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 Planctomycetes 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 Planctomycetes is the most abundant bacterial phylum on the alga Fucus sp., while it represents a minor fraction of the surface-associated bacterial community of Ulva sp. and Laminaria sp. Especially dominant within the phylum Planctomycetes were Blastopirellula sp., followed by Rhodopirellula sp., Rubripirellula sp., as well as other Pirellulaceae and Lacipirellulaceae, 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 Pirellulales, class Planctomycetia, phylum Planctomycetes.

Cultivation-Independent Analysis of the Bacterial Community Associated With the Calcareous Sponge Clathrina clathrus and Isolation of Poriferisphaera corsica Gen. Nov., Sp. Nov., Belonging to the Barely Studied Class Phycisphaerae in the Phylum Planctomycetes

Marine ecosystems serve as global carbon sinks and nutrient source or breeding ground for aquatic animals. Sponges are ancient parts of these important ecosystems and can be found in caves, the deep-sea, clear waters, or more turbid environments. Here, we studied the bacterial community composition of the calcareous sponge Clathrina clathrus sampled close to the island Corsica in the Mediterranean Sea with an emphasis on planctomycetes. We show that the phylum Planctomycetes accounts for 9% of the C. clathrus-associated bacterial community, a 5-fold enrichment compared to the surrounding seawater. Indeed, the use of C. clathrus as a yet untapped source of novel planctomycetal strains led to the isolation of strain KS4T. The strain represents a novel genus and species within the class Phycisphaerae in the phylum Planctomycetes and displays interesting cell biological features, such as formation of outer membrane vesicles and an unexpected mode of cell division.

Updates to the recently introduced family Lacipirellulaceae in the phylum Planctomycetes: isolation of strains belonging to the novel genera Aeoliella, Botrimarina, Pirellulimonas and Pseudobythopirellula and the novel species Bythopirellula polymerisocia and Posidoniimonas corsicana

Eight novel strains of the phylum Planctomycetes were isolated from different aquatic habitats. Among these habitats were the hydrothermal vent system close to Panarea Island, a public beach at Mallorca Island, the shore of Costa Brava (Spain), and three sites with brackish water in the Baltic Sea. The genome sizes of the novel strains range from 4.33 to 6.29 Mb with DNA G+C contents between 52.8 and 66.7%. All strains are mesophilic (Topt 24–30 °C) and display generation times between 17 and 94 h. All eight isolates constitute novel species of either already described or novel genera within the family Lacipirellulaceae. Two of the novel species, Posidoniimonas polymericola (type strain Pla123aT = DSM 103020T = LMG 29466T) and Bythopirellula polymerisocia (type strain Pla144T = DSM 104841T = VKM B-3442T), belong to established genera, while the other strains represent the novel genera Aeoliella gen. nov., Botrimarina gen. nov., Pirellulimonas gen. nov. and Pseudobythopirellula gen. nov. Based on our polyphasic analysis, we propose the species Aeoliella mucimassa sp. nov. (type strain Pan181T = DSM 29370T = LMG 31346T = CECT 9840T = VKM B-3426T), Botrimarina colliarenosi sp. nov. (type strain Pla108T = DSM 103355T = LMG 29803T), Botrimarina hoheduenensis sp. nov. (type strain Pla111T = DSM 103485T = STH00945T, Jena Microbial Resource Collection JMRC), Botrimarina mediterranea sp. nov. (type strain Spa11T = DSM 100745T = LMG 31350T = CECT 9852T = VKM B-3431T), Pirellulimonas nuda sp. nov. (type strain Pla175T = DSM 109594T = CECT 9871T = VKM B-3448T) and Pseudobythopirellula maris sp. nov. (type strain Mal64T = DSM 100832T = LMG 29020T).

The planctomycete Stieleria maiorica Mal15T employs stieleriacines to alter the species composition in marine biofilms

Bacterial strains of the phylum Planctomycetes occur ubiquitously, but are often found on surfaces of aquatic phototrophs, e.g. alga. Despite slower growth, planctomycetes are not outcompeted by faster-growing bacteria in biofilms on such surfaces; however, strategies allowing them to compensate for slower growth have not yet been investigated. Here, we identified stieleriacines, a class of N-acylated tyrosines produced by the novel planctomycete Stieleria maiorica Mal15T, and analysed their effects on growth of the producing strain and bacterial species likely co-occurring with strain Mal15T. Stieleriacines reduced the lag phase of Mal15T and either stimulated or inhibited biofilm formation of two bacterial competitors, indicating that Mal15T employs stieleriacines to specifically alter microbial biofilm composition. The genetic organisation of the putative stieleriacine biosynthetic cluster in strain Mal15T points towards a functional link of stieleriacine biosynthesis to exopolysaccharide-associated protein sorting and biofilm formation.