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BY2012 Microbiology Bacterial Endospores Bacterial Endospores – Variation in Endospore Morphology Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore; sometimes endospores are subterminal; spores may cause the spore mother cell to appear swollen where the spores are located (3 – 6); (2) has in addition a parasporal crystal toxin Steps in Endospore Formation Bacillus Endospores – Spore Stain Malachite Green spore stain -Endospores stain green and vegetative cells stain red Bacillus subtilis Endospores Spores are subterminal with very little swelling of vegetative cells; Malachite Green spore stain endospores stain green and vegetative cells stain red Bacillus Endospores Schaeffer-Fulton Staining Method Mixture of vegetative cells (red, Safranin counterstain) of a Bacillus species with its free endospores (blue) Bacillus anthracis - Anthrax Gram stain, endspores unstained, central and vegetative cells non-swollen; free endospores also present (arrowed) Bacillus anthracis - Anthrax Spore stain, endspores staining greyish-green, vegetative cells stain red Bacillus thuringiensis Phase contrast microscopy of B. thuringiensis cells producing endospores (clear refractile) and parasporal crystals (insecticidal toxins, arrowed) Bacillus thuringiensis Parasporal Crystalline Toxin Scanning electron micrograph of purified crystal toxin of B. thuringiensis – used in the commercial insecticides Dipel and Thuricide to kill caterpillars Bacillus sp. Endospore Spore coat Endospore Electron micrograph of Bacillus bacterium in section showing the endospore with its thick protective spore coat Bacterial Endospores Colourised scanning electron micrograph of Clostridium species that is forming spores (swollen area, blue arrow); flagella are present on the bacterial cells (blue, yellow arrow) Bacterial Endospores – Clostridium sp. Gram Stain In Gram stain the spores do not stain and appear as clear areas in stained cells (arrowed). Here the spores are sub-terminal and swollen Bacterial Endospores – Clostridium tetani - Tetanus Gram stain of Clostridium tetani showing swollen, round, terminal endospores giving the bacteria a drumstick appearance Bacterial Endospores – Clostridium tetani - Tetanus Gram stain of Clostridium tetani showing swollen, round, terminal endospores giving the bacteria a drumstick appearance Clostridium botulinum - Botulism Gram stain showing terminal or subterminal oval spores (arrows) in vegetative cells Clostridium sp. Endospore Condensed DNA Spore coat Endospore Cortex Electron micrograph of Clostridium bacterium in section showing the endospore with its thick protective spore coat
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