Endospores A - E-Lecture - De Montfort University

e-Lecture – Endospores A Endospore Biology Dr Raymond N Allan @RayAllan1980 [email protected] Overview Bacterial endospores – Importance Structure Formation Function...

e-Lecture – Endospores A Endospore Biology Dr Raymond N Allan @RayAllan1980 [email protected] Overview Bacterial endospores – Importance Structure Formation Function Important spore-forming bacteria & relevance – Bacillus sp. Clostridium sp. @RayAllan1980 [email protected] Learning Outcomes By the end of this e-Lecture series you should be able to: Describe what an endospore is, including its structure and function Describe the processes of sporulation and germination Discuss examples of sporulating bacteria and their importance @RayAllan1980 [email protected] What are endospores? Antarctica - Volcano Endospores (spores) are formed various bacterial species e.g. Bacillus sp. and Clostridium sp. Spores are produced when bacteria encounter unfavourable conditions Extreme changes in temperature Spore Lack of nutrients (starvation) Can remain dormant for extremely long Spore formation periods of time Bacterium (vegetative cell) Allan RN @RayAllan1980 [email protected] Why do bacteria produce spores? They offer protection against extreme conditions: Extreme Acid Radiation Toxic temperatures chemicals They allow bacteria to disperse in the environment: In here! @RayAllan1980 [email protected] Why spores are important They are very resistant structures so we need appropriate sterilization processes Autoclaving at 121oC is sufficient to kill most bacterial spores They can be responsible for causing a variety of infections Food poisoning, tetanus, anthrax They have beneficial uses: Vaccine delivery Probiotics @RayAllan1980 [email protected] Spore Structure Spores have a very distinct structure from vegetative cells Exosporium – outermost layer, made up of proteins Spore coat – layers of spore-specific proteins Cortex – loosely linked peptidoglycan Spore coat Cortex Exosporium DNA H.S. Pankratz Core wall T.C. Beaman P. Gerhardt Fig 2.30: Brock Biology of Microorganisms (15th Ed) @RayAllan1980 [email protected] Spore Structure – The Core The spore core consists of: Cell wall (core wall) Cytoplasmic membrane Cytoplasm DNA Ribosomes Other essentials Core H.S. Pankratz T.C. Beaman P. Gerhardt Fig 2.30: Brock Biology of Microorganisms (15th Ed) @RayAllan1980 [email protected] Spore Structure – The Core Key Characteristics: One chemical characteristic of endospores NOT found in vegetative cells is dipicolinic acid (DPA) High in calcium ions (Ca2+), most of which is combined with dipicolinic acid Core pH is lower than that of a vegetative cell Partially dehydrated (10-25% of water content of cell) – core cytoplasm has a gel-like consistency Contains high levels of core-specific proteins called small acid-soluble proteins (SASPs) produced during sporulation DNA-binding proteins that protect the bacterial DNA from chemical and enzymatic degradation @RayAllan1980 [email protected] Visualising Spores Vegetative cell Fixation spore Phase contract microscopy Stain with Malachite Green Heat R. Allan Spores are highly refractive - they appear bright Decolourise Endospore staining with water Spores are very impermeable to dyes so often appear as unstained regions within cells stained Counter-stain with basic dyes with safranin @RayAllan1980 [email protected] Using spores for identification Spores can form in different locations within the bacterial cell: R. Allan R. Allan Terminal Subterminal Central Lateral Spore location within cell can help in identification: Bacillus cereus - Central Distended (swollen) Bacillus subtilis - Subcentral Clostridium tetani - Terminal Fig 2.27: Brock Biology of Microorganisms (15th Ed) @RayAllan1980 [email protected] Sporulation @RayAllan1980 [email protected] Germination Endospores can remain dormant for hundreds (maybe millions) of years: Tombs of pharaohs Fossilized bee trapped in amber Frozen permafrost BUT they can germinate very quickly (sometimes within a few minutes) Spore germination occurs in 3 phases: Activation Germination Outgrowth @RayAllan1980 [email protected] Germination Activation Germination Outgrowth Triggered by heating Release of H+ ions (increases core pH) Enzyme activation at sub-lethal temperatures or in response to nutrients Release of DPA SASP degradation Amino-acids Sugars Hydration of core with H2O Macromolecular synthesis Nucleosides (or combinations) Hydrolysis of peptidoglycan Spore escape Swelling of core @RayAllan1980 [email protected] Summary Not all bacterial species can produce endospores, only certain species of Gram-Positives Endospores are different from vegetative cells and produced in response to stressed environments They are resistant to a lot of unfavourable conditions (chemicals, radiation, enzymes, heat) and can remain dormant for many years They are responsible for causing a number of important human infections (anthrax, gas gangrene, tetanus and botulism) @RayAllan1980 [email protected] Further Reading Key Textbook: Brock Biology of Microorganisms 15th Edition Chapters 2 & 7 - Endospores @RayAllan1980 [email protected]