Actinomadura jiaoheensis sp. nov. and Actinomadura sporangiiformans sp. nov., two novel actinomycetes isolated from muddy soil and emended description of the genus Actinomadura

Actinomadura graeca sp. nov.: A novel producer of the macrocyclic antibiotic zelkovamycin

As part of a screening programme for antibiotic-producing bacteria, a novel Actinomadura species was discovered from a soil sample collected in Santorini, Greece. Preliminary 16S rRNA gene sequence comparisons highlighted Actinomadura macra as the most similar characterised species. However, whole-genome sequencing revealed an average nucleotide identity (ANI) value of 89% with A. macra, the highest among related species. Further phenotypic and chemotaxonomic analyses confirmed that the isolate represents a previously uncharacterised species in the genus Actinomadura, for which the name Actinomadura graeca sp. nov. is proposed (type strain 32-07T). The G+C content of A. graeca 32-07 is 72.36%. The cell wall contains DL-diaminopimelic acid, intracellular sugars are glucose, ribose and galactose, the predominant menaquinone is MK-9(H6), the major cellular lipid is phosphatidylinositol and fatty acids consist mainly of hexadecanoic acid. No mycolic acid was detected. Furthermore, A. graeca 32-07 has been confirmed as a novel producer of the non-ribosomal peptide antibiotic zelkovamycin and we report herein a provisional description of the unique biosynthetic gene cluster.

Actinomadura soli sp. nov., isolated from the top soil layer on basaltic material in Turkey

An actinobacterium, designated 14C53^T, was isolated from a soil sample on basaltic material from Samsun, Turkey. The growth ranges for NaCl concentration and pH of strain 14C53^T were quite limited and the growth temperature range of the strain was 20-37 °C, with an optimum at 28 °C. Phylogenetic analysis of 16S rRNA gene sequences revealed that strain 14C53^T was most closely related to Actinomadura geliboluensis A8036^T (98.5 % similarity value), but in the phylogenetic tree, it formed a clade with Actinomadura alkaliterrae D310A^T. The genome tree revealed a close relationship between the strain and Actinomadura pelletieri DSM 43383^T. However, the digital DNA-DNA hybridization and average nucleotide identity values between strain 14C53^T with Actinomadura geliboluensis A8036^T and Actinomadura pelletieri DSM 43383^T were 28.6-30.2 % and 84.3-85.5 %, respectively, and comparative analyses based on the genome sequences demonstrated that it represents a novel species of the genus Actinomadura. The genome size of strain 14C53^T was approximately 9.0 Mb and the genomic DNA G+C content of the strain was 71.3 mol%. The major cellular fatty acids of strain 14C53^T were C_16 : 0 and iso-C_16 : 0. Strain 14C53^T contained meso-diaminopimelic acid as the diamino acid in the cell-wall peptidoglycan. The predominant menaquinones were MK-9(H₈) and MK-9(H₆). Based on evidence collected from the phenotypic, genotypic and phylogenetic analyses, a novel species Actinomadura soli sp. nov. is proposed, with 14C53^T (=DSM 104447^T=KCTC 39878^T) as the type strain.

Actinomadura litoris sp. nov., an actinobacterium isolated from sandy soil in Sanya

A novel actinobacterium, designated strain NEAU-AAG5^T, was isolated from sandy soil collected from Niuwang island in Sanya, Hainan Province, PR China. The taxonomic position of the strain was investigated using a polyphasic approach. On the basis of 16S rRNA gene sequence analysis, strain NEAU-AAG5^T belongs to the genus Actinomadura and shared highest sequence similarity with Actinomadura macra NBRC 14102^T (98.8 %). Strain NEAU-AAG5^T grows at 20-40 °C (optimum, 28 °C), pH 6-10 (optimum, pH 7) and has NaCl tolerance of 0-3 %. The menaquinones were identified as MK-9(H₄) (4.2 %), MK-9(H₆) (49.2 %) and MK-9(H₈) (46.5 %). The major fatty acids were C_16 : 0 (31.4 %), 10-methyl C_18 : 0 (21.3 %) and C_18 : 1  ω9c (15.7 %). The polar lipids were diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositolmannoside, phosphatidylglycerol and phosphoglycolipid. The genomic DNA G+C content of strain NEAU-AAG5^T based on whole genome sequences was 72.8 mol%. Digital DNA-DNA hybridization between strain NEAU-AAG5^T and its closest phylogenetic neighbour, A. macra NBRC 14102^T, resulted in similarity value of 28.0 % (<70 %). Additionally, the average nucleotide identity was 84.2 % for A. macra NBRC 14102^T. On the basis of phenotypic, genotypic and phylogenetic data, strain NEAU-AAG5^T can be characterized to represent a novel species of the genus Actinomadura, for which the name Actinomadura litoris sp. nov. is proposed. The type strain is NEAU-AAG5^T (=JCM 33456^T=CCTCC AA 2019043^T).

