The effect of organic carbon form and concentration on fungal selenite reduction

Fungi are essential to the transformation of carbon (C) and are well-known for degrading recalcitrant plant material. They are also increasingly recognized for their bioremediation potential in contaminated environments. Some fungi transform selenium (Se), an essential nutrient and toxin of growing concern, from an aqueous bioavailable phase (Se(+IV, VI)) to solid or volatile phases (Se(0, -II)). We examined the effect of C on growth and Se transformation for several Ascomycota fungi, including Alternaria alternata SRC1lrK2f, Paraphaeosphaeria sporulosa AP3s5-JAC2a and Pyrenochaeta sp. DS3sAY3a, grown in 0–60 mmol C/L glucose or acetate with 0.1 mM Se(IV) over 23 days. Higher C concentrations coincided with more Se removal, but some species preferred certain C sources. A. alternata generally reduced the most Se regardless of C source, but Pyrenochaeta sp. reduced more with glucose. A. alternata predominantly solidified Se, whereas P. sporulosa mainly volatilized Se. Glucose and acetate concentrations in cultures with and without Se trended downward throughout the experiment, suggesting that carbon consumption continues despite Se presence. As biomass did not substantially increase throughout the experiment for any organism with Se(IV) but C consumption continued, it is likely that the fungi experienced a toxicity effect with Se(IV) as observed with increased pigment production, and predominantly consumed C for cell maintenance and repair purposes. This study helps discern the effect of C on fungal Se transformations, providing greater insight into the coupling between C and Se biogeochemical cycling as well as improving Se bioremediation strategies.