BioProject

Selenium is an essential trace element at low levels but toxic at elevated levels. More...

Selenium is an essential trace element at low levels but toxic at elevated levels. Some areas in Colorado have seleniferous soil, others have low-selenium soil. The seleniferous soil has special vegetation containing selenium hyperaccumulator species Stanleya pinnata (Brassicaceae), Astragalus bisulcatus (Fabaceae) and Symphyotrichum ericoides (Asteraceae), which accumulate 0.1 to 1.5% of their dry weight in selenium. Our studies over the past decade indicate that these hyperaccumulator plants profoundly affect their local ecosystem by redistributing selenium and converting it from inorganic to organic forms. The rhizosphere soil of hyperaccumulator plants contained 6-14 fold higher selenium levels than bulk soil (for a review see El Mehdawi and Pilon-Smits, 2012). We are currently focusing on plant-microbe relationships in seleniferous areas. We have already found that selenium hyperaccumulator litter is decomposed fast in seleniferous areas, presumably by specialized selenium-resistant microbes and detrivores (Quinn et al. 2011). Indeed, we found higher levels of culturable microbes in selenium-rich litter than in low-selenium litter. We have also found evidence that endophytes in hyperaccumulators may affect the plant’s selenium metabolism (Valdez Barillas et al. 2012; Lindblom et al. 2013). Up to 30% elemental selenium was found in some hyperaccumulators in the field but not in other individuals from the same species, nor in greenhouse grown plants. The elemental selenium was found in root nodules, roots, stems and seeds. Our objective for the coming years is to investigate which microbes live in association with selenium hyperaccumulators, and how their microbiome compares with related non-hyperaccumulators in seleniferous and non-seleniferous areas. We also want to explore how microbial composition relates to plant selenium concentration within a hyperaccumulator population. In preliminary studies (unpublished) we could cultivate over 70 different bacterial isolated from surface-sterilized roots, stems and leaves of Stanleya pinnata and Astragalus bisulcatus. The many different genera of hyperaccumulator endophytes had in common extreme selenium tolerance (often >200 mM), much higher than control bacteria from non-seleniferous environments. They also showed ability to convert toxic forms of selenium to elemental selenium. While only 1% of bacteria are culturable, these are promising data for further studies into the full microbiome of hyperaccumulators. Less...