Metabolic diversity and adaptation of carbon-fixing microorganisms in extreme glacial cryoconite

Understanding the diversity and functionality of carbon-fixing microorganisms in glacial ecosystems is crucial for elucidating carbon cycling processes in extreme environments. This study investigates the composition, diversity, and metabolic potential of carbon-fixing microorganisms in Tibetan cryoconite. Through metagenomic sequencing, we identified 13 carbon-fixing metagenome-assembled genomes spanning ten known and three unclassified genera. Deoxyribonucleic acid -stable isotope probing experiments with ¹³C-labeled sodium bicarbonate confirmed the metabolic activity of key genera, including Cyanobacteria (Microcoleus and Phormidesmis) and Proteobacteria (Rhizobacter and Rhodoferax). Our results reveal a diverse array of carbon fixation pathways, with the Calvin-Benson-Bassham cycle and 3-hydroxypropionate bicycle being the most prominent. In addition to photoautotrophic microorganisms, chemoautotrophic microorganisms also contribute to carbon fixation through mechanisms such as sulfur oxidation and atmospheric reducing gas utilization. The study highlights the adaptability of microbial communities to varying environmental conditions, including fluctuations in oxygen, light, and substrate availability. The findings underscore the complex interplay between carbon fixation pathways and environmental factors in cryoconite ecosystems. It also emphasizes the importance of exploring alternative carbon fixation pathways to gain a more comprehensive understanding of carbon cycling in these harsh and dynamic ecosystems.