Growth of Microbes

Living organisms grow and reproduce. The growth indicates that an organism is in active metabolism. In plants and animals one see the increase in height or size. In a butterfly, a small larva hatching from egg grows in size, moults, pupates and become an adult butterfly through metamorphosis. Growth in a common use refers to increase in size but with microorganisms particularly with bacteria, this term refers to changes in total population rather than increase in size or mass of an individual organism. With fungi linear growth of hyphae and radial growth of colony is observed for growth on solid media but a biomass or mycelial dry weight on liquid media. In unicellular fungi like yeast that reproduce by fission or budding the population change is considered as growth.

The change in population in bacteria chiefly involves trans verse binary fission in most of the bacteria while budding is observed in Hyphomicrobium. In actinomycetes, fragmentation of hyphae and sporulation results in population change. In yeasts, budding and fission are observed that this depends upon the species. In fungi, growth fragmentation asexual and sexual spores serve as propagates for population increase.

The transverse binary fission, an asexual reproductive process is the most common in the growth cycle of bacterial population. A single cell divides after developing a transverse septum (cross wall) and continues to grow by continuous dividing with out cell death till it is subjected to stress.

A cell dividing by binary fission is immortal unless subjected to stress by nutrient depletion or environmental stress. Therefore a single bacterium continuously divides. One cell divides providing two cells and two cells divide giving four and so on. Therefore the population increases by geometric progression.

1   2    4    8    16    32———2n

1    2    22    23    24    25———2n

When a single bacterium is incubated into the liquid medium in flask and incubated, bacterium divides by fission and attains a period of rapid growth in which cells multiply at an exponential rate. If the logarithmic number

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