# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 3 Results and Discussion
### Microbiota Contained in the Soiling  
Identification and Characterization of Cultivable Bacteria  
The bacteria were isolated on three culture media (LPTMS, R2A, and LB) through serial dilutions from the soiling sampled from PV modules at the UA and PSDA. The bacterial isolates appeared as pigmented colonies in shades of yellow, orange, and pink. The greatest diversity of colonies was observed on a solid LB medium incubated at 30 \({}^{\circ}\)C for 96 h. A total of 34 colonies grown on the three media were selected according to their phenotypic diversity on the solid LB medium, of which 25 corresponded to the UA and 9 to the PSDA (Supplementary Figure S1). The phylogenetic relationship was constructed using 16S rRNA gene sequencing (Nanopore platform) for the 34 cultivable isolates obtained. The results indicated that these 34 cultivable bacteria corresponded to only seven different strains. In the UA, the genera _Arthrobacter_, _Kocuria_, and _Dietzia_ were identified. For the cultivable isolates obtained from the PSDA, the genera _Arthrobacter_ and _Dietzia_ were identified. Specifically, seven species were identified at the UA: _Arthrobacter tecti_, _Arthrobacter subterraneus_, _Arthrobacter tumbae_, _Arthrobacter parietis_, _Kocuria tufraneusis_, _Dietzia kunjamensis_ subsp. _schimae_, and _Dietzia maris_. Meanwhile, at the PSDA, four species were identified: _Arthrobacter subterraneus_, _Arthrobacter parietis_, _Dietzia kunjamensis_ subsp. _schimae_, and _Dietzia maris_ (Figure 5). The abundance of cultivable bacteria obtained in our research was lower than those found in the soiling deposited on the surface of solar panels sampled from Valencia, Spain, and Berkeley, CA, USA. This can be attributed to the harsh environmental conditions of the Atacama Desert, which make it an inhospitable environment for life. Likewise, our study revealed the presence of the genera _Arthrobacter_ and _Kocuria_, which was consistent with findings from studies conducted in Valencia and Berkeley [9; 10; 40]. In our research, the presence of the genus _Dietzia_ was obtained, which has not been reported in soiling samples deposited on PV modules in the previously mentioned locations, as well as in others, particularly in the investigations carried out by [PERSON] et al. [6] in Berlin, Germany, and [PERSON] et al. [41] in the Arctic and Antarctic territories. Additionally, the three genera identified in our study, which belonged to _Actinobacteria_, which is the most abundant cultivable phylum in the Atacama Desert, are representative of extreme and dry environments with high solar radiation. These were recently isolated in desert ecosystems to study the mechanisms of desiccation tolerance, water scarcity, and high radiation, where they play a relevant ecological role [34; 42; 43; 44]. The extreme properties of resistance to UV solar radiation and desiccation, as well as colonization on photovoltaic glass, were demonstrated for the genus _Arthrobacter_ in studies by [PERSON] et al. [9] and [PERSON] et al. [10]. Meanwhile, the genus _Dietzia_ has been recognized for its notable biological properties, including its antioxidant activity and protection against solar radiation [45]. The taxonomic composition of soiling deposited on PV modules at the UA and PSDA was studied using massive 16S rRNA gene sequencing (>1400 nt) with Nanopore technology. Samples from the UA were sequenced in triplicate using 0.7 g of soiling, which yielded 13.6 ng/\(\mu\)L of DNA. In contrast, a 2.3 g sample from the PSDA yielded only 0.5 ng/\(\mu\)L of DNA, which rendered it non-viable for preparation and sequencing according to the described procedure. Consequently, only DNA from the UA could be sequenced. These findings aligned with those reported by [PERSON] et. al. [13], who also failed to extract DNA from soil samples in the nearby Yungay sector adjacent to the PSDA, where they attributed this phenomenon to low nutrient and water availability, which limited the microbial growth in these environments.