Student Reader


Endospores are produced by sporulation. Endospores are differentiated cells highly ressistant to heat, chemicals & radiation. They are strongly refractile, impermeable to most dyes. Outermost layer is the exosporium, a thin protein covering. Within this are spore coats composed of spore-specific proteins. Then the cortex, composed of loosly corss-linked peptidoglycan. Then the core or spore protplast. Core wall, cm, cm, nucleoid, ribosomes & other cellular essentials. Differs from vegetative cell based on structure found outside core wall. Characteristic of endospores is dipicolinic acid. Located in the core. Endospores enriched in calclium ions, combined with dipicolinic acid. Repressents 10% of dry wight.

Intercalates in DNA & stabliizes it to heat denaturation. Calcium dipicolinate reduces H2O content of core. Dehydrations confers resistance to chemicals like H2O2 (hydrogen peroxide) & causes enzymes remaining in core to become inactive. pH of core one unit lower than vegetative cell cytoplasm. Small acid-soluble proteins in high concentration (SASPs). Made during sporulation & have 2 functions: bind tightly to DNA & protet it from UV, dessication & dry heat. SASPs make DNA the A form. They also function as a carbon & NRG source for the outgrowth of a new vegetative cell from endospore, process caled germination.

CharacteristicVegetative CellEndospore
StructureGram-positive cell; a few Gram-negative cellsThick spore cortex; spore coat; exosporium
Calcium contentLowHigh
Dipicolinic acidLowHigh
Enzymatic activityHighLow
Metabolism (O2 Uptake)HighLow or absent
Macromolecular synthesisPresentAbsent
mRNAHighLow or absent
Heat resistanceLowHigh
Radiation resistanceLowHigh
Chemical resistanceLowHigh
Stability by dyesStainableSpecial methods only
Lysozyme actionSensitiveResistant
H2O contentHigh, 80-90%Low, 10-25% in core
Small acid-soluble ssp genesAbsentPresent
Cytoplasmic pH75.5-6.0 in core