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A Gram-stain-negative, light khaki, strictly aerobic, rod-shaped, motile via multiple flagella, and catalase- and oxidase-positive bacterium, designated as SSM4.3 T , was isolated from the seaweed of Gouqi Island in the East China Sea. The novel isolate grows at 0-5.0% NaCl concentrations (w/v) (optimum 1%), pH 5.0-9.0 (optimum pH 7.0), and 15-37 °C (optimum 30 °C). The 16S rRNA gene sequences-based phylogeny indicates that the novel marine isolate belongs to the family Rhizobiaceae and that it shared the greatest sequence similarity (98.9%) with Peteryoungia rhizophila CGMCC 1.15691 T . This classification was also supported by phylogenetic analysis using core genes. The predominant fatty acids (≥ 10%) of the strain were identified as C 18:1 ω7c/C 18:1 ω6c. Q-10 was identified as the major isoprenoid quinone, with trace levels of Q-9 present. The major polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The complete genome size of strain SSM4.3 T is 4.39 Mb with a DNA G+C content of 61.3%. The average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values between the genomes of strain SSM4.3 T and its closely related representatives were 74.80-86.93%, 20.00-32.30%, and 70.30-91.52%, respectively. Phylogenetic analysis, grounded on the core genes, reveals the evolutionary relationship between SSM4.3 T and other Peteryoungia strains. Pan-genomics analysis of 8 previously classified Peteryoungia species and SSM4.3 T revealed their unique genetic features and functions. Overall, strain SSM4.3 T was considered to be a new species of the Peteryoungia genus; the name Peteryoungia algae sp. nov. has been proposed, with type strain SSM4.3 T (= LMG 32561 = MCCC 1K07170)., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

In mid-November 2021, there were large areas of white rot disease on cultivated Saccharina japonica in Rongcheng City, China, and diseases were undetected on Sargassum horneri and Porphyra yezoensis. The disturbance direction of bacterial community in the phycosphere after disease outbreak and the relationship with seawater nutrients remain unclear. Here, in situ studies of bacterial community in the non-diseased and diseased areas (Shawo and Dongchu islands) and seawater nutrient levels were carried out. 16S rRNA sequencing showed that the bacterial richness of the studied seaweeds increased in the diseased area. Only in S. japonica, Algitalea outcompeted abundant primary bacteria with probiotic relationships to the host of the non-diseased area, and dominated in the diseased area (17.6% of the total abundance). Nitrogen and phosphorus levels in seawater were 57.8% and 19.6% higher in the non-diseased area than those in the diseased area, respectively, and were strongly correlated with the phycosphere bacteria at the family level of S. japonica. There was no difference in potential pathogenicity between the two areas, while positive signal communications decreased, and nitrogen cycle, chemoheterotrophy, and cellulolysis increased in the diseased area compared to the non-diseased area. Overall, white rot disease caused a structural disturbance in phycosphere bacterial community of S. japonica that related to seawater nutrient levels. Enriched degraders and altered bacterial community functions may exacerbate the disease. This evaluation will provide information for white rot disease management to prevent and mitigate the occurrence of S. japonica outbreaks., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A novel bacterium designated SSM4.2 T was isolated from seaweed of Gouqi Island, which is the center of the Zhoushan fishing ground in the East China Sea. Strain SSM4.2 T was Gram-stain-negative, bright yellow-pigmented, short rod-shaped, non-flagellated, non-spore forming, aerobic and motile by gliding. Growth was observed at 4-37 °C (optimum 25-30 °C), pH 6.0-8.0 (optimum pH 7.0) and 0-2.0% (w/v) NaCl (optimum 0%) concentration. The strain was catalase- and oxidase-positive. Menaquinone-6 (MK-6) was found as the sole respiratory quinone and zeaxanthin as the main carotenoid pigment. The predominant fatty acids (≥ 10%) were iso-C 15:0 , iso-C 15:1 G, iso-C 17:0 3-OH and summed feature 3 (C 16:1 ω7c /C 16:1 ω6c). The major polar lipid was phosphatidylethanolamine (PE). The genome size was 5.7 Mbp. The DNA G + C content was 34.1 mol%. 16S rRNA gene sequence revealed that strain SSM4.2 T belongs to the genus Flavobacterium and shares high-sequence similarity with F. limi KACC 18851 T (98.1%), F. hydrophilum KACC 19591 T (97.6%), F. defluvii KCTC 12612 T (97.1%), F. cheongpyeongense KACC 19592 T (97.0%) and F. fluviatile KCTC 52446 T (96.9%). Strain SSM4.2 T had 73.2-84.6% average nucleotide identity and 19.1-29.4% digital DNA-DNA hybridization values with its closest type strains. Based on its phenotypic, chemotaxonomic, phylogenetic and genomic features, strain SSM4.2 T represents a novel species of the genus Flavobacterium, for which the name Flavobacterium ajazii sp. nov. is proposed. The type strain is SSM4.2 T (= KCTC 72807 T  = MCCC 1K04370 T ).

A novel agarase-producing, non-endospore-forming marine bacterium, WH0801(T), was isolated from a fresh seaweed sample collected from the coast of Weihai, China. Preliminary characterization based on 16S rRNA gene sequence analysis showed that WH0801(T) shared 96.1  % similarity with Agarivorans albus MKT 106(T), the type species of the genus Agarivorans. A polyphasic taxonomic study was conducted and confirmed the phylogenetic affiliation of strain WH0801(T) to the genus Agarivorans. Isolate WH0801(T) produces light-yellow-pigmented colonies; cells are Gram-stain-negative, straight or curved rods, which are motile with a single polar flagellum. Strain WH0801(T) grew in 0.5-5  % NaCl, with optimum growth at 3  % NaCl, and its optimal pH and cultivation temperature were 8.4-8.6 and 28-32 °C, respectively. Data from biochemical tests, whole-cell fatty acid profiling, 16S rRNA gene sequence studies and DNA-DNA hybridization clearly indicated that isolate WH0801(T) represented a novel species within the genus Agarivorans, for which the name Agarivorans gilvus sp. nov. is proposed. The type strain of Agarivorans gilvus sp. nov. is WH0801(T) (=NRRL B-59247(T) =CGMCC 1.10131(T)).