Endospore
1. Spore central
2. Spore terminal with inclusion body (protein)
3. Spore terminal, bacterium expanded in a club shape
4. Spore central, bacterium expanded in a spindle shape ("Clostridium shape")
5. Spore terminal, round = plectridium
6. Spore lateral, bacterium distended in a spindle-shaped manner
As Endospore refers to a Überdauerungsform formed within an organism or a cell. In contrast, exospores are formed outside of the organism.
Endospores in bacteria
education
Some Gram-positive bacteria form endospores ( sporulation ) in response to starvation . A lack of guanine nucleotides in the cytoplasm triggers an inequitable (unequal) division of the protoplast within the cell wall and a subsequent endocytosis- like process that forms the spore. In contrast to most other spores, endospores are predominantly not forms of reproduction, since each cell usually only forms one endospore and dies when it is released; only in rare cases (for example Anaerobacter polyendosporus ) several (up to seven) endospores are formed.
Known endospore formers are many species of the genera Bacillus and Clostridium , in particular Bacillus anthracis ( anthrax ), Clostridium botulinum ( botulism ) and Clostridium tetani ( tetanus ). But other genera such as Desulfotomaculum , Sporolactobacillus , Sporosarcina and Thermoactinomyces can form endospores. They all belong to the Firmicutes department .
Other genera of endospores are:
- Acetonema , Alkalibacillus , Ammoniphilus , Amphibacillus , Anaerobacter , Anaerospora , Aneurinibacillus , Anoxybacillus
- Brevibacillus
- Caldanaerobacter , Caloramator , Caminicella , Cerasibacillus , Clostridiisalibacter , Cohnella
- Dendrosporobacter , Desulfosporomusa , Desulfosporosinus , Desulfovirgula , Desulfunispora , Desulfurispora
- Filifactor , Filobacillus
- Gelria , Geobacillus , Geosporobacter , Gracilibacillus
- Heliobacterium , Heliophilum
- Lentibacillus
- Mahella , Moorella
- Oceanobacillus , Ornithinibacillus , Oxalophagus , Oxobacter
- Paenibacillus , Paraliobacillus , Pelospora , Pelotomaculum , Piscibacillus , Pontibacillus , Propionispora
- Salinibacillus , Salsuginibacillus , Sporacetigenium , Sporoanaerobacter , Sporobacter , Sporobacterium , Sporohalobacter , Sporomusa , Sporotalea , Sporotomaculum , Syntrophospora
- Tenuibacillus , Tepidibacter , Terri Bacillus , Thalasso Bacillus , Thermoacetogenium , thermal alkaline Bacillus , Thermoanaerobacter , Thermoanaeromonas , thermal Bacillus , Thermovenabulum , Tuberibacillus
- Virgibacillus , Vulcanobacillus
properties
Important characteristics of the bacterial endospores are on the one hand their high resistance to harmful environmental influences and on the other hand their metabolic inactivity ( dormancy ). A metabolism cannot be proven ( cryptobiosis ). They have a high resistance to heat, cold, dehydration, various types of radiation , chemical agents, lysozyme and extreme pH values . The resistances are based on the various morphological peculiarities of the spore: the multilayered shell ( protein coat and peptidoglycan cortex ), the very dense and poorly permeable inner spore membrane and the low water content in the spore core. The DNA of the endospores is protected by SASPs (small acid soluble [spore] proteins). The impermeability of the spore shell to radiochemical products and the binding of free radicals by sulfur-containing components give them resistance to ionizing radiation .
Bacterial endospores contain calcium dipicolinate , a characteristic substance that does not occur in vegetative cells.
Bacterial endospores as dormant stages can persist for a long time; viable spores were found in the stomach of a bee preserved in amber , which are over 25 million years old. However, it is discussed whether the investigated material was contaminated with recent endospores. What is certain, however, is that endospores can survive for a very long time.
Bacterial endospores can be seen in the phase contrast microscope as highly refractive, bright structures. Due to the impermeability of the casings to a large number of substances, which gives them resistance to these substances, they do not absorb any dye in the usual dyeing processes, but they can be colored using a special dyeing process ( endospore dyeing ).
germination
Under certain environmental conditions, active (“vegetative”) developmental stages of the bacteria can emerge from endospores. A single-celled bacterium develops from an endospore. There are three phases: In most cases, the endospore must first be activated. The activation probably consists essentially of an increase in the permeability of the spore envelope, so that material inducers (signal substances) of the spore germination can penetrate from the outside. This can happen through aging (promoted by high temperatures) or through mechanical damage. If, after this phase of activation, certain species-specific inductors are present in the outside environment, germination in the narrower sense (English germination ) is initiated. Those substances act as germination inducers which are usually present in the natural environment under conditions which are favorable for the growth of the bacterium. Examples of this are energy sources (e.g. glucose ) and nutrients (e.g. adenosine and L-alanine ) that can be used by the bacterium . During germination, the spore coat is weakened by partial degradation. When outgrowth (English outgrowth ) the cell increases due to water absorption and growth (formation of new cell components) in volume, breaks the spore coat and forms a new cell wall .
supporting documents
- ↑ Peter Setlow: Spore Resistance Properties . In: Microbiology Spectrum . American Society for Microbiology Press, 2014.
- ↑ RJ Cano, MK Borucki: Revival and identification of bacterial spores in 25- to 40-million-year-old Dominican amber . In: Science. Vol. 268, No. 5213, 1995, pp. 1060-1064. doi : 10.1126 / science.7538699
