International Journal of Systematic and Evolutionary Microbiology

A co-culture of a novel thermoacidophilic, obligate symbiotic archaeon, designated as strain MJ1T, with its specific host archaeon Metallosphaera sedula strain MJ1HA was obtained from a terrestrial hot spring in Japan. Strain MJ1T grew in the co-culture under aerobic conditions. Coccoid cells of strain MJ1T were 200–500 nm in diameter, and attached to the MJ1HA cells in the co-culture. The ranges and optima of the growth temperature and pH of strain MJ1T in the co-culture were 60–75 °C (optimum, 65–70 °C) and pH 1.0–4.0 (optimum, pH 2.5), respectively. Core lipids of dialkyl glycerol tetraethers (GDGT)−3 and GDGT-4 were highly abundant in MJ1T cells concentrated from the co-culture. Strain MJ1T has a small genome (0.67 Mbp) lacking genes for biosynthesis of essential biomolecules, such as nucleotides, lipids and ATP. The genomic DNA G+C content was 24.9 mol%. The 16S rRNA gene sequence of strain MJ1T was most closely related to that of the cultivated species, ‘Nanopusillus acidilobi’ strain N7A (85.8 % similarity). Based on phylogenetic and physiological characteristics, we propose the name Nanobdella aerobiophila gen. nov., sp. nov. to accommodate the strain MJ1T (=JCM 33616T=DSM 111728T). In addition, we propose the names Nanobdellaceae fam. nov., Nanobdellales ord. nov., and Nanobdellia class. nov. to accommodate the novel genus.

The genus ‘Candidatus Phytoplasma’ was proposed to accommodate cell wall-less bacteria that are molecularly and biochemically incompletely characterized, and colonize plant phloem and insect vector tissues. This provisional classification is highly relevant due to its application in epidemiological and ecological studies, mainly aimed at keeping the severe phytoplasma plant diseases under control worldwide. Given the increasing discovery of molecular diversity within the genus ‘Ca. Phytoplasma’, the proposed guidelines were revised and clarified to accommodate those ‘Ca. Phytoplasma’ species strains sharing >98.65 % sequence identity of their full or nearly full 16S rRNA gene sequences, obtained with at least twofold coverage of the sequence, compared with those of the reference strain of such species. Strains sharing <98.65 % sequence identity with the reference strain but >98.65 % with other strain(s) within the same ‘Ca. Phytoplasma’ species should be considered related strains to that ‘Ca. Phytoplasma’ species. The guidelines herein, keep the original published reference strains. However, to improve ‘Ca. Phytoplasma’ species assignment, complementary strains are suggested as an alternative to the reference strains. This will be implemented when only a partial 16S rRNA gene and/or a few other genes have been sequenced, or the strain is no longer available for further molecular characterization. Lists of ‘Ca. Phytoplasma’ species and alternative reference strains described are reported. For new ‘Ca. Phytoplasma’ species that will be assigned with identity ≥98.65 % of their 16S rRNA gene sequences, a threshold of 95 % genome-wide average nucleotide identity is suggested. When the whole genome sequences are unavailable, two among conserved housekeeping genes could be used. There are 49 officially published ‘Candidatus Phytoplasma’ species, including ‘Ca. P. cocostanzaniae’ and ‘Ca. P. palmae’ described in this manuscript.

A novel micro-organism designated AS10Twas isolated from dry salt collected from Aveiro saltern in the north of Portugal. Cells were Gram-stain-positive, non-motile, non-endospore-forming, rod-shaped and aerobic. Strain AS10Twas characterized by long filaments of rod-shaped cells, presenting also coccoid cellular forms at the end of the filaments, unveiling some pleomorphism. Rod-shaped cells varied from 0.3 to 0.6 µm wide and from 0.6 to 2 µm long. Growth of AS10Toccurred at 15–40 °C (optimum, 20–30 °C), 0–10% (w/v) NaCl (optimum, 2%) and pH 4.5–11.0 (optimum, pH 8.0–11.0). The peptidoglycan type was A1ϒ-type with 3-hydroxy-diaminopimelic acid. The major fatty acids were C16:0, iso-C14:0, C17:0and C14:0. The major respiratory quinone was MK-9(H4). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain AS10Twas similar to actinobacterial members of the classNitriliruptoria, withNitriliruptor alkaliphilusANL-iso2Tbeing the closest relative the species with a sequence pairwise similarity of 91.21%. Average nucleotide identity, average amino acid identity andin silicoDNA–DNA hybridization values between strain AS10TandN. alkaliphilusANL-iso2Twere 71.34, 53.57 and 18.90%, respectively. The genome DNA G+C content of AS10Twas 71.8 mol%. Based on genomic, phylogenetic, phenotypic and chemotaxonomic studies, we describe a new species of a novel genus represented by strain AS10T(=LMG 31937T=CECT 30148T) for which we propose the nameSalsipaludibacter albusgen. nov., sp. nov. We also propose that this organism represents a new family namedSalsipaludibacteraceaefam. nov. of a novel order namedSalsipaludibacteralesord. nov.

