Xanthomonas euroxanthea sp. nov., a new xanthomonad species including pathogenic and non-pathogenic strains of walnut
Leonor Martins, Camila Fernandes, Jochen Blom, Nay C. Dia, Joël F. Pothier, Fernando Tavares
Abstract
We describe a novel species isolated from walnut ( Juglans regia ) which comprises non-pathogenic and pathogenic strains on walnut. The isolates, obtained from a single ornamental walnut tree showing disease symptoms, grew on yeast extract–dextrose–carbonate agar as mucoid yellow colonies characteristic of Xanthomonas species. Pathogenicity assays showed that while strain CPBF 424 T causes disease in walnut, strain CPBF 367 was non-pathogenic on walnut leaves. Biolog GEN III metabolic profiles disclosed some differences between strains CPBF 367 and CPBF 424 T and other xanthomonads. Multilocus sequence analysis with seven housekeeping genes ( fyuA , gyrB , rpoD , atpD , dnaK , efp , glnA ) grouped these strains in a distinct cluster from Xanthomonas arboricola pv. juglandis and closer to Xanthomonas prunicola and Xanthomonas arboricola pv. populi . Average nucleotide identity (ANI) analysis results displayed similarity values below 93 % to X. arboricola strains. Meanwhile ANI and digital DNA–DNA hybridization similarity values were below 89 and 50 % to non- arboricola Xanthomonas strains, respectively, revealing that they do not belong to any previously described Xanthomonas species. Furthermore, the two strains show over 98 % similarity to each other. Genomic analysis shows that strain CPBF 424 T harbours a complete type III secretion system and several type III effector proteins, in contrast with strain CPBF 367, shown to be non-pathogenic in plant bioassays. Taking these data altogether, we propose that strains CPBF 367 and CPBF 424 T belong to a new species herein named Xanthomonas euroxanthea sp. nov., with CPBF 424 T (=LMG 31037 T =CCOS 1891 T =NCPPB 4675 T ) as the type strain.