Analysis of Bacterial Communities on North Sea Macroalgae and Characterization of the Isolated Planctomycetes Adhaeretor mobilis gen. nov., sp. nov., Roseimaritima multifibrata sp. nov., Rosistilla ulvae sp. nov. and Rubripirellula lacrimiformis sp. nov.

Planctomycetes are bacteria that were long thought to be unculturable, of low abundance, and therefore neglectable in the environment. This view changed in recent years, after it was shown that members of the phylum <i>Planctomycetes</i> can be abundant in many aquatic environments, e.g., in the epiphytic communities on macroalgae surfaces. Here, we analyzed three different macroalgae from the North Sea and show that <i>Planctomycetes</i> is the most abundant bacterial phylum on the alga <i>Fucus</i> sp., while it represents a minor fraction of the surface-associated bacterial community of <i>Ulva</i> sp. and <i>Laminaria</i> sp. Especially dominant within the phylum <i>Planctomycetes</i> were <i>Blastopirellula</i> sp., followed by <i>Rhodopirellula</i> sp., <i>Rubripirellula</i> sp., as well as other <i>Pirellulaceae</i> and <i>Lacipirellulaceae</i>, but also members of the OM190 lineage. Motivated by the observed abundance, we isolated four novel planctomycetal strains to expand the collection of species available as axenic cultures since access to different strains is a prerequisite to investigate the success of planctomycetes in marine environments. The isolated strains constitute four novel species belonging to one novel and three previously described genera in the order <i>Pirellulales</i>, class <i>Planctomycetia</i>, phylum <i>Planctomycetes</i>.