How clear is our current view on microbial dark matter? (Re-)assessing public MAG & SAG datasets with MDMcleaner.

As of today, the majority of environmental microorganisms remain uncultured and is therefore referred to as 'microbial dark matter' (MDM). Hence, genomic insights into these organisms are limited to cultivation-independent approaches such as single-cell- and metagenomics. However, without access to cultured representatives for verifying correct taxon-assignments, MDM genomes may cause potentially misleading conclusions based on misclassified or contaminant contigs, thereby obfuscating our view on the uncultured microbial majority. Moreover, gradual database contaminations by past genome submissions can cause error propagations which affect present as well as future comparative genome analyses. Consequently, strict contamination detection and filtering need to be applied, especially in the case of uncultured MDM genomes. Current genome reporting standards, however, emphasize completeness over purity and the de facto gold standard genome assessment tool, checkM, discriminates against uncultured taxa and fragmented genomes. To tackle these issues, we present a novel contig classification, screening, and filtering workflow and corresponding open-source python implementation called MDMcleaner, which was tested and compared to other tools on mock and real datasets. MDMcleaner revealed substantial contaminations overlooked by current screening approaches and sensitively detects misattributed contigs in both novel genomes and the underlying reference databases, thereby greatly improving our view on 'microbial dark matter'.

Stratiformator vulcanicus gen. nov., sp. nov., a marine member of the family Planctomycetaceae isolated from a red biofilm in the Tyrrhenian Sea close to the volcanic island Panarea.

A novel planctomycetal strain, designated Pan189T, was isolated from biofilm material sampled close to Panarea Island in the Tyrrhenian Sea. Cells of strain Pan189T are round grain rice-shaped, form pink colonies and display typical planctomycetal characteristics including asymmetric cell division through polar budding and presence of crateriform structures. Cells bear a stalk opposite to the division pole and fimbriae cover the cell surface. Strain Pan189T has a mesophilic (optimum at 24 °C) and neutrophilic (optimum at pH 7.5) growth profile, is aerobic and heterotrophic. Under laboratory-scale cultivation conditions, it reached a generation time of 102 h (µmax = 0.0068 h-1), which places the strain among the slowest growing members of the phylum Planctomycetota characterized so far. The genome size of the strain is with 5.23 Mb at the lower limit among the family Planctomycetaceae (5.1-8.9 Mb). Phylogenetically, the strain represents a novel genus and species in the family Planctomycetaceae, order Planctomycetales, class Planctomycetia. We propose the name Stratiformator vulcanicus gen. nov., sp. nov. for the novel taxon, that is represented by the type strain Pan189T (= DSM 101711 T = CECT 30699 T).

Mucisphaera calidilacus gen. nov., sp. nov., a novel planctomycete of the class Phycisphaerae isolated in the shallow sea hydrothermal system of the Lipari Islands.

For extending the current collection of axenic cultures of planctomycetes, we describe in this study the isolation and characterisation of strain Pan265T obtained from a red biofilm in the hydrothermal vent system close to the Lipari Islands in the Tyrrhenian Sea, north of Sicily, Italy. The strain forms light pink colonies on solid medium and grows as a viscous colloid in liquid culture, likely as the result of formation of a dense extracellular matrix observed during electron microscopy. Cells of the novel isolate are spherical, motile and divide by binary fission. Strain Pan265T is mesophilic (temperature optimum 30-33 °C), neutrophilic (pH optimum 7.0-8.0), aerobic and heterotrophic. The strain has a genome size of 3.49 Mb and a DNA G + C content of 63.9%. Phylogenetically, the strain belongs to the family Phycisphaeraceae, order Phycisphaerales, class Phycisphaerae. Our polyphasic analysis supports the delineation of strain Pan265T from the known genera in this family. Therefore, we conclude to assign strain Pan265T to a novel species within a novel genus, for which we propose the name Mucisphaera calidilacus gen. nov., sp. nov. The novel species is the type species of the novel genus and is represented by strain Pan265T (= DSM 100697T = CECT 30425T) as type strain.

Analysis of bacterial communities in a municipal duck pond during a phytoplankton bloom and isolation of Anatilimnocola aggregata gen. nov., sp. nov., Lacipirellula limnantheis sp. nov. and Urbifossiella limnaea gen. nov., sp. nov. belonging to the phylum Planctomycetes.

