MICROBIOLOGY - M.H. Serhiichuk - 2008

Chapter 4. BACTERIAL GENETICS

MODIFICATION VARIABILITY

Prokaryotes exhibit Two Types of Variability: non-heritable (modification) and heritable. Heritable changes in microorganisms are divided into two main groups: Mutations and genetic recombinations.

Microorganisms with identical genotypes may exhibit significant phenotypic differences, meaning variations in how hereditary traits are expressed.

Phenotypic differences among microorganisms sharing the same genotype are referred to as modifications. Modifications are evolutionarily fixed adaptive responses of a microorganism to changing environmental conditions, often called phenotypic adaptations. Thus, the interaction between a microorganism's genetic makeup and its external environment can result in diverse phenotypes. However, the potential range of these phenotypic variations is strictly constrained by the genotype. All morphological and physiological traits of microorganisms are governed by the Genetic information encoded within DNA. Each genotype possesses a specific reaction norm in response to various environmental conditions and factors.

Modifications manifest as alterations in morphological, biochemical, and other characteristics, followed by a reversion to the original phenotype once the inducing environmental factor ceases to act.

The information carried by DNA is not completely rigid or immutable. If the information transmitted from generation to generation were incapable of change, any sudden shift in living conditions could prove lethal.

For instance, under METABOLISM/18.html">The Influence of physical, chemical, or biological factors, bacterial Cells may transform into thickened filaments, club-shaped structures, or branches resembling fungal mycelium. When exposed to temperatures around ~41 ⁰С, acetic acid Bacteria form long filaments; returning these bacteria to their optimal Temperature results in the reappearance of typical rod-shaped forms.

Modifications can also be triggered directly by Antibiotics, such as penicillin. The resulting L-forms can persist within a host Organism or revert to the wild-type form after the antibiotic is withdrawn.

M. Gamaleya observed morphological alterations in various bacteria, including The formation of giant spheres, amoeboid shapes, thickened filaments, and others. He termed this phenomenon heteromorphism, The Essence of which lies in bacterial adaptation to unusual environmental conditions.

The BIOCHEMICAL BASIS OF modification involves the inducible synthesis of Enzymes, driven by the Induction and Repression of structural genes controlled by regulatory genes. For example, Escherichia coli synthesizes the enzymes required for lactose Fermentation only in the presence of lactose. Similarly, staphylococci produce the enzyme penicillinase—which degrades the antibiotic molecule—exclusively when penicillin is present.