Actinomadura harenae sp. nov., a novel actinomycete isolated from sea sand in Sanya

A novel actinomycete, designated strain NEAU-Ht49^T, was isolated from sea sand sampled in Sanya and characterized by using a polyphasic approach. The 16S rRNA gene sequence analysis showed that strain NEAU-Ht49^T was most closely related to Actinomadura rhizosphaerae SDA37^T (98.8 %), Actinomadura logoneensis NEAU-G17^T (98.6 %), Actinomadura oligospora ATCC 43269^T (98.6 %) and Actinomadura gamaensis NEAU-Gz5^T (98.6 %). The results of phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain NEAU-Ht49^T formed a cluster with A. rhizosphaerae SDA37^T, A. logoneensis NEAU-G17^T, A. oligospora ATCC 43269^T, A. gamaensis NEAU-Gz5^T and Actinomadura rupiterrae CS5-AC15^T (96.4 %). Meso-diaminopimelic acid was detected in its cell walls and glucose, madurose, mannose and ribose were detected in whole-cell hydrolysate. The polar lipids were found to consist of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannoside and two unidentified lipids. The majoy menaquinone was MK-10(H₆) and the minor menaquinones were MK-9(H₄) and MK-9(H₈). The major fatty acids were C_16 : 0, C_18 : 1ω9c, 10-methyl C_18 : 0 and iso-C_16 : 0. Moreover, morphological and chemotaxonomic characteristics of properties of strain NEAU-Ht49^T also confirmed the affiliation of the isolate to the genus Actinomadura. However, DNA-DNA relatedness, physiological and biochemical data showed that strain NEAU-Ht49^T could be distinguished from its closest relatives. Therefore, strain NEAU-Ht49^T represents a novel species of the genus Actinomadura, for which the name Actinomadura harenae sp. nov. is proposed, with strain NEAU-Ht49^T (=CGMCC 4.7499^T=JCM 32659^T) as the type strain.

Actinomadura roseirufa sp. nov., producer of semduramicin, a polyether ionophore

The taxonomic position of 'Actinomadura roseorufa' LMG 30035^T, a semduramicin-producing mutant of strain ATCC 53666^P, which was isolated from a soil sample collected in Yamae Village, Kamamoto, Japan, was clarified in the present study using a polyphasic approach. This Gram-positive, aerobic actinomycete formed a well-developed, extensively branched, non-fragmenting substrate and aerial mycelia which differentiated into single, smooth-appearing spores. Based on analysis of nearly complete 16S rRNA gene sequence, strain LMG 30035^T was found to be closely related to the type strains of Actinomadura fibrosa ATCC 49459^T (98.88 %) and Actinomadura formosensis JCM 7474^T (98.82 %) (pairwise similarity values in parentheses). Digital DNA-DNA hybridisation experiments revealed unambiguously that strain LMG 30035^T represents a novel Actinomadura species (OrthoANIu values less than 83.1 %; dDDH values less than 27.2 % with type strains of validly named Actinomadura species). Analysis of the cell wall revealed the presence of meso-diaminopimelic acid in the peptidoglycan. The whole-cell sugars were glucose, madurose, galactose, ribose and rhamnose. The major polar lipids included phosphatidylinositol and diphosphatidylglycerol. The predominant menaquinones were MK-9(H₆), MK-9(H₈), MK-9(H₄) and MK-9(H₂). The major fatty acids were C_16 : 00, 10-methyl C_18 : 0, C_18 : 1  ω9c and C_18 : 00. The DNA G+C content of its genome was 72.5 mol%. In summary, these characteristics distinguish strain LMG 30035^T from validly named species of the genus Actinomadura, and therefore, we propose to classify this strain formally as the novel species Actinomadura roseirufa sp. nov. with LMG 30035^T (=CECT 9808^T,=ATCC 53664^T) as the type strain.

