- Stages of sporulation
- Stage 0: Normal conditions
- Stage I: Axial filament formation stage
- Stage II: Pre-spore formation
- Stage III: Envelopment of the pre-spore
- Stage IV: synthesis of exosporium
- Stage V: synthesis of peptidoglycan
- Stage VI: Synthesis of soluble acids from the spore
- Stage VII: Cell lysis and endospore release
- References
The sporulation is the process of spore formation in biological systems. In plants and fungi it is a means of reproduction, while in bacteria it is a survival mechanism.
Fungal spores can be asexual or sexual in nature, functioning solely to form new filaments. Therefore, they are the means of propagation of these organisms. All filamentous fungi and most yeasts produce spores.
Spores under a fern leaf
In bacteria, sporulation occurs when conditions are not favorable, for example, lack of nutrients, excess heat or radiation, when there is desiccation, etc. Many bacteria can produce spores to improve their survival in adverse conditions.
Sporulation is not a mandatory stage of the cell's life cycle, but rather a disruption. Such latent forms are called endospores, cysts, or heterocysts (seen mainly in cyanobacteria), depending on the method of spore formation, which differs between various groups of bacteria.
Some primitive plants belonging to the cryptogams group also reproduce by means of spores. For example, mosses and ferns.
Stages of sporulation
Sporulation can be divided into several stages. In Bacillus subtilis bacteria, the entire sporulation process takes 8 hours to complete from stage 0 to stage VII.
Stage 0: Normal conditions
The bacterial cell is in its vegetative (normal) form.
Stage I: Axial filament formation stage
In this stage, the bacterial chromosome replicates and spreads forming an axial filament. These axial strands of genetic material are attached to the cytoplasmic membrane through the mesosome. The cell lengthens and uses its food reserve for the formation of the spore.
Stage II: Pre-spore formation
Asymmetric cell division occurs, a cell membrane septum forms near one end that encloses a small portion of DNA, thus forming the first version of the spore, a kind of "pre-spore."
Stage III: Envelopment of the pre-spore
The stem cell membrane grows around the pre-spore, enveloping it. The early spore now has two layers of membrane.
Stage IV: synthesis of exosporium
The stem cell chromosome disintegrates and exosporium synthesis begins. Next, the pre-spore begins to form a primordial crust between the two membranes that surround it. Eventually the cell becomes dehydrated.
Stage V: synthesis of peptidoglycan
The pre-spore produces a peptidoglycan shell between its original membrane and the mother cell membrane.
Stage VI: Synthesis of soluble acids from the spore
Dipicolinic acid is synthesized, which can incorporate calcium ions to form calcium dipicolonate. This promotes further dehydration of the cytoplasm and forms a coating layer.
Stage VII: Cell lysis and endospore release
The mature spore is released from the mother cell. The endospore, being a biological resistance structure, can remain inactive for years. When conditions are favorable, each endospore will germinate to give rise to a vegetative cell.
References
- Ghosh, J., Larsson, P., Singh, B., Pettersson, BMF, Islam, NM, Sarkar, SN,… Kirsebom, LA (2009). Sporulation in mycobacteria. Proceedings of the National Academy of Sciences, 106 (26), 10781–10786.
- Jabbari, S., Heap, JT, & King, JR (2011). Mathematical modeling of the sporulation-initiation network in Bacillus subtilis revealing the dual role of the putative quorum-sensing signal molecule PhrA. Bulletin of Mathematical Biology, 73 (1), 181–211.
- Karki, G. (2017). Bacterial Spore: structure, types, sporulation and germination. Recovered from: Online Biology Notes.
- Piggot, PJ, & Coote, JG (1976). Genetic aspects of bacterial endospore formation. Bacteriological Reviews, 40 (4), 908–62.
- Stephens, C. (1998). Bacterial sporulation: a question of commitment? Current Biology: CB, 8, R45-R48.