Waterbodies such as lakes and ponds are fragile environments affected by human influences. Suitable conditions can result in massive growth of phototrophs, commonly referred to as phytoplankton blooms. Such events benefit heterotrophic bacteria able to use compounds secreted by phototrophs or their biomass as major nutrient source. One example of such bacteria are Planctomycetes, which are abundant on the surfaces of marine macroscopic phototrophs; however, less data are available on their ecological roles in limnic environments. In this study, we followed a cultivation-independent deep sequencing approach to study the bacterial community composition during a cyanobacterial bloom event in a municipal duck pond. In addition to cyanobacteria, which caused the bloom event, members of the phylum Planctomycetes were significantly enriched in the cyanobacteria-attached fraction compared to the free-living fraction. Separate datasets based on isolated DNA and RNA point towards considerable differences in the abundance and activity of planctomycetal families, indicating different activity peaks of these families during the cyanobacterial bloom. Motivated by the finding that the sampling location harbours untapped bacterial diversity, we included a complementary cultivation-dependent approach and isolated and characterized three novel limnic strains belonging to the phylum Planctomycetes.

Tautonia plasticadhaerens sp. nov., a novel species in the family Isosphaeraceae isolated from an alga in a hydrothermal area of the Eolian Archipelago.

A novel planctomycetal strain, designated ElPT, was isolated from an alga in the shallow hydrothermal vent system close to Panarea Island in the Tyrrhenian Sea. Cells of strain ElPT are spherical, form pink colonies and display typical planctomycetal characteristics including division by budding and presence of crateriform structures. Strain ElPT has a mesophilic (optimum at 30 °C) and neutrophilic (optimum at pH 7.5) growth profile, is aerobic and heterotrophic. It reaches a generation time of 29 h (µmax = 0.024 h-1). The strain has a genome size of 9.40 Mb with a G + C content of 71.1% and harbours five plasmids, the highest number observed in the phylum Planctomycetes thus far. Phylogenetically, the strain represents a novel species of the recently described genus Tautonia in the family Isosphaeraceae. A characteristic feature of the strain is its tendency to attach strongly to a range of plastic surfaces. We thus propose the name Tautonia plasticadhaerens sp. nov. for the novel species, represented by the type strain ElPT (DSM 101012T = LMG 29141T).

Lignipirellula cremea gen. nov., sp. nov., a planctomycete isolated from wood particles in a brackish river estuary.

A novel planctomycetal strain, designated Pla85_3_4T, was isolated from the surface of wood incubated at the discharge of a wastewater treatment plant in the Warnow river near Rostock, Germany. Cells of the novel strain have a cell envelope architecture resembling that of Gram-negative bacteria, are round to pear-shaped (length: 2.2 ± 0.4 µm, width: 1.2 ± 0.3 µm), form aggregates and divide by polar budding. Colonies have a cream colour. Strain Pla85_3_4T grows at ranges of 10-30 °C (optimum 26 °C) and at pH 6.5-10.0 (optimum 7.5), and has a doubling time of 26 h. Phylogenetically, strain Pla85_3_4T (DSM 103796T = LMG 29741T) is concluded to represent a novel species of a novel genus within the family Pirellulaceae, for which we propose the name Lignipirellula cremea gen. nov., sp. nov.

Description of Polystyrenella longa gen. nov., sp. nov., isolated from polystyrene particles incubated in the Baltic Sea.

Planctomycetes occur in almost all aquatic ecosystems on earth. They have a remarkable cell biology, and members of the orders Planctomycetales and Pirellulales feature cell division by polar budding, perform a lifestyle switch from sessile to motile cells and have an enlarged periplasmic space. Here, we characterise a novel planctomycetal strain, Pla110T, isolated from the surface of polystyrene particles incubated in the Baltic Sea. After phylogenetic analysis, the strain could be placed in the family Planctomycetaceae. Strain Pla110T performs cell division by budding, has crateriform structures and grows in aggregates or rosettes. The strain is a chemoheterotroph, grows under mesophilic and neutrophilic conditions, and exhibited a doubling time of 21 h. Based on our phylogenetic and morphological characterisation, strain Pla110T (DSM 103387T = LMG 29693T) is concluded to represent a novel species belonging to a novel genus, for which we propose the name Polystyrenella longa gen. nov., sp. nov.

