Streptomyces lonarensis sp. nov., isolated from Lonar Lake, a meteorite salt water lake in India

Streptomyces: Still the Biggest Producer of New Natural Secondary Metabolites, a Current Perspective

There is a real consensus that new antibiotics are urgently needed and are the best chance for combating antibiotic resistance. The phylum Actinobacteria is one of the main producers of new antibiotics, with a recent paradigm shift whereby rare actinomycetes have been increasingly targeted as a source of new secondary metabolites for the discovery of new antibiotics. However, this review shows that the genus Streptomyces is still the largest current producer of new and innovative secondary metabolites. Between January 2015 and December 2020, a significantly high number of novel Streptomyces spp. have been isolated from different environments, including extreme environments, symbionts, terrestrial soils, sediments and also from marine environments, mainly from marine invertebrates and marine sediments. This review highlights 135 new species of Streptomyces during this 6-year period with 108 new species of Streptomyces from the terrestrial environment and 27 new species from marine sources. A brief summary of the different pre-treatment methods used for the successful isolation of some of the new species of Streptomyces is also discussed, as well as the biological activities of the isolated secondary metabolites. A total of 279 new secondary metabolites have been recorded from 121 species of Streptomyces which exhibit diverse biological activity. The greatest number of new secondary metabolites originated from the terrestrial-sourced Streptomyces spp.

Streptomyces xanthii sp. nov. and Streptomyces roseirectus sp. nov. isolated from a Chinese medicinal plant

Two strains of Actinobacteria, designated CRXT-Y-14^T and CRXT-G-22^T, were isolated from the healthy leaves and seeds, respectively, of a medicinal plant Xanthium sibiricum. Their taxonomic positions were determined using a polyphasic approach. Strain CRXT-Y-14^T produced flexuous chains of smooth-surfaced spores. Strain CRXT-G-22^T produced straight chains of smooth-surfaced spores. Their morphological features were consistent with the diagnostic characteristics of members of the genus Streptomyces. The results of 16S rRNA gene sequence analyses indicated two strains represented members of the genus Streptomyces. CRXT-Y-14^T shared 99.3, 98.9, 98.8 % sequence similarities to Streptomyces atriruber NRRL B-24165^T, Streptomyces avermitilis MA-4680^T and Streptomyces davaonensis JCM 4913^T, respectively. Whilst CRXT-G-22^T exhibited highest similarity to Streptomyces acidiscabies ATCC 49003^T (98.9 %). The results of phylogenetic analyses based on 16S rRNA gene sequences indicated that the closest phylogenetic neighbours of strains CRXT-Y-14^T and CRXT-G-22^T were S. atriruber NRRL B-24165^T and S. acidiscabies ATCC 49003^T, respectively. The phylogenomic analyses further confirmed the relative relationship between strain CRXT-G-22^T and S. acidiscabies ATCC 49003^T, but indicated that CRXT-Y-14^T could represent a novel species of the genus Streptomyce. However, the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between CRXT-Y-14^T and strain CRXT-G-22^T, between CRXT-Y-14^T and S. atriruber NRRL B-24165^T, and between CRXT-G-22^T and S. acidiscabies ATCC 49003^T were 85.4 and 23.2 %, 85.8 and 23.9 % and 89.1 and 34.1 %, respectively, far below the 95~96 and 70 % cut-off points recommended for delineating species. Furthermore, these two novel isolates were distinctly differentiated from their relatives in the genus Streptomyces with respect to phenotypic and chemotaxonomic characteristics. On the basis of these data, CRXT-Y-14^T and CRXT-G-22^T clearly represent two novel species within the genus Streptomyces, for which the names Streptomyces xanthii sp. nov. (type strain CRXT-Y-14^T = MCCC 1K04966^T= JCM 34527^T) and Streptomyces roseirectus sp. nov. (type CRXT-G-22^T = MCCC 1K04979^T= JCM 34565^T) are proposed.

