Sunlight-Exposed Biofilm Microbial Communities Are Naturally Resistant to Chernobyl Ionizing-Radiation Levels

Abstract

BackgroundThe Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well.Methodology/Principal FindingsTo test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates.Conclusions/SignificanceOur results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation.

Activation of Melanin Synthesis in Alternaria infectoria by Antifungal Drugs

“…A growing number of reports also associate sensitivity to Alternaria with asthma (5,(7)(8)(9), possibly due to the high spore germination rate of members of this genus and their release of protease (10). The rise in the incidence of asthma among adults and children may be linked to global climate changes and reductions in the ozone layer and the accompanying increased solar radiation (5,11,12). Since the melanin of fungal cell walls provides protection against UV, ionizing, and gamma radiation (13), this pigment may contribute to the higher survival rates and competitive abilities of melanized fungi, leading to further environmental proliferation.…”

Biological Indicators of Ionizing Radiation in Nature

“…Indeed, barn swallows Hirundo rustica have germline mutation rates for neutral microsatellite markers increased by a factor 2-10 ( Ellegren et al 1997). Numerous other studies have shown increases in mutation rates from bacteria (Ragon et al 2011) to humans (Dubrova et al 1996), with contaminated areas around Chernobyl having mutation rates that are increased 2-20-fold relative to controls . The effects of exposure to ionizing radiation may be long lasting due to genomic instability, causing DNA to be particularly susceptible to future environmental perturbations even after one or more generations (Morgan et al 1996).…”

Microbial influences on hormesis, oncogenesis, and therapy: A review of the literature

“…Most bacteria may have a higher resistance to radiation than mammalian cells but controlled in-vitro studies fail to assess how competition between bacteria can be affected by radiation. From a microbial studies standpoint, it seems that only low and high levels of radiation are indicative of competition while all ranges between will allow one species to overgrow the others (Ragon et al, 2011).…”

“…For example, a study performed in Chernobyl showed that bacterial competition is drastically affected by ionizing radiation (Ragon et al, 2011). In terms of the mammalian microbiota, this would not be a beneficial situation.…”