Sporulation in Bacillus


  • Many microorganisms including prokaryotes and eukaryotes respond to adverse conditions by forming spores.
  • When the good condition returns once, the spore germinates and the microorganism returns to its normal life cycle.
  • Among the bacterial group, the genus Bacillus is well known for the formation of endospores which means the spores formed inside the mother cell.
  • Prior to endospore formation, the cell divides asymmetrically.
  • The smaller cells develop into the endospore which is usually surrounded by the large mother cell.
  • Once the development is completed, the endospores are released by the bursting of mother cell.
  • Endospore formation in Bacillus is generally triggered by the adverse external conditions like starvation, desiccation, or growth-inhibitory temperatures.

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  • Infact, multiple aspects of environment get monitored by a group of five sensor kinases.
  • These function via a phosphotransfer relay system whose mechanism is similar to two-component regulatory system but is considerably a complex process.
  • The net result of multiple adverse conditions is the successive phosphorylation of several proteins which are called sporulation factors, culminating with the sporulation factor SpoOA.
  • When SpoOA is highly phosphorylated, sporulation process gets initiated.


Development of the endospore

sporulation in bacllusको लागि तस्बिर परिणाम   sporulation in bacllusको लागि तस्बिर परिणाम

  • Once triggered, endospore development is under the control of four different sigma factors, two of which (σF and σG) activates genes needed inside the developing endospore itself.
  • Remaining two (σE and σK) are responsible for activating genes needed in the mother cell that surrounds the endospore.
  • The sporulation signal transmitted via SpoOA activates σF in the smaller cell that is destined to become the endospore.
  • σF is already present but is in inactive form due to binding with anti-sigma factor.
  • The signal from SpoOA activates a protein that binds to the anti-sigma factor.
  • The anti-sigma factor then gets inactivated and liberates σF.
  • Once free, σF binds to RNA polymerase and allows transcription (inside the spore) of genes whose products are essential for the next stage of sporulation.
  • These include the gene for the sigma factor σG and the genes for proteins that cross into the mother cell and activate σE.
  • Active σE is required for transcription inside the mother cell of yet more genes, including the gene for the sigma factor σK.
  • The sigma factors σG (in the endospore) and σK ( in the mother cell) are required for transcription of genes which are needed in the later stages of sporulation process.
  • One fascinating aspect of endospore formation is that it is preceded by what is in effect cellular cannibalism.
  • Those cells where SpoOA has already been activated secrete a protein that lyses nearby cells of the same species whose SpoOA protein has not been activated.
  • This toxic protein is accompanied by a second protein that delays sporulation of neighboring cells.
  • Cells that are committed to sporulation also make antitoxin protein to protect themselves against the effects of their own toxin.
  • Their sacrificed sister cells are used as a source of nutrients that is required by developing endospores.
  • Shortages of certain nutrients such as phosphate increase the expression level of the toxin-encoding gene.


i) https://www.nature.com/articles/nrmicro2921#:~:text=Sporulation%20in%20Bacillus%20subtilis%20involves,composed%20of%20dozens%20of%20proteins.

ii) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4078662/

iii) http://microbialcell.com/researcharticles/2020a-riley-microbial-cell/

Sporulation in Bacillus