Genomic adaptation in the CAZyome and specialised metabolism of the plant-associated Streptomyces violaceusniger clade

Streptomycetes are Gram-positive actinobacteria largely represented in the plant root microbiota. The genetic determinants involved in the presence of Streptomyces in the rhizosphere are largely unknown and can rely on the ability to degrade plant-derived compounds such as cell-wall polysaccharides and on the production of specialised metabolites. To address whether Streptomyces strains recruited into root microbiota share genomic specificities related to these two functions, we engaged a comparative genomic analysis using a newly sequenced rhizospheric strain, Streptomyces sp. AgN23 and strains from the phylogenetically related S. violaceusniger clade. This analysis enlightens a shared prominent CAZyome potentially involved in plant polysaccharides degradation and a strong conservation of antimicrobials biosynthetic clusters (rustmicin, mediomycin, niphimycin, nigericin) as well as plant bioactive compounds (nigericin, echosides, elaiophylin). Taken together, our work supports the hypothesis that specific hydrolytic enzymes and specialised metabolites repertoires may play important roles in the development of Streptomyces strains in the rhizosphere.

Genome-based classification of the Streptomyces violaceusniger clade and description of Streptomyces sabulosicollis sp. nov. from an Indonesian sand dune

A polyphasic study was designed to determine the taxonomic provenance of a strain, isolate PRKS01-29T, recovered from an Indonesian sand dune and provisionally assigned to the Streptomyces violaceusniger clade. Genomic, genotypic and phenotypic data confirmed this classification. The isolate formed an extensively branched substrate mycelium which carried aerial hyphae that differentiated into spiral chains of rugose ornamented spores, contained LL-as the wall diaminopimelic acid, MK-9 (H6, H8) as predominant isoprenologues, phosphatidylethanolamine as the diagnostic phospholipid and major proportions of saturated, iso- and anteiso- fatty acids. Whole-genome sequences generated for the isolate and Streptomyces albiflaviniger DSM 41598T and Streptomyces javensis DSM 41764T were compared with phylogenetically closely related strains, the isolate formed a branch within the S. violaceusniger clade in the resultant phylogenomic tree. Whole-genome sequences data showed that isolate PRKS01-29T was most closely related to the S. albiflaviniger strain but was distinguished from the latter and from other members of the clade using combinations of phenotypic properties and average nucleotide identity and digital DNA:DNA hybridization scores. Consequently, it is proposed that isolate PRKS01-29T (= CCMM B1303T = ICEBB-02T = NCIMB 15210T) should be classified in the genus Streptomyces as Streptomyces sabulosicollis sp. nov. It is also clear that streptomycetes which produce spiral chains of rugose ornamented spores form a well-defined monophyletic clade in the Streptomyces phylogenomic tree., the taxonomic status of which requires further study. The genome of the type strain of S. sabulosicollis contains biosynthetic gene clusters predicted to produce new natural products.

Genome-based Classification of the Streptomyces Violaceusniger Clade and Description of Streptomyces Sabulosicollis sp. nov. from an Indonesian Sand Dune

A polyphasic study was designed to determine the taxonomic provenance of a strain, isolate PRKS01-29 T , recovered from an Indonesian sand dune and provisionally assigned to the Streptomyces violaceusniger clade. Genomic, genotypic and phenotypic data confirmed this classification. The isolate formed an extensively branched substrate mycelium which carried aerial hyphae that differentiated into spiral chains of rugose ornamented spores, contained LL-as the wall diaminopimelic acid, MK-9 (H 6 , H 8 ) as predominant isoprenologues, phosphatidylethanolamine as the diagnostic phospholipid and major proportions of saturated, iso - and antesio - fatty acids. Whole-genome sequences generated for the isolate and Streptomyces albiflaviniger DSM 41598 T and Streptomyces javensis DSM 41764 T were compared with phylogenetically closely related strains, the isolate formed a branch within the S. violaceusniger clade in the resultant phylogenomic tree. Genomic data showed that isolate PRKS01-29 T was most closely related to the S. albiflavinger strain but was distinguished from the latter and from other members of the clade using combinations of phenotypic properties and low average nucleotide identity and digital DNA:DNA hybridization scores. Consequently, it is proposed that isolate PRKS01-29 T (=CCMM B1303 T = ICEBB-02 T = NCIMB 15210 T ) should be classified in the genus Streptomyces as Streptomyces sabulosicollis sp. nov. It is also clear that streptomycetes which produce spiral chains of rugose ornamented spores form a well-defined monophyletic clade in the Streptomyces phylogenomic tree., the taxonomic status of which requires further study. The genome of the type strain of S. sabulosicollis contains biosynthetic gene clusters predicted to produce new natural products.

Streptomyces samsunensis sp. nov., a member of the Streptomyces violaceusniger clade isolated from the rhizosphere of Robinia pseudoacacia

The taxonomic position of a Streptomyces isolate, strain M1463T, recovered from the rhizosphere of Robinia pseudoacacia was established in a polyphasic study. The organism had chemical and morphological markers that were consistent with its classification in the Streptomyces violaceusniger clade. This assignment was confirmed by 16S rRNA gene sequence data, which also showed that the strain formed a distinct subclade together with Streptomyces malaysiensis DSM 41697T. However, the two strains were readily distinguished on the basis of DNA relatedness and phenotypic data. The combined genotypic and phenotypic data show that strain M1463T should be recognized as a representative of a novel species in the Streptomyces violaceusniger clade, for which the name Streptomyces samsunensis sp. nov. is proposed. The type strain of S. samsunensis is M1463T ( = DSM 42010T = NRRL B-24803T).