Abstract
The study aimed to evaluate the metabolism and resistance to the gastrointestinal tract conditions of Bacillus pumilus UAMX (BP-UAMX) isolated from overweight individuals using genomic tools. Specifically, we assessed its ability to metabolize various carbon sources, its resistance to low pH exposure, and its growth in the presence of bile salts. The genomic and bioinformatic analyses included the prediction of gene and protein metabolic functions, a pan-genome and phylogenomic analysis. BP-UAMX survived at pH 3, while bile salts (0.2–0.3% w/v) increased its growth rate. Moreover, it showed the ability to metabolize simple and complex carbon sources (glucose, starch, carboxymethyl-cellulose, inulin, and tributyrin), showing a differentiated electrophoretic profile. Genome was assembled into a single contig, with a high percentage of genes and proteins associated with the metabolism of amino acids, carbohydrates, and lipids. Antibiotic resistance genes were detected, but only one beta-Lactam resistance protein related to the inhibition of peptidoglycan biosynthesis was identified. The pan-genome of BP-UAMX is still open with phylogenetic similarities with other Bacillus of human origin. Therefore, BP-UAMX seems to be adapted to the intestinal environment, with physiological and genomic analyses demonstrating the ability to metabolize complex carbon sources, the strain has an open pan-genome with continuous evolution and adaptation.
Highlights
Gram-positive Bacillus pumilus are spore-forming bacteria that grow under aerobic or anaerobic conditions
(BP-UAMX) to survive at low pH or in the presence of bile salts that are related to the gastrointestinal transit from the gastric to the enteric sections, since the studied strain was previously isolated from the gut of overweight individuals
Bacillus pumilus UAMX (BP-UAMX) isolates were cultivated after being exposed to bile salts (0.2 and 0.3% w/v) or to low pHs (2 and 3), according to the methodologies reported by Kristoffersen and Dressman et al, respectively [58,59]
Summary
Gram-positive Bacillus pumilus are spore-forming bacteria that grow under aerobic or anaerobic conditions. These bacteria have been reported to be found in soil, water, air (spores), fermented foods, decomposing plant and animal tissues, and the human gastrointestinal tract (GIT). The environmental and nutritional conditions that vary throughout the GIT and the presence of other microorganisms can restrict Bacillus colonization. Their survival depends on the availability of specific carbon sources (provided by the diet of the individual) and on the activity of the various enzymes that are present in saliva and throughout the GIT.
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