Isolation of selenium-resistant bacteria and advancement under enrichment conditions for selected probiotic Bacillus subtilis (BSN313).

The main aim of this work was to screen, isolate, and identify a probiotic selenium (Se)-resistant strain of Bacillus subtilis, using the 16S rDNA sequencing approach and subsequently optimize conditions. Initially, conditions were enhanced in two univariate optimization environments: shakings flask and a bioreactor. After solving optimization for selected variables, conditions were further optimized using orthogonal array testing. The results were further evaluated by the analysis of variance, in support of Se enrichment. In a bioreactor, based on R and F values, the order of effect of selected conditions on Se enrichment was stirring speed > initial pH > temperature > Se addition time. The stirring speed of the bioreactor was most significant, due to the suspension of reduced Se, as it formed. After absolute optimization, strain BSN313 was able to enrich Se up to 2,123 µg/g of dry weight, which is 7.58 times greater than the baseline Se-resistance. PRACTICAL APPLICATIONS: Systematic studies of selenium enrichment conditions will facilitate the successful development of an organic selenium source and the safe use of Bacillus subtilis strain (BSN313) as a food supplement. Selenium-enriched probiotic bacteria are reported to provide many health benefits to the host, due to antipathogenic, antioxidative, anticarcinogenic, antimutagenic, and anti-inflammatory activities.