Streptomyces brasiliscabiei, a new species causing potato scab in south Brazil

This study aimed to characterize six Streptomyces strains associated with potato scab in south Brazil through polyphasic taxonomy involving morphology, pathogenicity and genetic features. These strains were compared with other potato-scab Streptomyces species mainly S. europaeiscabiei, S. scabiei and S. stelliscabiei. South-Brazilian Streptomyces strains were morphologically distinct from the type strains of S. scabiei (CFBP 4517T) and their genomospecies S. europaeiscabiei (CFBP 4497 T) and S. stelliscabiei (CFBP 4521T), producing a brown substrate mycelium with red borders and cream-grey brown aerial spores. Red-brown diffusible pigment on YME was also observed. The carbon sources L-Arabinose, D-Fructose, D-Glucose, D-Mannitol, meso-Inositol, Raffinose, Rhamnose, Sucrose, D-Xylose were tested for these strains. All strains were pathogenic causing symptoms of necrosis on radish and several potato cultivars commonly used in potato growing areas in Brazil. In greenhouse conditions, the strains caused scab disease and produced deep-pitted lesions covering large areas of the tuber. These results were correlated with presence of pathogenicity marker genes (txtAB, tomA or nec1) detected by PCR amplifications. In both phylogenetic analyses, 16S rRNA and MLSA, Streptomyces sp. Brazilian strains were closely related to S. europaeiscabiei, S. scabiei and S. stelliscabiei species, but they were allocated in separated branches supported by high bootstrap values and/or with low sequence similarity values. Sequencing of whole genome showed an 10,846,379 bp linear chromosome with high GC content (71.3%) consisting of 9179 putative genes, 3 rRNAs, 89 tRNAs and 1 CRISPRS. The molecular data, including genomic features, associated with morphological, biochemical and pathogenic characteristics warrant that the six Streptomyces Brazilian strains represent a new species associated with potato scab in Brazil, which would be named Streptomyces brasiliscabiei with IBSBF 2867T as the type strain.