# Phylogenomic reclassification of Cellulophaga species to Paracellulophaga gen. nov. and description of Allocellulophaga tsushimaensis gen. nov., sp. nov., a novel bacterium from coastal seawater of Tsushima Island, Japan

## TL;DR

A new marine bacterium, Allocellulophaga tsushimaensis, is described, and the genus Cellulophaga is reclassified into two new genera.

## Contribution

The paper introduces Allocellulophaga tsushimaensis and reclassifies four Cellulophaga species into a new genus, Paracellulophaga.

## Key findings

- Strain TSM-5T is distinct from Cellulophaga and represents a new genus, Allocellulophaga.
- Phylogenomic analysis suggests splitting Cellulophaga into two genera, with four species moved to Paracellulophaga.
- The new species Allocellulophaga tsushimaensis is characterized by unique physiological and biochemical traits.

## Abstract

A novel Gram-staining-negative, rod-shaped, aerobic bacterial strain, designated as TSM-5 T, was isolated from surface seawater of a marine inlet. This strain grew well at 10–30 °C, pH 5.0–10.0 and in the presence of 0–4% (w/v) NaCl. Strain TSM-5 T was non-flagellated and positive for catalase and oxidase activities, and the major respiratory quinone was menaquinone-6 (MK-6). The major fatty acids present in the strain were iso-C15:1 G, iso-C15:0, iso-C15:0 3-OH, iso-C17:0 3-OH, and summed feature 3 (comprising C16:1ω7c and/or C16:1ω6c). The major polar lipid of the strain was phosphatidylethanolamine. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain TSM-5 T shared 92.6 to 94.0% sequence similarity with valid species of the genus Cellulophaga, and the phylogenetic branch of this strain divided the genus into two groups. Based on the average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH) with genomes from the closely related family Flavobacteriacea, strain TSM-5 T represents a lineage distinct from genus Cellulophaga, suggesting that this genus should be divided into two genera. Physiological and biochemical comparisons between strain TSM-5 T and closely related species revealed additional differences, including optimal NaCl concentrations and pH for growth, as well as metabolic traits such as flexirubin pigment reaction. Based on these results, we propose a novel species in a new genus, Allocellulophaga tsushimaensis gen. nov. sp. nov., with TSM-5 T (= KCTC 52508 T = NBRC 112430 T) as the type strain. Furthermore, we propose that Cellulophaga baltica, Cellulophaga pacifica, Cellulophaga tyrosinoxydans, and Cellulophaga algicola, currently valid species of the genus Cellulophaga, be reclassified into a novel genus, Paracellulophaga gen. nov., with Paracellulophaga baltica NN015840T (= DSM 24729 T = ATCC 700862 T) as the type species.

The online version contains supplementary material available at 10.1007/s10482-026-02275-0.