Extrachromosomal factor determinants

Abstract

In the early days of bacteriology even eminent bacteriologists like Koch, Cohn and Migula believed in the doctrine of monomorphism - the constancy of bacterial species-despite conflicting observations made by Pasteur on attenuated strains of Bacillus anthracis. Any variants that were discovered were dismissed as contaminants or as "Aberrant" or "Degenerate" or "Involutionary" forms. Nowadays they might have called them "L" forms. The concept of variation began to be taken more seriously after the discovery of lactose-fermenting strains of E. coli which appeared in the papilla on the surface of a non-lactose fermenting strain, because such variants could hardly be contaminants or aberrant. There is evidence about another type of variation brought about by small genetic carrying particles in the cytoplasm. This has been shown by their non-random appearance during the growth of culture. These genetic-carrying particles which lie extrachromosomally are known as plamids and episomes.