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Levels and Characteristics of mRNAs in Dormant Spores of Firmicute Species

ABSTRACT: Spores of Bacillales and Clostridiales species contain 100s of different mRNAs, and their major function in Bacillus subtilis is to provide ribonucleotides for new RNA synthesis when spores germinate. In new work, RNA was isolated from spores of five Bacillales and one Clostridioides species and relative spore mRNA levels were determined by RNA-seq. Determination of RNA levels in single spores allowed calculation of RNA nt/spore, and assuming mRNA is 3% of spore RNA allowed calculation that only ~6% of spore mRNAs were present at ≥ 1/spore. Bacillus subtilis, Bacillus atrophaeus and Clostridioides difficile spores had 49, 42 and 51 mRNAs at >1/spore, respectively. Numbers of mRNAs at ≥1/spore were ~10 to 50% higher in Geobacillus stearothermophilus and Bacillus thuringiensis Al Hakam spores, respectively, and ~ 4-fold higher in Bacillus megaterium spores. Notably, in all species: i) many of the 60 most abundant spore mRNAs were transcribed by RNA polymerase with forespore-specific s factors; ii) some to many of the most abundant spore mRNAs encoded orthologs of those encoded by abundant B. subtilis spore mRNAs and proteins present in dormant spores ; and iii) some spore mRNAs were likely transcribed in the mother cell compartment of the sporulating cell. Indeed , analysis of the coverage of RNA-seq reads on mRNAs from all six species suggested that abundant spore mRNAs were at least somewhat fragmented. This observation was confirmed by RT-qPCR analysis of three abundant mRNAs each from B. subtilis and C. difficile spores. These data add to a growing body of evidence indicating that the great majority of mRNAs in spores of Firmicutes are degradation and function as a ribonucleotide depot for new RNA synthesis when spores germinate.

ORGANISM(S): Bacillus atrophaeus ATCC 9372 Clostridioides difficile 630 Bacillus subtilis Priestia megaterium QM B1551 Geobacillus stearothermophilus ATCC 12980 Bacillus thuringiensis str. Al Hakam

PROVIDER: GSE173854 | GEO | 2021/05/05

REPOSITORIES: GEO

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Project description:Description Bacillus subtilis forms highly resistant, metabolically inactive spores upon nutrient limitation. These endospores pose challenges to the food and medical sectors. Spores reactivate their metabolism upon contact with germinants through germination and outgrowth, and then develop into vegetative cells. However, the mechanism of the activation of the molecular machinery that triggers spore germination and outgrowth is unclear. To gain further insight into spore germination and outgrowth, the transcriptome and proteome changes during Bacillus subtilis spore conversion to vegetative cells were analyzed. The transcriptome analysis also allowed us to trace the different functional groups of genes expressed during this conversion. For each time-point sampled, the change in the spore proteome was quantitatively monitored relative to the reference proteome of 15N metabolically labelled vegetative cells. Of the quantified proteins, 60 percent are common to vegetative cells and spores, indicating that spores have a minimal set of proteins sufficient for the resumption of metabolism upon completion of germination. The shared proteins thus represent the most basic survival kit for spore-based life. Until the phase transition, defined as the completion of germination, we observed no significant change in the proteome or the transcriptome. Our analysis identified 34 abundant mRNA transcripts in the dormant spores, at least 31 of which were rapidly degraded after the phase transition. We observed 3152 differentially expressed genes, and demonstrated with our mass spectrometry analyses the differential expression of 323 proteins. Our data show that 173 proteins from dormant spores, both proteins unique to spores and proteins shared with vegetative cells, are lost after completion of germination. Further analysis is required to functionally interpret the observed protein loss. The observed diverse timing of the synthesis of different protein sets reveals a putative core-strategy of the revival of life starting from the B. subtilis spore.

Project description:The SOS response to DNA damage in bacteria is a well-known component of the complex transcriptional responses to genotoxic environmental stresses such as exposure to reactive oxygen species, alkylating agents, and many of the antibiotics targeting DNA replication. However, bacteria such as Bacillus subtilis also respond to conditions that perturb DNA replication via a transcriptional response mediated by the replication initiation protein DnaA. In addition to regulating the initiation of DNA replication, DnaA directly regulates the transcription of specific genes. Conditions that perturb DNA replication can trigger the accumulation of active DnaA, activating or repressing transcription of genes in the DnaA regulon. We report here that simply growing B. subtilis in LB medium altered DnaA-dependent gene expression in a manner consistent with the accumulation of active DnaA, and that this was part of a general transcriptional response to manganese limitation. The SOS response to DNA damage was not induced under these conditions. One of the genes positively regulated by DnaA in Bacillus subtilis encodes a protein that inhibits the initiation of sporulation, Sda. Sda expression was induced as cells entered stationary phase in LB but not in LB supplemented with manganese, and induction of Sda inhibited sporulation-specific gene expression and the onset of spore morphogenesis. In the absence of Sda, manganese-limited cells initiated spore development but failed to form mature spores. These data highlight that DnaA-dependent gene expression may influence the response of bacteria to a range of environmental conditions, including conditions that are not obviously associated with genotoxic stress. Cultures of Bacillus subtilis strains with the genetic background of sda+ or delta-sda were grown in LB and LB+100 micro-M MnCl2 at 37degC until 3 hours after the onset of stationary phase. At 3 timepoints, aliqots were removed and RNA isolated for each culture: 1) Mid exponential, 2) T0 (onset of stationary phase), and 3) T3 (3 hours after onset of stationary phase). cDNA was prepared from each sample using 10 micro-g of RNA. Reference cDNA was prepared from pooled RNA from all samples (common reference for all arrays).

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Levels and Characteristics of mRNAs in Dormant Spores of Firmicute Species

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