A new study reports the discovery and characterization of Paludibaculum sp. T20B24, a previously unknown member of the Acidobacteriota isolated from a boreal fen in northern Russia. Until now, the genus Paludibaculum had only one cultivated species — P. fermentans P105ᵀ — and cellulolytic abilities had never been confirmed experimentally.
The researchers isolated strain T20B24 using enrichment cultures with xylan and identified it as a close relative of P. fermentans, sharing 99.87% 16S rRNA similarity. However, T20B24 displayed distinct morphological and physiological differences, including its ability to grow on fibrous cellulose — a key new finding for this genus.
Microscopy confirmed strong attachment of T20B24 cells to cellulose microfibers, and growth experiments showed a ten-fold increase in cell numbers during cellulose utilization. Genome sequencing revealed a large 10.1 Mb genome harboring 8096 protein-coding genes and a wide array of carbohydrate-active enzymes (CAZymes), including potential cellulases and xylanases in GH5 and GH8 families. Phylogenetic analyses linked these enzymes to cellulolytic clusters commonly found in acidobacterial metagenome-assembled genomes from peatlands and soils.
Iron metabolism genes, including homologs of metal-reducing cytochromes (MtrC/MtrA), were also identified, suggesting that T20B24 may participate in Fe(III) reduction under anoxic conditions, similar to P105ᵀ.
Although genetically close, T20B24 and P105ᵀ showed ANI and DDH values below species thresholds, indicating that T20B24 may represent a new yet-to-be-named species. The authors note that further isolates are needed before formal taxonomic revision.
This study provides the first experimental evidence of cellulose degradation in the genus Paludibaculum, expanding understanding of the ecological roles of Acidobacteriota in peatland carbon turnover.
Reference
Kulichevskaya, I.S., Ivanova, A.A., Naumoff, D.G. et al. Cellulolytic Capabilities in Paludibaculum sp. T20B24, a Novel Acidobacterium from a Boreal Fen. Microbiology 94, 882–892 (2025). https://doi.org/10.1134/S0026261725602829
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