Comparative bioaccumulation and biotransformation of selenate, selenite, and selenomethionine in Cordyceps militaris

Selenium (Se) is an essential trace element for humans. Cordyceps militaris is an edible mushroom with nutritional value. To develop a selenium biofortification strategy for C . militaris , the absorption and transformation of selenium from selenate, selenite, and selenomethionine in mycelia were investigated. The half maximal inhibitory concentrations (IC 50 ) of selenate, selenite and selenomethionine were 1028 mg L -1 , 68.2 mg L -1 , and 1.5 mg L -1 , respectively. The kinetic fitting results indicated that the absorption rate of selenomethionine is higher than that of selenite and selenate. The absorption of selenium was inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (2,4-DNP), while the addition of sulfur, phosphorus, and methionine reduced the uptake of selenate, selenite, and selenomethionine by 80.6%, 81.9%, and 14.2%, respectively. The mycelium can convert selenite into elemental selenium at 40 mg L -1 . The major selenium species in selenium-enriched mycelium are selenomethionine, selenocysteine, and Se-methylselenocysteine. Our results indicate that selenium biofortification of C . militaris mycelium using selenite is the optimal strategy. The selenium-enriched C . militaris mycelium could serve as a novel selenium source in human diets.