Genetic Determinants of Xylan Utilization in Humisphaera borealis M1803T, a Planctomycete of the Class Phycisphaerae

Planctomycetes of the class Phycisphaerae are aerobic and anaerobic heterotrophic bacteria that colonize a wide range of marine and terrestrial habitats. Their functional roles in the environment, however, are still poorly understood. Humisphaera borealis M1803(T) is one of the very few characterized planctomycetes of this class. It is also the first described representative of the previously uncultured group WD2101, which is commonly detected in soils and peatlands. This work analyzed the genetic determinants that define the ability of Humisphaera borealis M1803(T) to grow on xylan, one of the plant cell wall polymers. The whole genome sequence analysis of this planctomycete resulted in identification of five genes encoding the proteins homologous to previously described endo-beta-xylanases. For two of these proteins, evolutionarily closer experimentally characterized homologs with other substrate specificities were found. In a member of the GH10 family of glycoside hydrolases, the active center of the enzyme was destroyed. We consider two proteins from GH62 and GH141 families as the most likely candidates for the role of beta-xylanase responsible for xylan utilization. Phylogenetic analysis of proteins of GH10, GH62, and GH141 families was carried out. The role of lateral transfers in the evolution of the genes for glycoside hydrolases and their close homologs is discussed.

Automated summary

Planctomycetes of the class Phycisphaerae are a diverse group of aerobic and anaerobic heterotrophic bacteria that inhabit various marine and terrestrial environments. Humisphaera borealis M1803(T) is a characterized member of this class, capable of utilizing xylan, a plant cell wall polymer. The genetic determinants for xylan utilization in this bacterium were identified through whole genome sequence analysis, shedding light on the evolution of genes for glycoside hydrolases.