Only well-adapted organisms can survive constant exposure to sunlight and temperature fluctuations during the day, not to mention scarcity of water. Researchers supported by FAPESP identified a group of bacteria and a yeast that have adapted to such conditions on photovoltaic panels, which convert sunlight into electricity. The panels are installed in Sorocaba and Itatiba, São Paulo state, Brazil.
An article reporting the results of the research is published in the Editor’s Choice section of FEMS Microbiology Letters, an official journal of the Federation of European Microbiology Societies.
In view of their characteristics, the microorganisms identified have significant potential to be developed into products that entail long periods of exposure to sunlight, such as sunscreens and pigments for processed foods, chemicals, textiles, pharmaceuticals and cosmetics, as well as more efficient detergents with antimicrobial action for cleaning the panels themselves.
“We concluded that the composition of this microbiota is very similar to that found on photovoltaic panels in Valencia [Spain], Berkeley [California, USA], and even in the Arctic and Antarctic,” said Juliane Moura, who conducted the study as part of her master’s research for the Program of Graduate Studies in Biotechnology and Environmental Monitoring (PPGBMA) at the Federal University of São Carlos (UFSCar) in Sorocaba, state of São Paulo, Brazil, with a scholarship from the Coordination for the Improvement of Higher Education Personnel (CAPES), an arm of Brazil’s Ministry of Education.
“Although the countries studied have different climates, the surface of panels in all of them is home to a community of microorganisms that have adapted to solar radiation, temperature fluctuation, water scarcity, and the very material the panels are made of,” said Iolanda Duarte, a professor in the Department of Biology at UFSCar’s Center for Human and Biological Sciences (CCHB) and last author of the article.
The samples were collected by scrubbing the panels located in Sorocaba and Itatiba with gauze bandage soaked in sterile saline. They were then stored in flasks and shipped to UFSCar’s Applied Microbiology Laboratory, where DNA was extracted.
Using 16S rRNA gene sequencing, the researchers identified similar compositions in all the samples, although diversity was slightly higher in the samples collected in the rural area of Sorocaba. 16S rRNA gene sequencing is commonly used for identification, classification and quantitation of microbes within complex biological mixtures such as environmental samples (e.g. seawater) and the human gut microbiome.
The results were similar to those of studies conducted in Spain, the United States, the Arctic and Antarctic despite the differences in geography and climate. The bacterial genera Methylobacterium methylorubrum and Hymenobacter accounted for over 90% of the total microbial diversity observed.
Understanding communities of microorganisms on photovoltaic panels can also help maintain the panels’ efficiency over time. In Brazil, studies show that soiling (accumulated dust and microorganisms) can reduce power production by 11% after 18 months. In deserts, the impairment can reach 39%, exceeding 50% when extreme weather events such as sand and dust storms occur.
Besides sand and other particles, the dust found on the panels is rich in microorganisms. As a survival strategy, some bacteria cluster in biofilms that line the panels and reduce their capacity to capture solar radiation.
In the next stage of their research, not covered by the article, the researchers isolated a pigmented yeast that is found on solar panels in regions with a cold climate and can be used to produce biodetergents.
These molecules are considered versatile in terms of applications, as they are tensoactive, meaning they reduce surface tension in water to help it blend with water-insoluble substances.
They also have potential applications as anti-microbials, in drugs that combat tumors, and in bioremediation processes to clean up 8soil and groundwater contaminated by discharged chemicals.
“Biofilm removal is difficult in many economic activities, so the study is an important contribution to the development of novel solar panel management strategies,” Duarte said. “Future research involving the biodetergent yeast could offer an alternative route for the formulation of more effective cleaning products for solar panels and other equipment.”
Organisms that can withstand and even thrive in conditions such as those found on photovoltaic panels are known as extremophiles. Some of the bacteria identified in Sorocaba and Itatiba, for example, had previously been detected in soil samples from the Taklamaken, Gobi and Atacama deserts in China, Mongolia and Chile respectively.
Some of the isolates were of particular interest to the researchers because they were pigmented and grew in different temperature bands ranging from 3 °C to 50 °C. The presence of pigment may be associated with the capacity to surmount oxidative stress, when excessive production of free radicals and reactive oxygen species is harmful to biological organisms.
Solar radiation and water loss are among the causes of oxidative stress. Photovoltaic panels have a smooth and sloping surface designed not to retain water.
The researchers isolated 63 microorganisms with the potential to withstand ultraviolet rays. These will be analyzed in the laboratory to discover their actual resistance to UV and explore possible biotech applications.