Streptomyces alkaliterrae sp. nov., isolated from an alkaline soil, and emended descriptions of Streptomyces alkaliphilus, Streptomyces calidiresistens and Streptomyces durbertensis

A polyphasic study was undertaken to establish the taxonomic position of six representative streptomycetes isolated from an alkaline soil adjacent to a meteoric alkaline soda lake in India. Chemotaxonomic, cultural and morphological properties of the isolates were consistent with their classification in the genus Streptomyces. The isolates formed extensively branched substrate mycelia and aerial hyphae that differentiated in straight chains of spores with smooth surfaces. They contained LL-diaminopimelic acid in the wall peptidoglycan, produced either hexa- or octa-hydrogenated menaquinones with nine isoprene units, major amounts of saturated, iso- and anteiso- fatty acids and phosphatidylethanolamine as the characteristic polar lipid. The isolates grew well at 30 °C, pH 9 and in the presence of 3 to 5% (w/v) sodium chloride. Isolates OF1^T, OF3 and OF8 formed a distinct clade within the Streptomyces 16S rRNA gene tree sharing relatively high sequence similarities with the type strains of Streptomyces durbertensis (99.3%), Streptomyces palmae (98.1%) and Streptomyces xinghaiensis (98.3%), but can be distinguished from them using combinations of phenotypic properties. A phylogenomic tree based on draft genome sequences of the isolates and S. durbertensis DSM 104538^T confirmed the phylogenetic relationships. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values calculated from the whole genome sequences of isolate OF1^T and S. durbertensis DSM 104538^T were low at 92.0% and 45.2%, respectively, indicating that they belong to different genomic species. Consequently, on the basis of the genomic, phylogenetic and associated phenotypic data it is proposed that isolates OF1^T, OF3 and OF8 be assigned to the genus Streptomyces as Streptomyces alkaliterrae sp. nov. with strain OF1^T (NCIMB 15195^T =PCM 3001^T) as the type strain. Isolates IF11, IF17 and IF19, and S. alkaliphilus DSM 42118^T were shown to belong to the same taxospecies and together with S. calidiresistens DSM 42108^T comprised a well supported clade in the Streptomyces 16S rRNA gene tree. Isolate IF17 and S. alkaliphilus DSM 42118^T formed a well-supported clade in the phylogenomic tree, had almost identical digital G + C similarity values, produced long straight chains of smooth-surfaced spores and shared ANI and dDDH values (98.0 and 79.6%, respectively) consistent with their assignment to the same genomic species. In light of all of the data isolates IF11, IF17 and IF19 should be seen as authentic stains of S. alkalihilus. Data acquired in the present study have also been used to emend the descriptions of S. alkaliphilus, S. calidiresistens and S. durbertensis. The genomes of isolates IF17, and OF1^T, OF3 and OF8 contain relatively high numbers of biosynthetic gene clusters some of which were discontinously distributed indicating ones predicted to express for novel specialised metabolites.

Draft Genome Sequence of Streptomyces sp. Strain ventii, Isolated from a Microbial Mat near Hydrothermal Vents within the Axial Seamount in the Pacific Ocean, and Resequencing of the Type Strains Streptomyces lonarensis NCL 716 and Streptomyces bohaiensis 11A07

The draft genome of Streptomyces sp. strain ventii, an environmental isolate recovered from deep-sea hydrothermal vents in the Pacific Ocean, is presented along with the resequenced draft genomes of the type strains Streptomyces bohaiensis 11A07 and Streptomyces lonarensis NCL 716.

The draft genome of Streptomyces sp. strain ventii, an environmental isolate recovered from deep-sea hydrothermal vents in the Pacific Ocean, is presented along with the resequenced draft genomes of the type strains Streptomyces bohaiensis 11A07 and Streptomyces lonarensis NCL 716.

