Genome Sequence of Bacillus cereus Strain A1, an Efficient Starch-Utilizing Producer of Hydrogen

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.

Complete genome sequencing of Bacillus sp. TK-2, analysis of its cold evolution adaptability

To date, a large number of Bacillus species from different sources have been identified. However, there are few investigations on genome information and evolutionary insights of Bacillus species from cold environments. Bacillus sp. TK-2, isolated from the soil of Changbai Mountain, is a gram-positive bacterium with cold adaptation characteristics. In this study, we present the annotated complete genome sequence of Bacillus sp. TK-2. The genome comprised 5,286,177 bp with a GC content of 35.88%, 5293 protein-encoding genes, 32 rRNA, and 77 tRNA. Numerous genes related to cold adaptation were detected in the genome of Bacillus sp. TK-2, mainly involving in energy supply, regulation of cell membrane fluidity, antioxidant, and molecular chaperones. In addition, the strain TK-2 classified in the Bacillus groups was distributed on a terminal branch with Bacillus cereus A1 by Blastn and phylogenetic analysis in NCBI database. Complete genome sequences of the strain TK-2 and Bacillus cereus A1 were compared by the online tool "Average Nucleotide Identity", showing that the average nucleotide identity of these two strains was 98.26%. In parallel, A comparative analysis of the genomes of both Bacillus sp. TK-2 and Bacillus cereus A1 was conducted. Through the analysis of core and specific genes with cd-hit, it was found that the two strains had 5691 pan gene, 4524 core gene, and 1167 specific gene clusters. Among the 624 specific gene clusters of Bacillus sp. TK-2, some cold tolerance genes were detected, which implied the unique adaptability of Bacillus sp. TK-2 in long-term low temperature environments. Importantly, enzyme-encoding genes related to the degradation of polysaccharides such as cellulose and hemicellulose were detected in the 477 CAZyme genes of this genome. This work on sequencing and bioinformatics analysis of the complete sequence of Bacillus sp. TK-2 promote the application and in-depth research of low-temperature biotechnology.

Multifaceted toxin profile, an approach toward a better understanding of probiotic Bacillus cereus

Strains of the Bacillus cereus group have been widely used as probiotics for human beings, food animals, plants, and environmental remediation. Paradoxically, B. cereus is responsible for both gastrointestinal and nongastrointestinal syndromes and represents an important opportunistic food-borne pathogen. Toxicity assessment is a fundamental issue to evaluate safety of probiotics. Here, we summarize the state of our current knowledge about the toxins of B. cereus sensu lato to be considered for safety assessment of probiotic candidates. Surfactin-like emetic toxin (cereulide) and various enterotoxins including nonhemolytic enterotoxin, hemolysin BL, and cytotoxin K are responsible for food poisoning outbreaks characterized by emesis and diarrhea. In addition, other factors, such as hemolysin II, Certhrax, immune inhibitor A1, and sphingomyelinase, contribute to toxicity and overall virulence of B. cereus.

Metabolite-based mutualism enhances hydrogen production in a two-species microbial consortium

Sustainable hydrogen production from renewable and low-cost substrates is very important to mitigate environmental and energy-related issues. Microbial consortia are promising for diverse bioenergy and environmental applications, yet microbial interactions are not fully understood. Here, we present comprehensive investigation on how two species in an artificial microbial consortium, consisting of Bacillus cereus A1 and Brevundimonas naejangsanensis B1, mutually cooperate to achieve an overall enhancement in hydrogen production and starch utilization. In this consortium, strains A1 and B1 secrete α-amylase and glucoamylase that are functionally complementary in starch hydrolysis. Moreover, strain A1 converts starch into lactate as a carbon source and electron donor, supporting the cell growth and hydrogen generation of strain B1. In return, strain B1 produces formate as an electron shuttle to strain A1 to enhance hydrogen production. The co-culture re-directs the overall metabolic flux, facilitates the cell growth, and up-regulates the key genes of hydrogen production and starch hydrolysis.

Wang and Tang et al. show that two-species microbial consortium is more efficient in hydrogen production and starch utilization, compared to pure cultures. This work underscores a utility of synthetic microbial consortia, which can be optimized for increasing production of a certain metabolite.