It is well known that healthy gut microbiota is essential to promote host health and well‐being. The intestinal microbiota of endothermic animals as well as fish are classified as autochthonous or ...indigenous, when they are able to colonize the host's epithelial surface or are associated with the microvilli, or as allochthonous or transient (associated with digesta or are present in the lumen). Furthermore, the gut microbiota of aquatic animals is more fluidic than that of terrestrial vertebrates and is highly sensitive to dietary changes. In fish, it is demonstrated that a dietary form (live feeds or pelleted diets), b dietary lipid (lipid levels, lipid sources and polyunsaturated fatty acids), c protein sources (soybean meal, krill meal and other meal products), d functional glycomic ingredients (chitin and cellulose), e nutraceuticals (probiotics, prebiotics, synbiotics and immunostimulants), f antibiotics, g dietary iron and h chromic oxide affect the gut microbiota. Furthermore, some information is available on bacterial colonization of the gut enterocyte surface as a result of dietary manipulation which indicates that changes in indigenous microbial populations may have repercussion on secondary host–microbe interactions. The effect of dietary components on the gut microbiota is important to investigate, as the gastrointestinal tract has been suggested as one of the major routes of infection in fish. Possible interactions between dietary components and the protective microbiota colonizing the digestive tract are discussed.
Vibrio anguillarum, also known as Listonella anguillarum, is the causative agent of vibriosis, a deadly haemorrhagic septicaemic disease affecting various marine and fresh/brackish water fish, ...bivalves and crustaceans. In both aquaculture and larviculture, this disease is responsible for severe economic losses worldwide. Because of its high morbidity and mortality rates, substantial research has been carried out to elucidate the virulence mechanisms of this pathogen and to develop rapid detection techniques and effective disease‐prevention strategies. This review summarizes the current state of knowledge pertaining to V. anguillarum, focusing on pathogenesis, known virulence factors, diagnosis, prevention and treatment.
Rhodomonas sp. Hf-1 strain (cryptophyte) has been known as an excellent feed for some marine animals in aquaculture. In this study, the Hf-1 strain was cultured under different nitrogen ...concentrations to evaluate the effect of N-starved conditions on its growth and biochemical profile. Two nitrate concentrations of 0.9 mM (Low-N) and 3.5 mM (High-N) were supplemented to the media. The cell suspensions were sampled on day 3 and 7 and analyzed for photosynthesis pigments, protein and relative fatty acids contents. The nitrate in Low-N and High-N cultures was exhausted by day 3 and 7, respectively, and growth in Low-N culture was significantly lower than in High-N culture. Phycoerythrin (PE) content decreased in both cultures compared to chlorophyll (Chl) a and c, and a cell-color change was only observed in Low-N culture, indicating that PE was preferentially degraded compared with Chl a and c when nitrogen in the medium was limiting. The intercellular carbon and hydrogen content in the Hf-1 cells cultured in both media showed similar changes throughout the experiment, hence C/H ratios did not differ in between. On the other hand, the intercellular nitrogen content in the Hf-1 cells cultured with High-N medium increased from 5.6 to 10.3% from day 3–7. However, Low-N culture showed a decrease in nitrogen content from 8.1 to 4.1%. Consequently, C/N ratio in Low-N and High-N culture showed entirely different tendency. Similarly, the protein content in the Hf-1 cell cultured with High-N medium increased during 4 days. In contrast, Low-N culture showed a decrease by 30% in protein content. Relative fatty acids content in the Hf-1 cell was lower in Low-N culture than High-N culture through the experiment. The dominant fatty acids in Low-N culture were poly-unsaturated fatty acids (PUFA) on day 3, which accounted for 37.4% of total fatty acid. However, the relative content of PUFA reduced to 24.7% of total fatty acid by the end of the experiment, and the dominant fatty acids shifted to saturated fatty acids (SFA). These data indicate that nitrogen starvation in the medium induced a simultaneous decrease in protein and relative fatty acids contents with the cell-color change for the Hf-1 cell, suggesting the possibility that this behavior on the cell-color change can be used as a valid indicator to determine the harvest timing of Rhodomonas species visually.
