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

Planctoellipticum variicoloris gen. nov., sp. nov., a novel member of the family Planctomycetaceae isolated from wastewater of the aeration lagoon of a sugar processing plant in Northern Germany

In the present study, we characterise a strain isolated from the wastewater aeration lagoon of a sugar processing plant in Schleswig (Northern Germany) by Heinz Schlesner. As a pioneer in planctomycetal research, he isolated numerous strains belonging to the phylum Planctomycetota from aquatic habitats around the world. Phylogenetic analyses show that strain SH412T belongs to the family Planctomycetaceae and shares with 91.6% the highest 16S rRNA gene sequence similarity with Planctopirus limnophila DSM 3776T. Its genome has a length of 7.3 Mb and a G + C content of 63.6%. Optimal growth of strain SH412T occurs at pH 7.0-7.5 and 28 °C with its pigmentation depending on sunlight exposure. Strain SH412T reproduces by polar asymmetric division ("budding") and forms ovoid cells. The cell size determination was performed using a semi-automatic pipeline, which we first evaluated with the model species P. limnophila and then applied to strain SH412T. Furthermore, the data acquired during time-lapse analyses suggests a lifestyle switch from flagellated daughter cells to non-flagellated mother cells in the subsequent cycle. Based on our data, we suggest that strain SH412T represents a novel species within a novel genus, for which we propose the name Planctoellipticum variicoloris gen. nov., sp. nov., with strain SH412T (= CECT 30430T = STH00996T, the STH number refers to the Jena Microbial Resource Collection JMRC) as the type strain of the new species.

A type III polyketide synthase cluster in the phylum Planctomycetota is involved in alkylresorcinol biosynthesis

Members of the bacterial phylum Planctomycetota have recently emerged as promising and for the most part untapped sources of novel bioactive compounds. The characterization of more than 100 novel species in the last decade stimulated recent bioprospection studies that start to unveil the chemical repertoire of the phylum. In this study, we performed systematic bioinformatic analyses based on the genomes of all 131 described members of the current phylum focusing on the identification of type III polyketide synthase (PKS) genes. Type III PKSs are versatile enzymes involved in the biosynthesis of a wide array of structurally diverse natural products with potent biological activities. We identified 96 putative type III PKS genes of which 58 are encoded in an operon with genes encoding a putative oxidoreductase and a methyltransferase. Sequence similarities on protein level and the genetic organization of the operon point towards a functional link to the structurally related hierridins recently discovered in picocyanobacteria. The heterologous expression of planctomycetal type III PKS genes from strains belonging to different families in an engineered Corynebacterium glutamicum strain led to the biosynthesis of pentadecyl- and heptadecylresorcinols. Phenotypic assays performed with the heterologous producer strains and a constructed type III PKS gene deletion mutant suggest that the natural function of the identified compounds differs from that confirmed in other bacterial alkylresorcinol producers. KEY POINTS: • Planctomycetal type III polyketide synthases synthesize long-chain alkylresorcinols. • Phylogenetic analyses suggest an ecological link to picocyanobacterial hierridins. • Engineered C. glutamicum is suitable for an expression of planctomycete-derived genes.

Uncovering the biotechnological capacity of marine and brackish water Planctomycetota

An appealing strategy for finding novel bioactive molecules in Nature consists in exploring underrepresented and -studied microorganisms. Here, we investigated the antimicrobial and tumoral anti-proliferative bioactivities of twenty-three marine and estuarine bacteria of the fascinating phylum Planctomycetota. This was achieved through extraction of compounds produced by the Planctomycetota cultured in oligotrophic medium followed by an antimicrobial screening against ten relevant human pathogens including Gram-positive and Gram-negative bacteria, and fungi. Cytotoxic effects of the extracts were also evaluated against five tumoral cell lines. Moderate to potent activities were obtained against Enterococcus faecalis, methicillin-sensitive and methicillin-resistant Staphylococcus aureus and vancomycin-sensitive and vancomycin-resistant Enterococcus faecium. Anti-fungal effects were observed against Trichophyton rubrum, Candida albicans and Aspergillus fumigatus. The highest cytotoxic effects were observed against human breast, pancreas and melanoma tumoral cell lines. Novipirellula caenicola and Rhodopirellula spp. strains displayed the widest spectrum of bioactivities while Rubinisphaera margarita ICM_H10T affected all Gram-positive bacteria tested. LC-HRMS analysis of the extracts did not reveal the presence of any known bioactive natural product, suggesting that the observed activities are most likely caused by novel molecules, that need identification. In summary, we expanded the scope of planctomycetal species investigated for bioactivities and demonstrated that various strains are promising sources of novel bioactive compounds, which reenforces the potential biotechnological prospects offered by Planctomycetota.

