Examination of Silicate Limitation of Primary Production in Jiaozhou Bay, China Ⅱ. Critical Value and Time of Silicate Limitation and Satisfaction of the Phytoplankton Growth

Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994 revealed the spatiotemporal variations of the ambient Si(OH) 4∶NO 3 (Si∶N) concentration ratios and the seasonal variations of (Si∶N) ratios in Jiaozhou Bay and showed that the Si∶N ratios were < 1 throughout Jiaozhou Bay in spring, autumn, and winter. These results provide further evidence that silicate limits the growth of phytoplankton (i.e. diatoms) in spring, autumn and winter. Moreover, comparison of the spatiotemporal variations of the Si∶N ratio and primary production in Jiaozhou Bay suggested their close relationship. The spatiotemporal pattern of dissolved silicate matched well that of primary production in Jiaozhou Bay. Along with the environmental change of Jiaozhou Bay in the last thirty years, the N and P concentrations tended to rise, whereas Si concentration showed cyclic seasonal variations. With the variation of nutrient Si limiting the primary production in mind, the authors found that the range of values of primary production is divided into three parts: the basic value of Si limited primary production, the extent of Si limited primary production and the critical value of Si limited primary production, which can be calculated for Jiaozhou Bay by Equations (1), (2) and (3), showing that the time of the critical value of Si limitation of phytoplankton growth in Jiaozhou Bay is around November 3 to November 13 in autumn; and that the time of the critical value of Si satisfaction of phytoplankton growth in Jiaozhou Bay is around May 22 to June 7 in spring. Moreover, the calculated critical value of Si satisfactory for phytoplankton growth is 2.15-0.76 μmol/L and the critical value of Si limitation of phytoplankton growth is 1.42-0.36 μmol/L; so that the time period of Si limitation of phytoplankton growth is around November 13 to May 22 in the next year; the time period of Si satisfactory for phytoplankton growth is around June 7 to November 3. This result also explains why critical values of nutrient silicon affect phytoplankton growth in spring and autumn are different in different waters of Jiaozhou Bay and also indicates how the silicate concentration affects the phytoplankton assemblage structure. The dilution of silicate concentration by seawater exchange affects the growth of phytoplankton so that the primary production of phytoplankton declines outside Jiaozhou Bay earlier than inside Jiaozhou Bay by one and half months. This study showed that Jiaozhou Bay phytoplankton badly need silicon and respond very sensitively and rapidly to the variation of silicon.

Studies on Factors Influencing Hydrodynamic Characteristics of Plates Used in Artificial Reefs

As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs. The models are grouped by various opening numbers and opening-area ratios. They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds. The simulation results are found in good agreement with the experimental measurements. By the non-dimensional analysis, the drag coefficient specified to each model is achieved and the effects of openings are examined. It is found that the key factor affecting the drag coefficient is the open-area ratio. Generally, the drag coefficient is a linear function of the open area ratio with a minus slope. The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data. They will be good references for the design of new artificial reefs. As a result of numerical simulation, the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models.

Silicon limitation on primary production and its destiny in Jiaozhou Bay,China Ⅶ:The complementary mechanism of the earth ecosystem

In this paper, the phenomenon that the variation in nutrient and water temperature could cause changes in phytoplankton growth and structure is examined; and the question of how a marine ecosystem make up the earth ecosystem step by step to auto-sustain the balance between phytoplankton and nutrient supply especially Si is discussed. Three major complementary mechanisms of the earth ecosys- tem for nutrient Si, water temperature and carbon were put forward. Understanding the mechanisms nowadays would explain the why the El Nifio and La Nifia occurred, and forecast the trend of human-impacted the earth, which would alert us with proactive countermeasures.

Examination of Daytime Length's Influence on Phytoplankton Growth in Jiaozhou Bay, China

This study showed how the daytime length in Jiaozhou Bay affected the water temperature, which in turn affected the phytoplankton growth when solar radiation was sufficient for phytoplankton photosynthesis. Jiaozhou Bay observation data collected from May 1991 to February 1994 were used to analyze the daytime length vs water temperature relationship. Our study showed that daytime length and the variation controlled the cycle of water temperature flunctuation. Should the cyclic variation curve of the daytime length be moved back for two months it would be superimposed with temperature change. The values of daytime length and temperature that calculated in the dynamical model of daytime length lag vs water temperature were consistent with observed values. The light radiation and daytime length in this model determined the photochemistry process and the enzymic catalysis process of phytoplankton photosynthesis. In addition, by considering the effect of the daytime length on water temperature and photosynthesis, we could comprehend the joint effect of daytime length, water temperature, and nutrients, on the spatiotemporal variation of primary production in Jiaozhou Bay.

