Bacterial Spores

A spore is a dormant stage in which the bacterium can survive despite unfavourable external conditions. The spore is characterized by zero metabolism, high chemical and physical resistance, high lightfastness and low water content. An endospore is a spore that forms from inside a bacterial cell, unlike an exospore. Endospores are formed by some G+ bacteria, specifically the genera Bacillus and Clostridium. Exospores are formed by the class Actinobacteria.

Sporation and spore structure

Sporulation

The process of sporulation begins with DNA replication and asymmetric cell division. The smaller part forms a double-membrane-coated spore. The larger part is called the sporangium and lyses when the spore is finished forming.

Spores of Bacillus subtilis (green)

Structure of the Bacterial Spore

The spore is a protoplast, contains a genome, a small amount of proteosynthetic apparatus and large amounts of calcium and k. dipicolin, cytochromes are absent.. Energy is provided by glycolysis. The spore contains almost no water. Water is replaced by calcium, forming calcium-dipicolinate bridges. The envelope is made up of several layers:

1. inner cytoplasmic membrane
2. a layer of peptidoglycans,
3. cortex - concentric layers of peptidoglycans - provides resistance,
4. outer membrane,
5. spore coat (protein rich in cysteine, insoluble in water) - provides resistance to UV and ionizing radiation.

1, 4 – central; 2, 3, 5 – terminal; 6 – Lateral; 3–6 Spora bubbling rod

Spore formation of the genus Bacillus (phase contrast)

Examples of bacterial spore morphology

Shape

• Oval - often; Bacillus anthracis, Clostridium botulinum;
• Round– Clostridium tetani.

Relative size to cell thickness

• Spora bubbling rod – C. botulinum, C. tetani;
• Spora non-bubbling rod – B. anthracis.

Placement

• Terminal – C. tetani;
• subterminal (paracentral) placement – C. botulinum;
• central placement – C. novyi.

Germination

Germination is the process by which a spore turns back into a vegetative cell. The whole process has 3 stages:

1. Spore activation – activation requires disruption of the spore shell structure. Disruption can occur e.g. mechanically, by pH, by temperature change
2. Germination (germination) - water uptake, hydrolysis of the cortex, loss of resistance, breakdown of stabilizing proteins.
3. Differentiation phase - formation of new proteins - formation of vegetative cell.

Spore resistance

Spore resistance is very high. For example, C. tetani spores require a 90-minute boil (at 100 °C), C. botulinum spores require a five-hour boil.. The spores also withstand disinfectants such as ethanol, phenol, surfactants. Sporicidal agents include e.g. ethylene oxide, beta-propiolactone, concentrated alkalis and acids, with prolonged exposure also formaldehyde, chloramine, peracetic acid, autoclaving (20 min. hot steam at a pressure of 2 atm and 120 °C). They are so resistant because they contain high concentrations of potassium, stabilising macromolecules and almost no water. In the form of spores, bacteria can survive for hundred of years, as evidenced, among other things, by the fact that Patočka revived bacterial spores from the intestinal contents of mummified medieval corpses in Klatovy.

Links

Sources

• JANSKÝ, Petr. Zpracované otázky z mikrobiologie [online]. [cit. 2012-01-30]. <https://www.yammer.com/wikiskripta.eu/uploaded_files/3804405>.

Bibliography

• BEDNÁŘ, Marek – SOUČEK, Andrej – FRAŇKOVÁ, Věra. Lékařská mikrobiologie : Bakteriologie, virologie, parazitologie. 1. edition. Praha : Marvil, 1996. 558 pp. ISBN 8023802976.

• HURYCH, Jakub, et al. Lékařská mikrobiologie. 2020. edition. 2020. ISBN 978-80-7553-844-4.