Abstract EANA2026-40

Background: Ultraviolet (UV) radiation is a major constraint on surface habitability in planetary environments with limited atmospheric UV shielding. High UV fluxes induce severe DNA damage and limit microbial survival. On Earth, Arctic environments experience periods of elevated UV radiation and represent valuable analogues for studying microbial adaptation to extreme environmental stress relevant to astrobiology. Microbial pigments such as melanins are known to contribute to protection against UV-induced damage and may enhance survival under radiation stress. To investigate the relationship between pigmentation and UV resistance, pigmented bacterial isolates were characterized and selected for further experiments: UV exposure experiments to evaluate DNA damage and repair, and pigment spectra in UV-Vis wavelengths.

Methods: Microorganisms were isolated from Arctic environmental samples using multiple culture media (PYGV, PYGVb and PYGV + NAG). Pigmented isolates were characterized based on colony morphology, pigmentation and cellular morphology using light microscopy, with a particular focus on brown to black colonies potentially producing melanins. In parallel, additional dark-pigmented strains from CIIMAR culture collection were selected for comparative analyses. A UV-Vis dataset from 12 literature studies on melanin was compiled to identify recurrent spectral profiles. Based on these observations, selected isolates and reference strains, including one yeast strain and one fungal strain, were analyzed by UV-visible spectrophotometry and exposed to controlled UV irradiation conditions. DNA was extracted before irradiation, immediately after exposure and after 48 h of recovery in order to evaluate potential UV resistance and DNA repair capacity. 

Results: In total, 185 environmental strains were isolated from Arctic environments, with 110 and 75 from lake and peat samples respectively.  Following purification steps, 108 pure isolates were obtained. Macroscopically, broad phenotypic diversity was observed through distinct colony morphologies. Darker-colored isolates represented a small proportion of the collection and were selected for further analyses. Identification at the molecular level via sequencing of 16S rRNA gene has been conducted on a few selected isolates after performing DNA extraction, PCR amplification and purification. Sequencing analyses provided several groups of diverse environmental bacteria such as Micrococcus luteus, Rhodococcus globerulus, Dermacoccus nishinomiyaensis, Pseudomonas kitaguniensis and Cryobacterium arcticum. Highest similarities (> 99%) were recorded when compared to the nearest type strain, in the majority of isolates. Preliminary UV-Vis spectrophotometry analyses performed on aqueous suspensions of selected isolates revealed distinct absorption profiles between strains. Brown-pigmented isolates displayed the strongest absorbance values in the UV range, supporting their selection for subsequent UV irradiation experiments aimed at evaluating potential melanin-associated UV resistance and DNA repair capacity.

Conclusions: Combining microbial isolation, sequencing techniques and characterization of UV-shielding pigments offers insights into survival strategies adopted by microorganisms under high UV radiation conditions. The diversity of pigmented Arctic isolates emphasizes their role as model organisms for astrobiology and planetary habitability studies where radiation is a major environmental stress factor. In addition, cataloguing the UV-Vis spectral properties of a wide-variety of microbial pigments marks an important step in the identification of potential biosignatures in future exoplanet observation missions.