Silicon limitation on primary production and its destiny in Jiaozhou Bay, China VI: The ecological variation process of the phytoplankton

The combination effect of light, water temperature and nutrients on phytoplankton growth in Jiaozhou Bay is studied in this paper. The order of importance of the influence on phytoplankton growth is de- termined as nutrients, water temperature, and light. The influence of these factors unveiled the mechanism of the influence, and revealed the variation process of the nutrients limiting phytoplankton primary production, and of the water temperature influencing the phytoplankton reproduction capacity, and hence influencing the structure of phytoplankton assemblage. Temporal and spatial quantification shows different stages of the influence by wa- ter temperature and nutrients on the phytoplankton growth. Moreover, the authors expatiated the ideal state of the phytoplankton growth and the reason of red tide occurrence. People should consider in their activity the input of nutrient Si first, and then the variation of water temperature, advocating sustainable development manner.

Examination of Silicate Limitation of Primary Production in Jiaozhou Bay,North ChinaⅢ.Judgment Method,Rules and Uniqueness of Nutrient Limitation Among N,P,and Si

Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994(12 seasonal investigations) provided by the Ecological Station of Jiaozhou Bay revealed the characteristic spatiotemporal variation of the ambient concentration Si:DIN and Si:16P ratios and the seasonal variation of Jiaozhou Bay Si:DIN and Si:16P ratios showing that the Si:DIN ratios were < 1 throughout the year in Jiaozhou Bay; and that the Si:16P ratios were < 1 throughout Jiaozhou Bay in spring, autumn and winter. The results proved that silicate limited phytoplankton growth in spring, autumn and winter in Jiaozhou Bay. Analysis of the Si:DIN and Si:P ratios showed that the nutrient Si has been limiting the growth of phytoplankton throughout the year in some Jiaozhou Bay waters; and that the silicate deficiency changed the phytoplankton assemblage structure. Analysis of discontinuous 1962 to 1998 nutrient data showed that there was no N or P limitation of phytoplankton growth in that period. The authors consider that the annual cyclic change of silicate limits phytoplankton growth in spring, autumn and winter every year in Jiaozhou Bay; and that in many Jiaozhou Bay waters where the phytoplankton as the predominant species need a great amount of silicate, analysis of the nutrients N or P limitation of phytoplankton growth relying only on the N and P nutrients and DIN:P ratio could yield inaccurate conclusions. The results obtained by applying the rules of absolute and relative limitation fully support this view. The authors consider that the main function of nutrient silicon is to regulate and control the mechanism of the phytoplankton growth process in the ecological system in estuaries, bays and the sea. The authors consider that according to the evolution theory of Darwin, continuous environmental pressure gradually changes the phytoplankton assemblage's structure and the physiology of diatoms. Diatoms requiring a great deal of silicon either constantly decrease or reduce their requirement for silicon. This will cause a series of huge changes in the ecosystem so that the whole ecosystem requires continuous renewal, change and balancing. Human beings have to reduce marine pollution and enhance the capacity of continental sources to transport silicon to sustain the continuity and stability in the marine ecosystem.nt

Influence of Seawater Temperature on Phytoplankton Growth in Jiaozhou Bay, China

The phytoplankton reproduction capacity (PRC), as a new concept regarding chlorophyll-a and primary production (PP) is described. PRC is different from PP, carbon assimilation number (CAN) or photosynthetic rate (P B). PRC quantifies phytoplankton growth with a special consideration of the effect of seawater temperature. Observation data in Jiaozhou Bay, Qingdao, China, collected from May 1991 to February 1994 were used to analyze the horizontal distribution and seasonal variation of the PRC in Jiaozhou Bay in order to determine the characteristics, dynamic cycles and trends of phytoplankton growth in Jiaozhou Bay; and to develop a corresponding dynamic model of seawater temperature vs. PRC. Simulation curves showed that seawater temperature has a dual function of limiting and enhancing PRC. PRC’s periodicity and fluctuation are similar to those of the seawater temperature. Nutrient silicon in Jiaozhou Bay satisfies phytoplankton growth from June 7 to November 3. When nutrients N, P and Si satisfy the phytoplankton growth and solar irradiation is sufficient, the PRC would reflect the influence of seawater temperature on phytoplankton growth. Moreover, the result quantitatively explains the scenario of one-peak or two-peak phytoplankton reproduction in Jiaozhou Bay, and also quantitatively elucidates the internal mechanism of the one- or two-peak phytoplankton reproduction in the global marine areas.

Morphological characteristics and genetic differentiation of Lutraria maxima in coast waters off southeast China