The taxonomic positions of members within the familyPseudonocardiaceaewere assessed based on phylogenomic trees reconstructed using core-proteome and genomeblastdistance phylogeny approaches. The closely clustered genome sequences from the type strains of validly published names within the familyPseudonocardiaceaewere analysed using overall genome-related indices based on average nucleotide identity, average amino acid identity and digital DNA–DNA hybridization values. The familyPseudonocardiaceaeconsists of the type genusPseudonocardia, as well as the generaActinoalloteichus,Actinocrispum,Actinokineospora,Actinomycetospora,Actinophytocola,Actinopolyspora,Actinorectispora,Actinosynnema,Allokutzneria,Allosaccharopolysporagen. nov.,Amycolatopsis,Bounagaea,Crossiella,Gandjariella,Goodfellowiella,Haloactinomyces,Haloechinothrix,Halopolyspora,Halosaccharopolysporagen. nov.,Herbihabitans,Kibdelosporangium,Kutzneria,Labedaea,Lentzea,Longimycelium,Prauserella,Saccharomonospora,Saccharopolyspora,Saccharothrix,Salinifilum,Sciscionella,Streptoalloteichus,Tamaricihabitans,Thermocrispum,ThermotunicaandUmezawaea. The G+C contents of thePseudonocardiaceaegenomes ranged from 66.2 to 74.6 mol% and genome sizes ranged from 3.69 to 12.28 Mbp. Based on the results of phylogenomic analysis, the namesAllosaccharopolyspora corallicomb. nov.,Halosaccharopolyspora lacisalsicomb. nov. andActinoalloteichus caeruleuscomb. nov. are proposed. This study revealed thatActinokineospora mzabensisis a heterotypic synonym ofActinokineospora spheciospongiae,Lentzea desertiis a heterotypic synonym ofLentzea atacamensis,Prauserella endophyticais a heterotypic synonym ofPrauserella coralliicola, andPrauserella flavaandPrauserella sediminisare heterotypic synonyms ofPrauserella salsuginis. This study addresses the nomenclature conundrums ofActinoalloteichus cyanogriseusandStreptomyces caeruleusas well asMicropolyspora internatusandSaccharomonospora viridis.

After the International Committee on Systematics of Prokaryotes (ICSP) had voted to include the rank of phylum in the rules of the International Code of Nomenclature of Prokaryotes (ICNP), and following publication of the decision in the IJSEM, we here present names and formal descriptions of 42 phyla to effect valid publication of their names, based on genera as the nomenclatural types.

The status Candidatus was introduced to bacterial taxonomy in the 1990s to accommodate uncultured taxa defined by analyses of DNA sequences. Here I review the strengths, weaknesses, opportunities and threats (SWOT) associated with the status Candidatus in the light of a quarter century of use, twinned with recent developments in bacterial taxonomy and sequence-based taxonomic discovery. Despite ambiguities as to its scope, philosophical objections to its use and practical problems in implementation, the status Candidatus has now been applied to over 1000 taxa and has been widely adopted by journals and databases. Although lacking priority under the International Code for Nomenclature of Prokaryotes, many Candidatus names have already achieved de facto standing in the academic literature and in databases via description of a taxon in a peer-reviewed publication, alongside deposition of a genome sequence and there is a clear path to valid publication of such names on culture. Continued and increased use of Candidatus names provides an alternative to the potential upheaval that might accompany creation of a new additional code of nomenclature and provides a ready solution to the urgent challenge of naming many thousands of newly discovered but uncultured species.

