Abstract
BackgroundSpore-forming Bacilli are Gram-positive bacteria commonly found in a variety of natural habitats, including soil, water and the gastro-intestinal (GI)-tract of animals. Isolates of various Bacillus species produce pigments, mostly carotenoids, with a putative protective role against UV irradiation and oxygen-reactive forms.ResultsWe report the annotation of carbohydrate active enzymes (CAZymes) of two pigmented Bacilli isolated from the human GI-tract and belonging to the Bacillus indicus and B. firmus species. A high number of glycoside hydrolases (GHs) and carbohydrate binding modules (CBMs) were found in both isolates. A detailed analysis of CAZyme families, was performed and supported by growth data. Carbohydrates able to support growth as the sole carbon source negatively effected carotenoid formation in rich medium, suggesting that a catabolite repression-like mechanism controls carotenoid biosynthesis in both Bacilli. Experimental results on biofilm formation confirmed genomic data on the potentials of B. indicus HU36 to produce a levan-based biofilm, while mucin-binding and -degradation experiments supported genomic data suggesting the ability of both Bacilli to degrade mammalian glycans.ConclusionsCAZy analyses of the genomes of the two pigmented Bacilli, compared to other Bacillus species and validated by experimental data on carbohydrate utilization, biofilm formation and mucin degradation, suggests that the two pigmented Bacilli are adapted to the intestinal environment and are suited to grow in and colonize the human gut.
Highlights
Spore-forming Bacilli are Gram-positive bacteria commonly found in a variety of natural habitats, including soil, water and the gastro-intestinal (GI)-tract of animals
Like strains of the B. subtilis/ B. amyloliquefaciens group, B. indicus and B. firmus showed a high number of glycoside hydrolases (GH) and carbohydrate binding modules (CBM) and average numbers of glycosyl transferases (GT), polysaccharide lyases (PL) and carbohydrate esterases (CE) (Table 1)
This analysis showed that in comparison with the other Bacilli considered in this study, B. indicus and B. firmus have a high number of carbohydrate active enzymes (CAZymes) of the GH13, GT2 and GT4 families and have some CAZymes of families not common in other Bacilli (GH2, GH16, GH31, GH35, GH36, GH66, GH84, GH94, GT5, GT27, GT32, CBM4, CBM13, CBM20, CBM41 and CBM56) (Additional File 3)
Summary
Spore-forming Bacilli are Gram-positive bacteria commonly found in a variety of natural habitats, including soil, water and the gastro-intestinal (GI)-tract of animals. Spore-forming Bacilli are aerobic, Gram positive organisms sharing a common attribute of being able to differentiate into an endospore (spore), a quiescent cell form characterized by several protective layers surrounding a dehydrated cytoplasm [1] This structural organization makes the spores extremely resistant to external physical and chemical insults and able to survive almost indefinitely in the absence of water and nutrients [1]. A large number of pigmented Bacilli have been isolated and their pigments identified as carotenoids [19] Those carotenoids, found associated with either vegetative cells or spores [20], are thought to provide resistance to UV irradiation and reactive oxygen species. Non-pathogenic bacteria, able to colonize the human gut and able to produce carotenoids are, desirable as food supplements and/or functional food ingredients
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