Extracelluar polysaccharide producing bacteria from permafrost. Permafrost microbiome

Permafrost thaw can result in two distinct environmental landscapes (i.e. “wet condition” soils rich in ice wedges and low drainage, and “dry condition” well drained areas with higher evapotranspiration). These different hydrological conditions influence the bacterial community composition and may impact their capacity to produce exopolysaccharides (EPSs). EPSs are important for bacteria as they provide protection and facilitate biofilm formation which is essential for survival, adaptation, and modulation of environments experiencing different conditions after permafrost thaw. EPS-producing bacteria promote the soil structure and may influence the stabilization of soil organic carbon (SOC) by occlusion soil organic matter (SOM) within soil aggregates. This study aimed to isolate and characterize EPSs-producing bacteria from the active layer of two permafrost degrading landscapes (dry and wet sites) as compared to an undisturbed permafrost soil (intact site). In total, we obtained 17, 20, and 17 bacterial soil isolates from dry, wet and intact site, respectively. According to the 16S rRNA gene sequencing, these isolates belonged to three phyla; Firmicutes, Actinomycetota, and Pseudomonadota. EPS production was assessed by determining the polysaccharide content measured as glucose equivalent, and 26 out of the 54 isolates were identified as potential EPSs-producers. Among the isolates, Curtobacterium oceanosedimentum, Frigoribacterium faeni, Streptomyces strains, Neobacillus bataviensis and Mesobacillus subterraneus had the highest polysaccharide yield. They were also found inhabiting in the different horizons of degraded permafrost soil and intact permafrost soil, by determining the relative proportion of the EPSs-producing isolates within the total bacterial community based on 16S rRNA gene sequences similarities. These findings suggest that the presence of bacterial communities of high EPSs-producing capabilities under conditions of permafrost degradation may have impact on soil aggregation, which physically protect the SOC from microbial degradation and thereby potentially enhancing the stability of SOC.