Stieleria tagensis sp. nov., a novel member of the phylum Planctomycetota isolated from Tagus River in Portugal

A bacterial strain was isolated from a brackish water sample of Tagus river, Alcochete, Portugal and was designated TO1_6T. It forms light pink colonies on M13 medium supplemented with N-acetylglucosamine. Cells are pear-shaped to spherical, form rosettes and divide by budding. Strain TO1_6T presents a mesophilic and neutrophilic profile, with optimum growth at 20 to 25 °C and pH 7.0 to 7.5, and vitamin supplementation is not required to promote its growth. The genome of the novel isolate is 7.77 Mbp in size and has a DNA G + C content of 56.3%. Based on its 16S rRNA gene sequence, this strain is affiliated with the phylum Planctomycetota. Further taxonomic characterization using additional phylogenetic markers, namely rpoB gene sequence (encoding the β-subunit of the DNA-dependent RNA polymerase), as well as Percentage of conserved proteins, average nucleotide identity and average amino acid identity, suggest the affiliation of strain TO1_6T to the genus Stieleria, a recently described taxon in the family Pirellulaceae, order Pirellulales and class Planctomycetia. Based on the genotypic, phylogenetic and physiological characterization, we here describe a new species represented by the type strain TO1_6T (= CECT 30432T, = LMG 32465T), for which the name Stieleria tagensis sp. nov. is proposed.

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).

Stieleria sedimenti sp. nov., a Novel Member of the Family Pirellulaceae with Antimicrobial Activity Isolated in Portugal from Brackish Sediments

The phylum Planctomycetota is known for having uncommon biological features. Recently, biotechnological applications of its members have started to be explored, namely in the genus Stieleria. Here, we formally describe a novel Stieleriaisolate designated as strain ICT_E10.1T, obtained from sediments collected in the Tagus estuary (Portugal). Strain ICT_E10.1T is pink-pigmented, spherical to ovoid in shape, and 1.7 µm ± 0.3 × 1.4 µm ± 0.3 in size. Cells cluster strongly in aggregates or small chains, divide by budding, and have prominent fimbriae. Strain ICT_E10.1T is heterotrophic and aerobic. Growth occurs from 20 to 30 °C, from 0.5 to 3% (w/v) NaCl, and from pH 6.5 to 11.0. The analysis of the 16S rRNA gene sequence placed strain ICT_E10.1T into the genus Stieleria with Stieleria neptunia Enr13T as the closest validly described relative. The genome size is 9,813,311 bp and the DNA G+C content is 58.8 mol%. Morphological, physiological, and genomic analyses support the separation of this strain into a novel species, for which we propose the name Stieleria sedimenti represented by strain ICT_E10.1T as the type of strain (=CECT 30514T= DSM 113784T). Furthermore, this isolate showed biotechnological potential by displaying relevant biosynthetic gene clusters and potent activity against Staphylococcus aureus.

Rhodopirellula aestuarii sp. nov., a novel member of the genus Rhodopirellula isolated from brackish sediments collected in the Tagus River estuary, Portugal

