Pseudomonas boreofloridensis sp. nov., and Pseudomonas citrulli sp. nov., isolated from watermelon in Florida.

Abstract

Three fluorescent bacterial strains, K1, K13 and K18, were obtained from watermelon (Citrullus lanatus) foliage symptomatic of bacterial leaf spot of cucurbits in Florida. The strains underwent phenotypic characterization, including LOPAT (levan production, oxidase activity, pectolytic activity on potato, arginine dihydrolase production and hypersensitive response (HR) on both tobacco and tomato) and pathogenicity testing on watermelon and squash seedlings. Whole-genome sequencing of the isolates was performed, and multi-locus sequence analysis (MLSA) utilizing housekeeping genes gltA, rpoD, gapA and gyrB placed the isolates into two distinct clades within the Pseudomonas genus. Average nucleotide identity based on blast (ANIb) was used to compare the isolates to Pseudomonas reference genomes. Using ANIb, the closest relatives to the novel strains were identified as Pseudomonas wayambapalatensis (K1 : 82.58%; K13 : 83.77%) and Pseudomonas kilonensis (K18 : 87.16%), although ANIb values were below the 95% threshold for species delineation. DNA-DNA hybridization (genome-genome distance calculation method), comparison to the online Type Genome Server, Biolog biochemical profiling and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were also unable to identify the isolates as any known species of Pseudomonas. Based on the combination of genetic and phenotypic data, we conclude that these isolates represent two novel Pseudomonas species, for which we propose the names Pseudomonas boreofloridensis sp. nov. (K1, K13^T, NCPPB 4759=LMG 33364) and Pseudomonas citrulli sp. nov. (K18^T, NCPPB 4761=LMG 33365). The specific epithet boreofloridensis was chosen for the geographic location of isolation (northern Florida), while citrulli designates the host of origin (C. lanatus).