Microbial potential for construction and degradation of the cryoconite biofilm matrix: Implications for carbon and nutrient cycling in Antarctic cryoconite holes.

Cryoconite granule formation underpins the physical structure and biogeochemical functioning of glacier cryoconite holes. Central to this process is the extracellular polymeric substance (EPS) matrix, produced by microorganisms, which binds microbial cells and mineral particles into stable aggregates while retaining organic matter and nutrients. However, the physiological traits governing the EPS matrix construction and degradation remain poorly understood. Here, we investigated microbial capacities for biofilm formation, EPS-related substrate utilization, and extracellular hydrolysis in Antarctic cryoconite communities over a 40-day melt season. After five weeks of incubation, 49 of 56 (88%) cryoconite debris samples formed detectable biofilms, with biofilm-forming capacity peaking in samples collected after 30 days and significantly exceeding that at the beginning and after 10 days of the melt season (p < 0.05). Across the melt season, the proportion of C-, N-, P- and S-containing substrates utilized increased from 33% to 90% of the 260 compounds tested, with significantly greater utilization of organic nitrogenous compounds than other substrate groups (p < 0.05). Biofilm-forming capacity correlated positively with utilization of EPS-backbone precursors, EPS-associated glycosides, and compounds associated with EPS modification (Spearman's ρ = 0.6, p < 0.05). Forty bacterial genera were recovered, dominated by Cryobacterium, Polaromonas, Arthrobacter, and Chryseobacterium, with representative isolates exhibiting biofilm-forming phenotypes and diverse extracellular enzyme activities. Together, these findings demonstrate complementary microbial capacities for biofilm formation and EPS matrix-associated organic matter transformation that may influence carbon and nutrient cycling in Antarctic cryoconite ecosystems.