Taxonogenomic analysis of the Xanthomonas translucens complex leads to the descriptions of Xanthomonas cerealis sp. nov. and Xanthomonas graminis sp. nov.

The pathovar-based taxonomy of the <i>Xanthomonas translucens</i> group is very confusing due to an overlap of plant host ranges and level of host specificity. Here, whole-genome sequence-based parameters (digital DNA-DNA hybridization and blast-based average nucleotide identity), phylogenomic, biochemical and phenotypical data were used to taxonomically analyse the 11 known pathovars of the <i>X. translucens</i> complex. This polyphasic approach taxonomically assigned the 11 pathovars of <i>X. translucens</i> complex into three distinct species, two of which are new: <i>X. translucens</i>, <i>X. cerealis</i> sp. nov. and <i>X. graminis</i> sp. nov. <i>X. translucens</i> consists of three pathovars: pv. <i>translucens</i> (=pv. <i>hordei</i>), pv. <i>pistaciae</i> strain A ICMP 16316^PT and pv. <i>undulosa</i> (=pv. <i>secalis</i>). <i>X. cerealis</i> sp. nov. encompasses the pv. <i>cerealis</i> strain LMG 679^PT and pv. <i>pistaciae</i> strain B ICMP 16317^PT with genome similarity of 92.7% (dDDH) and 99.0% (ANIb) suggesting taxonomically similar genotypes. The other new species, <i>X. graminis</i> sp. nov., consists of the remaining five designated pathovars (pv. <i>graminis</i>, pv. <i>arrhenatheri,</i> pv. <i>poae</i>, pv. <i>phleipratensis</i> and pv. <i>phlei</i>) with highly variable dDDH and ANIb values ranging from 74.5 to 93.0% and from 96.7 to 99.2%, respectively, an indication of a very divergent taxonomic group. Only strains of pvs. <i>phlei</i> and <i>phleipratensis</i> showed the highest genomic similarities of 93.0% (dDDH) and 99.2% (ANIb), suggesting synonymic pathovars as both infect the same plant hosts. The dDDH and ANI data were corroborated by phylogenomics clustering. The fatty acid contents were similar but the type strain of <i>X. graminis</i> sp. nov. exhibited 20% less C_{15 : 0} iso and 40% more C_{17 : 0} iso fatty acids than the other species. Based on phenotypic, biochemical and whole-genome sequence data, we propose two new species, <i>Xanthomonas cerealis</i> sp. nov. and <i>Xanthomonas graminis</i> sp. nov. with type strains LMG 679^T (=NCPPB 1944^T) and LMG 726^T (=NCPPB 2700^T), respectively.