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An obligate aerobic and bacteriochlorophyll a -containing bacterium, designated strain AI77 T , was isolated from a fish farm in Uwa Sea, Japan. Cells were Gram-stain-negative, coccoid- to oval-shaped, and showed no motility. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain AI77 T is a member of the genus Roseobacter and closely related to Roseobacter ponti MM-7 T (97.8 %), Roseobacter denitrificans OCh 114 T (97.3 %) and Roseobacter litoralis OCh 149 T (97.3 %). The G+C content of strain AI77 T was 61.0 mol%. The average amino acid identity values of the genome in strain AI77 T with those in R. denitrificans OCh 114 T and R. litoralis OCh 149 T were 73.26 % (SD 16.46) and 72.63 % (SD 16.76), respectively. The digital DNA-DNA hybridization values of strain AI77 T with the type strains R. denitrificans OCh 114 T and R. litoralis OCh 149 T were 18.70 and 18.50 %, respectively. The dominant fatty acids (>10 % of total fatty acids) of AI77 T were summed feature 8 (C 18 : 1  ω7 c and/or C 18 : 1  ω6 c ) and saturated fatty acid C 16 : 0 . The sole respiratory quinone was ubiquinone-10. The predominant polar lipids were phosphatidylcholine, phosphatidylglycerol and diphosphatidylglycerol. Based on the genetic and phenotypic data obtained herein, we conclude that strain AI77 T represents a new species of the genus Roseobacter , for which we propose the name Roseobacter cerasinus sp. nov.; the type strain is AI77 T (=DSM 110091 T =NBRC 114115 T ).

The use of antibiotics in aquaculture causes selection pressure for antibiotic-resistant bacteria (ARB). Antibiotic resistance genes (ARGs) may persist in ARB and the environment for long time even after stopping drug administration. Here we show monthly differences in the occurrences of genes conferring resistance to sulfonamides (i.e. sul1, sul2, sul3), and tetracyclines (tet(M)) in Japanese aquaculture seawater accompanied by records of drug administration. sul2 was found to persist throughout the year, whereas the occurrences of sul1, sul3, and tet(M) changed month-to-month. sul3 and tet(M) were detected in natural bacterial assemblages in May and July, but not in colony-forming bacteria, thus suggesting that the sul3 was harbored by the non-culturable fraction of the bacterial community. Comparison of results from Taiwanese, Japanese, and Finnish aquaculture waters reveals that the profile of sul genes and tet(M) in Taiwan resembles that in Japan, but is distinct from that in Finland. To our knowledge, this work represents the first report to use the same method to compare the dynamics of sul genes and tet(M) in aquaculture seawater in different countries., (Copyright © 2019 Elsevier B.V. All rights reserved.)