Solar UV radiation and microbial life in the atmosphere

Ecology and resistance to UV light and antibiotics of microbial communities on UV cabins in the dermatology service of a Spanish hospital

Microorganisms colonize all possible ecological habitats, including those subjected to harsh stressors such as UV radiation. Hospitals, in particular the UV cabins used in phototherapy units, constitute an environment in which microbes are intermittently subjected to UV irradiation. This selective pressure, in addition to the frequent use of antibiotics by patients, may represent a threat in the context of the increasing problem of antimicrobial resistance. In this work, a collection of microorganisms has been established in order to study the microbiota associated to the inner and outer surfaces of UV cabins and to assess their resistance to UV light and the antibiotics frequently used in the Dermatology Service of a Spanish hospital. Our results show that UV cabins harbor a relatively diverse biocenosis dominated by typically UV-resistant microorganisms commonly found in sun-irradiated environments, such as Kocuria, Micrococcus or Deinococcus spp., but also clinically relevant taxa, such as Staphylococcus or Pseudomonas spp. The UV-radiation assays revealed that, although some isolates displayed some resistance, UV is not a major factor shaping the biocenosis living on the cabins, since a similar pool of resistant microorganisms was identified on the external surface of the cabins. Interestingly, some Staphylococcus spp. displayed resistance to one or more antibiotics, although the hospital reported no cases of antibiotic-resistance infections of the patients using the cabins. Finally, no association between UV and antibiotic resistances was found.

UV and violet light can Neutralize SARS-CoV-2 Infectivity

We performed an in-depth analysis of the virucidal effect of discrete wavelengths: UV-C (278 nm), UV-B (308 nm), UV-A (366 nm) and violet (405 nm) on SARS-CoV-2. By using a highly infectious titer of SARS-CoV-2 we observed that the violet light-dose resulting in a 2-log viral inactivation is only 104 times less efficient than UV-C light. Moreover, by qPCR (quantitative Polymerase chain reaction) and fluorescence in situ hybridization (FISH) approach we verified that the viral titer typically found in the sputum of COVID-19 patients can be completely inactivated by the long UV-wavelengths corresponding to UV-A and UV-B solar irradiation. The comparison of the UV action spectrum on SARS-CoV-2 to previous results obtained on other pathogens suggests that RNA viruses might be particularly sensitive to long UV wavelengths. Our data extend previous results showing that SARS-CoV-2 is highly susceptible to UV light and offer an explanation to the reduced incidence of SARS-CoV-2 infection seen in the summer season.

Homeophasic Adaptation in Response to UVA Radiation in Pseudomonas aeruginosa: Changes of Membrane Fatty Acid Composition and Induction of desA and desB Expression

In bacteria, exposure to changes in environmental conditions can alter membrane fluidity, thereby affecting its essential functions in cell physiology. To adapt to these changes, bacteria maintain appropriate fluidity by varying the composition of the fatty acids of membrane phospholipids, a phenomenon known as homeophasic adaptation. In Pseudomonas aeruginosa, this response is achieved mainly by two mechanisms of fatty acid desaturation: the FabA-FabB and DesA-DesB systems. This study analyzed the effect of ultraviolet-A (UVA) radiation-the major fraction of solar UV radiation reaching the Earth's surface-on the homeophasic process. The prototypical strain PAO1 was grown under sublethal UVA doses or in the dark, and the profiles of membrane fatty acids were compared at early logarithmic, logarithmic and stationary growth phases. In the logarithmic growth phase, it was observed that growth under sublethal UVA doses induced the expression of the desaturase-encoding genes desA and desB and increased the proportion of unsaturated fatty acids; in addition, membrane fluidity could also increase, as suggested by the indices used as indicators of this parameter. The opposite effect was observed in the stationary growth phase. These results demonstrate the relevant role of UVA on the homeophasic response at transcriptional level.

Inactivation of SARS-CoV-2 by Simulated Sunlight on Contaminated Surfaces

We studied the stability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) under different simulated outdoor conditions by changing the temperature (20°C and 35°C), the illuminance (darkness, 10 klx, and 56 klx), and/or the cleanness of the surfaces at 50% relative humidity (RH). In darkness, the loss of viability of the virus on stainless steel is temperature dependent, but this is hidden by the effect of the sunlight from the first minutes of exposure. The virus shows a sensitivity to sunlight proportional to the illuminance intensity of the sunlight. The presence of interfering substances has a moderate effect on virus viability even with an elevated illuminance. Thus, SARS-CoV-2 is rapidly inactivated by simulated sunlight in the presence or absence of high levels of interfering substances at 20°C or 35°C and 50% relative humidity. IMPORTANCE Clinical matrix contains high levels of interfering substances. This study is the first to reveal that the presence of high levels of interfering substances had little impact on the persistence of SARS-CoV-2 on stainless steel following exposure to simulated sunlight. Thus, SARS-CoV-2 should be rapidly inactivated in outdoor environments in the presence or absence of interfering substances. Our results indicate that transmission of SARS-CoV-2 is unlikely to occur through outdoor surfaces, dependent on illuminance intensity. Moreover, most studies are interested in lineage S of SARS-CoV-2. In our experiments, we studied the stability of L-type strains, which comprise the majority of strains isolated from worldwide patients. Nevertheless, the effect of sunlight seems to be similar regardless of the strain studied, suggesting that the greater spread of certain variants is not correlated with better survival in outdoor conditions.

Potential of Solar UV Radiation for Inactivation of Coronaviridae Family Estimated from Satellite Data

The pandemic COVID-19 disease affects people dramatically overall the globe by illness and death. Several strategies are applied to restrict the spread of this disease such as lockdown, adequate social distance in different activities, hand disinfection and the use of masks. Potential hazard outdoors comes from released viruses, which may remain in the air for a while and settle down afterward and contaminating surfaces. Solar ultraviolet radiation (UVR) is known to act as a natural environmental virucide. The virucidal effectivity of UVR depends on a first order on the sensitivity of the virus against UVR as well as on the amount of incoming UVR. Here, we present estimates of the potential of solar UVR in inactivating SARS-CoV-2 in the environment. This is done by combining DNA-damaging surface solar UVR retrieved by satellites and the available information on fluence for inactivation of Coronaviridae. Our results show that solar UVR has a high potential to inactivate these viruses, but the degree depends strongly on location and season. In the subtropics (Sao Paulo, 23.5°S), the daily survival fraction is lower than 10-4 during the whole year, while close at norther latitudes (Reykjavik, 64°N), such a reduction can be found in June and July only.

Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.