Identifying the key factors affecting the trimethylamine N-oxide content of teleost fishes collected from the marginal seas of China and the epipelagic zone of the northwest Pacific Ocean.

To identify the key factors influencing the trimethylamine N-oxide (TMAO) content of teleost fishes living in shallow seas and the epipelagic zone of the deep ocean, the muscle TMAO content was measured in 152 teleost fishes (21 species) collected from the marginal seas of China and the epipelagic zone of the northwest Pacific Ocean (NWPO) during May-July 2021. The results showed that the TMAO content in all fishes varied from 4.99 to 82.97 mmol kg-1, and it varied notably among different species, e.g., the highest average content (72.71 ± 8.22 mmol kg-1 in Argyrosomus argentatus) was 1 order of magnitude higher than the lowest one (Scomber japonicus), but the ratios of the highest content to the lowest content in each species varied from 1.29 to 3.28, suggesting that the interspecific variations in TMAO content were obviously greater than the intraspecific variations. Moreover, no correlation was observed between the TMAO content of the 152 fishes and the corresponding environmental factors of seawater depth, salinity and temperature, indicating that species played a more important role than environmental factors in driving TMAO accumulation. To exclude the influence of species, intraspecies correlations between TMAO content and environmental factors were analyzed. In the marginal seas of China, only ∼8 % of the TMAO content of teleost fishes (1 species) showed a positive correlation with salinity and depth, but ∼50 % of the TMAO content (5 species) was negatively correlated with temperature. Moreover, the TMAO content of the fish increased by 4.66 ± 1.38 % compared with their corresponding intraspecific average values for every 1 °C of temperature decrease. A similar phenomenon was also found in the TMAO content of pelagic teleost fishes in the NWPO, suggesting that temperature was a key environmental factor affecting the TMAO content of teleost fishes in shallow seas and the epipelagic zone of the deep ocean.

Cloning, Expression and Characterization of a Novel Cold-adapted ß-galactosidase from the Deep-sea Bacterium Alteromonas sp. ML52.

The bacterium Alteromonas sp. ML52, isolated from deep-sea water, was found to synthesize an intracellular cold-adapted ß-galactosidase. A novel ß-galactosidase gene from strain ML52, encoding 1058 amino acids residues, was cloned and expressed in Escherichia coli. The enzyme belongs to glycoside hydrolase family 2 and is active as a homotetrameric protein. The recombinant enzyme had maximum activity at 35 °C and pH 8 with a low thermal stability over 30 °C. The enzyme also exhibited a Km of 0.14 mM, a Vmax of 464.7 U/mg and a kcat of 3688.1 S-1 at 35 °C with 2-nitrophenyl-ß-d-galactopyranoside as a substrate. Hydrolysis of lactose assay, performed using milk, indicated that over 90% lactose in milk was hydrolyzed after incubation for 5 h at 25 °C or 24 h at 4 °C and 10 °C, respectively. These properties suggest that recombinant Alteromonas sp. ML52 ß-galactosidase is a potential biocatalyst for the lactose-reduced dairy industry.

Overexpression and characterization of a novel cold-adapted and salt-tolerant GH1 ß-glucosidase from the marine bacterium Alteromonas sp. L82.

A novel gene (bgl) encoding a cold-adapted ß-glucosidase was cloned from the marine bacterium Alteromonas sp. L82. Based on sequence analysis and its putative catalytic conserved region, Bgl belonged to the glycoside hydrolase family 1. Bgl was overexpressed in E. coli and purified by Ni2+ affinity chromatography. The purified recombinant ß-glucosidase showed maximum activity at temperatures between 25°C to 45°C and over the pH range 6 to 8. The enzyme lost activity quickly after incubation at 40°C. Therefore, recombinant ß-glucosidase appears to be a cold-adapted enzyme. The addition of reducing agent doubled its activity and 2 M NaCl did not influence its activity. Recombinant ß-glucosidase was also tolerant of 700 mM glucose and some organic solvents. Bgl had a Km of 0.55 mM, a Vmax of 83.6 U/mg, a kcat of 74.3 s-1 and kcat/Km of 135.1 at 40°C, pH 7 with 4-nitrophenyl-ß-D-glucopyranoside as a substrate. These properties indicate Bgl may be an interesting candidate for biotechnological and industrial applications.

Hymenobacter profundi sp. nov., isolated from deep-sea water.

A Gram-stain-negative, rod-shaped, red-pigmented, aerobic bacterium, strain M2T, was isolated from a seawater sample collected from the western Pacific Ocean at a depth of 1000 m and characterized using polyphasic taxonomy. Strain M2T was catalase-positive and oxidase-negative. Cells grew at 4-33 °C (optimum, 25 °C), at pH 6-9 (optimum, 7) and with 0-4 % (w/v) (optimum, 1 %) NaCl. Phylogenetic trees based on 16S rRNA gene sequences showed that strain M2T was associated with the genus Hymenobacter. Strain M2T showed the highest 16S rRNA gene sequence similarities to Hymenobacter actinosclerus CCUG 39621T (95.7 %), Hymenobacter tibetensis XTM003T (95.6 %) and Hymenobacter psychrotolerans Tibet-IIU11T (95.2 %). The DNA G+C content was 59.98 mol%. Strain M2T contained C16 : 1ω5c (25.0 %), iso-C15 : 0 (23.9 %) and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c, 20.4 %) as major cellular fatty acids. The major quinone of strain M2T was menaquinone 7 and the major polar lipid was phosphatidylethanolamine. The major polyamine of strain M2T was sym-homospermidine. The phylogenetic analysis and physiological and biochemical data showed that strain M2T should be classified as representing a novel species of the genus Hymenobacter, for which the name Hymenobacter profundi sp. nov. is proposed. The type strain is M2T (=CCTCC AB 2017185T=KCTC 62120T).

