Despite the commercial rise of probiotics containing Bacillaceae spp., it remains important to assess the safety of each strain before clinical testing. Herein, we performed preclinical analyses to address the safety of Bacillus subtilis BS50. Using in silico analyses, we screened the 4.15 Mbp BS50 genome for genes encoding known Bacillus toxins, secondary metabolites, virulence factors, and antibiotic resistance. We also assessed the effects of BS50 lysates on the viability and permeability of cultured human intestinal epithelial cells (Caco-2). We found that the BS50 genome does not encode any known Bacillus toxins. The BS50 genome contains several gene clusters involved in the biosynthesis of secondary metabolites, but many of these antimicrobial metabolites (e.g., fengycin) are common to Bacillus spp. and may even confer health benefits related to gut microbiota health. BS50 was susceptible to seven of eight commonly prescribed antibiotics, and no antibiotic resistance genes were flanked by the complete mobile genetic elements that could enable a horizontal transfer. In cell culture, BS50 cell lysates did not diminish either Caco-2 viability or monolayer permeability. Altogether, BS50 exhibits a robust preclinical safety profile commensurate with commercial probiotic strains and likely poses no significant health risk to humans.
The first complete genome sequence of Bacillus glycinifermentans B-27 was determined by SMRT sequencing generating a genome sequence with a total length of 4,607,442 bases. Based on this sequence 4738 protein-coding sequences were predicted and used to identify gene clusters that are related to the production of secondary metabolites such as Lichenysin, Bacillibactin and Bacitracin. This genomic potential combined with the ability of B. glycinifermentans B-27 to grown in bile containing media might contribute to a future application of this strain as probiotic in productive livestock potentially inhibiting competing and pathogenic organisms.
The first whole transcriptome assessment of a Bacillus megaterium strain provides unanticipated insights into the degSU regulon considered to be of central importance for exo-enzyme production. Regulatory patterns as well as the transcription of degSU itself deviate from the model organism Bacillus subtilis; the number of DegU-regulated secretory enzymes is rather small. Targets for productivity optimization, besides degSU itself, arise from the unexpected DegU-dependent induction of the transition-state regulator AbrB during exponential growth. Induction of secretion-assisting factors, such as the translocase subunit SecY or the signal peptidase SipM, promote hypersecretion. B. megaterium DegSU transcriptional control is advantageous for production purposes, since the degU32 constitutively active mutant conferred hypersecretion of a heterologous Bacillus amyloliquefaciens amylase without the detrimental rise, as for B. subtilis and Bacillus licheniformis, in extracellular proteolytic activities.
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