Bioprospecting the Solar Panel Microbiome: High-Throughput Screening for Antioxidant Bacteria in a Caenorhabditis elegans Model

Abstract

Microbial communities that are exposed to sunlight typically share a series of adaptations to deal with the radiation they are exposed to, including efficient DNA repair systems, pigment production and protection against oxidative stress, which makes these environments good candidates for the search of novel antioxidant microorganisms. In this research project, we isolated potential antioxidant pigmented bacteria from a dry and highly-irradiated extreme environment: solar panels. High-throughput in vivo assays using Caenorhabditis elegans as an experimental model demonstrated the high antioxidant and ultraviolet-protection properties of these bacterial isolates that proved to be rich in carotenoids. Our results suggest that solar panels harbor a microbial community that includes strains with potential applications as antioxidants.

Keywords: Caenorhabditis elegans; antioxidant; bioprospecting; microbiome; sun-exposed environment.

FIGURE 1

(A) Oxidative stress assays of the selected isolates using the WT device. Worms were fed with the selected isolates at either an OD₆₀₀ of 30 or 60. Survival rate is represented in the Y-axis in the form of activity per worm, and results are shown after 15 and 30 min of incubation with hydrogen peroxide. Error bars indicate standard deviation. (B) Antioxidant index (AI) of the pigmented bacterial isolates from solar panels. AI was calculated by dividing the highest activity average (at an OD₆₀₀ of 30 or 60) of each isolate by the average activity of the positive control (vitC) after 30 min of incubation with hydrogen peroxide. (C) Manual oxidative stress assay results. Y-axis indicates percentage of survival of the worms after 5 h of incubation in nematode growth medium supplemented with 20 mM hydrogen peroxide. NG (Nematode growth), negative control. VitC (vitamin C), positive control. Error bars indicate standard deviation.

FIGURE 2

UV-light protection assay. Error bars indicate standard deviation. (A) Y-axis indicates percentage of survival of C. elegans irradiated with UV-light for 45 s every day over a period of 15 days (X-axis). NG-C indicates the non-irradiated controls: the basal survival rate of the worms over the 15-day period. NG refers to the negative control: worms incubated in NGM with no supplements and irradiated during the 15 days. CGA and VitC are two positive controls: worms incubated with antioxidant compounds (chlorogenic acid and vitamin C) and irradiated during 15 days. Finally, PS1, PS21, and PS75 (Planomicrobium sp., Rhodobacter sp., and Bacillus sp., respectively) indicate worms incubated with pigmented solar panel isolates and irradiated over the 15-day period in order to test the protective effect of these isolates against UV-light. (B) Results at day 11, in which the largest differences between the negative control and the worms fed with the pigmented isolates were observed.

FIGURE 3

Tentative identification and quantification of the carotenoid content from the three selected isolates (A) PS1, (B) PS21, (C) PS75) after harvesting from liquid (L) or solid (S) culture. The total amount of CRTs is indicated next to each chart in μg per gram of cellular pellet (dry pellet in the samples harvested from solid culture, and wet pellet in the samples harvested from liquid culture). Further details on the concentration of each carotenoid can be found in Supplementary Table 2.