Pseudomonas moraviensis subsp. stanleyae, a bacterial endophyte of hyperaccumulator Stanleya pinnata, is capable of efficient selenite reduction to elemental selenium under aerobic conditions

Abstract

Aims: To identify bacteria with high selenium tolerance and reduction capacity for bioremediation of wastewater and nanoselenium particle production. Methods and Results: A bacterial endophyte was isolated from the selenium hyperaccumulator Stanleya pinnata (Brassicaceae) growing on seleniferous soils in Colorado, USA. Based on fatty acid methyl ester analysis and multi-locus sequence analysis (MLSA) using 16S rRNA, gyrB, rpoB and rpoD genes, the isolate was identified as a subspecies of Pseudomonas moraviensis (97·3% nucleotide identity) and named P. moraviensis stanleyae. The isolate exhibited extreme tolerance to SeO<inf>3</inf>^2- (up to 120 mmol l^-1) and SeO<inf>4</inf>^2- (>150 mmol l^-1). Selenium oxyanion removal from growth medium was measured by microchip capillary electrophoresis (detection limit 95 nmol l^-1 for SeO<inf>3</inf>^2- and 13 nmol l^-1 for SeO<inf>4</inf>^2-). Within 48 h, P. moraviensis stanleyae aerobically reduced SeO<inf>3</inf>^2- to red Se(0) from 10 mmol l^-1 to below the detection limit (removal rate 0·27 mmol h^-1 at 30°C); anaerobic SeO<inf>3</inf>^2- removal was slower. No SeO<inf>4</inf>^2- removal was observed. Pseudomonas moraviensis stanleyae stimulated the growth of crop species Brassica juncea by 70% with no significant effect on Se accumulation. Conclusions: Pseudomonas moraviensis stanleyae can tolerate extreme levels of selenate and selenite and can deplete high levels of selenite under aerobic and anaerobic conditions. Significance and Impact of the Study: Pseudomonas moraviensis subsp. stanleyae may be useful for stimulating plant growth and for the treatment of Se-laden wastewater.