Planctomycetes of the Genus Singulisphaera Possess Chitinolytic Capabilities

Planctomycetes of the genus Singulisphaera are common inhabitants of soils and peatlands. Although described members of this genus are characterized as possessing hydrolytic capabilities, the ability to degrade chitin has not yet been reported for these bacteria. In this study, a novel Singulisphaera representative, strain Ch08, was isolated from a chitinolytic enrichment culture obtained from a boreal fen in Northern European Russia. The 16S rRNA gene sequence of this isolate displayed 98.2% similarity to that of Singulisphaera acidiphila MOB10^T. Substrate utilization tests confirmed that strain Ch08 is capable of growth on amorphous chitin. The complete genome of strain Ch08 determined in this study was 10.85 Mb in size and encoded two predicted chitinases, which were only distantly related to each other and affiliated with the glycoside hydrolase family GH18. One of these chitinases had a close homologue in the genome of S. acidiphila MOB10^T. The experimental verification of S. acidiphila MOB10^T growth on amorphous chitin was also positive. Transcriptome analysis performed with glucose- and chitin-growth cells of strain Ch08 showed upregulation of the predicted chitinase shared by strain Ch08 and S. acidiphila MOB10^T. The gene encoding this protein was expressed in Escherichia coli, and the endochitinase activity of the recombinant enzyme was confirmed. The ability to utilize chitin, a major constituent of fungal cell walls and arthropod exoskeletons, appears to be one of the previously unrecognized ecological functions of Singulisphaera-like planctomycetes.