PMC

Distribution of core sporulation genes conserved in the Epulopiscium and C. lentocellum genomes by regulon. Venn diagrams represent the conservation of genes in the four sporulation-specific sigma factor regulons. Circle size corresponds to the number genes on the core list for B. subtilis (outermost circle), C. lentocellum (middle circle) and Epulopiscium (inner circle). The numbers below each diagram indicate the total number of genes from B. subtilis in each regulon. Some genes were counted more than once if they are members of multiple regulons as indicated in Table 

An alignment of Spo0A homologs. The predicted amino acid sequences of Spo0A from B. subtilis 168, B. anthracis Ames, C. acetobutylicum ATCC 824, C. botulinum ATCC 3502, Cellulosilyticum lentocellum DSM 5427 and Epulopiscium sp. type B were aligned using CLUSTALΩ. The conserved phosphorylation site (highlighted in yellow), the conformational switch (in green) and the DNA recognition helix (light blue) are found in all homologs. The connector segment (outlined in black) links the upstream phospho-acceptor and downstream effector domains. Shaded bars below the effector domain indicate the helix-turn-helix (HTH) DNA binding motif.

Epulopiscium engulfment model. The Epulopiscium genome codes for all of the genes known to be essential for engulfment in B. subtilis, except spoIIM and spoIIQ which are also absent in C. lentocellum. A) SpoIID and SpoIIP assemble into a complex (red ovals) at the division septum and degrade the septal peptidoglycan. B) As the mother-cell membrane wraps around the offspring, the IIDP complex tracks along the leading edge where it is involved in interactions with the mother-cell peptidoglycan and synthesis of offspring cell wall. C) When it reaches the cell tip, membrane fusion is mediated by SpoIIIE (yellow circle). During engulfment, SpoIIIAH (green rectangles) produced in the mother cell and a hypothetical protein (blue rectangles) from the offspring cell bind and prevent backward movement of the mother-cell membrane. In this diagram, black lines indicate membranes and grey peptidoglycan.

Conservation of the B. subtilis sporulation regulatory cascade in Epulopiscium sp. type B. Sporulation-specific sigma factors (circles), associated transcription factors (diamonds) and other signal transduction or regulatory proteins involved in sigma activation (rectangles) are shown. Colors of the proteins indicate the gene presence in Epulopiscium (green), on the core list but not in Epulopiscium (red), and absence from the core list (blue). Control of gene expression is indicated by dotted lines and arrows. Signaling pathways and other protein interactions are denoted with solid lines and arrows. Temporal transcriptional progression through the cascade is shown by the position on the diagram with earlier stages near the top. A detailed explanation of the regulatory cascade as it occurs in B. subtilis is provided in the text. Figure is adapted from de Hoon et al. (2010).

The life cycles of B. subtilis and Epulopiscium sp. type B. A) In a favorable environment, B. subtilis undergoes growth and division. B) When nutrient limitations become critical, the cell may develop an endospore. Shown here are the morphological stages described for sporulation. The temporal and spatial activation of Spo0A and the four sporulation-specific sigma factors are shown. The grey circle around the forespore indicates the cortex. The thick black circle around the forespore at stage V and beyond represents the spore coat. C) Earliest stages of offspring development in Epulopiscium sp. type B are based on the similar morphological transitions described for sporulation in B. subtilis. See text for a detailed explanation of the process. Offspring frequently initiate the next round of reproduction prior to exiting the mother cell. Those stages that are seen in offspring still within their mother cell are highlighted with grey boxes. For all diagrams, DNA is shown in blue.