Geomicrobiology of the built environment

Microbial colonization and growth can have significant effects in the built environment, resulting in a range of effects from discolouration and staining to biodeterioration and decay. In some cases, formation of biofilms, crusts and patinas may confer bioprotection of the substrate. This perspective aims to discuss how geomicrobial transformations in the natural environment - particularly involving rocks, minerals, metals and organic matter - may be applied to understand similar processes occurring on fabricated human structures. However, the built environment may offer further strictures as well as benefits for microbial activity and these should be taken into consideration when considering analogy with natural processes, especially when linking observations of microbial biodiversity to the more obvious manifestations of microbial attack

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

BACKGROUND: The 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 FINDINGS: To 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/SIGNIFICANCE: Our 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

Adaptive Melanin Response of the Soil Fungus Aspergillus niger to UV Radiation Stress at “Evolution Canyon”, Mount Carmel, Israel

BACKGROUND:Adaptation is an evolutionary process in which traits in a population are tailored by natural selection to better meet the challenges presented by the local environment. The major discussion relating to natural selection concerns the portraying of the cause and effect relationship between a presumably adaptive trait and selection agents generating it. Therefore, it is necessary to identify trait(s) that evolve in direct response to selection, enhancing the organism's fitness. "Evolution Canyon" (EC) in Israel mirrors a microcosmic evolutionary system across life and is ideal to study natural selection and local adaptation under sharply, microclimatically divergent environments. The south-facing, tropical, sunny and xeric "African" slope (AS) receives 200%-800% higher solar radiation than the north-facing, temperate, shady and mesic "European" slope (ES), 200 meters apart. Thus, solar ultraviolet radiation (UVR) is a major selection agent in EC influencing the organism-environment interaction. Melanin is a trait postulated to have evolved for UV-screening in microorganisms. Here we investigate the cause and effect relationship between differential UVR on the opposing slopes of EC and the conidial melanin concentration of the filamentous soil fungus Aspergillus niger. We test the working hypothesis that the AS strains exhibit higher melanin content than strains from the ES resulting in higher UV resistance. METHODOLOGY/PRINCIPAL FINDINGS:We measured conidial melanin concentration of 80 strains from the EC using a spectrophotometer. The results indicated that mean conidial melanin concentration of AS strains were threefold higher than ES strains and the former resisted UVA irradiation better than the latter. Comparisons of melanin in the conidia of A. niger strains from sunny and shady microniches on the predominantly sunny AS and predominantly shady ES indicated that shady conditions on the AS have no influence on the selection on melanin; in contrast, the sunny strains from the ES displayed higher melanin concentrations. CONCLUSIONS/SIGNIFICANCE:We conclude that melanin in A. niger is an adaptive trait against UVR generated by natural selection

Capacity of blood plasma is higher in birds breeding in radioactively contaminated areas

Background Environmental pollution in general, and radioactive contamination in particular, may deeply affect host-parasite relationships and their consequences for the evolution of organisms. The nuclear accident that occurred more than 30 years ago in Chernobyl resulted in significant changes in diversity and richness of microbial communities that could influence characteristics of animal-bacteria interactions, including host immune responses and competitive interference by bacteria. Given the high mortality rate of birds breeding in radioactively contaminated zones, those with stronger defences against infections should experience significant fitness advantages. Methodology/Principal Findings Here we characterized antimicrobial capacity of barn swallows (Hirundo rustica) from different Ukrainian populations (subject to a gradient of ionizing radiation) against 12 bacterial species. We also quantified constitutive innate immunity, which is the non-specific first barrier of protection of hosts against microbial parasites. We found a positive association between specific antimicrobial capacity of individual hosts and radiation levels in breeding habitats even after controlling for other confounding variables such as sex and age. However, no significant relationship was found between immunocompetence (non-specific response) and background radiation. Conclusions/Significance These results suggest that radiation selects for broad antimicrobial spectra of barn swallows, although not for all bacterial strains. We discuss these results in the framework of host-parasite evolution under extreme environmental conditions.M. Ruiz-Rodríguez had a postdoc stipend from the program “Andalucía Talent Hub” (Agencia Andaluza del Conocimiento, Junta de Andalucía). Funding was provided in part by the Samuel Freeman Charitable Trust, the US Fulbright Program, the CNRS (France), the American Council of Learned Societies, the University of South Carolina College of Arts and Sciences, and the Spanish Ministerio de Economía y Competitividad (European funds (FEDER)) (CGL2013- 48193-C3-1-P).Peer reviewe