Phenotypic Variations of Bacterial Properties
Phenotypic variations or modifications can appear due to the influences of environment on microbial cells. They change the rate of various metabolic reactions in response against external or internal challenges. Phenotypic variations are controlled by genome but don’t affect primary sequence of genome structures (genomic DNA). Sometimes modifications depend on alternative expression of different microbial genes.
Usually modifications are based on concerted variation of bacterial enzymatic activity, their induction or repression.
Basic factors, stimulating phenotypic diversity in bacterial populations, are related with the cultivation conditions for the microbial strain (temperature, humidity, salt concentrations, medium chemical composition, etc.) Also antibiotic and disinfectant action potentially increases the incidence of modifications. For instance, bacterial cells can transform into L-forms, devoid of cell wall.
Modifications are considered to be the temporary changes in microbial reactivity. However the stable forms of modifications exist, which can be preserved in several bacterial generations.
The discrimination between genotypic or phenotypic alterations rests on several assumptions. Genotypic changes are rare and result from the new order of the nucleotide sequence in DNA (e.g., after mutations); therefore, only a few cells in a large population will be altered towards the acquisition of a new trait. In contrast, phenotypic changes will involve almost all cells in the population (e.g., by the action of quorum sensing mechanism). Further, phenotypic variations are readily reversible, and most of the bacteria in the population can reverse back to their initial property as the environmental conditions resolve to the original state. On the contrary, genotypic changes are generally stable.