The Fish Microbiota:Research Progress and Potential Applications

The gut microbiota plays an important role in host health and disease.Our understanding of the fish microbiota lags far behind our knowledge of that of humans and other mammals.Nevertheless,research has highlighted the importance of the microbiota in the health,performance,and various physiological functions of fish.The microbiota has been studied in various fish species,including model animals,economic fish,and wild fish species.The composition of the fish microbiota depends on host selection,diet,and environmental factors.The intestinal microbiota affects the nutritional metabolism,immunity,and disease resistance of the fish host,while the host regulates the intestinal microbiota in a reciprocal way through both immune and non-immune factors.Improved and novel gnotobiotic fish models have been developed,which are important for the mechanistic study of host–microbiota interactions in fish.In this review,we discuss recent progress in fish microbiota research.We describe various aspects of this research,including both studies on fish microbiota variations and fundamental research extending our knowledge of host–microbiota interaction in fish.Perspectives on how fish microbiota research may benefit fish health and industrial sustainability are also discussed.

模拟增温增雨对典型草原优势种羊草功能性状的影响

全球气候变化情景下,植物功能属性对于揭示植物对环境变化的响应和适应规律至关重要。本研究以内蒙古典型草原优势种羊草(Leymus chinensis)为研究对象,通过开顶式生长室(open top chamber,OTC)人工模拟增温和降雨,量化分析了羊草植物功能性状对增温和增雨处理的响应。得到以下结果:1)单因素方差分析表明,增温增水和增温处理都显著增加了羊草植物株高、茎鲜质量和茎干质量,对其余指标没有显著影响;增水处理对羊草所有指标都没有显著影响(P>0.05)。2)双因素方差分析结果显示,增温增水对植物的功能性状不存在明显的交互作用(P>0.05)。3)各处理下,叶片干物质含量与比叶面积呈负相关关系。在内蒙古典型草原,未来气候暖湿化对羊草的生长在一定程度上起促进作用。

Pollution-Free from Seed to Feed

FOUNDED in 1997, Chaoda Modern Agriculture (Holdings) Ltd is an integrated modern agriculture enterprise engaged in the production and marketing of high quality organic vegetables and fruits. In August last year, Chaoda was listed as one of the top 500 famous and valuable Chinese brands for 2005. In the same year, the company was also ranked 177th in terms of the overall strength of large Chinese enterprises.

Effects of solid-state fermentation product of yeast supplementation on liver and intestinal health,and resistance of common carp(Cyprinus carpio)against spring viraemia carp virus

This study aimed to investigate the effects of solid-state fermentation products of yeast(SFPY)on liver and intestinal health and disease resistance of common carp(Cyprinus carpio).A total of 200 common carp with an initial average weight of 2.55±0.004 g were divided into 5 groups(4 replications per group and 10 fish per replication),and were fed with one of five diets,including a control diet and 4 diets supplemented with 2‰(Y2),3‰(Y3),4‰(Y4),or 5‰(Y5)SFPY,respectively,for 8 weeks.Results indicated that,the addition of SFPY to the diet of common carp did not affect the growth performance or survival rate of fish(P=0.253).Interestingly,with the addition of SFPY,the triacylglycerol(TAG)content of the liver presented a linear decreasing tendency(P=0.004),with significantly decreased in Y4 and Y5 groups(P=0.035)compared with control.Serum lipopolysaccharide(LPS)content and diamine oxidase(DAO)activity presented a negative linear relationship with the addition of SFPY(P=0.015,P=0.030),while serum lipopolysaccharide binding protein(LBP)content first decreased and then increased(P<0.001).The total antioxidant capacity(T-AOC)in the intestine of fish increased continuously with increasing SFPY supplementation(P=0.026),reaching the highest level in Y5 group.The villus height in all experimental groups were significantly higher than that in the control group(P<0.001).Furthermore,compared to the control,adding 3‰SFPY to the control diet of common carp significantly increased the relative abundance of Fusobacteria(P=0.018)and decreased that of Proteobacteria(P=0.039)at phylum level,and increased the relative abundance of Cetobacterium(P=0.018)and decreased that of Shewanella(P=0.013)at genus level.Compared with the control,the relative mRNA expression level of spring viraemia of carp virus N protein(SVCV-n)in the kidney was lower than that of the control group without significance and bottomed out in Y4 group(P=0.138).In conclusion,dietary SFPY enhanced the SVCV resistance capacity of common carp by improving liver and intestinal health and modulating the gut microbiota.Thus,SFPY is a potential feed additive to be used in aquaculture to reduce the huge economic loss of common carp due to SVCV disease.Based on liver TAG content and intestinal villus height,the optimal addition level of SFPY was 3.02‰and 2.72‰,respectively.

