Abstract
Xanthomonas translucens is the etiological agent of the wheat bacterial leaf streak (BLS) disease. The isolation of this pathogen is usually based on the Wilbrink’s-boric acid–cephalexin semi-selective medium which eliminates 90% of other bacteria, some of which might be novel species. In our study, a general purpose nutrient agar was used to isolate 49 bacterial strains including X. translucens from necrotic wheat leaf tissues. Maximum likelihood cluster analysis of 16S rRNA sequences grouped the strains into 10 distinct genera. Pseudomonas (32.7%) and Pantoea (28.6%) were the dominant genera while Xanthomonas, Clavibacter and Curtobacterium had 8.2%, each. Erwinia and Sphingomonas had two strains, each. BLAST and phylogenetic analyses of multilocus sequence analysis (MLSA) of specific housekeeping genes taxonomically assigned all the strains to validly described bacterial species, except three strains (10L4B, 12L4D and 32L3A) of Pseudomonas and two (23L3C and 15L3B) of Sphingomonas. Strains 10L4B and12L4D had Pseudomonas caspiana as their closest known type strain while strain 32L3A was closest to Pseudomonas asturiensis. Sphingomonas sp. strains 23L3C and 15L3B were closest to S. faeni based on MLSA analysis. Our data on MLSA, whole genome-based cluster analysis, DNA-DNA hybridization and average nucleotide identity, matrix-assisted laser desorption/ionization-time-of-flight, chemotaxonomy and phenotype affirmed that these 5 strains constitute three novel lineages and are taxonomically described in this study. We propose the names, Sphingomonas albertensis sp. nov. (type strain 23L3CT = DOAB 1063T = CECT 30248T = LMG 32139T), Pseudomonas triticumensis sp. nov. (type strain 32L3AT = DOAB 1067T = CECT 30249T = LMG 32140T) and Pseudomonas foliumensis sp. nov. (type strain 10L4BT = DOAB 1069T = CECT 30250T = LMG 32142T). Comparative genomics of these novel species, relative to their closest type strains, revealed unique repertoires of core secretion systems and secondary metabolites/antibiotics. Also, the detection of CRISPR-Cas systems in the genomes of these novel species suggests an acquired mechanism for resistance against foreign mobile genetic elements. The results presented here revealed a cohabitation, within the BLS lesions, of diverse bacterial species, including novel lineages.
Highlights
Members of the Xanthomonas translucens group are gramnegative plant pathogenic bacteria that can cause serious diseases to important cereal crops as well as forage grasses (Hersemann et al, 2017; Curland et al, 2018; Sapkota et al, 2020)
Thirty-nine (80%) out of the 49 strains were Gram-negative bacteria while 10 strains were Gram-positive suggesting that the former major group is more abundant in the infected wheat leaf that showed typical symptoms of the bacterial leaf streak caused by X. translucens (Figure 1)
Fourteen of the 16 strains belonging to the family Erwiniaceae were classified as Pantoea while two strains were assigned to the genus Erwinia (Cluster II) (Figure 1 and Supplementary Table 1)
Summary
Members of the Xanthomonas translucens group are gramnegative plant pathogenic bacteria that can cause serious diseases to important cereal crops as well as forage grasses (Hersemann et al, 2017; Curland et al, 2018; Sapkota et al, 2020). Translucens, hordei, cerealis, secalis and phleipratensis belong to the translucens subgroup and cause bacterial leaf streak (BLS) on wheat, barley, oat, triticale, and rye (Duveiller, 1994; Vauterin et al, 1995; Sapkota et al, 2020). The “graminis” subgroup comprises of four pathovars (arrhenatheri, graminis, poae, and phlei) that cause bacterial wilt diseases on forage grasses (Vauterin et al, 1995; Sapkota et al, 2020). Duveiller (Duveiller, 1994) indicated the elimination of over 90% of “saprophytic” bacteria from washes of wheat and triticale lots using WBC, facilitating the identification of the pale yellow X. translucens pv
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
