Pseudomonas serbiensis sp. nov. isolated from watermelon and muskmelon in Serbia

Abstract

Six Pseudomonas strains isolated from muskmelon and watermelon seedlings affected by stem rot and wilting in Serbia were reported as P. cichorii based on pathogenicity, LOPAT and cell wall fatty acid analyses. Recent bacterial isolates from cucurbit crops displaying P. cichorii-like symptoms in Alabama, USA, were identified as P. capsici, prompting polyphasic re-evaluation of the Serbian strains. All six strains were found to cause severe disease in watermelon and squash seedlings under greenhouse conditions. Strains KFB 138 and KFB 140 underwent whole-genome sequencing and were found to have the highest level of 16S rRNA similarity to P. lijiangensis LJ2T (both 99.87%). Phylogenies based on housekeeping genes and core-genome analysis placed both strains into phylogroup 11 of the Pseudomonas syringae species complex, with KFB 138 forming a lineage basal to all other phylogroup 11 members. In core-genome phylogeny, KFB 140 was placed into a clade alongside P. lijiangensis LJ2T. Average nucleotide identity based on blast (ANIb) identified KFB 140 as a member of P. lijiangensis (95.85%), though KFB 138 did not produce an ANIb value over 95% to any Pseudomonas type strain to which it was compared. Values for in silico DNA–DNA hybridization for both strains were below 70% to all reference strains tested, though KFB 140 was found to be most similar to P. lijiangensis (68.2%). KFB 138 and KFB 140 were further characterized using the online Type Genome Server, biochemical profiling with the Biolog Gen III MicroPlate system, matrix-assisted laser desorption/ionization time of flight mass spectrometry and imaged with transmission electron microscopy. From the results of the above analyses, we conclude that KFB 140 is a member of the species P. lijiangensis and that KFB 138 represents a novel Pseudomonas species, for which we propose the name Pseudomonas serbiensis (KFB 138T, NCPPB 4762=LMG 33366), named for its location of isolation.