BIOAVAILABILITY OF SELENIUM ACCUMULATED BY SELENITE-REDUCING BACTERIA

The bioavailability of selenium (Se) was determined in bacterial strai ns that reduce selenite to red elemental Se (Se degrees). A laboratory strain of Bacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Mic robacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na2SeO3). After harvest, the washed, lyophilized B. subtilis and M. arborescens samples contained 2.62 and 4.23% total Se, respect ively, which was shown to consist, within error, entirely of Se degree s. These preparations were fed to chicks as supplements to a low-Se, v itamin E-free diet. Three experiments showed that the Se in both bacte ria had bioavailabilities of approx 2% that of selenite. A fourth expe riment revealed that gray Se degrees had a bioavailability of 2% of se lenite, but that the bioavailability of red Se degrees depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray Se degrees and b acterial Se; when ascorbate was the reductant, bioavailability was twi ce that level (3-4%). These findings suggest that aerobic bacteria suc h as B. subtilis and M. arborescens may be useful for the bioremediati on of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.