Moraxella tarda sp. nov., a Novel Species Isolated from Nasal Cavity of Cattle with Infectious Bovine Keratoconjunctivitis

Abstract

A novel bacterial species was isolated from the nasal mucosa of Hereford cattle exhibiting early clinical signs of infectious bovine keratoconjunctivitis on a beef cattle farm in the Pampa biome, southern Brazil, in 2018. Cells were Gram-stain-negative cocci and exhibited slow growth under standard laboratory conditions, with optimal growth at 35 °C, pH 7.5, and 1.0% NaCl. The draft genome comprised approximately 1.86 Mbp (GenBank accession number GCF_035181365.1). Phylogenetic analysis based on the 16 S rRNA gene sequence showed that the closest relative was ar Moraxella nasibovis , with 97.9% sequence identity. Genome-based comparisons revealed average nucleotide identity (ANI) values ranging from 77% to 79% and digital DNA–DNA hybridization (dDDH) values ranging from 20.5% to 33.7% when compared to other Moraxella species, all below the accepted thresholds for species delineation. Phylogenomic analyses based on whole-genome and core gene datasets consistently placed the isolate in a distinct lineage within the genus Moraxella , most closely related to M. nasibovis and M. oculi . Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) did not match the isolate with any known Moraxella species. Morphological, physiological, and genomic analyses supported its classification within the genus Moraxella while clearly distinguishing it from previously described species. Based on the combined phenotypic and genomic evidence, we propose the novel species as Moraxella tarda sp. nov., with strain 7624LNᵀ (= CCP 570ᵀ = IAL 11705ᵀ = LMG 34122ᵀ) designated as the type strain.

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