Genomic Insights into the Diversity of Non-Coding RNAs in Bacillus Cereus Sensu Lato.

Bacillus cereus sensu lato is a group of bacteria of medical and agricultural importance in different ecological niches and with controversial taxonomic relationships. Studying the composition of non-coding RNAs (ncRNAs) in several bacterial groups has been an important tool for identifying genetic information. However, to date, no comparative genomics study of ncRNA has been performed in this group. Thus, this study aimed to identify and characterize the set of ncRNAs from 132 strains of Bacillus cereus, Bacillus thuringiensis and Bacillus anthracis to obtain an overview of the diversity and distribution of these genetic elements in these species. We observed that the number of ncRNAs differs in the chromosomes of the three species, but not in the plasmids, when species or phylogenetic clusters were compared. The prevailing functional/structural category was Cis-reg and the most frequent class was Riboswitch. However, in plasmids, the class Group II intron was the most frequent. Also, nine ncRNAs were selected for validation in the strain B. thuringiensis 407 by RT-PCR, which allowed to identify the expression of the ncRNAs. The wide distribution and diversity of ncRNAs in the B. cereus group, and more intensely in B. thuringiensis, may help improve the abilities of these species to adapt to various environmental changes.

Effect of infant meal home preparation temperature on surviving of Bacillus cereus sensu lato: A case of Bechar city, Algeria

This work aimed to enumerate the Bacillus cereus sensu lato from infant’s flour sampled at Béchar city and evaluate its resistance to different heating conditions during meal preparation patterns at home. Our findings revealed a prevalence of 74% with 2.4 to 3.9 CFU/g in the analyzed samples. Regarding the heat resistance at 90 °C to 98 °C, our results showed heat resistance variability which depends on the isolate, for example, D90 °C and zT °C values varied from 3.24 to 5.52 min and 11.56 to 89.74 °C respectively. Then, the decimal reduction (n) was calculated at all preparation temperatures (50, 60, 70, 80, 90 and 100 °C). Low “n” was observed with the preparation at T≤50 °C as recommended by the fabricant. However, at the other temperatures, high “n” was observed at 100°C with median and 95th values of 2.22 and 12.36 respectively. Therefore, bacterial concentrations (99th) were estimated at 0.124 log CFU/g for 100 °C. These concentrations could be increased with bacterial growth during meal storage and then achieve critical concentrations. Thus, the results of this work highlight the interest to establish a risk assessment for babies and to improve the production, preparation, and storage conditions of the infant’s flour.

Enigmatic Pilus-like Endospore Appendages of Bacillus cereus Group Species

The endospores (spores) of many Bacillus cereus sensu lato species are decorated with multiple hair/pilus-like appendages. Although they have been observed for more than 50 years, all efforts to characterize these fibers in detail have failed until now, largely due to their extraordinary resilience to proteolytic digestion and chemical solubilization. A recent structural analysis of B. cereus endospore appendages (Enas) using cryo-electron microscopy has revealed the structure of two distinct fiber morphologies: the longer and more abundant “Staggered-type” (S-Ena) and the shorter “Ladder-like” type (L-Ena), which further enabled the identification of the genes encoding the S-Ena. Ena homologs are widely and uniquely distributed among B. cereus sensu lato species, suggesting that appendages play important functional roles in these species. The discovery of ena genes is expected to facilitate functional studies involving Ena-depleted mutant spores to explore the role of Enas in the interaction between spores and their environment. Given the importance of B. cereus spores for the food industry and in medicine, there is a need for a better understanding of their biological functions and physicochemical properties. In this review, we discuss the current understanding of the Ena structure and the potential roles these remarkable fibers may play in the adhesion of spores to biotic and abiotic surfaces, aggregation, and biofilm formation.

