Season and soil properties structure bacterial communities in hyperacid (pH ≤ 2) fumarolic soils of the Tatun Volcanic Group

BACKGROUND: Volcanic fumaroles are extreme habitats with high temperatures, sulfur‑rich gases, and low pH, creating challenging niches for life. Soil microbiota in these environments remain underexplored, particularly at near‑vent sites with pH below 2. We characterized bacterial communities in hyperacid soils of Taiwan's Tatun Volcanic Group to examine how season and soil properties shape these communities. We sampled 39 soils and 8 hot spring waters from four fumaroles during dry and wet seasons. Soil pH, nutrients (nitrate, ammonium), organic matter, and altitude were recorded, and bacterial diversity was profiled via 16S rRNA gene sequencing. RESULTS: Pseudomonadota overwhelmingly dominated the communities, followed by Bacillota and Actinomycetota. Wet-season soils displayed more homogeneous assemblages, whereas dry-season soils exhibited greater heterogeneity. Soil taxonomy and texture also modulated patterns, with Andisols supporting more consistent communities than Inceptisols. Environmental variables such as nitrate, ammonium, organic matter, and altitude correlated with community composition. Heatmap and network analyses highlighted Delftia and Pseudomonas as key taxa. CONCLUSIONS: Extreme acidity and seasonal hydrology thus select for specialized bacterial assemblages in these fumarolic soils. These findings advance understanding of microbial adaptation to geochemical extremes and reveal how seasonal and edaphic factors structure communities, offering implications for biogeochemical cycling and astrobiology.