Streptomyces hilarionis sp. nov. and Streptomyces hayashii sp. nov., two new strains associated with potato scab in Brazil.

Two new actinobacteria, designated strains IBSBF 2807T and IBSBF 2953T, isolated from scab lesions on potato tubers grown in the southern Brazilian states of Rio Grande do Sul and Santa Catarina, respectively, were characterized and identified through a polyphasic approach. Phylogenetic analyses of 16S rRNA sequences revealed that these two strains belong to the genus Streptomyces. Multilocus sequence analysis using five concatenated genes, atpD, gyrB, recA, rpoB and trpB, allocated strains IBSBF 2807T and IBSBF 2953T in distinct branches of Streptomyces phytopathogenic strains. PCR-RFLP analysis of the atpD gene also confirmed that these strains differ from the type strains of Streptomyces associated with potato scab. The morphological, physiological and biochemical characterization, along with the overall genome-related index properties, indicated that these two strains could be distinguished from their closest phylogenetic relatives and each other. According to the data, IBSBF 2807T and IBSBF 2953T represent two new Streptomyces species related to potato scab. The proposed names for these strains are Streptomyces hilarionis sp. nov. (IBSBF 2807T=CBMAI 2674T=ICMP 24297T=MUM 22.66T) and Streptomyces hayashii sp. nov (IBSBF 2953T=CBMAI 2675T=ICMP 24301T=MUM 22.68T).

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.