Streptomyces pyxinae sp. nov. and Streptomyces pyxinicus sp. nov. isolated from lichen Pyxine cocoes (Sw.) Nyl

Two novel actinobacteria, designated as LP05-1T and LP11T, were isolated from the lichen Pyxine cocoes (Sw.) Nyl. collected in Bangkok, Thailand. Genotypic and phenotypic analyses revealed that both strains represented members of the genus Streptomyces. The 16S rRNA gene of LP05-1T showed the highest similarity to the genome of Streptomyces gelaticus (98.41 %), while the 16S rRNA gene of LP11T was most similar to that of Streptomyces cinerochromogenes (98.93 %). The major menaquinones in LP05-1T were MK-9(H8), MK-9(H6), MK-9(H4) and MK-9(H2), and in LP11T, they were MK-9(H8) and MK-9(H6). Both strains exhibited the major fatty acids iso-C15 : 0, anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0, with LP05-1T also possessing iso-C17 : 0. The polar lipids of LP05-1T included phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside and an unidentified lipid, while those of LP11T consisted of phosphatidylethanolamine, lyso-phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, an unidentified aminolipid and an unidentified glycolipid. The digital DNA-DNA hybridisation (dDDH) and average nucleotide identity (ANI) values indicated that both strains are distinct from each other with values below 70 and 95 %, respectively. dDDH, ANI by blast (ANIb) and ANI by MUMmer (ANIm) values between LP05-1T and its closely related type strains were 26.07-26.80 %, 81.24-82.01 % and 86.82-86.96 %, respectively, while those for LP11T and its closely related type strains were 30.70-31.70 %, 84.09-85.31 % and 88.02-88.39 %, respectively. The results of the taxonomic investigation, including dDDH and ANI values, indicate that LP05-1T and LP11T are novel type strains of two novel species within the genus Streptomyces. The names proposed are Streptomyces pyxinae sp. nov. for strain LP05-1T (=TBRC 15494T, =NBRC 115434T) and Streptomyces pyxinicus sp. nov. for strain LP11T (=TBRC 15493T, =NBRC 115421T).

Streptomyces chengmaiensis sp. nov., isolated from the stem of a mangrove plant in Hainan

A novel Streptomyces strain, designated as HNM0663T, was isolated from the stem of a mangrove plant (Avicennia marina) collected from the coast of Chengmai city, Hainan Island, PR China. On the basis of the alignment of 16S rRNA gene sequences, strain HNM0663T was closely related to Streptomyces lichenis LCR6-01T (98.67 %), Streptomyces nanningensis YIM 33098T (98.12 %) and Streptomyces palmae CMU-AB204T (97.93 %). Genome-based comparisons showed that strain HNM0663T was distinguished from its closest related species with 80.3 % average nucleotide identity and 20.2 % digital DNA-DNA hybridization values. The main cellular fatty acids were iso-C16 : 0, iso-C15 : 0 and anteiso-C15 : 0. The main menaquinones were MK-9 (H6), MK-9 (H4) and MK-8 (H4). The predominant phospholipids contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylcholine. Based on these polyphasic taxonomy results, strain HNM0663T should represent a novel Streptomyces species, for which the name Streptomyces chengmaiensis sp. nov. is proposed. The type strain is HNM 0663T (=CCTCC AA 2019075T=LMG 31909T).

Lichen-Derived Actinomycetota: Novel Taxa and Bioactive Metabolites

Actinomycetes are essential sources of numerous bioactive secondary metabolites with diverse chemical and bioactive properties. Lichen ecosystems have piqued the interest of the research community due to their distinct characteristics. Lichen is a symbiont of fungi and algae or cyanobacteria. This review focuses on the novel taxa and diverse bioactive secondary metabolites identified between 1995 and 2022 from cultivable actinomycetota associated with lichens. A total of 25 novel actinomycetota species were reported following studies of lichens. The chemical structures and biological activities of 114 compounds derived from the lichen-associated actinomycetota are also summarized. These secondary metabolites were classified into aromatic amides and amines, diketopiperazines, furanones, indole, isoflavonoids, linear esters and macrolides, peptides, phenolic derivatives, pyridine derivatives, pyrrole derivatives, quinones, and sterols. Their biological activities included anti-inflammatory, antimicrobial, anticancer, cytotoxic, and enzyme-inhibitory actions. In addition, the biosynthetic pathways of several potent bioactive compounds are summarized. Thus, lichen actinomycetes demonstrate exceptional abilities in the discovery of new drug candidates.

