# Ewingella allii sp. nov. isolated from a diseased onion plant in the Columbia Basin of Washington State, USA

## TL;DR

A new bacterial species, Ewingella allii, was discovered in a diseased onion plant in Washington State and is distinct from related species based on genetic and pathogenic characteristics.

## Contribution

The discovery and characterization of a novel species, Ewingella allii, based on genomic and phenotypic data.

## Key findings

- Strain 20WA0182T is a new species in the genus Ewingella, distinct from E. americana based on phylogenetic and genomic analyses.
- The strain is pathogenic to onion bulbs and weakly pathogenic to onion leaves.
- ANI and dDDH scores confirm that 20WA0182T is a novel species within the Ewingella genus.

## Abstract

Isolation of strain 20WA0182T from a diseased onion plant grown in the Columbia Basin of Washington State, USA, led to preliminary identification as a member of the genus Ewingella. The strain was characterised as a Gram-stain-negative, facultative anaerobe that is rod-shaped, motile with polar flagella, catalase positive, and oxidase negative. The strain 20WA0182T isolated was pathogenic to yellow onion bulbs, weakly pathogenic on onion leaves of the cv. Ranchero, and caused a pathogenic response using the red onion bulb scale necrosis assay. Phylogenetic analyses using the 16S rRNA gene and four housekeeping genes, atpD, gyrB, infB, and rpoB, showed that strain 20WA0182T formed a branch that clustered with E. americana strains, but on a separate node, indicating it is a novel species of this genus. Whole-genome sequencing of strain 20WA0182T revealed a genome size of 4,604,541 nt, with 25 contigs and a G + C content of 53.8%, strain 20WA0182T was 99.2% complete. The average nucleotide identity of strain 20WA0182T compared with E. americana strains scores ranged from 92.85 to 93.96%, below the 95% threshold to classify strains as the same species. Similarly, dDDH scores were 56.0 to 56.2%, less than the 70% threshold required to delineate prokaryotes as the same species. Strain 20WA0182T and Ewingella sp. CoE-038-23 shared the ANI score above 97.59% and 81.0% dDDH score to be classified as a novel species of Ewingella. As the type strain 20WA0182T (= BD 3290 T = LMG 33618 T) was pathogenic to onion bulbs and leaves, the name Ewingella allii is proposed. GenBank accession number = JAWUDN000000000.

The online version contains supplementary material available at 10.1007/s10482-025-02116-6.