Microbial Ecology on Solar Panels in Berkeley, CA, United States

Abstract

Solar panels can be found practically all over the world and represent a standard surface that can be colonized by microbial communities that are resistant to harsh environmental conditions, including high irradiation, temperature fluctuations and desiccation. These properties make them not only ideal sources of stress-resistant bacteria, but also standard devices to study the microbial communities and their colonization process from different areas of Earth. We report here a comprehensive description of the microbial communities associated with solar panels in Berkeley, CA, United States. Cultivable bacteria were isolated to characterize their adhesive capabilities, and UV- and desiccation-resistance properties. Furthermore, a parallel culture-independent metagenomic and metabolomic approach has allowed us to gain insight on the taxonomic and functional nature of these communities. Metagenomic analysis was performed using the Illumina HiSeq2500 sequencing platform, revealing that the bacterial population of the Berkeley solar panels is composed mainly of Actinobacteria, Bacteroidetes and Proteobacteria, as well as lower amounts of Deinococcus-Thermus and Firmicutes. Furthermore, a clear predominance of Hymenobacter sp. was also observed. A functional analysis revealed that pathways involved in the persistence of microbes on solar panels (i.e., stress response, capsule development, and metabolite repair) and genes assigned to carotenoid biosynthesis were common to all metagenomes. On the other hand, genes involved in photosynthetic pathways and general autotrophic subsystems were rare, suggesting that these pathways are not critical for persistence on solar panels. Metabolomics was performed using a liquid chromatography tandem mass spectrometry (LC-MS/MS) approach. When comparing the metabolome of the solar panels from Berkeley and from Valencia (Spain), a very similar composition in polar metabolites could be observed, although some metabolites appeared to be differentially represented (for example, trigonelline, pantolactone and 5-valerolactone were more abundant in the samples from Valencia than in the ones from Berkeley). Furthermore, triglyceride metabolites were highly abundant in all the solar panel samples, and both locations displayed similar profiles. The comparison of the taxonomic profile of the Californian solar panels with those previously described in Spain revealed striking similarities, highlighting the central role of both selective pressures and the ubiquity of microbial populations in the colonization and establishment of microbial communities.

Extremophilic microbial communities on photovoltaic panel surfaces: a two‐year study

“…The microbial composition is characterized by a set of highly resistant bacterial genera ( Deinococcus, Hymenobacter, Roseomonas ) and fungi ( Alternaria , among others), which are marginally present on the panels at the beginning of the experiment, but increase in frequency and become dominant by the end of the experiment. Some of the most abundant bacterial genera, such as Hymenobacter, Modestobacter and Deinococcus , have in fact previously been isolated from warm, irradiated environments, such as arid soil crusts or hyper‐arid desert soils (Reddy and Garcia‐Pichel, 2013; Busarakam et al ., 2016; Gundlapally and Garcia‐Pichel, 2017), and they have also been reported as frequent taxa inhabiting solar panel surfaces (Dorado‐Morales et al ., 2016; Tanner et al ., 2018; Porcar et al ., 2018). In fact, the microbial communities inhabiting solar panel surfaces around the world are similar in both functional and phylogenetic terms (Tanner et al ., 2018; Porcar et al ., 2018), suggesting the presence of not only common strong selective pressures (leading to functional similarity), but also of common structuring principles (leading to phylogenetic conservation) that include, among others, assembly history (the timing and order in which species arrive) and priority effects (the imprint of arrival order on community structure) (Carlström et al ., 2019).…”

“…The most abundant bacterial taxa detected in this work (mean value throughout time) are consistent with those previously described to inhabit solar panel surfaces (Dorado‐Morales et al ., 2016; Tanner et al ., 2018; Porcar et al ., 2018) and other radiation‐exposed environments, suggesting that the strong selection pressure imposed by solar radiation and other factors, such as desiccation, temperature or limited nutrient availability, is what shapes the microbial communities in these environments. For example, a previous study reported that concrete walls exposed to sunlight and ionizing radiation in Chernobyl proved to harbour similar communities to those present in a sun‐exposed environment from a control area (without ionizing radiation), and these were dominated by Actinobacteria , Deinococcales and pigmented ascomycete fungi (Ragon et al ., 2011).…”

“…The microbial communities present on the solar panels from Valencia proved rather similar, in taxonomic terms, to those on solar panels located in Arctic and Antarctic regions, with the most abundant genera being Hymenobacter , Sphingomonas and Deinococcus in all cases (Tanner et al ., 2018). Furthermore, the microbiome of solar panel surfaces from Berkeley (California, USA) also displayed similar profiles, both in taxonomic and functional terms, to those observed on the Spanish solar panels, highlighting the role of selective pressures in the establishment of these microbial communities (Porcar et al ., 2018). Nevertheless, and despite the previous taxonomic and functional characterization of the solar panel microbiome, little is known about the colonization process of these surfaces.…”

Characterization and Analysis of the Skin Microbiota in Rosacea: Impact of Systemic Antibiotics

“…The DNA cleanup was then conducted with a fecal DNA extraction kit (ZR Fecal DNA MiniPrep; Zymo Research (Irvine, CA, USA). After DNA extraction, the V3-V4 hypervariable region of the 16S rRNA gene was amplified by polymerase chain reaction and sequenced using the Illumina HiSeq platform (250 base pairs, paired-end reads) as reported previously [16,17].…”

Characterization and Analysis of the Skin Microbiota in Acne: Impact of Systemic Antibiotics

“…The DNA cleanup was then conducted with a fecal DNA extraction kit (ZR Fecal DNA MiniPrep; Zymo Research). After DNA extraction, the V3-V4 hypervariable region of the 16S rRNA gene was amplified by polymerase chain reaction and sequenced using the Illumina HiSeq platform (250 base pairs, paired-end reads) as reported previously [10,11].…”