ECOLOGICAL BIOCHEMISTRY - Study Guide - V. M. Isaienko 2005

Chapter 9. RADIORESISTANCE OF ORGANISMS

9.2. Radioresistance of Viruses

The BIOLOGICAL EFFECTS OF Ionizing Radiation on Viruses can be divided into three main categories: 1) inactivation (lethal effect); 2) alteration of properties without genetic consequences (non-lethal effect); 3) mutagenic effect (non-lethal effect).

Studies on virus viability during irradiation in nutrient media indicate that the direct effect of ionizing radiation is predominant. However, when irradiated in an aqueous medium in the absence of free radical scavengers (products of Water radiolysis), the indirect effect of ionizing radiation becomes the primary mechanism.

The Radioresistance of viruses is closely related to the Molecular Weight of their nucleic acid, as the nucleic acid serves as the primary target for radiation. Table 9.1 presents data on the molecular weight of various viruses along with their calculated D₀ values.

It should be noted that although viruses are relatively simple systems compared to Cells, the exact mechanisms of their inactivation by ionizing radiation remain fully unestablished. This primarily concerns viral reproduction within the host Cell and the identification of critical targets within the nucleic acid.

Non-lethal, non-heritable radiation damage in viruses is primarily identified by a delay in the latent period During the first cycle of intracellular Replication.

Viruses subjected to non-lethal radiation damage can be repaired by the host cell's DNA Repair systems. Notably, host cell reactivation of radiation-damaged viruses is less pronounced than reactivation from Damage caused by ultraviolet radiation.

Class="center">Table 9.1

RADIORESISTANCE OF CERTAIN VIRUSES

(according to Hrodzynskyi, 2000)

Ionizing radiation damages only a portion of the viral genome, leaving parts of it intact. Studies on irradiated Bacteriophages have shown that they retain The ability to adsorb onto the host cell surface and inject their nucleic acid into The Cell. Multiple damaged viruses often enter a single cell. Through a phenomenon known as cross-reactivation, inactivated segments of one viral genome can be replaced by homologous, undamaged segments from another. Consequently, the damaged viral genome is successfully repaired within host cells equipped with active recombination systems.