Proposal for Acinetobacter higginsii sp. nov. to accommodate organisms of human clinical origin previously classified as Acinetobacter genomic species 16

In 1989, Bouvet and Jeanjean delineated five proteolytic genomic species (GS) of Acinetobacter, each with two to four human isolates. Three were later validly named, whereas the remaining two (GS15 and GS16) have been awaiting nomenclatural clarification. Here we present the results of the genus-wide taxonomic study of 13 human strains classified as GS16 (n=10) or GS15 (n=3). Based on core genome phylogenetic analysis, the strains formed two respective but closely related phylogroups within the Acinetobacter haemolytic clade. The intraspecies genomic average nucleotide identity based on blast (ANIb) values for GS16 and GS15 reached ≥94.9 % and ≥98.7, respectively, whereas ANIb values between them were 92.5-93.5% and those between them and the known species were ≤91.5 %. GS16 and GS15 could be differentiated from the other Acinetobacter species by their ability to lyse gelatin and sheep blood and to assimilate d,l-lactate, along with their inability to acidify d-glucose and assimilate glutarate. In contrast, GS16 and GS15 were indistinguishable from one another by metabolic/physiological features or whole-cell MALDI-TOF mass spectra. All the GS15/GS16 genomes contained genes encoding a class D β-lactamase, Acinetobacter-derived cephalosporinase and aminoglycoside 6'-N-acetyltransferase. Searching NCBI databases revealed genome sequences of three additional isolates of GS16, but none of GS15. We conclude that our data support GS16 as representing a novel species, but leave the question of the taxonomic status of GS15 open, given its close relatedness to GS16 and the small number of available strains. We propose the name Acinetobacter higginsii sp. nov. for GS16, with the type strain NIPH 1872T (CCM 9243T=CIP 70.18T=ATCC 17988T).

Acinetobacter amyesii sp. nov., widespread in the soil and water environment and animals

We studied a novel taxon of the genus Acinetobacter , which comprised six strains collected in Czechia, Germany, Indonesia and Turkey between 2015 and 2021. The organisms were isolated from environmental soil, water samples and cow faeces. Their genome sizes varied between 3.3 and 3.5 Mb, with a G+C content of 40.4–40.8 mol%. Based on genus-wide core genome analysis, the taxon formed a distinct clade, with Acinetobacter gandensis being the phylogenetically closest related species. The intrataxon genomic average nucleotide identity based on blast (ANIb) and digital DNA–DNA hybridization (dDDH) values reached 95.3–97.4% and 62.5–77.8 %, respectively, whereas its ANIb/dDDH values against the known Acinetobacter type strains were ≤82.7 %/≤25.7 %. Cluster analysis of whole-cell MALDI-TOF mass spectra corroborated the distinctness and cohesiveness of the taxon. The novel strains were non-glucose-oxidizing, non-haemolytic and non-proteolytic, growing at up to 37–41 °C but not at 44 °C and utilizing 8–10 of the 36 carbon sources tested. Growth on glutarate, tricarballylate and at 37 °C combined with the inability to assimilate 4-aminobutyrate and d-malate differentiated them from all validly named Acinetobacter species. The inspection of genome sequences in the NCBI database revealed the existence of numerous strains conspecific with this group, which were collected from pig faeces and environmental samples in China. We conclude that the taxon represents an ecologically and geographically widespread species, for which we propose the name Acinetobacter amyesii sp. nov., with ANC 5579T (= CCM 9242T=CCUG 76274T=CNCTC 8134T) as the type strain.

Acinetobacter silvestris sp. nov. discovered in forest ecosystems in Czechia

We investigated a taxonomically novel group of the genus Acinetobacter , which included five strains isolated from soil and water samples collected in preserved forest areas in Czechia between 2013 and 2021. The whole-genome sequences of the strains were 3.1–3.2 Mb in size, with G+C contents of 38.0–38.2 mol%. Core genome-based phylogenetic analysis showed that they formed a compact and deeply branched clade within the genus. The genomic average nucleotide identity based on blast/digital DNA–DNA hybridization values for the novel strains were 99.2–99.6 %/95.2–98.4 %, whereas those between the novel strains and the type strains of the known Acinetobacter species reached <78 %/<24 %. The results of the genus-wide analysis of whole-cell MALDI-TOF mass spectra supported the sharp distinctness of the group. The five strains were non-glucose acidifying, nonhaemolytic, nonproteolytic and growing at 28 °C, but not at 32 °C; they assimilated acetate, benzoate, ethanol, l-histidine, 4-hydroxybenzoate, dl-lactate and malonate but not 4-aminobutyrate, l-aspartate or 2,3-butanediol; this phenotype is unique among the known Acinetobacter species. We conclude that the five strains represent a novel environmental species, for which the name Acinetobacter silvestris sp. nov. is proposed, with the type strain ANC 4999T (=CCM 9207T=CCUG 75877T=CNCTC 8124T).

