Many bacteria have developed strategies for metamorphosis into sophisticated survival forms to survive extended periods of environmental stress. As a global causative agent of vibriosis in marine fish farming, Vibrio anguillarum (V. anguillarum) can efficiently grow and proliferate under environmental stress, but the specific mechanism is not clear. In the present study, survival, virulent characteristics, and transcriptomic analysis of the V. anguillarum BH1 were performed under starvation stress. The results demonstrated that V. anguillarum was still culturable and showed rippled surface after 6 months of starvation. Starved cells maintained their infectivity in half-smooth tongue sole (Cynoglossus semilaevi). Detection of virulence factors and virulence-associated genes in starved cells showed that the starved strain still produced β-hemolysis on rabbit blood agar, caseinase, dnase, and gelatinase, and possessed empA, vah1, vah2, vah3, vah4, vah5, rtxA, flaA, flaD, flaE, virC, tonB, mreB, toxR, rpoS, and ftsZ virulence-related genes. In addition, we first reported the RNA-seq study for V. anguillarum with and without starvation treatment for a period of 6 months and emphasized the regulation of gene expression at the whole transcriptional level. It indicated that V. anguillarum expressed 3,089 and 3,072 genes in the control group and starvation stress group, respectively. The differently expressed genes (DEGs) of the starved strain were thereby identified, including 251 up-regulated genes and 272 down-regulated genes in comparison with the non-starved strain. Gene Ontology (GO) analysis and Kyto Encyclopedia Genes and Genomes (KEGG) enrichment analysis of DEGs were also analyzed. GO functional classification revealed that among the significantly regulated genes with known function categories, more genes affiliated with signal transducer activity, molecular transducer activity, and cell communication were significantly up-regulated, and more genes affiliated with cellular macromolecule, cellular component, and structural molecule activity were significantly down-regulated. In addition, the DEGs involved in the pathway of two-component system was significantly up-regulated, and the pathways of ribosome and flagellar assembly were significantly down-regulated. This study provides valuable insight into the survival strategies of V. anguillarum and suggests that a portion of the bacterial populations may remain pathogenic while persisting under starvation stress by up-regulating or down-regulating a series of genes.

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Adiponectin plays critical roles in the regulation of energy metabolism in mammals. However, its roles in fish remain to be evaluated. In this study, we examined the tissue distribution characteristics of two adiponectin genes, namely, adipoqa and adipoqb, at transcriptional level, and detected the changes of their mRNA expressions during oral glucose tolerance test (OGTT). Furthermore, we prepared recombinant proteins of grass carp adiponectin A and adiponectin B and studied their roles in the regulation of glucose metabolism in the hepatopancreas of grass carp in vivo. The results showed that adipoqa mRNA was mainly expressed in the heart of grass carp, followed by red muscle, white muscle, and adipose tissue, while adipoqb mRNA was highly expressed in adipose tissue, red muscle, and white muscle. The mRNA levels of adipoqa and adipoqb in the white muscle and heart were significantly decreased at 1 h post OGTT, and their expressions in the heart were also suppressed at 3 h, whereas the transcriptional levels of adipoqa and adipoqb in the red muscle were elevated significantly at 12 h after glucose load. Intraperitoneal injection of adiponectin A or adiponectin B reduced basal serum glucose levels of grass carp and caused an increase of glycogen content in the hepatopancreas. Adiponectin A upregulated the expression of enzyme genes related to glycolysis (gk and pk) and glycogen synthesis (gys) in the hepatopancreas, and adiponectin B promoted the expression of pk and gys, as well as g6pase in the glycogenetic pathway. Besides, adiponectin A and adiponectin B have opposite regulatory effects on glut2 mRNA expression. These results suggested that adiponectin A and adiponectin B promoted glycolysis, gluconeogenesis, and glycogen synthesis, increased glycogen content of hepatopancreas, and reduced basal blood glucose level, and they may have an antagonistic regulatory mechanism in regulating glucose uptake.

Bitter melon extract (BME), which contains a variety of natural bioactive substances, has diversified biological functions. The present study is aimed at evaluating the effects of dietary supplementation of BME on growth performance, antioxidant capacity, inflammatory cytokine expression, and intestinal microbiota in common carp (Cyprinus carpio L.). An 8-week feeding trial was conducted using four isonitrogenous and isoenergetic diets containing different levels of BME (0%, 0.25%, 0.5%, and 1% for control, LBME, MBME, and HBME groups, respectively). The results showed that there were no significant differences in the growth performance of common carp among all groups, including final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), and viscera index (VSI) ( p > 0.05 ), but the condition factor (CF) was decreased by all BME treatments ( p < 0.05 ). Serum superoxide dismutase (SOD) activity was significantly improved in all BME groups ( p < 0.05 ), and serum catalase (CAT) activity was significantly higher in the MBME group ( p < 0.05 ). Serum malondialdehyde (MDA) level was lowest while serum total antioxidant capacity (T-AOC) was highest in the HBME group ( p < 0.05 ). Dietary BME supplementation inhibited proinflammatory cytokine (il-1β and il-8) mRNA expression, while anti-inflammatory cytokine (il-6 and il-10) mRNA expressions were promoted ( p < 0.05 ). Furthermore, principal coordinate analysis (PCoA) showed that there were no differences in bacterial communities among different groups, and Shannon index and Simpson index of intestinal microbiota were unaffected ( p > 0.05 ). Whereas dietary BME reduced Firmicutes abundance and the ratio of Firmicutes to Bacteroidetes at phylum level, the relative abundance of streptococcaceae at family level, Streptococcus and Exiguobacterium at genus level were also decreased ( p < 0.05 ). Overall, these results suggested that dietary supplementation of BME improved serum antioxidant capacity, anti-inflammatory activity, and modified intestinal microbiota in common carp.

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