RESUMO
Endospore-forming bacteria related to the Bacillus cereus group produce toxins that cause illnesses in organisms from invertebrates to mammals, including foodborne illnesses in humans. As commercial bee pollen can be contaminated with these bacteria, a comprehensive microbiological risk assessment of commercial bee pollen must be incorporated into the relevant regulatory requirements, including those that apply in Mexico. To facilitate detection of members of this group of bacteria, we have developed a PCR strategy that is based on the amplification of the single-copy tRNACys gene and specific genes associated with tRNACys to detect Bacillus cereus sensu lato (B. cereus s.l.). This tRNACys-PCR-based approach was used to examine commercial bee pollen for endospore-forming bacteria. Our analysis revealed that 3% of the endospore-forming colonies isolated from a commercial source of bee pollen were related to B. cereus s.l., and this result was corroborated by phylogenetic analysis, bacterial identification via MALDI-TOF MS, and detection of enterotoxin genes encoding the HBL and NHE complexes. The results show that the isolated colonies are closely related phylogenetically to B. cereus, B. thuringiensis, and B. bombysepticus. Our results indicate that the tRNACys-PCR, combined with other molecular tools, will be a useful approach for identifying B. cereus s.l. and will assist in controlling the spread of potential pathogens.
RESUMO
Background: In spore-forming bacteria, the molecular mechanisms of accumulation of transfer RNA (tRNA) during sporulation must be a priority as tRNAs play an essential role in protein synthesis during spore germination and outgrowth. However, tRNA processing has not been extensively studied in these conditions, and knowledge of these mechanisms is important to understand long-term stress survival. Methods:To gain further insight into tRNA processing during spore germination and outgrowth, the expression of the single copy tRNA Cys gene was analyzed in the presence and absence of 1.2 M NaCl in Bacillus subtilis using RNA-Seq data obtained from the Gene Expression Omnibus (GEO) database. The CLC Genomics work bench 12.0.2 (CLC Bio, Aarhus, Denmark, https://www.qiagenbioinformatics.com/) was used to analyze reads from the tRNA Cys gene. Results:The results show that spores store different populations of tRNA Cys-related molecules. One such population, representing 60% of total tRNA Cys, was composed of tRNA Cys fragments. Half of these fragments (3´-tRF) possessed CC, CCA or incorrect additions at the 3´end. tRNA Cys with correct CCA addition at the 3´end represented 23% of total tRNA Cys, while with CC addition represented 9% of the total and with incorrect addition represented 7%. While an accumulation of tRNA Cys precursors was induced by upregulation of the rrnD operon under the control of σ A -dependent promoters under both conditions investigated, salt stress produced only a modest effect on tRNA Cys expression and the accumulation of tRNA Cys related species. Conclusions:The results demonstrate that tRNA Cys molecules resident in spores undergo dynamic processing to produce functional molecules that may play an essential role during protein synthesis.
