Sporulation in Bacillus subtilis: Difference between revisions

[[File:Sporulation in Bacillus subtilis.jpg|alt=Figure Caption: The Bacillus subtilis (Stage I) in vegetative growth is in unfavorable conditions, so it begins the process of sporulation. Examples of unfavorable conditions are an environment that lacks the required nutrients, is too hot, or too cold. Asymmetric (unequal) division occurs from the tightening of the Z-ring (Stage II). The Z-ring is multiple FtsZ proteins assembled into a ring that depolymerizes to cause an inward constriction, which will form the septum that results in two daughter cells. The mother cell, which is the bigger of the two daughter cells, engulfs the pre-spore (Stage III). Next, the cortex (Stage IV) and the coat (Stage V) form around the spore. The cortex is made of peptidoglycan and the coat is composed of several layers of specific proteins. Once the spore is mature, the cell lyses (Stage VI and VII). Thus, a free endospore is formed that can withstand harsh environments. This endospore can later germinate into a vegetative cell. Vegetative cycle occurs in favorable conditions, such as nutrient abundance and a moderate temperature. This is a cycle of medial division and growth creating more vegetative Bacillus subtilis.|thumb|187x187px|Fig1. The sporulation process of Bacillus subtilis]]

''[[Bacillus subtilis]]'' is a rod-shaped, [[Gram-positive bacteria|Gram-positive]] [[bacteria]] that is naturally found in soil and vegetation, and is known for its ability to form a small, tough, protective and metabolically dormant [[endospore]]. ''B. subtilis'' can divide symmetrically to make two [[Cell division|daughter cells]] ([[Fission (biology)|binary fission]]), or asymmetrically, producing a single endospore that is resistant to environmental factors such as heat, [[desiccation]], radiation and chemical insult which can persist in the environment for long periods of time. The endospore is formed at times of nutritional stress, allowing the organism to persist in the environment until conditions become favourable. The process of endospore formation has profound [[Morphology (biology)|morphological]] and [[Physiology|physiological]] consequences: radical post-replicative remodelling of two progeny cells, accompanied eventually by cessation of metabolic activity in one daughter cell (the spore) and death by [[lysis]] of the other (the ‘mother cell’).

=== Commitment to sporulation ===

Although sporulation in'' B. subtilis'' is induced by starvation, the sporulation developmental program is not initiated immediately when growth slows due to nutrient limitation. A variety of alternative responses can occur, including the activation of [[Flagellum|flagellar]] motility to seek new food sources by [[chemotaxis]], the production of [[Antibacterial|antibiotics]] to destroy competing soil microbes, the secretion of hydrolytic [[enzyme]]s to scavenge extracellular proteins and [[polysaccharide]]s, or the induction of ‘[[Competence (biology)|competence]]’ for uptake of exogenous [[DNA]] for consumption, with the occasional side-effect that new genetic information is stably integrated. Sporulation is the last-ditch response to starvation and is suppressed until alternative responses prove inadequate. Even then, certain conditions must be met such as [[chromosome]] integrity, the state of chromosomal replication, and the functioning of the [[Citric acid cycle|Krebs cycle]].

=== Nature of regulation ===

Sporulation requires a great deal of time and also a lot of energy and is essentially irreversible, making it crucial for a cell to monitor its surroundings efficiently and ensure that sporulation is embarked upon at only the most appropriate times. The wrong decision can be catastrophic: a vegetative cell will die if the conditions are too harsh, while bacteria forming spores in an environment which is conducive to vegetative growth will be out competed. In short, initiation of sporulation is a very tightly [[Regulation of gene expression|regulated]] [[Biological network|network]] with numerous checkpoints for efficient control.

== Control points ==

Two [[Transcription (genetics)|transcriptional]] regulators, σH and Spo0A, play key roles in initiation of sporulation. Several additional proteins participate, mainly by controlling the accumulated concentration of Spo0A~P. Spo0A lies at the end of a series of inter-protein phosphotransfer reactions, Kin–Spo0F–Spo0B–Spo0A, termed as a ‘[http://en.wiktionary.org/wiki/phosphorelay phosphorelay]’. The regulation of these various factors controlling the accumulated concentration of Spo0A~P, and their interactions are described in detail in [http://commons.wikimedia.org/wiki/File:Gene_Regulatory_Network_for_Initiation_of_Sporulation_in_Bacillus_subtilis.png Figure2]:

[[File:Gene Regulatory Network for Initiation of Sporulation in Bacillus subtilis.png|thumb|Fig2. Gene Regulatory Network for Initiation of Sporulation in Bacillus subtilis]]

In the table below, the term ''''Activators'''' refers to genes/proteins that ultimately result in initiation of sporulation and ''''Repressors'''' refers to the ones that inhibit this initiation of sporulation.

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== Homologous networks in eukaryotes ==

Spores form a part of the life cycles of a diverse range of organisms such as many bacteria, [[plant]]s, [[algae]], [[Fungus|fungi]] and some [[protozoa]]. In ''[[Saccharomyces cerevisiae]]'' (Kingdom Fungi), the set of early genes activating sporulation is induced by Ime1 (Inducer of Meiosis 1) and a regulator of middle genes is Ndt80p.

== See also ==

* [[Bacillus]]

* [[Bacillus subtilis]]

== External links ==

* [http://genolist.pasteur.fr/SubtiList/ SubtiList - GenoList - Institut Pasteur]

* [https://www.youtube.com/watch?v=UHsqFjP1dZg Video - Sporulation in ''Bacillus subtilis'']

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{{二次利用|date=3 December 2023}}

[[Category:Bacillus]]

[[Category:Bacteriology]]

[[Category:Gram-positive bacteria]]