Pichia pastoris composition expressed aerolysin mutant of Aeromonas veronii as an oral vaccine evaluated in zebrafish(Danio rerio)

Vaccines are one of the most practical means to stop the spreading of Aeromonas veronii in aquaculture.In this study,virulence factor aerolysin mutant NTaer which has lost its hemolytic activity was used as a target antigen.Pichia pastoris constitutive secretory expression NTaer(GS115-NTaer)was used as a potential safe oral vaccine to evaluate its effectiveness on zebrafish immunity.The result shows that vaccination of GS115-NTaer for four weeks did not affect the growth performance of the host,while eliciting an effective immune protective response.Compared with the control group,the GS115-NTaer could significantly up-regulate the relative expression level of the intestinal tight junction protein 1α(TJP1α)gene,and significantly increased the contents of lysozyme(LYZ),complement C3 and C4 in the gut,indicating that the innate immune response of the fish was activated.The relative gene expression levels of macrophage-expressed gene 1(MPEG1)and T cell receptor(TCR-α)in the gut,and MPEG1,CD4,CD8,TCR-α,GATA3,and T-bet in the spleen were all increased significantly,indicating that the cellular immune response of the fish was activated.Furthermore,the contents of serum IgM and intestinal mucosa IgZ antibodies were significantly increased,which showed that humoral immunity was also activated.Moreover,inoculation with GS115-NTaer significantly changed the structure of gut microbiota.In particular,the relative ratio of(Firmicutes+Fusobacteriota+Bacteroidota)/Proteobacteria was significantly higher than that of the control and GS115 groups.Lastly,the vaccinated fish were challenged with A.veronii,and the relative percent survival of GS115 and the GS115-NTear groups was 14.28%and 33.43%.This improvement of immunity was not only due to the specific immune response but also attributed to the improvement of innate immunity and the gut microbiota which was demonstrated by the germ-free zebrafish model.Collectively,this study provides information on the effectiveness of GS115-NTear as an oral vaccine for the green prevention and control of A.veronii infection in fish aquaculture.

The direct and gut microbiota-mediated effects of dietary bile acids on the improvement of gut barriers in largemouth bass(Micropterus salmoides)

Fish gut barrier damage under intensive culture model is a significant concern for aquaculture industry.This study aimed to investigate the effects of bile acids(BAs)on gut barriers in Micropterus salmoides.A germ-free(GF)zebrafish model was employed to elucidate the effects of the direct stimulation of BAs and the indirect regulations mediated by the gut microbiota on gut barrier functions.Four diets were formulated with BAs supplemented at 0,150,300 and 450 mg/kg,and these 4 diets were defined as control,BA150,BA300 and BA450,respectively.After 5 weeks of feeding experiment,the survival rate of fish fed with BA300 diet was increased(P<0.05).Histological analysis revealed an improvement of gut structural integrity in the BA150 and BA300 groups.Compared with the control group,the expression of genes related to chemical barrier(mucin,lysozyme and complement 1)and physical barrier(occludin and claudin-4)was increased in the BA150 and BA300 groups(P<0.05),and the expression of genes related to immunological barrier(interleukin[IL]-6,tumor growth factorβ,IL-10,macrophage galactosetype lectin and immunoglobulin M[Ig M])was significantly increased in the BA300 group(P<0.05),but the expression of genes related to chemical barrier(hepcidin)and immunological barrier(IL-1β,tumor necrosis factor-a,IL-6 and arginase)was significantly decreased in the BA450 group(P<0.05).Gut microbiota composition analysis revealed that the abundance of Firmicutes was augmented prominently in the BA150 and BA300 groups(P<0.05),while that of Actinobacteriota and Proteobacteria showed a downward trend in the BA150 and BA300 groups(P>0.05).The results of the gut microbiota transferring experiment demonstrated an upregulation of gut barrier-related genes,including immunoglobulin Z/T(Ig Z/T),IL-6,IL-1βand IL-10,by the gut microbiota transferred from the BA300 group compared with the control(P<0.05).Feeding the BA300 diet directly to GF zebrafish resulted in enhanced expression of Ig M,Ig Z/T,lysozyme,occludin-2,IL-6 and IL-10(P<0.05).In conclusion,BAs can improve the gut barriers of fish through both direct and indirect effects mediated by the gut microbiota.

Research advances in the structure,function,and regulation of the gill barrier in

The gill is an important organ in fish that is involved in various physiological functions,including respiration,filter-feeding,ammonia nitrogen excretion,and osmoregulation.The physiological functions of gills are closely related to their structure,external feeding conditions,and environmental factors.Herein,we first briefly summarize the basic structure and functions of the gills of teleosts,then explain the structure and function of the gill barrier(as a microbial barrier,a chemical barrier,a physical barrier,and an immune barrier)in detail.Finally,we introduce the regulation of fish gill barrier health by ubiquitous feeding factors and environmental factors,and provide an outlook on the prospects of gill barrier health.We found that improving health through modulating feed factors is more convenient than improving environmental factors.This review increases our understanding of how nutrient composition and level in fish diet influences gill health and overall growth performance of fish.