Streptomyces dysideae sp. nov., isolated from a marine Mediterranean sponge Dysidea tupha

A Gram-stain-positive bacterium, strain RV15^T, forming an extensively branched substrate mycelium and aerial hyphae that differentiate into spiral chains of spores, was isolated from a marine sponge Dysidea tupha collected from Rovinj (Croatia). Comparison of 16S rRNA gene sequences showed that strain RV15^T is a member of the genus Streptomyces with highest sequence similarity to the type strains of Streptomyces caeruleatus (98.8 %), Streptomyces cyaneochromogenes (98.6 %) and Streptomyces shaanxiensis (98.5 %). Sequence similarities to all other Streptomyces types strains were below 98.5 %. The multilocus sequence analysis-based evolutionary distance, the average nucleotide identity value and the genome-to-genome distance of strain RV15^T and the type strain of S. caeruleatus were clearly below the species cut-off values. Strain RV15^T exhibited a quinone system composed of the major menaquinones MK-9(H₄), MK-9(H₆) and MK-9(H₂), typical for the genus Streptomyces. The polar lipid profile of strain RV15^T consisted of the predominant compounds diphosphatidylglycerol and phosphatidylethanolamine, moderate amounts of phosphatidylinositol, phosphatidylinositol mannoside, an unidentified lipid and an unidentified phospholipid. Major polyamines were spermine and spermidine. The diagnostic diaminoacid of the peptidoglycan was meso-diaminopimelic acid. The major fatty acids were iso C_16 : 0, anteiso C_17 : 1 ω9c and anteiso C_17 : 0. The results of physiological and biochemical tests allowed further phenotypic differentiation of strain RV15^T from its most-related species and hence clearly merits species status. We propose the name Streptomyces dysideae sp. nov. with the type strain RV15^T (=DSM 42110^T=LMG 27702^T).

Pseudomonas defluvii sp. nov., isolated from hospital sewage

A novel Gram-negative, obligate aerobic, mobile, rod-shaped and non-spore-forming bacterial strain, WCHP16^T, was isolated from the wastewater treatment plant at West China Hospital in Chengdu, PR China. It was characterized using a polyphasic approach. Analysis of its 16S rRNA gene sequence showed that strain WCHP16^T belonged to the genus Pseudomonas with the highest similarity to Pseudomonas qingdaonensis JJ3^T (99.34 %), Pseudomonas shirazica VM14^T (99.0 %), Pseudomonas plecoglossicida NBRC 103162^T (99.0 %) and Pseudomonas asiatica RYU5^T (99.0 %). Phylogenomic analysis based on 107 core gene sequences demonstrated that WCHP16^T was a member of the Pseudomonas putida group but was distant from all closely related species. Whole-genome comparisons, using average nucleotide identity based on blast (ANIb) and in silico DNA-DNA hybridization (isDDH), confirmed low genome relatedness to all the known Pseudomonas species (below the recommended thresholds of 95 % [ANIb] and 70 % [isDDH] for species delineation). Phenotypic characterization tests showed that the utilization of phenylacetic acid and capric acid, but not d-arabitol, and inability to produce fluorescent (King B medium) in combination could distinguish this strain from other related species of the genus Pseudomonas. Therefore, based on genetic and phenotypic evidence, it is clear that strain WCHP16^T represents a novel species, for which the name Pseudomonas defluvii sp. nov. is proposed. The type strain is WCHP16^T (GDMCC1.1215^T=CCTCC AB 2017103^T=KCTC 52991^T).

Campylobacter blaseri sp. nov., isolated from common seals (Phoca vitulina)

During a study to assess the faecal microbiome of common seals (Phoca vitulina) in a Dutch seal rehabilitation centre, 16S rRNA gene sequences of an unknown Campylobacter taxon were identified. Campylobacter isolates, which differed from the established Campylobacter taxa, were cultured and their taxonomic position was determined by a polyphasic study based on ten isolates. The isolates were characterized by 16S rRNA and atpA gene sequence analyses and by conventional phenotypic testing. Based on the whole genome sequences, the average nucleotide identity and core genome phylogeny were determined. The isolates formed a separate phylogenetic clade, divergent from all other Campylobacter taxa and most closely related to Campylobacter corcagiensis, Campylobacter geochelonis and Campylobacter ureolyticus. The isolates can be distinguished phenotypically from all other Campylobacter taxa based on their lack of motility, growth at 25 °C and growth on MacConkey agar. This study shows that these isolates represent a novel species within the genus Campylobacter, for which the name Campylobacter blaseri sp. nov. is proposed. The type strain for this novel species is 17S00004-5^T (=LMG 30333^T=CCUG 71276^T).

A Proposal for a Genome Similarity-Based Taxonomy for Plant-Pathogenic Bacteria that Is Sufficiently Precise to Reflect Phylogeny, Host Range, and Outbreak Affiliation Applied to Pseudomonas syringae sensu lato as a Proof of Concept

Taxonomy of plant pathogenic bacteria is challenging because pathogens of different crops often belong to the same named species but current taxonomy does not provide names for bacteria below the subspecies level. The introduction of the host range-based pathovar system in the 1980s provided a temporary solution to this problem but has many limitations. The affordability of genome sequencing now provides the opportunity for developing a new genome-based taxonomic framework. We already proposed to name individual bacterial isolates based on pairwise genome similarity. Here, we expand on this idea and propose to use genome similarity-based codes, which we now call life identification numbers (LINs), to describe and name bacterial taxa. Using 93 genomes of Pseudomonas syringae sensu lato, LINs were compared with a P. syringae genome tree whereby the assigned LINs were found to be informative of a majority of phylogenetic relationships. LINs also reflected host range and outbreak association for strains of P. syringae pathovar actinidiae, a pathovar for which many genome sequences are available. We conclude that LINs could provide the basis for a new taxonomic framework to address the shortcomings of the current pathovar system and to complement the current taxonomic system of bacteria in general.