Kohn_2016_Front.Microbiol_7_2079

Members of the phylum Planctomycetes are ubiquitous bacteria that dwell in aquatic and terrestrial habitats. While planctomycetal species are important players in the global carbon and nitrogen cycle, this phylum is still undersampled and only few genome sequences are available. Here we describe strain NH11(T), a novel planctomycete obtained from a crustacean shell (Wadden Sea, Germany). The phylogenetically closest related cultivated species is Gimesia maris, sharing only 87% 16S rRNA sequence identity. Previous isolation attempts have mostly yielded members of the genus Rhodopirellula from water of the German North Sea. On the other hand, only one axenic culture of the genus Pirellula was obtained from a crustacean thus far. However, the 16S rRNA gene sequence of strain NH11(T) shares only 80% sequence identity with the closest relative of both genera, Rhodopirellula and Pirellula. Thus, strain NH11(T) is unique in terms of origin and phylogeny. While the pear to ovoid shaped cells of strain NH11(T) are typical planctomycetal, light-, and electron microscopic observations point toward an unusual variation of cell division through budding: during the division process daughter- and mother cells are connected by an unseen thin tubular-like structure. Furthermore, the periplasmic space of strain NH11(T) was unusually enlarged and differed from previously known planctomycetes. The complete genome of strain NH11(T), with almost 9 Mb in size, is among the largest planctomycetal genomes sequenced thus far, but harbors only 6645 protein-coding genes. The acquisition of genomic components by horizontal gene transfer is indicated by the presence of numerous putative genomic islands. Strikingly, 45 "giant genes" were found within the genome of NH11(T). Subsequent analysis of all available planctomycetal genomes revealed that Planctomycetes as such are especially rich in "giant genes". Furthermore, Multilocus Sequence Analysis (MLSA) tree reconstruction support the phylogenetic distance of strain NH11(T) from other cultivated Planctomycetes of the same phylogenetic cluster. Thus, based on our findings, we propose to classify strain NH11(T) as Fuerstia marisgermanicae gen. nov., sp. nov., with the type strain NH11(T), within the phylum Planctomycetes.