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Reproduction in Bacteria 1. By Binary fission It occurs normally under favorable conditions. The cell elongates and becomes constricted at its middle. The cytoplasm divides and the constriction increases until the cell is split into two cells ( Fig. 5). The generation time (time needed for the cell to divide into two) differs according to species and prevailing conditions. The generation time ranges from 20 minutes to 6 hours. In 24 hours , under optimum conditions a single individual would produce several billions, a behavior which does not prevail due to the interference of other factors. Fig. 5. Binary fission in bacteria.
2. By Endospore formation. They are small spherical or oval bodies formed within the cell, due to the contraction of the cytoplasm. They become surrounded with a thick wall and appear as glistening bodies which stain poorly. They are capable of resisting unfavorable environmental conditions for many years. They can withstand boiling, desiccation and high concentrations of disinfectants. When conditions become favorable, the spores germinate and are transformed into vegetative cells. Spore formation usually occurs in rod-shaped bacteria (Bacillus and Clostridium). The formed spore may be located either : a) centrally , b) terminally or c) sub-terminally (Fig. 6). In some species the spore diameter is greater than the width of the bacterial cell. Central Terminal Sub-terminal endo-spore endo-spore endo-spore Fig. 6. Endospore formation
The sporulation process is not one of multiplication , since most rod-shaped forms produce only one spore each. It is considered as a method for keeping the organism intact and surviving during un-favourable conditions.
3. By Conidia formation It occurs in members of certain families belonging to Actionmycetes, e.g. Streptomyces. The ends of the filaments become septated forming a chain of conidia similar to those produced by true fungi. These conidia can resist desiccation (similar to endospores) but they cannot resist high temperatures.