Complete mitochondrial genome and the phylogenetic position of the tigertooth croaker Otolithes ruber (Perciformes: Sciaenidae).

In this study, the complete mitogenome of the tigertooth croaker Otolithes ruber was first determined. This mitogenome is 16,589 bp in length, and consists of 37 genes with the typical gene order and direction of transcription in vertebrates. The overall nucleotide composition is: 27.4% A; 29.1% C; 16.1% G and 27.4% T. Sizes of the 22 tRNA genes range from 66 to 74 bp. Four start codons (ACG, CTG, GTG and ATG) and three stop (AGA, TAG and TAA/TA/T) codons were detected in 13 protein-coding genes. In the Bayesian treebased on the complete mitogenomes of 18 species (including O. ruber) from the family Sciaenidae, all nodes were strongly supported. The phylogenetic results suggested that O. ruber was closed to the black-spotted croaker Protonibea diacanthus.

A method for molecular analysis of catalase gene diversity in seawater.

Catalase plays an important role in the metabolism of marine bacteria and has potential impact on the marine environment. Four PCR primers were designed to amplify the catalase gene fragments in marine bacteria by applying metagenomic DNA from Yellow Sea surface water as the template. Of the four reproducible target PCR products, the longest one with 900 bp were chosen for catalase gene library construction by the T-vector and the white Escherichia coli colonies in the library was screened through restriction-digesting the reamplified insert fragments by the selected restriction endonuclease MboI, and then the bands of the resulting products were displayed in the agarose gel by electrophoresis. The unique restriction fragment length polymorphism (RFLP) pattern was selected and the corresponding catalase gene fragments were sequenced, which verified that every unique RFLP pattern represented one type of catalase. This PCR-RFLP method above was established to investigate the bacterial catalase diversity in seawater.

Development of 20 microsatellite markers for Solenocera crassicornis and their cross-species application in Solenocera melantho.

Twenty microsatellite markers were isolated and characterized for Solenocera crassicornis from a (GT)13-enriched genomic library. Their polymorphisms were investigated using 44 wild individuals from the South Yellow Sea. Our investigation revealed that all the markers were polymorphic. The number of alleles per locus varied from 6 to 19 with an average of 12.35. The observed and expected heterozygosities ranged from 0.400 to 0.977 and from 0.609 to 0.940, with averages of 0.788 and 0.859, respectively. Four loci significantly deviated from Hardy-Weinberg equilibrium after Bonferroni's correction. Cross-species amplification was also conducted in Solenocera melantho collected from the East China Sea. The result showed that 14 loci could be amplified from Solenocera melantho DNAs. These polymorphic markers would be useful for assessment of genetic variation and population structure of S. crassicornis and S. melantho.

[Effects of macro-jellyfish abundance dynamics on fishery resource structure in the Yangtze River estuary and its adjacent waters].

Based on the bottom trawl survey data in May 2007 and May and June 2008, this paper analyzed the effects of the abundance dynamics of macro-jellyfish on the species composition, distribution, and abundance of fishery resource in the Yangtze River estuary and its adjacent waters. From May 2007 to June 2008, the average catch per haul and the top catch per haul of macro-jellyfish increased, up to 222.2 kg x h(-1) and 1800 kg x h(-1) in June 2008, respectively. The macro-jellyfish were mainly distributed in the areas around 50 m isobath, and not beyond 100 m isobath where was the joint front of the coastal waters of East China Sea, Yangtze River runoff, and Taiwan Warm Current. The main distribution area of macro-jellyfish in June migrated northward, as compared with that in May, and the highest catches of macro-jellyfish in May 2007 and May 2008 were found in the same sampling station (122.5 degrees E, 28.5 degrees N). In the sampling stations with higher abundance of macro-jellyfish, the fishery abundance was low, and the fishery species also changed greatly, mainly composed by small-sized species (Trachurus japonicus, Harpadon nehereus, and Acropoma japonicum) and pelagic species (Psenopsis anomala, Octopus variabilis) and Trichiurus japonicus, and P. anomala accounted for 23.7% of the total catch in June 2008. Larimichthys polyactis also occupied higher proportion of the total catch in sampling stations with higher macro-jellyfish abundance, but the demersal species Lophius litulon was not found, and a few crustaceans were collected. This study showed that macro-jellyfish had definite negative effects on the fishery community structure and abundance in the Yangtze River estuary fishery ecosystem, and further, changed the energy flow patterns of the ecosystem through cascading trophic interactions. Therefore, macro-jellyfish was strongly suggested to be an independent ecological group when the corresponding fishery management measures were considered.