Albibacterium profundi sp. nov., isolated from sediment of the Challenger Deep of Mariana Trench, and reclassification of Pedobacter indicus as Albibacterium indicum comb. nov

A rod-shaped, white-pigmented, non-motile, Gram-stain-negative bacterium, designated RHL897T, was isolated from sediments collected at the Mariana Trench Challenger Deep (10,816 m). Strain RHL897T was strictly aerobic and grew at 4-37 °C, pH 6.0-10.0 and in the presence of 0-11.0 % (w/v) NaCl. Its genomic DNA G+C content was 41.2%. Metabolic analysis revealed mechanisms for salt tolerance, abundant metal ion transport proteins and stronger resistance to heavy metals such as arsenic and mercury compared to the closest reference strains, likely linked to adaptation to the hadal sediment environment. The predominant menaquinone was MK-7, and the major polar lipids were phosphatidylethanolamine, an unidentified aminophospholipid and an unidentified glycolipid. The main fatty acids were iso-C15 : 0, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and iso-C17 : 0 3OH. Strain RHL897T exhibited the highest 16S rRNA gene sequence similarity to the type strain of Pedobacter indicus (97.9%) and Albibacterium bauzanense (96.1%). Phylogenetic trees constructed based on 16S rRNA gene sequences and a 549 core gene set indicated that strain RHL897T was closely related to P. indicus and A. bauzanense, with all three species clustering within a distinct clade. Combined with the analyses of average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization, strain RHL897T represented a novel species of the genus Albibacterium, for which the name Albibacterium profundi sp. nov. is proposed. The type strain is RHL897T (=MCCC 1K09221T=KCTC 102276T). Furthermore, the revised phylogeny with the inclusion of RHL897T suggested that P. indicus should be reclassified under the genus Albibacterium and renamed Albibacterium indicum.

Flagellimonas baculiformis sp. nov. and Flagellimonas crocea sp. nov., isolated from surface seawater of the Pacific Ocean

Two Gram-negative, non-spore-forming, non-motile, non-flagellated bacteria, designated strains D6T and DH64T, were isolated from surface water of the Pacific Ocean. For strain D6T, growth occurred at 10-40 °C, pH 5.5-9.0 and in the presence of 0-8.0 % NaCl (w/v). For strain DH64T, growth occurred at 10-40 °C, pH 5.5-8.5 and in the presence of 0.5-8.0 % NaCl (w/v). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strains D6T and DH64T both belonged to the genera Flagellimonas, with the highest sequence identities to Flagellimonas taeanensis JCM 17757T (98.2 %) and Flagellimonas marinaquae JCM 11811T (98.6 %), respectively. The 16S rRNA gene sequence identity between strains D6T and DH64T was 95.9 %. The average amino acid identity and digital DNA-DNA hybridization values between the two strains and the nearest phylogenetic neighbours were 66.7-93.3 % and 16.1-38.5 %, respectively. The major respiratory quinone of both strains was menaquinone-6. The major polar lipid was phosphatidylethanolamine. The major fatty acids were identified similarly as iso-C15 : 1 G, iso-C15 : 0 and iso-C17 : 0 3-OH. The genomic G+C contents of strains D6T and DH64T were determined to be 45.5 and 42.6 mol%, respectively. The combined genotypic and phenotypic data show that the strains represent two novel species within genera Flagellimonas, for which the names Flagellimonas baculiformis sp. nov. and Flagellimonas crocea sp. nov. are proposed, with type strains D6T (=MCCC M28982T=KCTC 92604T) and DH64T (=MCCC M28986T=KCTC 92975T).

Reclassification of Allomuricauda and Muricauda species as members of the genus Flagellimonas Bae et al. 2007 and emended description of the genus Flagellimonas

The recently proposed genus Allomuricauda Deshmukh and Oren 2023 is illegitimate because it includes the type species of the genera Flagellimonas Bae et al. 2007 and Spongiibacterium Yoon and Oh 2012, contravening Rule 51b(1) of the International Code of Nomenclature of Prokaryotes. As Flagellimonas Bae et al. 2007 is the earlier described genus, we here reclassify 36 species earlier described as belonging to the illegitimate genus Muricauda as species of Flagellimonas. We also present an emended description of the genus Flagellimonas.

Proposal of Allomuricauda gen. nov. and Allofranklinella gen. nov. as replacement names for the illegitimate prokaryotic generic names Muricauda and Franklinella, respectively

The prokaryotic generic names Muricauda Bruns et al. 2001 and Franklinella Bernard et al. 2022 are illegitimate because they are later homonyms of the genus names Muricauda Small 1903 (synonym of Arisaema; Tracheophyta - Liliopsida - Araceae) and Franklinella Stewart and Hendrix 1945 (a Devonian ostracod genus) and Franklinella Lenz 1973 (a Devonian brachiopod genus), respectively (Principle 2 and Rule 51b(4) of the International Code of Nomenclature of Prokaryotes). We therefore propose the replacement generic names Allomuricauda and Allofranklinella, with type species Allomuricauda ruestringensis and Allofrankinella schreckenbergeri, respectively.

