Microbial Diversity Across Chemolithotrophic and Phototrophic Biofilms in Cold Sulfur Springs.

Sulfur-rich environments host specialized microbial communities that drive key biogeochemical processes, particularly sulfur cycling. While sulfur-oxidizing microbiota from hydrothermal vents and volcanic systems are well studied, microbial communities in cold terrestrial sulfur springs remain less understood. In this study, we used 16S rRNA gene sequencing to examine how sulfur availability and environmental conditions shape microbial assemblages across different biofilm types in a cold sulfur spring system at Blount Springs, Alabama (33.9301° N, 86.7928° W). Sulfur-oxidizing chemolithotrophs, including Sulfurovum and Halothiobacillus, represented the majority of the recovered reads in sulfur-rich white biofilms, while purple phototrophic biofilms were enriched with anoxygenic sulfur-oxidizing bacteria, such as Chromatium and Chlorobium. Nonsulfur biofilms from adjacent environments displayed greater microbial diversity, including a high abundance of photosynthetic diatoms, like, Melosira. Notably, Sulfurovum was abundant across both sulfur-rich and phototrophic niches, suggesting ecological flexibility and a central role in sulfur metabolism. These findings highlight the influence of sulfur chemistry and light availability in structuring microbial communities and contribute to a broader understanding of microbial adaptation and sulfur cycling in cold sulfur spring ecosystems.