Identification and characterization of Streptomyces alkaliscabies sp. nov.

A new bacterial species is described, for which we propose the name Streptomyces alkaliscabies. This organism causes a scab disease of potatoes (Solanum tuberosum). The alkaline scab symptoms caused by this organism are indistinguishable from the symptoms of common scab caused by Streptomyces scabies. In culture, S. alkaliscabies is distinct from other scab-causing Streptomyces species, having flexuous spore chains and grey mass colour with non-diffusible pigments. S. alkaliscabies grows on agar media at pH 7-11 (versus pH 5.0 for S. scabies) and has high utilization of all tested sugars including mannitol, sucrose, glucose, raffinose, fructose, melibiose, cellulose, maltose and lactose as carbon source. It is intolerant to 1% phenol and salinity (NaCl at 5, 6 and 7%), melanoid pigments are produced from peptone-iron agar and tyrosine, it degrades arbutin and allantoin and is sensitive to thallium acetate at 100 µg/ml, streptomycin (25 µg/ml), oleandomycin (100 µg/ml) and penicillin (10 IU/ml) and tolerates thallium acetate at 10 µg/ml. The 16S-23S ITS region sequence was 466 bp in length and showed relatively low sequence similarity, less than 60%, with other strains. A phylogenetic tree constructed on the basis of 16S rRNA gene sequence showed that the Streptomyces spp. that cause potato scab, including S. scabies, S. acidiscabies, S. turgidiscabies, S. reticuliscabie, S. stelliscabiei, S. chiniscabies and S. europaeiscabies, constitute unique branches. It is evident that strain 8 (S. alkaliscabies) forms a distinct phyletic line from known pathogenic strains.