Actinomadura logoneensis sp. nov., a novel actinomycete isolated from the soil

One novel actinobacterial isolate, designated strain NEAU-G17^T, was isolated from muddy soil collected from a riverbank in Chad and characterised using polyphasic approach. Morphological and chemotaxonomic characteristics of this strain coincided with those of the genus Actinomadura. The 16S rRNA gene sequence analysis showed that strain NEAU-G17^T was most closely related to Actinomadura oligospora JCM 10648^T (98.7 %) and Actinomadura gamaensis NEAU-Gz5^T (98.6 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NEAU-G17^T formed a cluster with Actinomadura oligospora JCM 10648^T, Actinomadura gamaensis NEAU-Gz5^T and Actinomadura rupiterrae CS5-AC15^T (96.4 %). However, the combination of DNA-DNA hybridisation values and some phenotypic characteristics allowed the isolate to be differentiated from their most closely related species. The major menaquinones were identified as MK-9(H₄), MK-9(H₆) and MK-9(H₈). Their polar lipid profile was found to contain diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside, an unidentified phospholipid and an unidentified lipid. The major fatty acids were identified as C_16 : 0, iso-C_16 : 0 and C_18 : 1 ω9c. Therefore, it is proposed that strain NEAU-G17^T should be classified as representative of a novel species of the genus Actinomadura, for which the name Actinomadura logoneensis sp. nov. is proposed. The type strains is NEAU-G17^T (=CGMCC 4.7411^T=DSM 105122^T).

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Actinomadura barringtoniae sp. nov., an endophytic actinomycete isolated from the roots of Barringtonia acutangula (L.) Gaertn

A novel actinomycete strain, designated GKU 128^T, isolated from the roots of an Indian oak tree [Barringtonia acutangula (L.) Gaertn.] at Khao Khitchakut district, Chantaburi province, Thailand, was characterized by using a polyphasic approach. The strain formed a branched substrate and aerial mycelia which differentiated into straight to flexuous chains of smooth-ornamented spores. Analysis of the cell wall revealed the presence of meso-diaminopimelic acid and N-acetylmuramic acid in the peptidoglycan. The whole-cell sugars were glucose, madurose, mannose, rhamnose and ribose. Mycolic acids were absent. The major phospholipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and phosphatidylinositolmannoside. The predominant menaquinones were MK-9(H6), MK-9(H8), MK-9(H0) and MK-9(H4). The major fatty acids were C16 : 0, C18 : 1ω9c and 10-methyl C18 : 0 (tuberculostearic acid). The genomic DNA G+C content was 70.5 mol%. Based on 16S rRNA gene sequence analysis, strain GKU 128^T was closely related to the type strains of Actinomadura nitritigenes NBRC 15918^T (99.2 % sequence similarity) and Actinomadura fibrosa JCM 9371^T (98.7 %). The levels of DNA-DNA relatedness between strain GKU 128^T and the closely related type species were less than 19 %. On the basis of phenotypic and genotypic characteristics, strain GKU 128^T could be distinguished from its closely related type strains and represents a novel species of the genus Actinomadura, for which the name Actinomadura barringtoniae sp. nov. (=TBRC 7225^T=NBRC 113074^T) is proposed.

Actinomadura alkaliterrae sp. nov., isolated from an alkaline soil

A polyphasic study was undertaken to establish the taxonomic status of an Actinomadura strain isolated from the margin of a saline, alkaline lake in Central Anatolia, Turkey. Strain D310AT^T was shown to have chemotaxonomic, cultural and morphological properties consistent with its classification in the genus Actinomadura such as hooked or irregular spiral spore chains, meso-diaminopimelic acid as the major cell wall diaminopimelic acid, and diphosphatidylglycerol and phosphatidylinositol as major polar lipids. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain D310AT^T is closely, albeit loosely, associated with Actinomadura darangshiensis DLS-70^T with 97.2% sequence similarity, but was readily separated from the latter using diverse phenotypic properties. Consequently, the isolate is considered to represent a new species of Actinomadura for which the name Actinomadura alkaliterrae sp. nov. is proposed, with the type strain D310AT^T (=DSM 101185^T = KCTC 39657^T).