•Effects of nitrogen starvation on growth and biochemical profile of Rhodomonas sp. Hf-1 strain were examined.•Nitrogen starvation induced low growth performance and negatively affected the biochemical profile with a distinct cell-color change.•Our results indicated the possibility that the cell-color change can be used as a valid indicator to timely harvest.
Heat shock proteins (HSPs), also known as stress proteins and extrinsic chaperones, are a suite of highly conserved proteins of varying molecular weight (c. 16-100 kDa) produced in all cellular ...organisms when they are exposed to stress. They develop following up-regulation of specific genes, whose transcription is mediated by the interaction of heat shock factors with heat shock elements in gene promoter regions. HSPs function as helper molecules or chaperones for all protein and lipid metabolic activities of the cell, and it is now recognized that the up-regulation in response to stress is universal to all cells and not restricted to heat stress. Thus, other stressors such as anoxia, ischaemia, toxins, protein degradation, hypoxia, acidosis and microbial damage will also lead to their up-regulation. They play a fundamental role in the regulation of normal protein synthesis within the cell. HSP families, such as HSP90 and HSP70, are critical to the folding and assembly of other cellular proteins and are also involved in regulation of kinetic partitioning between folding, translocation and aggregation within the cell. HSPs also have a wider role in relation to the function of the immune system, apoptosis and various facets of the inflammatory process. In aquatic animals, they have been shown to play an important role in health, in relation to the host response to environmental pollutants, to food toxins and in particular in the development of inflammation and the specific and non-specific immune responses to bacterial and viral infections in both finfish and shrimp. With the recent development of non-traumatic methods for enhancing HSP levels in fish and shrimp populations via heat, via provision of exogenous HSPs or by oral or water administration of HSP stimulants, they have also, in addition to the health effects, been demonstrated to be valuable in contributing to reducing trauma and physical stress in relation to husbandry events such as transportation and vaccination.
To study the potential biocontrol activity of bioflocs technology. Glycerol-grown bioflocs were investigated for their antimicrobial and antipathogenic properties against the opportunistic pathogen ...Vibrio harveyi. The bioflocs did not produce growth-inhibitory substances. However, bioflocs and biofloc supernatants decreased quorum sensing-regulated bioluminescence of V. harveyi. This suggested that the bioflocs had biocontrol activity against this pathogen because quorum sensing regulates virulence of vibrios towards different hosts. Interestingly, the addition of live bioflocs significantly increased the survival of gnotobiotic brine shrimp (Artemia franciscana) larvae challenged to V. harveyi. Bioflocs grown on glycerol as carbon source inhibit quorum sensing-regulated bioluminescence in V. harveyi and protect brine shrimp larvae from vibriosis. The results presented in this study indicate that in addition to water quality control and in situ feed production, bioflocs technology could help in controlling bacterial infections within the aquaculture pond.
Aims
A variety of pathogens use quorum sensing (QS) to control the expression of their virulence factors. QS interference has hence been proposed as a promising antivirulence strategy. The specific ...aim of this study was to isolate bacteria from trout tissue able to degrade N‐acyl homoserine lactones (AHL), a QS molecule family.
Methods and Results
In total 132 isolates were screened for AHL degradation using Chromobacterium violaceum CV026 as a biosensor. Twenty‐four quorum‐quenching (QQ) isolates were identified biochemically and characterized using 16S rDNA sequencing. They belong to Bacillus, Enterobacter, Citrobacter, Acinetobacter, Agrobacterium, Pseudomonas and Stentrophomonas genera. Four Bacillus spp. showed the highest and fastest QQ activity. AHL degradation proved to be enzymatic in most isolates (except for Stentrophomonas spp. and Pseudomonas sp.) as QQ activity could be destroyed by heat and/or proteinase K treatments. All QQ activity proved to be cell‐bound except for Pseudomonas sp., where it could be detected in the supernatant. The results of aiiA gene homology analysis revealed the presence of aiiA gene encoding AHL lactonase in all examined isolates except Pseudomonas syringae and Enterobacter cloacae. The HXHXDH motif conserved in all AHL lactonases and considered to be essential for AHL degradation was detected in all AiiAs after sequence alignment.