Bacteria within the phylum Planctomycetota are biologically relevant due to unique characteristics among prokaryotes. Members of the genus Rhodopirellula can be abundant in marine habitats, however, only six species are currently validly described. In this study, we expand the explored genus diversity by formally describing a novel species. The pink-coloured strain ICT_H3.1^T was isolated from brackish sediments collected in the Tagus estuary (Portugal) and a 16S rRNA gene sequence-based analysis placed this strain into the genus Rhodopirellula (family Pirellulaceae). The closest type strain is Rhodopirellula rubra LF2^T, suggested by a similarity of 98.4% of the 16S rRNA gene sequence. Strain ICT_H3.1^T is heterotrophic, aerobic and able to grow under microaerobic conditions. The strain grows between 15 and 37 °C, over a range of pH 6.5 to 11.0 and from 1 to 8% (w/v) NaCl. Several nitrogen and carbon sources were utilized by the novel isolate. Cells have an elongated pear-shape with 2.0 ± 0.3 × 0.9 ± 0.2 µm in size. Cells of strain ICT_H3.1^T cluster in rosettes through a holdfast structure and divide by budding. Younger cells are motile. Ultrathin cell sections show cytoplasmic membrane invaginations and polar fimbriae. The genome size is 9,072,081 base pairs with a DNA G + C content of 56.1 mol%. Genomic, physiological and morphological comparison of strain ICT_H3.1^T with its relatives suggest that it belongs to a novel species within the genus Rhodopirellula. Hence, we propose the name Rhodopirellula aestuarii sp. nov., represented by ICT_H3.1^T (=CECT30431^T = LMG32464^T) as the type strain of this novel species. 16S rRNA gene accession number: GenBank = OK001858. Genome accession number: The Whole Genome Shotgun project has been deposited at DDBJ/ENA/GenBank under the accession JAMQBK000000000. The version described in this paper is version JAMQBK010000000.

Isolation, diversity and antimicrobial activity of planctomycetes from the Tejo river estuary (Portugal)

The discovery of new bioactive compounds is an invaluable aid to the development of new drugs. Strategies for finding novel molecules can focus on the exploitation of less studied organisms and ecosystems such as planctomycetes and brackish habitats. The unique cell biology of the underexplored Planctomycetota mean it is of particular interest. In this study, we aimed to isolate planctomycetes from the estuary of the Tejo river (Portugal). To reach this goal, macroalgae, water and sediments were sampled and diverse media and isolation techniques applied. Sixty-nine planctomycetal strains were brought into pure culture. An analysis of the 16S rRNA genes found that the majority of the isolates were affiliated to the genus Rhodopirellula. Putative novel taxa belonging to genera Stieleria and Rhodopirellula were also isolated and characterized morphologically. Enterobacterial Repetitive Intergenic Consensus fingerprinting analyses showed higher diversity and different genotypes within close strains. Relevant biosynthetic gene clusters were found in most isolates and acetone extracts from representative strains exhibited mild antimicrobial activities against Escherichia coli and Staphylococcus aureus. Our work has not only enlarged the number and diversity of cultured planctomycetes but also shown the potential for the discovery of bioactive compounds from the novel taxa.

Rubinisphaera margarita sp. nov., a novel planctomycete isolated from marine sediments collected in the Portuguese north coast

The phylum Planctomycetota is constituted by bacteria with unique features that are well adapted to a vast range of habitats. Here, we describe a novel planctomycete isolated from marine sediments collected on a beach in Matosinhos (Portugal) using an iChip-based culturing technique. Strain ICM_H10T forms beige-coloured colonies in modified M14 medium and its cells are spherical to ovoid in shape, stalked, rosette-forming and showing motility in a phase of the life cycle. Transmission electron microscopy observations showed a typical planctomycetal cell plan and cell division by budding. This strain requires salt for growth and grows in the range of 2.0–5.0 % (w/v) NaCl, from 20 to 37 °C, within a pH of 6.0–9.0 and is able to use diverse nitrogen and carbon sources. It is heterotrophic, aerobic and capable of microaerobic growth. This strain has a genome size of approximately 6.0 Mb and a G+C content of 58.1 mol%. A 16S rRNA gene-based phylogenetic analysis supports the association of strain ICM_H10T to the phylum Planctomycetota and the family Planctomycetaceae , as it shares only 96.8 and 96.4% similarity to its closest relatives Rubinisphaera italica Pan54T and Rubinisphaera brasiliensis IFAM 1448T, respectively. Other phylogenetic markers also support the separation of this strain into a novel species. Morphological, physiological and genomic comparisons between strain ICM_H10T and its closest relatives strongly suggest that ICM_H10T represents a new species of the genus Rubinisphaera , for which we propose the name Rubinisphaera margarita sp. nov., with ICM_H10T (=CECT 30326T=LMG 32234T) as type strain.