模拟增温增雨对典型草原土壤酶活性的影响

气候变化对生态系统的影响呈增加趋势。土壤酶作为草地土壤中活跃的组分之一,与草地土壤养分含量关系密切。为探究半干旱地区酶活性及土壤养分对气候变化的响应,利用开顶式生长室于2011—2016年在典型草原进行模拟增温增雨试验。结果表明：（1）增温使0-10 cm土层的硝态氮和铵态氮含量分别增加40.2%和129.1%,增雨使硝态氮含量增加63.5%,铵态氮含量降低63.6%。（2）土层的增温使0-10 cm土层的过氧化氢酶活性和蔗糖酶活性分别降低4.8%和13.3%。与增温的效果相反,增雨使碱性磷酸酶活性、蔗糖酶活性和脲酶活性分别提高7.1%、35.7%和14.9%,对过氧化氢酶无显著影响（P〉0.05）。（3）0-10 cm土层的硝态氮和铵态氮含量有增加趋势（P〈0.05）,不同种类的土壤酶活性对气候变化的响应存在差异,这可能与气候变化趋势下土壤养分循环的变化有关。

不同放牧强度对典型草原土壤胞外酶活性的影响

与碳(C)、氮(N)和磷(P)分解矿化相关的土壤胞外酶的相对活性可以揭示微生物的生长和代谢过程。为探讨不同放牧强度对典型草原土壤胞外酶活性的影响,本研究对不同放牧强度下0-10和10-20cm土层的胞外酶活性展开调查。本研究的胞外酶包括:β-1,4-葡萄糖苷酶(BG)、β-1,4-N-乙酰葡糖氨糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)、磷酸酶(AP)。结果显示:0-10cm土层,轻度放牧强度显著增加NAG和LAP活性;中度放牧强度显著增加了BG, NAG, LAP和AP活性;重度放牧强度显著增加LAP活性。10-20cm土层,轻度放牧强度显著增加NAG和LAP活性;中度放牧强度显著增加BG, NAG和LAP活性。随放牧强度的增加,两个土层土壤胞外酶活性均呈先增加后降低趋势;随土壤深度增加酶活性均呈降低趋势。冗余分析结果表明,土壤胞外酶活性(EEA)在0-10cm土层主要受微生物碳、铵态氮和土壤水分的影响,而10-20cm层受微生物氮、pH值、土壤水分和硝态氮的影响。在本研究区域尺度上,轻度和中度放牧强度下的土壤胞外酶具有更高的活性。

Antibiotic growth promoter olaquindox increases pathogen susceptibility in fish by inducing gut microbiota dysbiosis

Low dose antibiotics have been used as growth promoters in livestock and fish. The use of antibiotics has been associated with reduced pathogen infections in livestock. In contrast, antibiotic growth promoter has been suspected of leading to disease outbreaks in aquaculture. However, this phenomenon is circumstantial and has not been confirmed in experimental conditions. In this study,we showed that antibiotic olaquindox increased the susceptibility of zebrafish to A. hydrophila infection. Olaquindox led to profound alterations in the intestinal microbiota of zebrafish, with a drastic bloom of Enterobacter and diminishing of Cetobacterium. Moreover, the innate immune responses of zebrafish were compromised by olaquindox(P<0.05). Transfer of microbiota to GF zebrafish indicated that while the immuo-suppression effect of olaquindox is a combined effect mediated by both OLA-altered micro biota and direct action of the antibiotic(P<0.05), the increased pathogen susceptibility was driven by the OLA-altered microbiota and was not dependent on direct antibiotic effect. Taken together, these data indicate that low level of OLA induced gut microbiota dysbiosis in zebrafish, which led to increased pathogen susceptibility.

Building biological foundries for next-generation synthetic biology

Synthetic biology is an interdisciplinary field that takes top-down approaches to understand and engineer biological systems through design-build-test cycles. A number of advances in this relatively young field have greatly accelerated such engineering cycles. Specifically, various innovative tools were developed for in silico biosystems design, DNA de novo synthesis and assembly, construct verification, as well as metabolite analysis, which have laid a solid foundation for building biological foundries for rapid prototyping of improved or novel biosystems. This review summarizes the state-of-the-art technologies for synthetic biology and discusses the challenges to establish such biological foundries.

