Nutrient budgets and biogeochemical dynamics in the coastal regions of northern Beibu Gulf, South China Sea: Implication for the severe impact of human disturbance.

This study examined the nutrient budgets and biogeochemical dynamics in the coastal regions of northern Beibu Gulf (CNBG). Nutrient concentrations varied spatially and seasonally among the different bays. High nutrient levels were found in the regions with high riverine inputs and intensive mariculture. Using a three end-member mixing model, nutrient biogeochemistry within the ecosystem was estimated separately from complex physical mixing effects. Nutrient consumption dominated in most bays in summer, whereas nutrient regeneration dominated in winter, likely due to phytoplankton decomposition, vertical mixing and desorption. Through the Land-Ocean Interaction Coastal Zone (LOICZ) model, the robust nutrient budgets were constructed, indicating that the CNBG behaved as a sink of dissolved inorganic nitrogen, phosphorus and silicon. River-borne nutrient inputs were the dominant nutrient source, while residual flows and water exchange flows transported nutrient off the estuaries. This study could help us better understand nutrient cycles and nutrient sources/sinks in the CNBG.

Transcriptome analysis of the ink sac and brain tissues from Sepiella inermis: A resource for discovering genes related to the inking of cephalopods.

The common Chinese cuttlefish (Sepiella inermis) is an important cephalopod with nutritional and commercial value. Intensive inking stimulated by swilling seawater in transfer containers threatens the survival of cephalopods during transportation. However, the molecular basis for the inking behavior of S. inermis remains unclear. In the present study, transcriptome analysis was performed on ink sac and brain tissues from S. inermis under two different conditions, i.e. the control group (with individuals immersed in static seawater) and the experimental group (with individuals immersed in swilling seawater) to determine the global gene expression differences. The individuals from the experimental group ejected ink in response to the swilling of seawater. 330,699 unigenes were obtained from twelve transcriptome libraries via the Illumina Hiseq X platform, and the differentially expressed genes in the ink sac and brain tissues were identified respectively. Multiple upregulated genes in the ink sac were involved in cation transporter activity. Besides, an autocrine/paracrine factor wnt10b like and two important transcription factors (homeobox 1 and Hes-1-b-like) were also significantly upregulated in the ink sac. Moreover, a neuronal nitric oxide synthase (nNOS) was significantly downregulated in the brain. The findings from this study provide an important transcriptomic resource for discovering critical genes related to inking behavior of S. inermis, providing a basis for developing potential methods for protecting S. inermis from intensive inking.

Transcriptome analysis reveals potential key immune genes of Hong Kong oyster (Crassostrea hongkongensis) against Vibrio parahaemolyticus infection.

Hong Kong oyster (Crassostrea hongkongensis) is one of the main species of economic shellfish cultivated in the coastal areas of southern China. The cultivation of this shellfish may be adversely impacted by Vibrio parahaemolyticus, a harmful pathogenic bacterium for many mariculture species, as it usually exists on the surface of Hong Kong oysters. Although previous studies have discovered that oysters rely on non-specific immune system to fight pathogen invasion, the genes corresponding to the complex immune system against Vibrio is still not fully elucidated. Therefore, we conducted a transcriptome analysis on the gill from Hong Kong oysters at two time points (i.e., 12 h and 24 h after V. parahaemolyticus or PBS challenge) to identify potential immune genes against V. parahaemolyticus infection. A total of 61779 unigenes with the average length of 1221 bp were obtained, and the annotation information of 39917 unigenes were obtained from Nr, SwissProt, KEGG and COG/KOG. After a pairwise comparison between V. parahaemolyticus or PBS challenge at the two time points, three groups of differentially expressed genes induced by V. parahaemolyticus were captured and analyzed. GO and KEGG analyses showed that multiple immune-related genes played an important role in pathogen infection, including HSP70, PCDP3 and TLR4. Furthermore, genes annotation indicated that LITAF, TNFSF10, Duox2 and big defensin family are also involved in immune regulation. Our study provides a reference for further exploration the molecular mechanism that defenses the pathogen infection regarding the identified immune-related genes in Hong Kong oysters.

Gene structure and expression patterns of Acdaf-1, a TGF-ß type I receptor in Ancylostoma caninum.

