Sporulation and Theory of Endosymbiosis

Endospores

• Specialized spores

• Highly differentiated

• Formant cells

• Resistant to…

  • Heat

  • Radiation

  • Chemical exposure

  • Drying

  • Lack of nutrients

• Survival structures to endure unfavorable growth conditions

• Disperse via wind, water, animal gut

• Only present in some gram +

• Botulism, tetanus, anthrax

Types of endospores 

• Terminal endospores - form at an end

• Subterminal endospores - little bit inside terminal end

• Central endospore - middle 

Structure of endospores

• Outer - inner

  • Exosporium

  • Endspore coat

  • Outer spore membrane

  • Cortex

  • Inner membrane

  • Core

  • DNA  

Life cycle of endospore (simple) 

• Vegetative cell

• Sporulating cell + Developing endospore - poor growth conditions

• Sporulating cell + mature endospore = return to good growth condition

• Asymmetric cell division and forespore formation

• Mother cell engulfs forespore to form outer membrane

Endospore formation and germination

• Sporulation = vegetative cell differentiates to nongrowing, heat resistant, light refractive structure

• Triggered by limiting nutrients

• Dehydration blocks enzyme activity 

• Can remain dormant for years - converts rapidly back to vegetative

• Germination = nutrient availability 

• Three steps

  • Activation

  • Germination

  • Outgrowth

Endospore structure and features

• Special stains (malachite green)

• Many layers (core, inner membrane, cortex, outer membrane, endospore coat, exosporium)

• Contains dipicolinic acid rich in Ca2+

  • UV resistant = decrease DNA degradation/gene expression 

• Small acid-soluble spore proteins (SAPS) = bind/protect DNA as carbon energy source for outgrowth 

Vegetative cell vs endospore

• Vegetative

  • NO dipicolinic acid

  • PRESENT macromolecular synthesis 

  • Lysozyme SENSITIVE 

  • HIGH enzyme activity, respiration rate 

  • LOW heat/radiation/chemical resistance

• Endospore

  • dipicolinic acid

  • ABSENT macromolecular synthesis 

  • Lysozyme RESISTANT 

  • LOW enzyme activity, respiration rate 

  • HIGH heat/radiation/chemical resistance

Sporulation formation 

• Stimulus (nutrient depletion) = commits cell to forming endospore

• 6-10hrs

• 1. DNA duplicates

• 2. Cell sprites into sporangium + forespores (becomes endspore)

  • Asymmetric

• 3. Sporangium engults forespore = spore layers around forespore

• 4. Cortex + outer coat layers develop

• 5. Mature spore completely spore 

Germination

• Break dormancy of endspore

• Need good growth conditions

• chemical/environmental stimulus + H2O

• Enzymes degrade cortex = outer core exposed to H2O

  • Rehydration of core

  • Cell grows out of coat 

Endospore staining

• Malachite green

• High resistant to chemicals

• 1. Smear, air dry, heat fix slide

• 2. Malachite green added over smear 

• 3. 1 min stain (stain into endospore)

• 4. Rinse with H2O + safranin (counter stain for vegetative cells) 

Theory of Endosymbiosis 

• Prokaryotes = single-cells/no membrane bound organelles

• Endocytosis via bacterial cell (eating bacteria, odd time, stayed intact = photosynthetic)

• Cells living together (one inside other) = endosymbiosis

• Adapted to changing environment

• 1. chloroplast/mitochondria multiply same way as ancient bacteria

• 2. chloroplast/mitochondria contain own DNA/ribosomes

• 3. Both have 2 membranes (from one engulfing the other) 

  • Sma lipids/proteins as ancient one 

Early eukaryotes

• Infolding of membrane = nucleus has similar membranes

• absorption/symbiotic nature of mitochondria

• Chloroplast (only in photosynthetic) 

Prokaryote vs eukaryotic transcription, translation

• Prokaryote 

  • Concurrent (at same time)

  • DNA + RNA polymerase to make mRMA + ribosomes to make proteins 

• Eukaryote 

  • Translation and transcription occurs separately and inside the nucleus