Streptomyces macrolidinus sp. nov., a novel soil actinobacterium with potential anticancer and antimalarial activity

A novel actinomycete, strain RY43-2^T, belonging to the genus Streptomyces, was isolated from a peat swamp forest soil collected from Rayong Province, Thailand. The strain was characterized by using a polyphasic approach. The cell-wall peptidoglycan contained ll-diaminopimelic. Ribose and glucose were detected in its whole-cell hydrolysates. The strain contained anteiso-C_15:0, iso-C_14:0 and iso-C_16:0 as the predominant fatty acids, and MK-9(H₄), MK-9(H₆) and MK-9(H₈) as the major menaquinones. The phospholipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, three unidentified ninhydrin-positive phospholipids and two unidentified phospholipids. Strain RY43-2^T showed the highest 16S rRNA gene similarity to Streptomyces misionensis JCM 4497^T (98.9 %) and Streptomyces lichenis LCR6-01^T (98.9 %). The draft genome of RY43-2^T was 6.7 Mb with 6078 coding sequences with an average G+C content of 70.8 mol%. Genomic analysis revealed that the average nucleotide identity (ANI) values based on blast (ANIb) and MUMmer (ANIm) between strain RY43-2^T and S. misionensis JCM 4497^T were 80.1 and 86.1%, respectively. The ANIb and ANIm values between strain RY43-2^T and S. lichenis LCR6-01^T were 77.0 and 85.5%, respectively. The digital DNA-DNA hybridization values were 25.2 and 23.0% in comparison with the draft genomes of S. misionensis JCM 4497^T and S. lichenis LCR6-01^T, respectively. The results of taxonomic analysis suggested that strain RY43-2^T represented a novel species of the genus Streptomyces for which the name Streptomyces macrolidinus sp. nov. is proposed. The type strain is RY43-2^T (=TBRC 7286^T=NBRC 115640^T). Strain RY43-2^T exhibited antimicrobial activity against Enterococcus faecium ATCC 51559, Colletotrichum capsici BMGC 106 and Colletotrichum gloeosporioides BMGC 107 with the minimum inhibitory concentration values of 25.0, 12.5, and 6.25 µg ml^-1. It also exhibited potent antimalarial activity against Plasmodium falciparum K1 with IC₅₀ of 0.0031 µg ml^-1. In addition, it showed cytotoxicity against Vero, KB, MCF-7 and NCI-H187 with IC₅₀ values of 0.0347, 6.15, 3.36 and 0.0352 µg ml^-1, respectively.

Streptomyces solincola sp. nov., isolated from soil in Malaysia

A urease-producing Gram-stain-positive actinobacterium, designated strain T5^T, was isolated from a soil sample collected at a highway hillslope in Selangor, Malaysia. The strain was found to produce pale yellowish-pink aerial mycelia with smooth long chain spores and extensively branched light yellowish-pink substrate mycelia on oatmeal agar. Strain T5^T grew at 15-37 °C, pH 6-11, and tolerated up to 9 % (w/v) NaCl, with optimal growth occurring at 28 °C, pH 6-9 and without NaCl. The whole-cell sugar hydrolysate of strain T5^T contained galactose, glucose and ribose. The ll-diaminopimelic acid isomer was detected in the cell wall. Diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol were found to be the predominant polar lipids. The main fatty acids were anteiso-C_17 : 0, iso-C_16 : 0, anteiso-C_15 : 0 and iso-C_14 : 0. Comparative analysis of the 16S rRNA gene sequences indicated that strain T5^T belonged to Streptomyces of the family Streptomycetaceae with the highest 16S rRNA gene sequence similarity to Streptomyces lichenis LCR6-01^T (99.0 %). The overall genome relatedness indices revealed that the closest related species was S. lichenis LCR6-01^T with 89.4 % average nucleotide identity and 33.7 % digital DNA-DNA hybridization. Phylogeny analyses showed that strain T5^T was closely related to Streptomyces fradiae, Streptomyces lavendofoliae, Streptomyces lichenis, Streptomyces roseolilacinus and Streptomyces somaliensis. Based on these polyphasic data, strain T5^T represents a novel species, for which the name Streptomyces solincola sp. nov. is proposed. The type strain is T5^T (=TBRC 5137^T= DSM 42166^T).