Conclusions
Some known and novel QQ bacteria were isolated from trouts and characterized in terms of enzymatic or nonenzymatic AHL degradation activity and their extracellular or intracellular location. In addition, an aiiA gene and its HXHXDH motif were detected in most isolates.
Significance and Impact of the Study
We could isolate and identify some novel QQ bacteria including Enterobacter hormaechei, Acinetobacter radioresistens and Citrobacter gillenii. The aiiA gene was detected for the first time in these strains as well as in Stenotrophomonas maltophilia. Our QQ isolates could be used for biocontrol of bacterial infections in aquaculture.
Beta-glucans have been studied in animal species, from earthworms to humans. They are a heterogeneous group of glucose polymers found in fungi, plants, some bacteria, and sea weeds. The recognition ...of conserved microbial structures is a key aspect of metazoan immunity, and β-glucans are emerging as major target for the recognition of fungal pathogens. However, the receptors and mechanisms by which this is achieved differ significantly between vertebrates and invertebrates. In this review, we will highlight the known receptors for β-glucans and will discuss the various immune responses they can initiate, with some applications of these products, in both vertebrates and invertebrates.
Exposure to TEX‐OE®, a patented extract of the prickly pear cactus (Opuntia ficus indica) containing chaperone‐stimulating factor, was shown to protect common carp, Cyprinus carpio L., fingerlings ...against acute ammonia stress. Survival was enhanced twofold from 50% to 95% after exposure to 5.92 mg L−1 NH3, a level determined in the ammonia challenge bioassay as the 1‐h LD50 concentration for this species. Survival of TEX‐OE®‐pre‐exposed fish was enhanced by 20% over non‐exposed controls during lethal ammonia challenge (14.21 mg L−1 NH3). Increase in the levels of gill and muscle Hsp70 was evident in TEX‐OE®‐pre‐exposed fish but not in the unexposed controls, indicating that application of TEX‐OE® accelerated carp endogenous Hsp70 synthesis during ammonia perturbation. Protection against ammonia was correlated with Hsp70 accretion.
This study investigated the protective effect of poly‐β‐hydroxybutyrate (PHB) on Chinese mitten crab, Eriocheir sinensis, zoea larvae challenged with pathogenic Vibrio anguillarum. PHB was delivered ...to the crab larvae through rotifer and Artemia bioencapsulation. Zoea 3 larvae were challenged with V. anguillarum at a final concentration of 105 CFU mL−1. PHB‐enriched rotifers and Artemia nauplii were added to the culture water 24 h prior to, upon and 24 h after challenge. The results confirmed that PHB could enhance the survival and growth of unexposed E. sinensis larvae. Moreover, PHB protected larvae from the pathogen as the larvae fed PHB‐enriched live food showed the highest survival and development rate in all challenged groups (P < 0.05). Furthermore, larval performance was the best when PHB was delivered to the larvae 24 h before challenge (P < 0.05). In conclusion, our results indicate that PHB can be used as part of an effective strategy to protect E. sinensis larvae from V. anguillarum resulting in higher survival and better growth, especially when applied before the challenge.
Due to the increase in international trade in seafood and seafood products, authentication has become a necessity. Authentication can either be done by generating species- specific protein profiles ...or DNA profiles. Use of PCR-based techniques has been studied since they are reliable, reproducible and low cost and they enable construction of worldwide databanks. Techniques like FINS (forensically informative nucleotide sequencing), RFLP (restriction fragment length polymorphism), SSCP (single-stranded conformational polymorphism), RAPD and LP-RAPD (long-primer random amplified polymorphic DNA) and AFLP (amplified fragment length polymorphism) all can contribute to establishment of methods for authentication.
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