Aerobic, Selenium-Utilizing Bacillus Isolated from Seeds of Astragalus crotalariae

Abstract

Bacillus sp. strain SS, an aerobic, gram-positive sporeformer, was isolated from seeds of Astragalus crotalariae, a selenium-accumulating plant. This bacillus grew in a nutrient broth (containing beef extract and peptone) if the medium was supplemented with high concentrations of selenium. Concentrations of Na2SeO3 that supported growth ranged from 3 to 100 mM. After 24 h of growth, the culture developed a deep red color characteristic of elemental selenium. When selenium was provided in the form of selenate, the pattern of growth showed a prolonged lag period, from 24 to 48 h. Final growth remained below that of cells cultured in the presence of selenite, and only a light red color developed. Concentrations of selenate below 40 mM failed to support growth. Tellurate, though not tellurite, could replace selenite, but only over a narrow concentration range, 5 to 10 mM. By 24 h, the typical black color of elemental tellurium developed. Bacillus sp. strain SS grew also in brain heart infusion broth and Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) without the addition of selenium or tellurium compounds. When added to these media, 50 mM selenite was tolerated and metabolized by the organism. The crucial distinction between this bacillus and other selenium-tolerant organisms (e.g., Salmonella) remains: under certain conditions, growth requirements of Bacillus sp. strain SS are fulfilled by selenium (and tellurium) compounds.

Selenate Reduction to Elemental Selenium by Anaerobic Bacteria in Sediments and Culture: Biogeochemical Significance of a Novel, Sulfate-Independent Respiration

“…6), a fact which confirms that these organisms carry out a novel respiration. Although there were previous observations of what appeared to be Se°(s) precipitation from selenate in various bacterial cultures (7,9,13,17), these reports usually consisted of casual observations peripheral to the main thrusts of the investigations. Recently, Maiers et al (24) reported Se°(s) precipitation from selenate (maximum concentration, 1 mM) by enrichment cultures; however, it was not clear whether this occurred under aerobic or anaerobic conditions, and a respiratory linkage was not reported.…”

Selenium and nitrate removal from agricultural drainage using the AIWPS® technology

“…Selenium is required by higher animals as a trace nutrient (Garberg and Hogberg, 1986) and by some microbes (Lindblow-Kull, Shrift, and Gherna, 1982;Lindstrom, 1983). In excess, selenium is toxic to all organisms.…”