Potential transformation of organic matter by microbes in cryoconite, Tibetan Plateau

Microorganisms play an essential role in the glacier carbon cycle; how they transform organic matter in mountain glacial cryoconite remains to be studied. Here, we applied ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and deep sequencing of 16S rRNA gene, to investigate the temporal microbial transformation of dissolved organic matter (DOM) of the Tibetan Plateau cryoconite. During the 60-day incubation, we found that DOM in cryoconite underwent a three-stage transformation, with decreasing bioavailability over time. The microbial community did not change much in the first week while degrading DOM molecules that were associated with higher H/Cwa and lower O/Cwa. During days 15–30, DOM composition remained stable while microbial diversity increased. By day 60, the DOM was microbially converted into a higher state of recalcitrance, with higher values of aromatic index, O/Cwa and lower H/Cwa, which contained molecules containing more heteroatoms. Cooperation among various microbial taxa, like Cyanobacteria, Bacteroidota, Gammaproteobacteria, Firmicutes, and Actinobacteriota, drove the DOM transformation in cryoconite. This study sheds light on the in-situ transformation of DOM composition meditated by microbial populations in cryoconite at a temporal scale, providing new insights into understanding the microbial roles in the glacier organic carbon transformation.