Caulifigura coniformis gen. nov., sp. nov., a novel member of the family Planctomycetaceae isolated from a red biofilm sampled in a hydrothermal area.

Pan44T, a novel strain belonging to the phylum Planctomycetes, was isolated from a red biofilm in a hydrothermal area close to the island Panarea in the Tyrrhenian Sea north of Sicily, Italy. The strain forms white colonies on solid medium and displays the following characteristics: cell division by budding, formation of rosettes, presence of matrix or fimbriae and long stalks. The cell surface has an interesting and characteristic texture made up of triangles and rectangles, which leads to a pine cone-like morphology of the strain. Strain Pan44T is mesophilic (temperature optimum 26 °C), slightly alkaliphilic (pH optimum 8.0), aerobic and heterotrophic. The strain has a genome size of 6.76 Mb with a G + C content of 63.2%. Phylogenetically, the strain is a member of the family Planctomycetaceae, order Planctomycetales, class Planctomycetia. Our analysis supports delineation of strain Pan44T from all known genera in this family, hence, we propose to assign it to a novel species within a novel genus, for which we propose the name Caulifigura coniformis gen. nov., sp. nov., represented by Pan44T (DSM 29405T = LMG 29788T) as the type strain.

Three novel Rubripirellula species isolated from plastic particles submerged in the Baltic Sea and the estuary of the river Warnow in northern Germany.

Planctomycetes are a unique and important phylum containing mostly aquatic bacteria, which are often associated with phototrophic surfaces. A complex lifestyle, their potential for the production of bioactive small molecules, their unusual cell biology and a large number of giant and hypothetical genes in their genomes make these microorganisms a fascinating topic for further research. Here, we characterise three novel planctomycetal strains isolated from polystyrene and polyethylene particles that were submerged in the German part of the Baltic Sea and the estuary of the river Warnow. All three strains showed typical planctomycetal traits such as division by polar budding and formation of rosettes. The isolated strains were mesophilic and neutrophilic chemoheterotrophs and reached generation times of 10-25 h during laboratory-scale cultivation. Taxonomically, the three strains belong to the genus Rubripirellula. Based on our analyses all three strains represent novel species, for which we propose the names Rubripirellula amarantea sp. nov., Rubripirellula tenax sp. nov. and Rubripirellula reticaptiva sp. nov. The here characterised strains Pla22T (DSM 102267T = LMG 29691T), Poly51T (DSM 103356T = VKM B-3438T) and Poly59T (DSM 103767T = LMG 29696T) are the respective type strains of these novel species. We also emend the description of the genus Rubripirellula.

Rubinisphaera italica sp. nov. isolated from a hydrothermal area in the Tyrrhenian Sea close to the volcanic island Panarea.

Planctomycetes is a fascinating phylum of mostly aquatic bacteria, not only due to the environmental importance in global carbon and nitrogen cycles, but also because of a unique cell biology. Their lifestyle and metabolic capabilities are not well explored, which motivated us to study the role of Planctomycetes in biofilms on marine biotic surfaces. Here, we describe the novel strain Pan54T which was isolated from algae in a hydrothermal area close to the volcanic island Panarea in the Tyrrhenian Sea, north of Sicily in Italy. The strain grew best at pH 9.0 and 26 °C and showed typical characteristics of planctomycetal bacteria, e.g. division by polar budding, formation of aggregates and presence of stalks and crateriform structures. Phylogenetically, the strain belongs to the genus Rubinisphaera. Our analysis suggests that Pan54T represents a novel species of this genus, for which we propose the name Rubinisphaera italica sp. nov. We suggest Pan54T (= DSM 29369 = LMG 29789) as the type strain of the novel species.

Stieleria varia sp. nov., isolated from wood particles in the Baltic Sea, constitutes a novel species in the family Pirellulaceae within the phylum Planctomycetes.