Effects of dietary yeast nucleotides on growth, non-specific immunity intestine growth and intestinal microbiota of juvenile hybrid tilapia Oreochromis niloticus ♀ × Oreochromis aureus ♂

This study investigated the effect of dietary supplementation of yeast nucleotides on the growth, nonspecific immunity, intestine growth and intestinal microbiota of juvenile hybrid tilapia. Tilapia(initial average weight of 8.02 g) was fed test diets supplemented with a yeast-originated nucleotide mixture(0,0.15, 0.30, 0.60, and 1.20 g/100 g diet) for 8 weeks. Fish fed the diet with 0.60% nucleotide had significantly higher weight gain than the control group(P < 0.05). Feed efficiency was improved in the fish fed 0.60 and 1.20% nucleotide compared with that in the control group. The optimal doses of nucleotides supplementation for growth and feed efficiency of fish were determined as 0.63 and 0.81%, respectively.Intestinal growth was improved in the 0.30 and 0.60% groups, as indicated by significant increase in intestine length. The fish fed 0.60 and 1.20% nucleotide showed higher super oxide dismutase(SOD)activity and lower malondialdehyde(MDA) level in the liver than the control fish, indicating enhancement of the anti-oxidant status. Serum lysozyme activity was significantly increased in the 0.15 and 0.3%nucleotide supplementation groups, suggesting an enhancement effect on the non-specific immune response. Lastly, dietary nucleotides supplementation exerted moderate influence on the intestinal microbiota of hybrid tilapia. A reduction in the cumulative abundance of putative butyrate-producing species was observed in the intestinal microbiota of fish fed diets with 0.60% nucleotide compared with the control, implying an interaction between dietary nucleotides and butyrate production. Briefly, dietary supplementation with 0.60% nucleotide improve the growth performance, immune activity and intestine growth in tilapia.

Interactions between commensal bacteria and viral infection:insights for viral disease control in farmed animals

Viral diseases cause serious economic loss in farmed animals industry.However,the efficacy of remedies for viral infection in farmed animals is limited,and treatment strategies are generally lacking for aquatic animals.Interactions of commensal microbiota and viral infection have been studied in recent years,demonstrating a third player in the interaction between hosts and viruses.Here,we discuss recent developments in the research of interactions between commensal bacteria and viral infection,including both promotion and inhibition effect of commensal bacteria on viral pathogenesis,as well as the impact of viral infection on commensal microbiota.The antiviral effect of commensal bacteria is mostly achieved through priming or regulation of the host immune responses,involving differential microbial components and host signaling pathways,and gives rise to various antiviral probiotics.Moreover,we summarize studies related to the interaction between commensal bacteria and viral infection in farmed animals,including pigs,chickens,fish and invertebrate species.Further studies in this area will deepen our understanding of antiviral immunity of farmed animals in the context of commensal microbiota,and promote the development of novel strategies for treatment of viral diseases in farmed animals.

Effect of Trace O Element on High-temperature Wettability Between Ni_3Al Melt and Y_2O_3 Ceramic

Effect of trace O element on the high-temperature wettability between Ni3Al scrap melt and Y2O3 ceramic at 1873 K is investigated. With the increase in O content in Ni3Al scrap melt from 6 to 21 ppm, the equilibrium contact angle decreases from 93.3° to 88.9°. The initial surface tension and adhesive work of molten Ni3Al scrap drop from 3153.5 to 807.4 mN m^-1 and from 2974.6 to 882.2 mN m^-1, respectively. The average spreading rate increases from 0.03° s^-1 to 0.17° s^-1. The whole wetting processes are divided into four periods. The main driving force for spreading in period（1） is the adsorption and diffusion of active atoms around the interface. Trace O content in Ni3Al scrap has a significant impact on interfacial reactions which mostly take place in the second stage, and can accelerate the spreading process on Y2O3 substrate. The reaction products during wetting process are Y3Al5O12, YAlO3 and Al2O3.

Effect of Open Porosity of Y2O3 Ceramic on the Apparent Contact Angles and Interactions Between Ti47Al Alloys and Y2O3 Ceramic

The effect of open porosity of Y2O3ceramic on the apparent contact angle and interaction between molten Ti47 Al alloy and Y2O3ceramic substrates under pure Ar was investigated by using a sessile drop method at 1600 °C. As the open porosity increased from 9.6% to 30.3%, the spreading rate of molten Ti47 Al alloys on Y2O3ceramic substrates reduced from 2.3 to 1.1°/s; meanwhile, the final equilibrium contact angles increased from 55.8° to 63.6°. The microstructure observations revealed that with increasing the open porosity of the Y2O3substrates, the thickness of sand adhesion at the interfaces of the alloy droplets increased from 5.4 to 15.7 lm, and ceramic particles in the alloy matrix increased as well. The increasing contact area between the molten alloy and the substrate played a dominant role in determining the interaction on Ti Al/Y2O3interface.