Streptomyces turgidiscabies and Streptomyces reticuliscabiei: one genomic species, two pathogenic groups

Abstract

Three strains ofStreptomyces reticuliscabieiand two strains ofStreptomyces turgidiscabieswere analysed, together with reference and type strains of otherStreptomycesspecies, for phenotypic traits, DNA–DNA relatedness, comparison of 16S rRNA gene sequences and presence of necrotic protein gene (nec1) homologues in order to clarify their phylogenetic relationships. A numerical analysis of phenotypic characteristics showed thatS. reticuliscabieiandS. turgidiscabiesbelong to the same cluster and share almost all morphological and biochemical traits that are important in the identification ofStreptomycesspecies. DNA–DNA hybridization and phylogenetic comparisons of 16S rRNA gene sequences confirmed that the two species are genomically closely related. In contrast, pathological data showed thatS. turgidiscabiesandS. reticuliscabieicause two distinct diseases. Gene homologues ofnec1were detected inS. turgidiscabiesand other common scab species (Streptomyces scabiei,Streptomyces europaeiscabieiandStreptomyces stelliscabiei), but not inS. reticuliscabiei. To avoid confusion between agents causing separate diseases, it is proposed that the existing distinct species names are retained:S. turgidiscabiesinvolved in common scab andS. reticuliscabieiinvolved in netted scab.