Species belonging to the bacterial phylum Planctomycetes are ubiquitous members of the microbial communities in aquatic environments and are frequently isolated from various biotic and abiotic surfaces in marine and limnic water bodies. Planctomycetes have large genomes of up to 12.4 Mb, follow complex lifestyles and display an uncommon cell biology; features which motivate the investigation of members of this phylum in greater detail. As a contribution to the current collection of axenic cultures of Planctomycetes, we here describe strain Pla52T isolated from wood particles in the Baltic Sea. Phylogenetic analysis places the strain in the family Pirellulaceae and suggests two species of the recently described genus Stieleria as current closest neighbours. Strain Pla52nT shows typical features of members of the class Planctomycetia, including division by polar budding and the presence of crateriform structures. Colonies of strain Pla52nT have a light orange colour, which is an unusual pigmentation compared to the majority of members in the phylum, which show either a pink to red pigmentation or entirely lack pigmentation. Optimal growth of strain Pla52nT at 33 °C and pH 7.5 indicates a mesophilic (i.e. with optimal growth between 20 and 45 °C) and neutrophilic growth profile. The strain is an aerobic heterotroph with motile daughter cells. Its genome has a size of 9.6 Mb and a G + C content of 56.0%. Polyphasic analyses justify delineation of the strain from described species within the genus Stieleria. Therefore, we conclude that strain Pla52nT = LMG 29463T = VKM B-3447T should be classified as the type strain of a novel species, for which we propose the name Stieleria varia sp. nov.

Additions to the genus Gimesia: description of Gimesia alba sp. nov., Gimesia algae sp. nov., Gimesia aquarii sp. nov., Gimesia aquatilis sp. nov., Gimesia fumaroli sp. nov. and Gimesia panareensis sp. nov., isolated from aquatic habitats of the Northern Hemisphere.

Thirteen novel planctomycetal strains were isolated from five different aquatic sampling locations. These comprise the hydrothermal vent system close to Panarea Island (Italy), a biofilm on the surface of kelp at Monterey Bay (CA, USA), sediment and algae on Mallorca Island (Spain) and Helgoland Island (Germany), as well as a seawater aquarium in Braunschweig, Germany. All strains were shown to belong to the genus Gimesia. Their genomes cover a size range from 7.22 to 8.29 Mb and have a G+C content between 45.1 and 53.7%. All strains are mesophilic (Topt 26-33 °C) with generation times between 12 and 32 h. Analysis of fatty acids yielded palmitic acid (16:0) and a fatty acid with the equivalent chain length of 15.817 as major compounds. While five of the novel strains belong to the already described species Gimesia maris and Gimesia chilikensis, the other strains belong to novel species, for which we propose the names Gimesia alba (type strain Pan241wT = DSM 100744T = LMG 31345T = CECT 9841T = VKM B-3430T), Gimesia algae (type strain Pan161T = CECT 30192T = STH00943T = LMG 29130T), Gimesia aquarii (type strain V144T = DSM 101710T = VKM B-3433T), Gimesia fumaroli (type strain Enr17T = DSM 100710T = VKM B-3429T) and Gimesia panareensis (type strain Enr10T = DSM 100416T = LMG 29082T). STH numbers refer to the Jena Microbial Resource Collection (JMRC).

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).

Calycomorphotria hydatis gen. nov., sp. nov., a novel species in the family Planctomycetaceae with conspicuous subcellular structures.

A novel strain belonging to the family Planctomycetaceae, designated V22T, was isolated from sediment of a seawater fish tank in Braunschweig, Germany. The isolate forms pink colonies on solid medium and displays common characteristics of planctomycetal strains, such as division by budding, formation of rosettes, a condensed nucleoid and presence of crateriform structures and fimbriae. Unusual invaginations of the cytoplasmic membrane and filamentous putative cytoskeletal elements were observed in thin sections analysed by transmission electron microscopy. Strain V22T is an aerobic heterotroph showing optimal growth at 30 °C and pH 8.5. During laboratory cultivations, strain V22T reached generation times of 10 h (maximal growth rate of 0.069 h-1). Its genome has a size of 5.2 Mb and a G + C content of 54.9%. Phylogenetically, the strain represents a novel genus and species in the family Planctomycetaceae, order Planctomycetales, class Planctomycetia. We propose the name Calycomorphotria hydatis gen. nov., sp. nov. for the novel taxon, represented by the type strain V22T (DSM 29767T = LMG 29080T).