An intracellular bacterium, strain IAST, was observed to infect several species of the plant-parasitic nematode genus Xiphinema (Xiphinema astaregiense, Xiphinema incertum, Xiphinema madeirense, Xiphinema pachtaicum, Xiphinema parapachydermum and Xiphinema vallense). The bacterium could not be recovered on axenic medium. The 16S rRNA gene sequence of IAST was found to be new, being related to the family Burkholderiaceae, class Betaproteobacteria. Fungal endosymbionts Mycoavidus cysteinexigens B1-EBT (92.9 % sequence identity) and ‘Candidatus Glomeribacter gigasporarum’ BEG34 (89.8 % identity) are the closest taxa and form a separate phylogenetic clade inside Burkholderiaceae. Other genes (atpD, lepA and recA) also separated this species from its closest relatives using a multilocus sequence analysis approach. These genes were obtained using a partial genome of this bacterium. The localization of the bacterium (via light and fluorescence in situ hybridization microscopy) is in the X. pachtaicum females clustered around the developing oocytes, primarily found embedded inside the epithelial wall cells of the ovaries, from where they are dispersed in the intestine. Transmission electron microscopy (TEM) observations supported the presence of bacteria inside the nematode body, where they occupy ovaries and occur inside the intestinal epithelium. Ultrastructural analysis of the bacterium showed cells that appear as mostly irregular, slightly curved rods with rounded ends, 0.8–1.2 µm wide and 2.5–6.0 µm long, possessing a typical Gram-negative cell wall. The peptidoglycan layer is, however, evident only occasionally and not detectable by TEM in most cells. Another irregularly occurring shell surrounding the endosymbiont cells or the cell clusters was also revealed, probably originating from the host cell membrane. Flagella or spore-like cells do not occur and the nucleoid is diffusely distributed throughout the cell. This endosymbiont is transmitted vertically through nematode generations. These results support the proposal of IAST as a new species, although its obligate intracellular and obligate endosymbiont nature prevented isolation of a definitive type strain. Strain IAST is therefore proposed as representing ‘Candidatus Xiphinematincola pachtaicus’ gen. nov., sp. nov.

In Iran, polyphasic studies of unicellular cyanobacteria are still scarce, with more emphasis being placed on filamentous cyanobacteria in paddy fields and fresh water regions. In an effort to increase the knowledge of the diversity of unicellular cyanobacteria from paddy fields in Iran, we have isolated and characterized a new unicellular cyanobacterium strain. The strain was studied using a polyphasic approach based on morphological, ecological and phylogenetic analyses of the 16S–23S ITS rRNA gene region. Complementarily, we have searched for the presence of cyanotoxin genes and analysed the pigment content of the strain. Results showed that the strain was morphologically indistinguishable from the genus Chroococcus , but phylogenetic analyses based on the Bayesian inference and maximum-likelihood methods placed the strain in a separated monophyletic and highly supported (0.99/98, posterior probability/maximum-likelihood) genus-level cluster, distant from Chroococcus sensu stricto and with Chalicogloea cavernicola as sister taxa. The calculated p-distance for the 16S rRNA gene also reinforced the presence of a new genus, by showing 92 % similarity to C. cavernicola . The D1–D1′, Box-B and V3 ITS secondary structures showed the uniqueness of this strain, as it shared no similar pattern with closest genera within the Chroococcales. For all these reasons, and in accordance with the International Code of Nomenclature for Algae, Fungi and Plants, we here proposed the description of a new genus with the name Alborzia gen. nov. along with the description of a new species, Alborzia kermanshahica sp. nov. (holotype: CCC1399-a; reference strains CCC1399-b; MCC 4116).

The cyanobacterial genus Nostoc is an important contributor to carbon and nitrogen bioavailability in terrestrial ecosystems and a frequent partner in symbiotic relationships with non-diazotrophic organisms. However, since this currently is a polyphyletic genus, the diversity of Nostoc -like cyanobacteria is considerably underestimated at this moment. While reviewing the phylogenetic placement of previously isolated Nostoc -like cyanobacteria originating from Brazilian Amazon, Caatinga and Atlantic forest samples, we detected 17 strains isolated from soil, freshwater, rock and tree surfaces presenting patterns that diverged significantly from related strains when ecological, morphological, molecular and genomic traits were also considered. These observations led to the identification of the evaluated strains as representative of three novel nostocacean genera and species: Amazonocrinis nigriterrae gen. nov., sp. nov.; Atlanticothrix silvestris gen. nov., sp. nov.; and Dendronalium phyllosphericum gen. nov., sp. nov., which are herein described according to the rules of the International Code of Nomenclature for algae, fungi and plants. This finding highlights the great importance of tropical and equatorial South American ecosystems for harbouring an unknown microbial diversity in the face of the anthropogenic threats with which they increasingly struggle.