Screening for Biofilm-Stimulating Factors in the Freshwater Planctomycete Planctopirus limnophila to Improve Sessile Growth in a Chemically Defined Medium

Planctomycetes such as Planctopirus limnophila offer a promising source of bioactive molecules, particularly when they switch from planktonic to sessile growth, but little is known about the corresponding biosynthetic gene clusters and how they are activated. We therefore screened for factors that promote sessile growth and biofilm formation to enable the cultivation of P. limnophila in a fixed-bed reactor. We carried out screening in microtiter plates focusing on biofilm formation and changes in optical density in response to various C:N ratios, metal ions, and oxidative stress. We used MTT assays and crystal violet staining to quantify biofilm formation. Positive factors were then validated in a fixed-bed bioreactor. The initial screen showed that D1ASO medium supplemented with NH4Cl to achieve a C:N ratio of 5.7:1, as well as 50 µM FeSO4 or CuSO4, increased the biofilm formation relative to the control medium. Exposure to H2O2 did not affect cell viability but stimulated biofilm formation. However, the same results were not replicated in the fixed-bed bioreactor, probably reflecting conditions that are unique to this environment such as the controlled pH and more vigorous aeration. Although we were able to cultivate P. limnophila in a fixed-bed bioreactor using a chemically defined medium, the factors that stimulate biofilm formation and inhibit planktonic growth were only identified in microtiter plates and further evaluation is required to establish optimal growth conditions in the bioreactor system.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.

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 Pan265^T 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 Pan265^T 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 Pan265^T from the known genera in this family. Therefore, we conclude to assign strain Pan265^T 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 Pan265^T (= DSM 100697^T = CECT 30425^T) as type strain.

The Planctomycetia: an overview of the currently largest class within the phylum Planctomycetes

The phylum Planctomycetes comprises bacteria with uncommon features among prokaryotes, such as cell division by budding, absence of the bacterial tubulin-homolog cell division protein FtsZ and complex cell plans with invaginations of the cytoplasmic membrane. Although planctomycetes are ubiquitous, the number of described species and isolated strains available as axenic cultures is still low compared to the diversity observed in metagenomes or environmental studies. An increasing interest in planctomycetes is reflected by the recent description of a large number of new species and their increasing accessibility in terms of pure cultures. In this review, data from all taxonomically described species belonging to Planctomycetia, the class with the currently highest number of characterized members within the phylum Planctomycetes, is summarized. Phylogeny, morphology, physiology, ecology and genomic traits of its members are discussed. This comprehensive overview will help to acknowledge several aspects of the biology of these fascinating bacteria.

Novel and Conventional Isolation Techniques to Obtain Planctomycetes from Marine Environments

Bacteria from the distinctive Planctomycetes phylum are well spread around the globe; they are capable of colonizing many habitats, including marine, freshwater, terrestrial, and even extreme habitats such as hydrothermal vents and hot springs. They can also be found living in association with other organisms, such as macroalgae, plants, and invertebrates. While ubiquitous, only a small fraction of the known diversity includes axenic cultures. In this study, we aimed to apply conventional techniques to isolate, in diverse culture media, planctomycetes from two beaches of the Portuguese north-coast by using sediments, red, green, and brown macroalgae, the shell of the mussel Mytilus edulis, an anemone belonging to the species Actinia equina, and seawater as sources. With this approach, thirty-seven isolates closely related to seven species from the families Planctomycetaceae and Pirellulaceae (class Planctomycetia) were brought into pure culture. Moreover, we applied an iChip inspired in-situ culturing technique to successfully retrieve planctomycetes from marine sediments, which resulted in the isolation of three additional strains, two affiliated to the species Novipirellula caenicola and one to a putative novel Rubinisphaera. This work enlarges the number of isolated planctomycetal strains and shows the adequacy of a novel methodology for planctomycetes isolation.

