Selenium (IV,VI) reduction and tolerance by fungi in an oxic environment

Abstract

Microbial processes are known to mediate selenium (Se) oxidation-reduction reactions, strongly influencing Se speciation, bioavailability, and transport throughout the environment. While these processes have commonly been studied in anaerobic bacteria, the role that aerobic fungi play in Se redox reactions could be important for Se-rich soil systems, dominated by microbial activity. We quantified fungal growth, aerobic Se(IV, VI) reduction, and Se immobilization and volatilization in the presence of six, metal-tolerant Ascomycete fungi. We found that the removal of dissolved Se was dependent on the fungal species, Se form (i.e., selenite or selenate), and Se concentration. All six species grew and removed dissolved Se(IV) or Se(VI) from solution, with five species reducing both oxyanions to Se(0) biominerals, and all six species removing at least 15%-20% of the supplied Se via volatilization. Growth rates of all fungi, however, decreased with increasing Se(IV,VI) concentrations. All fungi removed 85%-93% of the dissolved Se(IV) within 10 d in the presence of 0.01 mm Se(IV), although only about 20%-30% Se(VI) was removed when grown with 0.01 mm Se(VI). Fungi-produced biominerals were typically 50- to 300-nm-diameter amorphous or paracrystalline spherical Se(0) nanoparticles. Our results demonstrate that activity of common soil fungi can influence Se form and distribution, and these organisms may therefore play a role in detoxifying Se-polluted environments.

Persistent Bacterial and Fungal Community Shifts Exhibited in Selenium-Contaminated Reclaimed Mine Soils

“…Soils with average Se concentrations greater than 30 mg · kg −1 were categorized as “high Se,” while locations with average Se concentrations less than 30 mg · kg −1 were categorized as “low Se.” This concentration value was selected as the cutoff between high and low Se based on typical concentrations in Se-contaminated environments ( 3 ) and laboratory studies showing significant fungal growth inhibition and aerobic Se reduction of both Se(IV) and Se(VI) ( 17 ). Across the 2 years, 8 out of 26 mined soil samples were categorized in the high-Se category.…”

“…Some organisms can reduce selenate via nitrate reductases ( 66 ), and several nitrate-reducing OTUs were seen to increase significantly in a saturated soil experiment following selenate amendment ( 35 ). While this suggests that there is a shared enzymatic mechanism for nitrate and selenate reduction in certain bacterial populations, it is also known that there are alternative pathways for Se reduction that remain poorly understood ( 17 ).…”

“…The resident communities in Se-contaminated oxic soil environments remain completely unknown. Furthermore, no known studies have examined the fungal community in Se-impacted environments, despite the existing knowledge of fungal activity influencing Se biogeochemistry ( 17 , 36 ). The objective of the current study was to comprehensively investigate the bacterial and fungal communities in Se-impacted surface soils in two reclaimed phosphorus mines of southeastern Idaho.…”

Techno-Economic Evaluation of Iron and Aluminum Coagulants on Se(IV) Removal

“…Purification of polluted waters has been studied by applying various treatment processes, such as physical, biological, and chemical, including adsorption with inorganic [11,12] or organic adsorbents [13] that mostly demonstrate low sorption capacities or weak chemical affinity. Biological removal [14] is a time-consuming process and not compatible with potable water. Reductive precipitation [15] results in high removal costs due to posttreatment processes necessary to remove residual reductants.…”

Respiratory Selenite Reductase from Bacillus selenitireducens Strain MLS10

“…A stunning array of bacteria are capable of rapidly and efficiently detoxifying up to millimolar quantities of both Se(VI) and Se(IV) aerobically and anaerobically via reduction to red elemental selenium [Se(0)] via several different mechanisms (7). The phenomenon has also been observed in the Archaea (20) and the Eukarya (21,22). This poses a significant challenge in determining whether an anaerobically grown organism reducing Se(VI) or Se(IV) is coupling this reduction with energy conservation or is merely doing this as a detoxification strategy.…”