Submerged Fermentation Of Cordyceps Taii: Effect Of Oxygen Supply

Cordyceps taii is a traditional mushroom as health-care product, which exhibits important pharmacological effects and has various metabolites. The application of Cordyceps in health food industry is huge. Natural Cordyceps species are very hard for harvest due to their strict requirement for growth condition, which limited its application. Now, it is critical to know how to obtain large quantities of biomass and bioactive components by submerged fermentation. Cordyceps taii is one of the species and as tonic in Guizhou province in China, which has anticancer, antimutation, immune regulation and scavenging free radicals activities. However, there is lack of studies on the submerged fermentation of Cordyceps taii.In this study, antitumor-guided separation of Cordyceps mycelium was done at first, and it resulted in the isolation and identification of an antitumor metabolite helvolic acid. Our in vitro experiments revealed that helvolic acid exhibited notable cytotoxicity against cancer cell lines such as HeLa, HepG,95-D and SW1990. Helvolic acid was therefore taken as a major active component to evaluate the fermentation of Cordyceps taii.Oxygen supply is an important parameter in submerged fermentation. This study used volumetric oxygen transfer coefficient(KLα) to evaluate oxygen supply, and the effect of Kia within10.1h-1to33.8h-1on production of biomass and bioactive helvolic acid was studied in shake-flask fermentation of Cordyceps taii. The highest cell concentration (17.2g/L) was obtained at an initial KLα value of14.3h-1. The results showed that relative lower oxygen supply was beneficial for cell growth. Oxygen uptake rate (OUR) increased with cell growth and reached the highest value of196.13mmol L-1h-1at initial KLα of33.8h-1on day6. The results showed that OUR was tightly related with cell growth. The highest helvolic acid production (9.6mg/L) was attained at10.1h-1of initial KLa and the highest helvolic acid productivity was attained at33.8h-1of initial KLα.To provide an insight into the probable mechanism underlying the effect of oxygen supply on helvolic acid production, expression levels of three genes encoding hydroxymethylglutaryl-CoA synthase (hmgs), hydroxymethylglutaryl-CoA reductase (hmgr) and squalene synthase (sqs) of helvolic acid synthetic pathway were detected. The transcription levels of three genes hmgs, hmgr and sqs were down-regulated on day2and day8but up-regulated on day14at an intial KLα value of10.1h-1vs.33.8h-1, which well corresponded to the helvolic acid biosynthesis at those two oxygen supply conditions. The results showed that expressions of related biosynthetic genes were affected by oxygen supply conditions.The information obtained in this study would be helpful for improving biomass and helvolic acid production in submerged fermentation of Cordyceps taii on a large scale and might be useful for commercial development of Cordyceps taii as health product.