Marine Bacterial Secondary Metabolites: A Treasure House for Structurally Unique and Effective Antimicrobial Compounds

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in preventing and treating infectious diseases caused by pathogenic organisms, such as bacteria, fungi, and viruses. Because of the burgeoning growth of microbes with antimicrobial-resistant traits, there is a dire need to identify and develop novel and effective antimicrobial agents to treat infections from antimicrobial-resistant strains. The marine environment is rich in ecological biodiversity and can be regarded as an untapped resource for prospecting novel bioactive compounds. Therefore, exploring the marine environment for antimicrobial agents plays a significant role in drug development and biomedical research. Several earlier scientific investigations have proven that bacterial diversity in the marine environment represents an emerging source of structurally unique and novel antimicrobial agents. There are several reports on marine bacterial secondary metabolites, and many are pharmacologically significant and have enormous promise for developing effective antimicrobial drugs to combat microbial infections in drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (1996–2020) on antimicrobial secondary metabolites from marine bacteria evolved in marine environments, such as marine sediment, water, fauna, and flora.

The bacterial phylum Planctomycetes as novel source for bioactive small molecules

Extensive knowledge and methodological expertise on the bacterial cell biology have been accumulated over the last decades and bacterial cells have now become an integral part of several (bio-)technological processes. While it appears reasonable to focus on a relatively small number of fast-growing and genetically easily manipulable model bacteria as biotechnological workhorses, the for the most part untapped diversity of bacteria needs to be explored when it comes to bioprospecting for natural product discovery. Members of the underexplored and evolutionarily deep-branching phylum Planctomycetes have only recently gained increased attention with respect to the production of small molecules with biomedical activities, e.g. as a natural source of novel antibiotics. Next-generation sequencing and metagenomics can provide access to the genomes of uncultivated bacteria from sparsely studied phyla, this, however, should be regarded as an addition rather than a substitute for classical strain isolation approaches. Ten years ago, a large sampling campaign was initiated to isolate planctomycetes from their varied natural habitats and protocols were developed to address complications during cultivation of representative species in the laboratory. The characterisation of approximately 90 novel strains by several research groups in the recent years opened a detailed in silico look into the coding potential of individual members of this phylum. Here, we review the current state of planctomycetal research, focusing on diversity, small molecule production and potential future applications. Although the field developed promising, the time frame of 10 years illustrates that the study of additional promising bacterial phyla as sources for novel small molecules needs to start rather today than tomorrow.

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.

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).

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 Pla52^T 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 Pla52n^T shows typical features of members of the class Planctomycetia, including division by polar budding and the presence of crateriform structures. Colonies of strain Pla52n^T 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 Pla52n^T 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 Pla52n^T = LMG 29463^T = VKM B-3447^T should be classified as the type strain of a novel species, for which we propose the name Stieleria varia sp. nov.

Stieleriacines, N-Acyl Dehydrotyrosines From the Marine Planctomycete Stieleria neptunia sp. nov

Bacteria of the phylum Planctomycetes occur ubiquitously in marine environments and play important roles in the marine nitrogen- and carbon cycle, for example as scavengers after phototrophic blooms. Here, we describe the isolation and characterization of the planctomycetal strain Enr13^T isolated from a Posidonia sp. biofilm obtained from seawater sediment close to Panarea Island, Italy. Phylogenetic tree reconstruction based on 16S rRNA gene sequences and multi-locus sequence analysis supports the delineation of strain Enr13^T from characterized species part of the phylum of Planctomycetes. HPLC-MS analysis of culture broth obtained from strain Enr13^T revealed the presence of lipophilic metabolites, of which the major compound was isolated by preparative reversed-phase HPLC. The structure of this compound, named stieleriacine D (1), was elucidated utilizing HRESIMS, 1D- and 2D-NMR data as a new N-acylated dehydrotyrosine derivative. Its biosynthesis was proposed based on an in silico gene cluster analysis. Through analysis of the MS/MS spectrum of 1 and its minor derivative, stieleriacine E (2), it was possible to assign the structure of 2 without isolation. 1 showed antibacterial activity, however, the wide distribution of structurally related compounds indicates a potential role as a signaling molecule.