Fungi from seleniferous habitats and the relationship of selenium to fungal oxidative stress

Saprobic rhizosphere fungi from four seleniferous sites in Colorado and Wyoming were isolated from feeder roots of selenium (Se) hyperaccumulator and non-accumulator plants. The 259 fungal isolates were identified to genus and evaluated for Se tolerance. Among the 24 represented genera, eleven genera comprised 86% of the isolates. The majority of the isolates from the seleniferous sites were visually unaffected by 10 mg L-1 Se, irrespective of host plant (hyperaccumulator vs. non-accumulator) and original isolation agar (0 or 10 mg L-1 Se). Two previously undescribed species of Altemaria were isolated from hyperaccumulators; one isolate was highly selenophilic. Rhizosphere fungi also were isolated from plant roots from a control site where no Se accumulators were present; these fungi were highly sensitive to Se at 10 mg L-1 and, as a group, exhibited reduced (p ≤ 0.05) tolerance when compared to the isolates from the seleniferous sites.; A selected group of isolates was evaluated for Se tolerance, accumulation and volatilization, as well as their trolox equivalent antioxidant capacity, total phenolics and recovery after exposure to UV light. Several Altemaria and related genera and one Fusarium isolate showed up to a five-fold increase in oxidative quenching ability when grown on media containing Se. Further, some of these isolates accumulated Se in their tissues, exhibited a significant increase in growth rate in the presence of Se, and exhibited decreased recovery time after exposure to UV light in the presence of Se. One Aspergillus isolate tolerated high levels of Se (≤600 mg Se L-1), volatilized Se, and failed to accumulate Se. This fungus may be a good candidate for Se mycoremediation. Five of the twelve isolates characterized utilize or to benefit from the Se as judged from a combination of tolerance and an increase in reactive oxygen species quenching and total phenolics without a negative impact on growth. The effects of these responses were seen in the reduction of recovery time from UV light. These fungi may provide a biological resource for oxidative stress treatment and model organisms to study oxidative stress and antioxidant capacity in relation to Se.