Acidophilic planctomycetes: Expanding the horizons of new planctomycete diversity

Abstract

As evidenced by the results of cultivation-independent studies, members of the bacterial phylum Planctomycetes colonize various acidic environments including soils, hot springs, and wetlands. Until recently, however, acidophilic planctomycetes were absent from the public culture collections as well as from the list of taxonomically described bacteria. Research on acidic northern peatlands using fluorescence in situ hybridization (FISH) revealed planctomycetes as one of the most numerous bacterial groups in these ecosystems. The use of acidic dilute media and FISH-based monitoring of the enrichment procedure resulted in isolation of several peat-inhabiting planctomycetes in pure cultures. These isolates were further described as representing the novel genera Schlesneria, Singulisphaera, Zavarzinella, and Telmatocola, which accommodate moderately acidophilic planctomycetes growing at pH values between 4 and 7, with an optimum at pH 5-6. One more acidophilic peat-inhabiting planctomycete, Candidatus Nostocoida acidiphila that grows optimally at pH 3.6-4.0, has also been isolated. All currently described acidophilic planctomycetes are chemoheterotrophs, which grow best in aerobic conditions on media containing carbohydrates. However, they are also capable of utilizing various heteropolysaccharides of plant and microbial origin, and Telmatocola sphagniphila possesses cellulolytic potential, which suggests their role as slow-acting primary degraders in habitats with a bulk of decay-resistant organic matter.