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 tardus sp. nov.: A Slow-Growing Actinobacterium Producing Candicidin, Isolated From Sediments of the Trondheim Fjord

Marine environments are home to an extensive number of microorganisms, many of which remain unexplored for taxonomic novelty and functional capabilities. In this study, a slow-growing Streptomyces strain expressing unique genomic and phenotypic characteristics, P38-E01^T, was described using a polyphasic taxonomic approach. This strain is part of a collection of over 8,000 marine Actinobacteria isolates collected in the Trondheim fjord of Norway by SINTEF Industry (Trondheim, Norway) and the Norwegian University of Science and Technology (NTNU, Trondheim, Norway). Strain P38-E01^T was isolated from the sediments of the Trondheim fjord, and phylogenetic analyses affiliated this strain with the genus Streptomyces, but it was not closely affiliated with other described species. The closest related type strains were Streptomyces daliensis YIM 31724^T (98.6%), Streptomyces rimosus subsp. rimosus ATCC 10970^T (98.4%), and Streptomyces sclerotialus NRRL ISP-5269^T (98.3%). Predominant fatty acids were C_16:0 iso, C_16:0, and Summed Feature 3, and the predominant respiratory quinones were MK-10(H₆), MK-10(H₄), and MK9(H₄). The main polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, and phosphoglycolipid. The whole-cell sugars were glucose, ribose, and in minor amounts, mannose. The cell wall peptidoglycan contained LL-diaminopimelic acid. The draft genome has a size of 6.16 Mb, with a %G + C content of 71.4% and is predicted to contain at least 19 biosynthetic gene clusters encoding diverse secondary metabolites. Strain P38-E01^T was found to inhibit the growth of the pathogenic yeast Candida albicans ATCC 90028 and a number of Gram-positive bacterial human and plant pathogens. Metabolites extracted from cultures of P38-E01^T were analyzed by mass spectrometry, and it was found that the isolate produced the antifungal compound candicidin. Phenotypic and chemotaxonomic signatures, along with phylogenetic analyses, distinguished isolate P38-E01^T from its closest neighbors; thus, this isolate represents a novel species of the genus Streptomyces for which the name Streptomyces tardus sp. nov. (P38-E01^T = CCM 9049^T = DSM 111582^T) is proposed.

Streptomyces tibetensis sp. nov., an actinomycete isolated from the Tibetan Plateau

A novel actinomycete, designated strain XZ 46^T, was isolated from acid sandy soil collected from the Tibetan Plateau, China. Its taxonomic position was determined using a polyphasic approach. Strain XZ 46^T shows the typical morphological and chemotaxonomic features of members of the genus Streptomyces: slightly yellow to brown substrate mycelia and grayish white to slightly yellow aerial hyphae forming cylindrical and spiny spores; meso-diaminopimelic acid in the cell wall peptidoglycan; MK-9(H₈), MK-9(H₄) and MK-9(H₂) as predominant menaquinones; diphosphatidylglycerol, phospatidylethanolamine, phosphatidylglycerol and phosphatidylinositol as main polar lipids; and iso-C_15:0, iso-C_16:0 and anteiso-C_15:0 as major cellular fatty acids. The G+C content of the draft genome sequence, consisting of 8,995,813 bp, is 71.23%. The16S rRNA gene sequence analysis indicated that strain XZ 46^T shows high sequence similarity to Streptomyces luteogriseus NBRC 13402^T as well as forming an independent lineage clade with it in phylogenetic trees. Multilocus sequence analysis (MLSA) of five housekeeping genes (atpD, gyrB, recA, rpoB and trpB) illustrated that Streptomyces hawaiiensis is also a very closely related taxon. However, DNA-DNA hybridization, MLSA evolutionary distance and phenotypic properties demonstrate that strain XZ 46^T can be distinguished from these phylogenetically related Streptomyces species. Therefore, it is concluded that strain XZ 46^T represents a novel species of the genus Streptomyces, for which the name Streptomyces tibetensis is sp. nov. proposed. The type strain is XZ 46^T (= CGMCC 4.7579^T = KCTC 49221^T).