Aureliella helgolandensis gen. nov., sp. nov., a novel Planctomycete isolated from a jellyfish at the shore of the island Helgoland.

A novel planctomycetal strain, designated Q31aT, was isolated from a jellyfish at the shore of the island Helgoland in the North Sea. The strain forms lucid white colonies on solid medium and displays typical characteristics of planctomycetal strains, such as division by budding, formation of rosettes, presence of crateriform structures, extracellular matrix or fibre and a holdfast structure. Q31aT is mesophilic (temperature optimum 27 °C), neutrophilic (pH optimum 7.5), aerobic and heterotrophic. A maximal growth rate of 0.017 h- 1 (generation time of 41 h) was observed. Q31aT has a genome size of 8.44 Mb and a G + C content of 55.3%. Phylogenetically, the strain represents a novel genus and species in the recently introduced family Pirellulaceae, order Pirellulales, class Planctomycetia. We propose the name Aureliella helgolandensis gen. nov., sp. nov. for the novel species, represented by Q31aT (= DSM 103537T = LMG 29700T) as the type strain.

Rosistilla oblonga gen. nov., sp. nov. and Rosistilla carotiformis sp. nov., isolated from biotic or abiotic surfaces in Northern Germany, Mallorca, Spain and California, USA.

Planctomycetes are ubiquitous bacteria with fascinating cell biological features. Strains available as axenic cultures in most cases have been isolated from aquatic environments and serve as a basis to study planctomycetal cell biology and interactions in further detail. As a contribution to the current collection of axenic cultures, here we characterise three closely related strains, Poly24T, CA51T and Mal33, which were isolated from the Baltic Sea, the Pacific Ocean and the Mediterranean Sea, respectively. The strains display cell biological features typical for related Planctomycetes, such as division by polar budding, presence of crateriform structures and formation of rosettes. Optimal growth was observed at temperatures of 30-33 °C and at pH 7.5, which led to maximal growth rates of 0.065-0.079 h-1, corresponding to generation times of 9-11 h. The genomes of the novel isolates have a size of 7.3-7.5 Mb and a G + C content of 57.7-58.2%. Phylogenetic analyses place the strains in the family Pirellulaceae and suggest that Roseimaritima ulvae and Roseimaritima sediminicola are the current closest relatives. Analysis of five different phylogenetic markers, however, supports the delineation of the strains from members of the genus Roseimaritima and other characterised genera in the family. Supported by morphological and physiological differences, we conclude that the strains belong to the novel genus Rosistilla gen. nov. and constitute two novel species, for which we propose the names Rosistilla carotiformis sp. nov. and Rosistilla oblonga sp. nov. (the type species). The two novel species are represented by the type strains Poly24T (= DSM 102938T = VKM B-3434T = LMG 31347T = CECT 9848T) and CA51T (= DSM 104080T = LMG 29702T), respectively.

Thalassoglobus polymorphus sp. nov., a novel Planctomycete isolated close to a public beach of Mallorca Island.

Access to axenic cultures is crucial to extend the knowledge of the biology, lifestyle or metabolic capabilities of bacteria from different phyla. The phylum Planctomycetes is an excellent example since its members display an unusual cell biology and complex lifestyles. As a contribution to the current collection of axenic planctomycete cultures, here we describe strain Mal48T isolated from phytoplankton material sampled at the coast of S'Arenal close to Palma de Mallorca (Spain). The isolated strain shows optimal growth at pH 7.0-7.5 and 30 °C and exhibits typical features of Planctomycetes. Cells of the strain are spherical to pear-shaped, divide by polar budding with daughter cells showing the same shape as the mother cell, tend to aggregate, display a stalk and produce matrix or fimbriae. Strain Mal48T showed 95.8% 16S rRNA gene sequence similarity with the recently described Thalassoglobus neptunius KOR42T. The genome sequence of the novel isolate has a size of 6,357,355 bp with a G+C content of 50.3%. A total of 4874 protein-coding genes, 41 tRNA genes and 2 copies of the 16S rRNA gene are encoded in the genome. Based on phylogenetic, morphological and physiological analyses, we conclude that strain Mal48T (= DSM 100737T = LMG 29019T) should be classified as the type strain of a new species in the genus Thalassoglobus, for which the name Thalassoglobus polymorphus sp. nov. is proposed.

