Stick together: Isolation and characterization of exopolysaccharide producing bacteria from degraded permafrost soils

Bacterial exopolysaccharides (EPSs) are the high-molecular-weight polymers secreted into their surrounding that play a crucial role in bacterial survival, environmental adaptation, biofilms formation, and interaction with surrounding matrices. EPSs may also contribute to soil structure development by enhancing soil aggregate stability, promoting soil cohesion, and interacting with soil particles through their diverse functional group constituents and conditioning film characteristics. This study aimed to isolate and characterize potential EPSs-producing bacteria from the active layer of two different hydrological landscape of degraded permafrost soils, and from undisturbed intact permafrost soil. A total of 54 bacterial isolates were obtained, representing three phyla: Firmicutes, Actinomycetota, and Pseudomonadota. EPSs production was assessed by determining the polysaccharide content measured as glucose equivalent, and 26 isolates were identified as potential EPSs producers. Among the isolates, Curtobacterium oceanosedimentum, Frigoribacterium faeni, Streptomyces strains, Neobacillus bataviensis and Mesobacillus subterraneus exhibited the highest polysaccharide yield. The carbohydrate content of the extracted EPSs varied in both composition and quantity across the different isolates. Uronic acids such as glucuronic acid was found in the EPSs produced by the isolates closely related to Curtobacterium oceanosedimentum and Neobacillus bataviensis, while the amino hexoses were identified in EPSs extracted from various isolates, including those affiliated with Bacillus, Streptomyces, Luteimonas, and Phyllobacterium. The potential EPSs producing bacteria were also found inhabiting in the different horizons of both degraded permafrost soil and undisturbed intact permafrost soil, by determining their relative proportion within the total bacterial community based on 16S rRNA gene sequences similarities.