Sporulation efficiency and spore quality in a human intestinal isolate of Bacillus cereus

Abstract

The Bacillus cereus group is a species complex of the Bacillus genus that includes several closely related species. Within this group, bacteria indicated as B. cereus sensu stricto (B. cereus) are the causative agent of two different types of gastrointestinal diseases associated with food poisoning. Outbreaks of this opportunistic pathogen are generally due to the resistance of its spores to heat, pH and desiccation that makes hard their complete inactivation from food products. B. cereus is commonly isolated from a variety of environments, including intestinal samples of infected and healthy people. We report the genomic and physiological characterization of MV19, a human intestinal strain closely related (ANI value of 98.81%) to the reference strain B. cereus ATCC 14579. MV19 cells were able to grow in a range of temperatures between 20 and 44{degrees}C. At the optimal temperature the sporulation process was induced very rapidly and mature spores efficiently released, however these appeared structurally and morphologically defective. At the sub-optimal growth temperature of 25{degrees}C sporulation was slow and less efficient but a high total number of fully functional spores was produced. Altogether, results reported here indicate that the reduced rapidity and efficiency of sporulation at 25{degrees}C are compensated by a high quality and quantity of released spores, suggesting the relevance of different performances at different growth conditions for the adaptation of this bacterium to diverse environmental niches.