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

Chapter 9. RADIORESISTANCE OF ORGANISMS

9.3. Radioresistance of microorganisms

In addition, microscopic algae function as producers, supplying supplementary oxygen to the environment.

The Radioresistance of various bacterial species varies within a very wide range (Table 9.2).

Class="center">Table 9.2

RADIORESISTANCE OF CERTAIN BACTERIAL SPECIES (according to Hrodzynskyi, 2000)

The data presented in Table 9.2 are relative, as LD values depend significantly on the state of the bacterial culture (resting or proliferating). It should be noted that when bacteria or other organisms are in a multiplying state, they are considerably more resistant to chronic irradiation than in a resting state. This is because proliferating Cells are exposed to ionizing radiation only during the time interval between successive Cell divisions.

Studies on bacteria established the fundamental radiobiological principle that chromosomal DNA is the primary target of ionizing radiation, and that radioresistance is controlled by genetic systems.

Eukaryotic microorganisms (protozoa, microscopic algae, and Fungi) exhibit a radioresistance comparable to that of bacteria.

Cyanobacteria (blue-green algae) belong to prokaryotic organisms capable of surviving in conditions unsuitable for other life forms—such as drastic Temperature fluctuations and hot springs—and they also possess significant radioresistance. In cyanobacterial species such as Synechococcus cedorum, Microcoleus vaginatus, and Phormidium tenuis, radioresistance is even higher than that of the bacterium Micrococcus radiodurans listed in Table 9.2.

Unicellular eukaryotic algae, whose radioresistance is evaluated based on population growth and habitat, vary in their radiation tolerance. This is presumably related to genes involved in DNA Repair. Green algae are among such organisms, and LD₉₀ values for some of them are given in Table 9.3.

Table 9.3

RADIORESISTANCE OF CERTAIN GREEN ALGAE (according to Hrodzynskyi, 2000)

Nuclear Organization and reproductive characteristics confer high radioresistance to microscopic fungi (yeasts, molds, etc.) (Table 9.4).

Table 9.4

RADIORESISTANCE OF CERTAIN MICROSCOPIC FUNGI

(according to Hrodzynskyi, 2000)

The radioresistance of microscopic fungi decreases as the number of nuclei per cell increases. At the same time, cell death is associated not only with radiation-induced recessive and dominant lethal Mutations, but also with lethal injuries unrelated to structural chromosomal changes. Radiosensitive mutants have been identified in the basidiomycete Ustilago maydis, the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, Pullularia pullulans, Neurospora crassa, and others. The primary reasons for decreased radioresistance include the blocking of DNA repair systems and the impairment of post-irradiation recovery.

When investigating the effects of ionizing radiation on natural communities of bacteria, fungi, and actinomycetes in soil samples irradiated at a dose of 25 Gy, it was found that their population recovery occurs within 30–40 days, whereas at a dose of 100 Gy, it takes 40–60 days.

Numerous studies on The impact of ionizing radiation on microbial activity indicate that microorganisms are highly resistant to irradiation, showing no adverse response to environmental contamination levels up to 3.7 • 10⁵ Bq/km². At the same time, it should be kept in mind that, on the one hand, microorganisms facilitate The conversion of bound radioisotopes into soluble forms; on the other hand, possessing high accumulation coefficients and productivity, they concentrate radioisotopes and transform them into states bound to Organic compounds. In both cases, microorganisms play a vital role in maintaining the equilibrium of their inhabiting environment.