The morphology of Ganoderma lucidum mycelium in a repeated-batch fermentation for exopolysaccharide production

•Extended fermentation strategy for G. lucidum mycelium in shake flask and bioreactor.•Repeated-batch fermentation affected the morphology with reduced fermentation time.•Ovoid pellet favours exopolysaccharide production in a shake flask.•Starburst-like pellet favours exopolysaccharide production in a bioreactor.

The morphology of Ganoderma lucidum BCCM 31549 mycelium in a repeated-batch fermentation (RBF) was studied for exopolysaccharide (EPS) production. RBF was optimised for time to replace and volume to replace. G. lucidum mycelium showed the ability to self-immobilise and exhibited high stability for repeated use in RBF with engulfed pellets. Furthermore, the ovoid and starburst-like pellet morphology was disposed to EPS production in the shake flask and bioreactor, respectively. Seven RBF could be carried out in 500 mL flasks, and five repeated batches were performed in a 2 L bioreactor. Under RBF conditions, autolysis of pellet core in the shake flask and shaving off of the outer hairy region in the bioreactor were observed at the later stages of RBF (R4 for the shake flask and R6 for the bioreactor). The proposed strategy showed that the morphology of G. lucidum mycelium can withstand extended fermentation cycles.