Streptomyces otsuchiensis sp. nov., a biosurfactant-producing actinobacterium isolated from marine sediment

A novel actinobacterium producing biosurfactant, designated OTB305^T, was isolated from marine sediment sampled at Otsuchi Bay, Iwate Prefecture, Japan and its taxonomic position was examined using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences exhibited that strain OTB305^T was closely related to Streptomyces bohaiensis JCM 19630^T (98.8 %) and Streptomyces lonarensis DSM 42084^T (98.8 %). The chemotaxonomic characteristics of strain OTB305^T corresponded to those of the genus Streptomyces as follows: the diamino acid of the cell-wall peptidoglycan was ll-diaminopimelic acid; whole-cell hydrolysates contained glucose and lacked characteristic major sugars; the predominant isoprenoid quinones were MK-9(H₈) and MK-9(H₆); the polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and an unidentified phospholipid; the major cellular fatty acids were iso-C_16 : 0, C_16 : 0 and C_16 : 1 ω7c; and the genomic DNA G+C content was 72.83 mol%. However, genomic relatedness analysis based on the average nucleotide identity and some phenotypic characteristics revealed that strain OTB305^T was distinguished from closely related Streptomyces species. Therefore, strain OTB305^T represents a novel species of the genus Streptomyces, for which the name Streptomyces otsuchiensis sp. nov. is proposed. The type strain is OTB305^T (=NBRC 113255^T=TBRC 9682^T).

Streptomyces sediminis sp. nov. isolated from crater lake sediment

A novel actinobacterial strain, MKSP12^T, was isolated from coastal sediment of a crater lake in central Anatolia, Turkey. The taxonomic position of the strain was clarified using a polyphasic approach. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain MKSP12^T is closely related to Streptomyces specialis GW 41-1564^T with 97.1% sequence similarity. The strain produces aerial hyphae that differentiate into spiral chains of smooth surfaced spores and grows over a temperature range of 20-37 °C, at pH 7-11 and in the presence of 3% (w/v) sodium chloride. The cell wall amino acid is LL-diaminopimelic acid and the whole cell sugars are glucose and ribose. The polar lipids profile consists of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, an unidentified aminophospholipid, two unidentified phospholipids, an unidentified glycophospholipid and eight unidentified glycolipids; iso-C_16:0, iso-C_16:1 G, anteiso-C_17:0 and anteiso-C_17:1 ω9c were identified as the predominant cellular fatty acids (> 10%). Based on morphological and chemotaxonomic characteristics, and phylogenetic analyses, the strain is considered to represent a novel species in the genus Streptomyces, for which the name Streptomyces sediminis sp. nov. is proposed with the type strain MKSP12^T (= DSM 100692^T = KCTC 39613^T).

Emended description of the family Chromatiaceae, phylogenetic analyses of the genera Alishewanella, Rheinheimera and Arsukibacterium, transfer of Rheinheimera longhuensis LH2-2T to the genus Alishewanella and description of Alishewanella alkalitolerans sp. nov. from Lonar Lake, India

Phylogenetic analyses were performed for members of the family Chromatiaceae, signature nucleotides deduced and the genus Alishewanella transferred to Chromatiaceae. Phylogenetic analyses were executed for the genera Alishewanella, Arsukibacterium and Rheinheimera and the genus Rheinheimera is proposed to be split, with the creation of the Pararheinheimera gen. nov. Furthermore, the species Rheinheimera longhuensis, is transferred to the genus Alishewanella as Alishewanella longhuensis comb. nov. Besides, the genera Alishewanella and Rheinheimera are also emended. Strain LNK-7.1^T was isolated from a water sample from the Lonar Lake, India. Cells were Gram-negative, motile rods, positive for catalase, oxidase, phosphatase, contained C_16:0, C_17:1ω8c, summed feature3 (C_16:1ω6c and/or C_16:1ω7c) and summed feature 8 (C_18:1ω7c) as major fatty acids, PE and PG as the major lipids and Q-8 as the sole respiratory quinone. Phylogenetic analyses using NJ, ME, ML and Maximum parsimony, based on 16S rRNA gene sequences, identified Alishewanella tabrizica RCRI4^T as the closely related species of strain LNK-7.1^T with a 16S rRNA gene sequence similarity of 98.13%. The DNA-DNA similarity between LNK-7.1^T and the closely related species (A. tabrizica) was only 12.0% and, therefore, strain LNK-7.1^T was identified as a novel species of the genus Alishewanella with the proposed name Alishewanella alkalitolerans sp. nov. In addition phenotypic characteristics confirmed the species status to strain LNK-7.1^T. The type strain of A. alkalitolerans is LNK-7.1^T (LMG 29592^T = KCTC 52279^T), isolated from a water sample collected from the Lonar lake, India.