Streptomyces krungchingensis sp. nov., isolated from soil

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 himalayensis sp. nov. including Streptomyces himalayensis subsp. himalayensis subsp. nov. and Streptomyces himalayensis subsp. aureolus subsp. nov. isolated from Western Himalaya

Two novel actinobacteria, strain PSKA28^T and PSKA54^T were isolated from soil sample of Kashmir-Himalaya, India (latitude 34°-01' N; longitude 74°-47' E; altitude 5328 ft). Polyphasic-taxonomic analysis revealed that these strains belong to the genus Streptomyces. The 16S rRNA gene-sequence similarity of these strain were highest (98.6%) with that of the Streptomyces torulosus NRRLB-3889^T. They showed 92.1% gyrB gene-sequence similarity but 92.9 and 94.6% rpoB gene-sequence similarity, respectively, with Streptomyces torulosus NRRLB-3889^T. The sequence similarities were significantly lower than the recommended threshold value for novel taxonomic position and the 16S rRNA sequence-based phylogenetic analysis indicated that these two isolates are in distinct clade. Phylogenomic analysis with their genome sequences, conferred by Type Strain Genome Server separated them from rest of the Streptomyces type strains. The cell wall contained LL-diaminopimelic acid and the whole-cell hydrolysate contained glucose and ribose. Major fatty acid methyl esters were 15:0 anteiso, 16:0 iso and 17:0 anteiso. Average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization (dDDH) values as well as evolutionary distance based on multilocus sequence analysis, between closely related type strains and either of the strain PSKA28^T or PSKA54^T, were considerably lower than the recommended threshold value (< 70% dDDH or < 95-96% ANI/AAI or > 0.007 MLSA distance). Therefore, these isolates represent a novel Streptomyces species, for which we proposed the name Streptomyces himalayensis sp. nov. Genotypic and phenotypic analyses clearly split these strains into two closely related sub-clusters. Based on this, two novel subspecies Streptomyces himalayensis subsp. himalayensis subsp. nov. and Streptomyces himalayensis subsp. aureolus subsp. nov. are proposed, with type strains JCM33755^T (= MTCC12933^T, MCC4145^T) and JCM33759^T (= MTCC12938, MCC4180), respectively.