Maioricimonas rarisocia gen. nov., sp. nov., a novel planctomycete isolated from marine sediments close to Mallorca Island.

Planctomycetes are ubiquitous bacteria with environmental and biotechnological relevance. Axenic cultures of planctomycetal strains are the basis to analyse their unusual biology and largely uncharacterised metabolism in more detail. Here, we describe strain Mal4T isolated from marine sediments close to Palma de Mallorca, Spain. Strain Mal4T displays common planctomycetal features, such as division by polar budding and the presence of fimbriae and crateriform structures on the cell surface. Cell growth was observed at ranges of 10-39 °C (optimum at 31 °C) and pH 6.5-9.0 (optimum at 7.5). The novel strain shows as pear-shaped cells of 2.0 ± 0.2 × 1.4 ± 0.1 µm and is one of the rare examples of orange colony-forming Planctomycetes. Its genome has a size of 7.7 Mb with a G+C content of 63.4%. Phylogenetically, we conclude that strain Mal4T (= DSM 100296T = LMG 29133T) is the type strain representing the type species of a novel genus, for which we propose the name Maioricimonas rarisocia gen. nov., sp. nov.

Three marine strains constitute the novel genus and species Crateriforma conspicua in the phylum Planctomycetes.

Planctomycetes is a ubiquitous phylum of mostly aquatic bacteria that have a complex lifestyle and an unusual cell biology. Here, we describe three strains of the same novel genus and species isolated from three different environments; from a red biofilm at a hydrothermal vent in the Mediterranean Sea, from sediment in a salt-water fish tank, and from the surface of algae at the coast of the Balearic island Mallorca. The three strains Mal65T (DSM 100706T = LMG 29792T, Pan14r (DSM 29351 = LMG 29012), and V7 (DSM 29812 = CECT 9853 = VKM B-3427) show typical characteristics of the Planctomycetaceae family, such as cell division by budding, crateriform structures and growth in aggregates or rosettes.  The strains are mesophilic, neutrophilic to alkaliphilic as well as chemoheterotrophic and exhibit doubling times between 12 and 35 h. Based on our phylogenetic analysis, the three strains represent a single novel species of a new genus, for which we propose the name Crateriforma conspicua gen. nov. sp. nov.

Description of the novel planctomycetal genus Bremerella, containing Bremerella volcania sp. nov., isolated from an active volcanic site, and reclassification of Blastopirellula cremea as Bremerella cremea comb. nov.

Planctomycetes are part of the PVC superphylum together with Verrucomicrobia, Chlamydiae and others. They are budding bacteria with very distinctive characteristics, such as a remarkable morphology and cell biology. Planctomycetes can be found in almost all habitats, and seem to have a preference for marine biotic and abiotic surfaces, on which they frequently occur in biofilm-forming communities. To extend the number of axenic cultures of planctomycetal strains, we isolated Pan97T from a biofilm in a volcanic site close to the Italian island Panarea in the Thyrrhenian Sea. The physiology, genome and morphology of the novel strain were characterised revealing typical planctomycetal characteristics, such as, division by polar budding and presence of crateriform structures. The strain shows pear-shaped cells of 1.5 ± 0.3 µm × 0.8 ± 0.2 µm and forms white- to cream-coloured colonies on solid medium. Strain Pan97T is mesophilic and neutrophilic, since growth was observed  at a pH range of 5.5-9.5 with optimal growth at pH 7.0 and at a temperature range of 15-40 °C with a maximal growth rate at 36 °C. Pan97T has a genome size of 6,496,182 bp with a G + C content of 56.2%. 5264 protein-coding genes were identified, of which 2141 genes (41%) encode hypothetical proteins. Based on the phylogenetic analysis, we suggest that Pan97T (DSM 101992T = LMG 29460T) represents a novel species of a novel genus within the family Planctomycetaceae, for which we propose the name Bremerella gen. nov., with strain Pan97T classified as Bremerella volcania sp. nov. Based on our analysis, we also propose the reclassification of Blastopirellula cremea Lee et al. 2013 as Bremerella cremea comb. nov., as this species is considered to be the type species of the novel genus Bremerella.