidation of their regulatory mechanisms are vital for the further development of macrofungal fermentation technology. In this study, microparticles were used to control the morphology of Paraisaria dubia (P. dubia) in submerged fermentation, and the underlying regulatory mechanisms were revealed by transcriptomic. The relative frequency of S-type pellet diameter increased significantly from 7.14 to 88.31%, and biomass increased 1.54 times when 15 g/L talc was added. Transcriptome analysis showed that the morphological regulation of filamentous fungi was a complex biological process, which involved signal transduction, mycelium polar growth, cell wall synthesis and cell division, etc. It also showed a positive impact on the basic and secondary metabolism of P. dubia. We provided a theoretical basis for controlling the mycelium morphology of P. dubia in submerged fermentation, which will promote the development of macrofungal fermentation technology., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

A stable culture environment is the key for optimal growth and metabolic activity of microorganisms, especially in marine species, and intermittent feeding during DHA production using Schizochytrium sp. generates an unstable culture environment. To investigate the effect of unstable culture environment on the cells' physiological status and DHA synthesis, fermentations with different feeding strategies were performed on the lab scale. The intermittent feeding strategy caused fluctuations of substrate concentration and osmotic pressure, which had a negative effect on cell division and product synthesis. The physiological status and metabolic level of Schizochytrium sp. were relatively stable under a continuous feeding strategy with a relatively stable substrate concentration of 20-25 g/L, which was beneficial for the efficient transformation of substrate, leading to an improvement of DHA productivity. This strategy was further applied to pilot scale, whereby the DHA content, DHA productivity, convert ratio of glucose to lipid and DHA reached 55.02%, 320.17 mg/(L·h), 24.35%, and 13.40%, respectively. This study therefore provides an efficient strategy for ensuring a stable culture environment for the production of DHA and similar metabolites. Graphical Abstract.