The genera Ningiella and Marinicella, belonging to the families Alteromonadaceae and Marinicellaceae, respectively, within the class Gammaproteobacteria of the phylum Pseudomonadota, were initially established with the descriptions of Ningiella ruwaisensis (Fotedar et al., 2020) and Marinicella litoralis (Romanenko et al., 2010) as their respective type species. As of December 12, 2025, Ningiella comprises a single species with validated name, N. ruwaisensis, isolated from marine water (Fotedar et al., 2020; https://lpsn.dsmz.de/genus/ningiella), whereas Marinicella includes seven species with validated names, isolated from various marine habitats, including coastal seawater (Romanenko et al., 2010), open seawater (Wang et al., 2016), coastal sediments (Zhong et al., 2020), marine sediments (Wang et al., 2018), and coastal mudflat sediments (Zhang et al., 2023; Liu et al., 2024) (https://lpsn.dsmz.de/genus/marinicella).

The genus Ningiella is characterized as Gram-stain-negative, obligately aerobic, short rod-shaped, and motile with a single polar flagellum. Cells are catalase-negative, oxidase-positive, and contain ubiquinone-8 (Q-8) as the major respiratory quinone. The DNA G + C content is approximately 43.0 %. Major fatty acids include C16:0, summed feature 3 (C16:1ω7c and/or C16:1ω6c), and isoC15:0 3-OH, with phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) as the predominant polar lipids (Fotedar et al., 2020). In contrast, Marinicella species are Gram-stain-negative, strictly aerobic, non-motile rods that are catalase- and oxidase-positive, with genomic G + C contents ranging from 42.0 % to 51.6 % (Romanenko et al., 2010; Wang, Liu, Zhang, Zheng and Zhang, 2016, Wang, Li, Dunlap, Rooney and Du, 2018; Zhong et al., 2020; Zhang et al., 2023; Liu et al., 2024). They also contain Q-8 as the sole respiratory quinone, with isoC15:0 as the predominant fatty acid. Their polar lipid profiles typically include PE, phosphatidylcholine (PC), PG, diphosphatidylglycerol (DPG), and phosphatidylmonomethylethanolamine (PME). As part of our ongoing study of marine algae-associated bacterial communities (Bayburt et al., 2024; Lee et al., 2024; Kim et al., 2025), two novel strains were isolated from the phycosphere of marine red algae. Based on polyphasic taxonomic analyses, these strains are proposed as novel species of the genera Ningiella and Marinicella, respectively.

The genus Alteromonas currently comprises 39 species with validated names and 12 species with invalid names with correct names (https://lpsn.dsmz.de/genus/alteromonas). In this study, a phylogenomic analysis of closely related species within Alteromonas revealed that seven species with validated names, Alteromonas lipolytica (Shi et al., 2017), A. alba (Sun et al., 2019), A. oceani (Jin et al., 2018), A. sediminis (Ye et al., 2019), A. facilis (Zhang et al., 2019), A. flava (Zhang et al., 2019), and A. arenosi (Luo et al., 2024), require reclassification. Specifically, A. lipolytica, A. alba, and A. oceani clustered within the genus Marisediminitalea (Zhang et al., 2020), supporting their transfer to that genus. In contrast, A. facilis, A. flava, A. arenosi, and A. sediminis formed distinct phylogenetic lineages separate from known genera, indicating the need for their reclassification into new genera. Accordingly, we propose the reclassification of these six species with validated names. Additionally, based on genomic evidence, Methylophaga aminisulfidivorans (Kim et al., 2007) is reclassified as a later heterotypic synonym of Methylophaga thalassica (Janvier et al., 1985).