Adaptation and phenotypic diversification of Bacillus thuringiensis 407 biofilm are accompanied by a fuzzy spreader morphotype

Bacillus cereus group (Bacillus cereus sensu lato) has a diverse ecology, including various species that produce biofilms on abiotic and biotic surfaces. While genetic and morphological diversification enable the adaptation of multicellular communities, this area remains largely unknown in the Bacillus cereus group. In this work, we dissected the experimental evolution of Bacillus thuringiensis 407 Cry-during continuous recolonization of plastic beads. We observed the evolution of a distinct colony morphotype that we named fuzzy spreader (FS) variant. Most multicellular traits of the FS variant displayed higher competitive ability versus the ancestral strain, suggesting an important role for diversification in the adaptation of B. thuringiensis to the biofilm lifestyle. Further genetic characterization of FS variant revealed the disruption of a guanylyltransferase gene by an insertion sequence (IS) element, which could be similarly observed in the genome of a natural isolate. The evolved FS and the deletion mutant in the guanylyltransferase gene (Bt407ΔrfbM) displayed similarly altered aggregation and hydrophobicity compared to the ancestor strain, suggesting that adaptation process highly depends on the physical adhesive forces.

Putative plasmid prophages of Bacillus cereus sensu lato may hold the key to undiscovered phage diversity

Bacteriophages are bacterial viruses and the most abundant biological entities on Earth. Temperate bacteriophages can form prophages stably maintained in the host population: they either integrate into the host genome or replicate as plasmids in the host cytoplasm. As shown, tailed temperate bacteriophages may form circular plasmid prophages in many bacterial species of the taxa Firmicutes, Gammaproteobacteria and Spirochaetes. The actual number of such prophages is thought to be underestimated for two main reasons: first, in bacterial whole genome-sequencing assemblies, they are difficult to distinguish from actual plasmids; second, there is an absence of experimental studies which are vital to confirm their existence. In Firmicutes, such prophages appear to be especially numerous. In the present study, we identified 23 genomes from species of the Bacillus cereus group that were deposited in GenBank as plasmids and may belong to plasmid prophages with little or no homology to known viruses. We consider these putative prophages worth experimental assays since it will broaden our knowledge of phage diversity and suggest that more attention be paid to such molecules in all bacterial sequencing projects as this will help in identifying previously unknown phages.

The Crystal Structure of Bacillus cereus HblL1

The Hbl toxin is a three-component haemolytic complex produced by Bacillus cereus sensu lato strains and implicated as a cause of diarrhoea in B. cereus food poisoning. While the structure of the HblB component of this toxin is known, the structures of the other components are unresolved. Here, we describe the expression of the recombinant HblL1 component and the elucidation of its structure to 1.36 Å. Like HblB, it is a member of the alpha-helical pore-forming toxin family. In comparison to other members of this group, it has an extended hydrophobic beta tongue region that may be involved in pore formation. Molecular docking was used to predict possible interactions between HblL1 and HblB, and suggests a head to tail dimer might form, burying the HblL1 beta tongue region.

Enterotoxin Gene Distribution and Genotypes of Bacillus cereus sensu lato Isolated from Cassava Starch

Bacillus cereus is a human pathogenic bacterium found in foods with the potential to cause emesis and diarrhea. This study estimated the presence, toxigenic and genomic diversity of B. cereus s.l. obtained from cassava starch samples collected in bakeries and powdered food companies in Medellín (Colombia). Bacillus cereuss.l. was found in 43 of 75 (57%) cassava starch samples and 98 isolates were obtained. The nheABC, hblCDAB, cytK2, entFM and cesB toxin genes were detected by multiplex PCR and the most frequent operon was nheABC, whereas cesB gene was not found. Twelve toxigenic profiles were determined by the detection of toxin genes, and the most frequent profiles harbored all enterotoxin genes. A broad genomic diversity was detected according to GTG5-PCR fingerprinting results with 76 B. cereus s.l. grouped in sixteen clusters and the 22 isolates clustering separately. No relationship was observed between genomic background and toxigenic profiles. In general, the results showed a high genomic and enterotoxigenic diversity in B. cereus s.l. found in cassava starch. These results should incentive future studies to understand the distribution of B. cereus s.l. isolated on raw materials in comparison with finished products.