Vibrio splendidus is identified as one of the major pathogenic factors for the skin ulceration syndrome in sea cucumber (Apostichopus japonicus), which has vastly limited the development of the sea cucumber culture industry. In order to screen the immune genes involving Vibrio splendidus challenge in sea cucumber and explore the molecular mechanism of this process, the related transcriptome and gene expression profiling of resistant and susceptible biotypes of sea cucumber with Vibrio splendidus challenge were collected for analysis. A total of 319,455,942 trimmed reads were obtained, which were assembled into 186,658 contigs. After that, 89,891 representative contigs (without isoform) were clustered. The analysis of the gene expression profiling identified 358 differentially expression genes (DEGs) in the bacterial-resistant group, and 102 DEGs in the bacterial-susceptible group, compared with that in control group. According to the reported references and annotation information from BLAST, GO and KEGG, 30 putative bacterial-resistant genes and 19 putative bacterial-susceptible genes were identified from DEGs. The qRT-PCR results were consistent with the RNA-Seq results. Furthermore, many DGEs were involved in immune signaling related pathways, such as Endocytosis, Lysosome, MAPK, Chemokine and the ERBB signaling pathway.

The diseases caused by Vibrio during shrimp breeding program have the risk of spreading in different aquatic areas through larvae transportation between different regions. Therefore, the population distribution and the virulence and antibiotic resistance risk of 5 pathogenic Vibrio in shrimp (Penaeus vannamei) breeding system in China were evaluated for the first time. A total of 418 isolates were recovered from shrimp, breeding water and biological baits samples, and 312 isolates were identified as Vibrio genus based on 16s rDNA, among which V. alginolyticus, V. harveyi, V. parahaemolyticus, V. cholerae and V. campbellii were the dominant species. And 10/20 kinds of virulence genes (chiA, luxR, vhh, tlh, chxA, sepro, flaA, vch, VAC and rpoS) were detected among the 5 Vibrio species. Multiple antibiotic resistance (MAR) index of the 5 dominant Vibrio isolates were 0.13-0.88 %, and 36.5 % isolates with MAR < 0.2. But the antibiotic resistance pattern abundance (ARPA) index ranged from 0.25 to 0.56, which indicated the antibiotic phenotypes of Vibrio species in the shrimp breeding system in China were homogeneity. Furthermore, resistance quotients (RQs) calculation results displayed that the dominant Vibrio species in the shrimp breeding system in China showed no or low selection pressure for resistance to cefoperazone/sulbactam, enrofloxacin, ciprofloxacin, fluoroquine, florfenicol, tetracycline and doxycycline. But only 5 resistance genes were detected, which were strA (43.8 %), strB (11.7 %), QnrVC (2.9 %), sul2 (8.8 %) and Int4 (8.8 %), respectively, and the antimicrobial resistance genotypes were not previously correlated with their phenotypes. The relevant research results provide theoretical basis for epizootic tracking in aquatic system in China, and targeting its final risk in aquatic ecosystem and public health perspectives.

DNA methylation is an important epigenetic modification that regulates many biological processes. The sea cucumber Apostichopus japonicus often suffers from heat stress that affects its growth and leads to significant economic losses. In this study, the mRNA expression patterns and DNA methylation characteristics in the body wall of A. japonicus under heat stress were analyzed by whole-genome bisulfite sequencing (WGBS) and transcriptome sequencing (RNA-seq). We found that CpG was the main DNA methylation type, and heat stress caused a significant increase in the overall methylation level and methylation rate, especially in the intergenic region of the A. japonicus genome. In total, 1,409 differentially expressed genes (DEGs) and 17,927 differentially methylated genes (DMGs) were obtained by RNA-seq and WGBS, respectively. Association analysis between DNA methylation and transcription identified 569 negatively correlated genes in both DMGs and DEGs, which indicated that DNA methylation affects on transcriptional regulation in response to heat stress. These negatively correlated genes were significantly enriched in pathways related to energy metabolism and immunoregulation, such as the thyroid hormone signaling pathway, renin secretion, notch signaling pathway and microRNAs in cancer. In addition, potential key genes, including heat shock protein (hsp70), calcium-activated chloride channel regulator 1(clca1), and tenascin R (tnr), were obtained and their expression and methylation were preliminarily verified. The results provide a new perspective for epigenetic and transcriptomic studies of A. japonicus response to heat stress, and provide a reference for breeding sea cucumbers resistant to high temperatures.

Vibrio rotiferianus is an important marine pathogen of various aquatic organisms and can be found widely distributed in the marine environment. To further characterize this pathogen, the pathogenic properties and genome of V. rotiferianus SSVR1601 isolated from Sebastes schlegelii with skin ulcer were analysed. SSVR1601 was shown to be short rod‐shaped cell with a single polar flagellum. Different degrees of pathological changes in fish kidney, intestine, gills and liver were observed after SSVR1601 challenge. The SSVR1601 genome consists of two chromosomes and two plasmids with a total of 5,717,113 bp, 42.04%–44.93% GC content, 5,269 predicted CDSs, 134 tRNAs and 40 rRNAs. The common virulence factors including OMPs, haemolysin, flagellin, DNase, entF, algU, tcpI, acfB and rfaD were found in strain SSVR1601. Furthermore, factors responsible for iron uptake (fur, fepC and ccmC) and types II, IV and VI secretion systems were detected, which are likely responsible for the pathogenicity of SSVR1601. The antimicrobial resistance genes, bacA, tet34 and norM, were detected based on Antibiotic Resistance Genes Database. The phylogenetic analysis revealed SSVR1601 to be most closely related to V. rotiferianus strains CAIM577 and B64D1.

Increasing discoveries of new species of the genus Melanochlamys Cheeseman, 1881 in the recent years indicate that the biodiversity of this group remains underestimated. Recently, several aglajid sea slugs were collected from Laizhou Bay, Shandong Province, China. Morphological observation of their external and internal anatomy revealed that they represent an undescribed species of Melanochlamys. This new species, Melanochlamys aquilina sp. nov., is closely related to Melanochlamys fukudai Cooke, Hanson, Hirano, Ornelas-Gatdula, Gosliner, Chernyshev & Valdés, 2014 in body size and dark external coloration, but can be differentiated from the latter by features of both shell and male reproductive organ. Phylogenetic analyses of two mitochondrial (COI, 16S rRNA) and a nuclear (H3) genes using Bayesian inference, maximum likelihood, and species delimitation analysis also support the separation of Melanochlamys aquilina sp. nov. from its related congeners.