Muricauda abyssi sp. nov., a marine bacterium isolated from deep seawater of the Mariana Trench

A Gram-stain-negative, non-motile and rod-shaped bacterium, designated as strain W52^T, was isolated from deep seawater of the Mariana Trench and characterized phylogenetically and phenotypically. The strain could grow at 10-47 °C (optimum 32 °C), at pH 5.0-8.0 (optimum 6.0) and with 0-9% NaCl (optimum 3 %, w/v). The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that W52^T was related to members of the genus Muricauda and shared the highest identity with Muricauda oceani 501str8^T (99.0 %), followed by Muricauda aquimarina JCM 11811^T, Muricauda ruestringensis DSM 13258^T, Muricauda oceanensis 40DY170^T, Muricauda beolgyonensis KCTC 23501^T and Muricauda zhangzhouensis 12C25^T with 97.0-98.8 % sequence similarity. 16S rRNA gene sequence identities between W52^T and other members of the genus Muricauda were below 97.0 %. The major respiratory quinone was MK-6. The polar lipids were phosphatidylethanolamine (PE), one unidentified aminolipid and three unidentified lipids. The strain had iso-C_15 : 0, iso-C_17 : 0 3-OH and iso-C_15 : 1G as the major fatty acids. The G+C content of the genomic DNA was 41.7 %. The combined genotypic and phenotypic data indicated that strain W52^T represents a novel species of the genus Muricauda, for which the name Muricauda abyssi sp. nov. is proposed, with the type strain W52^T (=MCCC 1K05111^T= KCTC 82315^T).

Muricauda chongwuensis sp. nov., isolated from coastal seawater of China

In the course of screening for bacterial predators, a Gram-stain-negative, non-flagellated, gliding, long rod-shaped, and yellow-pigmented bacterium, designated strain HICW^T, was isolated from coastal seawater of China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain HICW^T represented a member of the genus Muricauda and showed the highest sequence similarity to M. aquimarina JCM11811^T (98.8%) and M. ruestringensis DSM13258^T (98.1%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain HICW^T and M. aquimarina JCM11811^T were 79.2% and 34.1%, respectively. NaCl was required for growth. Optimum growth occurred at 25-30 °C, 2.0-3.0% (w/v) NaCl with pH 7.0. Strain HICW^T showed some similar characteristics to the nonobligate bacterial predators, and the cells can attach to the prey cells. Strain HICW^T contained MK-6 as the predominant respiratory quinone and had iso-C_15:0, iso-C_15:1 G, and iso-C_17:0 3-OH as the major cellular fatty acids. The polar lipids contained phosphatidylethanolamine (PE), three unidentified phospholipids (PL1-PL3), one unidentified amino lipids (AL), and three unidentified polar lipids (L1-L3). The genome size of strain HICW^T was approximately 3.8 Mbp, with a G + C content of 41.4%. Based on the polyphasic evidence, strain HICW^T is proposed as representing a new species of the genus Muricauda, for which the name Muricauda chongwuensis sp. nov. is proposed. The type strain is HICW^T (= JCM 33643 ^T = MCCC 1K03769^T).

Muricauda onchidii sp. nov., isolated from a marine invertebrate from South China Sea, and transfers of Flagellimonas algicola, Flagellimonas pacifica and Flagellimonas maritima to Muricauda algicola comb. nov., Muricauda parva nom. nov. and Muricauda aurantiaca nom. nov., respectively, and emended description of the genus Muricauda

An aerobic, Gram-stain-negative, rod-shaped and non-motile strain (XY-359^T) was isolated from the mouth of a marine invertebrate Onchidium species from the South China Sea. It grew at pH 6.0-8.5 (optimum, pH 7.5), at 15-37 °C (optimum, 30 °C) and in the presence of 0.5-4.5 % (w/v) NaCl (optimum, 2.5 %). It could not hydrolyse Tweens 20, 40, 60 or 80 and no flexirubin-type pigments were produced. The major polar lipids were phosphatidylethanolamine, one unidentified aminolipid, six unidentified phospholipids and two unidentified polar lipids. The major fatty acids were iso-C_17:0 3-OH, iso-C_15:1 G and iso-C_15:0 3-OH. The respiratory quinone was MK-6. Strain XY-359^T showed the greatest degree of 16S rRNA sequence similarity to Flagellimonas algicola AsT0115^T (96.54 %), followed by Muricauda flava DSM 22638^T (96.27 %). Phylogenetic analysis based on 16S rRNA gene sequences and 31 core genes indicated that strain XY-359^T belongs to the genus Muricauda. The genome size of strain XY-359^T was 4 207 872 bp, with 39.1 mol% of DNA G+C content. The average nucleotide identity and digital DNA-DNA hybridization values between strain XY-359^T and F. algicola AsT0115^T were 74.58 % and 18.5 %, respectively, and those between strain XY-359^T and M. flava DSM 22638^T were 74.2 % and 18.3 %. The combined phenotypic, chemotaxonomic and phylogenetic data suggest that strain XY-359^T represents a novel species of the genus Muricauda, for which the name Muricauda onchidii sp. nov. is proposed. The type strain is XY-359^T (=MCCC 1K03658^T =KCTC 72218^T). Moreover, based on the proposal of nesting Spongiibacterium and Flagellimonas within Muricauda by García (Validation List No. 193) and the analyses of phylogenetic trees and average amino acid identities in this study, the transfers of F. algicola, F. pacifica and F. maritima to the genus Muricauda as Muricauda algicola comb. nov., Muricauda parva nom. nov. and M. aurantiaca nom. nov., respectively, are proposed, with an emended description of the genus Muricauda.