The components of the transforming growth factor ß (TGF-ß) signaling pathway in parasitic nematodes remain unknown. In this research, a type I receptor for TGF-ß was isolated from the hookworm Ancylostoma caninum. The new gene was designated as Acdaf-1, a Caenorhabditis elegans daf-1 homolog. The full-length cDNA of Acdaf-1 encodes a 595-amino-acid protein with an NH2-terminal signal peptide. This protein has a cytoplasm tail (209-595aa region) which corresponds to the type 1a membrane topology. Between amino acid position 295-500, the protein contains the ATP binding site, substrate binding sites, and PKC-kinase-like domain. Real-time RT-PCR showed that the transcript was expressed in three main stages of A. caninum. It reached the maximal level in the female adult worm stage with lower transcript level in the first and second larvae (L1/L2) and intermediate level in L3 stages as well as in the male worms. After serum activation, the activity of Acdaf-1 was decreased in L3 larvae. These data implied that Acdaf-1 might relate to the infection ability of the larvae. Immunolocalization revealed that AcDAF-1 was present in eggs, intestine, and epidermis cells of larvae (L1, L2, and L3 stages) with strong signal in primordium of the gonads in L3 and was abundant in epidermis, intestine, and ovary of adult worm. These results suggested that Acdaf-1 might be involved in the interaction of the parasite and host relationship and provide a potential target for parasite control.

Complete mitochondrial genome and phylogenetic analysis of Stonogobiops yasha (Perciformes, Gobiidae).

The complete mitochondrial genome sequence of Stonogobiops yasha was first determined in this study. The circle genome was 16,566 bp long and consisted of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and 1 control region. The mitochondrial gene arrangement of S. yasha is similar to those of most other gobies. The phylogenetic analysis using the neighbor-joining method showed that the kinship between Stonogobiops and Acentrogobius is closer than those between Stonogobiops and other selected genera. This is the first record of the complete mitogenome for the genus Stonogobiops.

Complete mitochondrial genome and phylogenetic analysis of the barred mudskipper Periophthalmus argentilineatus (Perciformes, Gobiidae).

The complete mitochondrial genome sequence of the barred mudskipper Periophthalmus argentilineatus was first determined in this study. The circle genome was 16 509 bp long and consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region. The nucleotide composition of the heavy strand of P. argentilineatus is 28.28% for A, 27.83% for C, 16.01% for T, and 27.88% for G, with a slight G + C bias of 55.71%. Only the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes were encoded on the light strand, other mitochondrial genes were all encoded on the heavy strand. The mitochondrial gene arrangement of P. argentilineatus is similar to those of most other gobies. The phylogenetic analysis using the neighbor-joining method showed that the kinship between Periophthalmus and Boleophthalmus is closer than those between Periophthalmus and other selected genera. Periophthalmus argentilineatus was clustered into one branch with other four species from the same genus Periophthalmus.

Complete mitochondrial genome and phylogenetic analysis of the serpent mudskipper Parapocryptes serperaster (Perciformes, Gobiidae): repetitive sequences in the control region.

The complete mitochondrial genome sequence of the serpent mudskipper Parapocryptes serperaster was first determined in this study. The circle genome was 17 243 bp long and consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region. The nucleotide composition of the heavy strand of P. serperaster is 28.65% for A, 30.07% for C, 25.31% for T, and 15.97% for G, with a slight A + T bias of 53.96%. Only the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes were encoded on the light strand, all other mitochondrial genes were encoded on the heavy strand. A 178-bp tandem repeat, which started from the 827-bp site of the control region, was identified. Like most other gobies, P. serperaster also has the typical vertebrate mitochondrial gene arrangement. The phylogenetic analysis showed that the kinship between Parapocryptes and Boleophthalmus is closer than those between Parapocryptes and other selected genera.

Characterization of TsDAF-21/HSP90 protein from the parasitic nematode Trichinella spiralis.

The Tsdaf-21 cDNA was cloned into pET-32a and subsequently expressed in Escherichia coli. The recombinant protein TsDAF-21 was purified and evaluated as an antigen in Western blot. The serum from mouse 14, 21, and 28 days after being infected with Trichinella spiralis recognized rTsDAF-21, but the serum from mouse 7 days post infection of T. spiralis could not react with rTsDAF-21. It implied that the antibody of TsDAF-21 did appear in the host 14 days after infection of T. spiralis. Western blot analysis revealed that the expression of TsDAF-21 in the muscle larvae incubated at room temperature for 8 h and at 37 °C for 4 and 8 h was increased compared to the muscle larvae incubated at 4 °C for 4 and 8 h. The results imply that the expression of TsDAF-21 could be induced at high temperature, not by the cold stress. The expression of TsDAF-21 could be attenuated under the different concentrations of geldanamycin (GA) treatment. Western blot showed that the expression of TsDAF-21 was reduced in the muscle larvae of T. spiralis treated with GA compared to Ampicillin and Gentamycin sulfate treated as control, and this inhibition effect was GA dependent. Other antibiotic treatments did not show any inhibition effects. Immunolocalization showed that TsDAF-21 was expressed in the different stages of T. spiralis including newborn larvae, muscle larvae, and adult worms. TsDAF-21 was mostly localized in nuclei of the cells in the worm. These results suggest that the expression of TsDAF-21 could be induced by the heat stress and attenuated by GA treatment, and TsDAF-21 might be a diagnostic marker for Trichinellosis.