Geothermal gradients restructure metabolism in hot spring microbial communities

Hot springs are employed as model systems for understanding how environmental stress structures microbial communities, yet the mechanisms by which geothermal stress reorganizes community metabolism remain poorly understood. Here we combined genome-resolved metagenomics, metatranscriptomics, aqueous geochemistry, and community metabolic modelling to investigate photosynthetic biofilms across the geothermal gradient of a hot spring in Singapore. We reconstructed community taxonomic and functional composition via metagenome-assembled genomes and identified three transcriptionally coordinated ecological guilds defined by convergent metabolic strategies rather than phylogeny. Community metabolic models revealed that increasing geothermal stress reorganized nutrient exchange networks, progressively reducing metabolic redundancy and increasing dependence on reciprocal interactions among thermophilic guilds. Increasing geothermal stress redirected relative modelled elemental demand from carbon-associated metabolism towards nitrogen and sulfur metabolism, highlighting nitrogen limitation and sulfur-linked bioenergetics as defining features of stress adaptation. Electron allocation modelling further demonstrated a systems-level transition from growth-oriented biosynthesis toward catabolic energy conservation, respiratory metabolism, and oxidative stress management under geothermal stress. These coordinated metabolic shifts indicate that hot spring communities become increasingly specialized and energetically constrained near their upper geothermal limits. Overall, the findings demonstrate how environmental stress restructures microbial ecosystems through guild-level metabolic partitioning and cooperative resource exchange and establishes an integrative systems biology framework for predicting microbial ecosystem function in extreme environments.