Small-Scale Mineral and Microbial Heterogeneities near a Fumarole at the Furnas Hydrothermal Zone on the Azores

The Azores are characterized by intense volcanic activity, creating unique environments such as fumarole sites, where geothermal gases and high temperatures drive distinct chemical and biological processes. To investigate small-scale heterogeneity within such a site, six visually distinct samples were collected within a 30 cm radius at an active fumarole on São Miguel Island. The samples were analyzed for elemental and mineralogical composition, bacterial lipid biomarkers (PLFAs), and microbial community structure using a novel DNA separation technique to specifically target the living microbiome. Despite mineralogical similarities across all samples—predominantly composed of alunite, alkali-feldspar, and quartz—significant microbial heterogeneity was observed. Both PLFA and bacterial iDNA analyses revealed distinct microbial communities associated with specific conditions indicated by the specific colors: red and brown samples were dominated by Proteobacteria and Actinobacteriota, yellow and green by Thermoplasmatota and Actinobacteriota, and white and gray by Crenarchaeota. Interestingly, the gray samples exhibited a broader microbial composition, sharing some taxa with all other samples. These striking color variations are likely driven by differences in both specific mineral composition and microbial pigmentation, reflecting localized biogeochemical processes. Our findings demonstrate that extreme microbial heterogeneity can occur over remarkably small spatial scales within fumarolic systems, underscoring the complex interplay between chemical and biological factors in these dynamic volcanic habitats.