Description of Streptomyces borealis sp. nov. and Streptomyces saintjeani sp. nov., associated with potato common scab.

Six Streptomyces strains were isolated from scab-infected potato tubers collected in the province of Quebec, Canada. All isolates produced disease symptoms characteristic of potato common scab. Multilocus sequence analysis showed that the strains clustered into two putative novel species-level groups represented by strains LBUM1542T and LBUM3076T. Strains LBUM1542T and LBUM3076T shared the highest 16S rRNA gene sequence similarity with Streptomyces rishiriensis NBRC 13407T (99.73%) and Streptomyces acidiscabies ATCC 49003T (99.67%), respectively. Genome-based taxonomic analyses, including digital DNA-DNA hybridization and average nucleotide identity, supported the delineation of two novel species. Comparative genomic analyses revealed that both strains lacked the thaxtomin biosynthetic gene cluster classically associated with potato common scab but possessed other virulence determinants. Their predicted carbohydrate-active enzyme repertoires also differed markedly from those of their closest relatives. Morphological and phenotypic characteristics, together with genome-based chemotaxonomic predictions, were consistent with assignment to the genus Streptomyces. Some phenotypic traits, such as carbon source utilization, distinguished each strain from its closest phylogenetic neighbours. Taken together, these results demonstrate that LBUM1542T and LBUM3076T represent novel species, for which the names Streptomyces borealis sp. nov. (LBUM1542T=NCPPB 4834T=NRRL B-65796T) and Streptomyces saintjeani sp. nov. (LBUM3076T=NCPPB 4835T=NRRL B-65797T) are proposed.