Understanding microbial adaptation to extreme environments remains a key challenge in microbial ecology. Geothermal hot springs, characterized by temperature gradients and varying geochemical conditions, represent valuable natural laboratories for studying microbial diversity, adaptive strategies, and evolutionary mechanisms. However, despite many studies of hot spring communities, how temperature gradients shape key microbial adaptation strategies remains insufficiently understood, limiting our ability to explain survival and function in extreme environments. Our study investigated microbial community composition and functional profiles across a natural thermal gradient (50–93 °C) in six hot springs on the Western Sichuan Plateau using optimized contig- and MAG-based metagenomic strategies. Enhanced annotation approaches significantly improved taxonomic resolution in these extreme environments. Metagenomic analyses revealed distinct shifts in microbial communities along the thermal gradient: moderate-temperature springs (50–70 °C) were dominated by Pseudomonadota and Bacteroidota, exhibiting heterotrophic flexibility and utilizing the Calvin–Benson–Bassham cycle and diverse nitrogen reduction pathways; high-temperature springs (70–90 °C) were enriched in Chloroflexota, which primarily employed the Wood–Ljungdahl pathway coupled with enhanced sulfur metabolism; and extreme-temperature springs (≥ 90 °C) were characterized by Aquificota and Thermoproteota, relying on specialized autotrophic pathways (rTCA, DH/HH cycles), streamlined nitrogen assimilation, and sulfur oxidation pathways. These thermophilic lineages showed genome streamlining, reduced regulatory complexity, and specialized metabolic strategies, reflecting narrower ecological niches and deeper phylogenetic branches. This metagenomic investigation across a temperature gradient in western Sichuan hot springs highlights temperature as an essential driver of microbial community structure, genome evolution, and adaptive specialization. Thermophilic lineages in extreme-temperature environments exhibited streamlined genomes, specialized metabolic functions, and narrower ecological niches, consistent with adaptation to persistent thermal stress. The findings enhance understanding of microbial evolutionary strategies and underscore the ecological significance of temperature-driven adaptation in extreme environments. Temperature-driven microbial community structure shifts across thermal gradients. Thermophiles in hotter springs show deeper phylogeny and narrower niche breadth. Carbon fixation transition from rTCA, DH, HH to 3H, CBB along thermal gradients. Genome Streamlining and GC/amino acid shifts enhance thermal structural stability. Composite mapping strategy improves metagenome annotation in extreme environments.
Luo et al. (Tue,) studied this question.