Muricauda amphidinii sp. nov., a novel marine bacterium isolated from the phycosphere of dinoflagellate Amphidinium carterae

A Gram-stain-negative, aerobic, rod-shaped and non-motile bacterium was isolated from a liquid culture of dinoflagellate Amphidinium carterae and further designated as LMIT004^T. Optimal growth was observed at 25 °C, pH 7.0 and in the presence of 2 % (w/v) NaCl. Oxidase and catalase were positive. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain LMIT004^T showed high similarities to type strains Muricauda nanhaiensis SM17004^T (96.77 %) and Muricauda aquimarina JCM11811^T (95.60 %) but formed a separate branch in the genus Muricauda. The G+C content of strain LMIT004^T was 39.0 mol%. The dominant fatty acids were iso-C_15 : 0 and iso-C_15 : 1 G. The polar lipids mainly contained phosphatidylethanolamine, five unidentified phospholipids and five unidentified polar lipids. The sole respiratory quinone was menaquinone-6 (MK-6). The draft genome of the type strain was 3.88 Mbp. The average nucleotide identity values between strain LMIT004^T and the two reference strains M. nanhaiensis SM17004^T and M. aquimarina JCM11811^T were 77.47 and 73.49 %, respectively. Based on the polyphasic analysis, strain LMIT004^T is suggested to represent a novel specie in the genus of Muricauda, for which the name Muricauda amphidinii sp. nov. is proposed. The type strain is LMIT004^T (=CICC 24871^T=KCTC 72948^T).

Muricauda maritima sp. nov., Muricauda aequoris sp. nov. and Muricauda oceanensis sp. nov., three marine bacteria isolated from seawater

Three Gram-stain-negative, non-motile, rod-shaped strains, designated 72T, NH166T and 40DY170T, were isolated from seawater samples of the West Pacific Ocean, South China Sea and West Pacific Ocean, respectively. The 16S rRNA gene sequence similarity results revealed that strains 72Tand NH166T were most closely related to Muricauda antarctica Ar-22T, Muricauda taeanensis JCM 17757T, Muricauda beolgyonensis KCTC 23501T, Muricauda lutimaris KCTC 22173T and Muricauda hadalis MT-229T with 97.2–98.0% sequence similarity. 16S rRNA gene sequence analysis also indicated that strain 40DY170T was most closely related to Muricauda ruestringensis DSM 13258T, Muricauda aquimarina JCM 11811T, Muricauda lutimaris KCTC 22173T and Muricauda oceani 501str8T with 97.6–98.1% sequence similarity. The 16S rRNA gene sequence similarity values among strains 72T, NH166T and 40DY170T were 96.5–99.2%. Phylogenetic analyses indicated that three new isolates represented three novel species by forming two distinctive lineages within the genus Muricauda . The DNA G+C contents of strain 72T, NH166T and 40DY170T were 43.4, 43.4 and 42.4 mol%, respectively. The average nucleotide identity and in silico DNA–DNA hybridization values between strains 72T, NH166T, 40DY170T and the reference strains were 76.5–93.5% and 19.2–53.5%, respectively. The sole respiratory quinone in all strains was menaquinone-6. Their major fatty acids were iso-C17:0 3-OH, iso-C15:0 and iso-C15 : 1 G. The major polar lipids of strains 72T and NH166T were phosphatidylethanolamine, one unidentified aminolipid and two unidentified lipids. The major polar lipids of strain 40DY170T were phosphatidylglycerol, one unidentified phospholipid, one unidentified aminolipid and two unidentified lipids. On the basis of their distinct taxonomic characteristics, the three isolates represent three novel species of the genus Muricauda , for which the names Muricauda maritima sp. nov. (type strain 72T=KCTC 62229T=MCCC 1K03350T), Muricauda aequoris sp. nov. (NH166T=KCTC 62228T=MCCC 1K03449T) and Muricauda oceanensis sp. nov. (40DY170T=KCTC 72200T=MCCC 1K03569T) are proposed.