141-11 Photoprotective Pigments in Dryland Microbial Biogeochemistry

Session: New Advances in Geobiology

Presenting Author:

Authors:

Abstract:

Photosynthetic microorganisms inhabiting dryland soils and other normally dry locations evolved strategies allowing them to persist between wetting events. They rapidly increase metabolism when moistened resulting in “greening up” that persists until they return to their dry state. While drying and desiccated, microbes are especially susceptible to oxidative stress induced by UV radiation and salt stress. In biological soil crusts and microbial mats, the UV absorbing pigment scytonemin produced by cyanobacteria provides protection from UV exposure that also benefits other members of the microbial community. UV protection enhances the capacity for microbial ecosystems to influence global biogeochemical cycles by facilitating microbial metabolism where otherwise it would be inhibited. In this study we analyzed the cooccurrence of scytonemin and fungal anthraquinone pigments in normally dry environments using high performance liquid chromatography with photo diode array detection and mass spectrometry. The stress responses and photoprotective roles of these pigments are well documented; however, there has been relatively little work on their combined contribution to microbial ecosystem development in extreme environments. We focus our environmental analysis on dryland biological soil crusts and supratidal coastal mats, and report on laboratory experiments using tree bark samples encrusted with amorphous black microbial colonies crusts. In a two-week experiment with non-lichenized samples, scytonemin content was enhanced 10-fold by desiccation. Exposure to UV radiation and high salinity resulted in 6-fold and 5-fold scytonemin increases, respectively. Conversely, the anthraquinone parietin decreased by 50% with desiccation, 60% with UV exposure, and 90% with high salinity. Thus, the fungal stress response appears to consume parietin in contrast with scytonemin by cyanobacteria. In the lichen Physcia, the increase in scytonemin was similar to that in the black crust, but in Xanthoria the response was diminished. Among pigments in the lichen stress experiments, xanthophyll content was enhanced by exposure to desiccation, UV, and salt, suggesting that carotenoid antioxidant properties were important, possibly for quenching reactive oxygen species. Overall the data support the hypothesis that complexity in microbial ecosystems enhances their influence on biogeochemical cycles.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10535

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.