To explore genetic diversity and estimate the genetic differences among populations of Lutraria maxima in the coastal waters off south to southeast China,the morphology of the species of five different geographical populations(Beihai,Weizhou Island,Zhanjiang,Xiamen,and Fuzhou)in Guangxi,Guangdong,and Fujian provinces was studied statistically in combination with the microsatellite markers.As revealed by morphological principal component analysis(PCA),the cumulative contribution rate of the first three principal components was 72.596%.The discrimination accuracy ranged from 47.5%to 80.0%,and the scatter plots of principal component and discriminant analysis were consistent in overall,showing that the Xiamen and Fuzhou populations were overlapped obviously.For microsatellite markers,10 pairs of polymorphic primers were obtained by high-throughput transcriptome sequencing,and used for genetic diversity analysis.It was showed that the average number of alleles and eff ective alleles observed in each population ranged from 8.100 to 10.900,and from 3.497 to 4.228,respectively.The average observed heterozygosity(H_(o))and expected heterozygosity(H_(e))in the five populations ranged from 0.541 to 0.615,and from 0.642 to 0.733,respectively.The genetic distance(DA)ranged from 0.078 to 0.523,and the population genetic differentiation index(F_(ST))ranged from 0.027 to 0.139.The unweighted pair-population method with arithmetic means(UPGMA)and structure analysis showed that the five populations could be divided into two main clusters,the Beibu Gulf group(Beihai and Weizhou Island)and the Southeast China Sea group(Zhanjiang,Xiamen,and Fuzhou),suggesting that L.maxima has been separated geographically by the barrier of the Leizhou Peninsula into two groups in evolution,which provided us with a scientific clue to better protect the bioresource and establish an appropriate fishery management stocks for L.maxima populations in south China.

Detection of health hazard insecticide dichlorodiphenyltrichloroethane (DDT) in some common marine dry fish samples from Bangladesh

Objectives: The general purpose of this study is to detection and determination of the concentration level of dichlorodiphenyltrichloroethane (DDT) in some commercially available marine dry fishes and to investigate the contamination status of dichlorodiphenyltrichloroethane (DDT) of these dry fishes. Methods: Samples were collected from six largest dry fish markets (three from Chittagong district and three from Cox’s Bazar district) and four types of dry fishes were taken in this study are Ribbon fish (Lepturacanthus savala), Sin Croaker (Johnius dussumieri), Bombay duck (Harpodon nehereus) and Shrimp (mixed species). Total numbers of samples were 24 that were analyzed in the laboratory. Results: The results of the study show that the mean concentrations of dichlorodiphenyltrichloroethane (DDT) in the samples of Ribbon fish, Bombay duck and Sin croaker were ranged between 130.85 - 153.47ppb, 125.21 - 181.4ppb and 119.86 – 208.65ppb respectively. The mean concentrations of dichlorodiphenyltrichloroethane (DDT) were found at a lower amount in shrimp sp. than the other. Conclusions: This result indicates that the concentration of dichlorodiphenyltrichloroethane (DDT) in dry fish samples from Bangladesh are higher and may causes chronic disease and potential long-term risk for human health.

Identification and Characterization of Nuclear Localization Signals within the Nucleocapsid Protein VP15 of White Spot Syndrome Virus

The nucleocapsid protein VP15 of white spot syndrome virus (WSSV) is a basic DNA-binding protein. Three canonical bipartite nuclear localization signals (NLSs), called NLS1 (aa 11-27), NLS2 (aa 33-49) and NLS3 (44-60), have been detected in this protein, using the ScanProsite computer program. To determine the nuclear localization sequence of VP15, the full-length open reading frame, or the sequence of one of the three NLSs, was fused to the green fluorescent protein (GFP) gene, and transiently expressed in insect Sf9 cells. Transfection with full-length VP15 resulted in GFP fluorescence being distributed exclusively in the nucleus. NLS1 alone could also direct GFP to the nucleus, but less efficiently. Neither of the other two NLSs (NLS2 and 3) was functional when expressed alone, but exhibited similar activity to NLS1 when they were expressed as a fusion peptide. Furthermore, a mutated VP15, in which the two basic amino acids (11RR12) of NLS1 were changed to two alanines (11AA12), caused GFP to be localized only in the cytoplasm of Sf9 cells. These results demonstrated that VP15, as a nuclear localization protein, needs cooperation between its three NLSs, and that the two residues (11RR12) of NLS1 play a key role in transporting the protein to the nucleus.

Selection and Molecular Biological Identification of a Strain of Bacillus sp. Inhibiting the Growth of Saprolegnia ferax

Based on the theory of biological control of Saprolegnia ferax,antagonism test of nine strains of Bacillus sp. to S. ferax JL was carried out. Bacillus sp.BA1 was screened to have significantly inhibitory effects on the growth of S. ferax JL( P 【 0. 05). Then,the effects of Bacillus sp. BA1 on different sources of S. ferax were carried out. Results showed that BA1 also had significantly inhibitory effects on S. ferax 6#,10# and S2( P 【 0. 05). Sequence of 16 S r DNA of BA1 was analyzed; and homologous alignment analysis showed that BA1 had more than 99% similarity with Bacillus cereus. Therefore,it could be concluded that strain BA1 was B. cereus,which significantly inhibited the growth of S. ferax and could be used as the biological control agent for S. ferax diseases in aquaculture.

The Effects of Environmental Factors on the Growth and Competition of Algae

In order to study the effect of environmental factors on the algae growth and competition,the author summarized overseas and domestic related researches in recent years.Most of the researches are about the influence of single factor on growth of algae.However,there is insufficient investment on the interaction of different factors and the competition between algae growth.This paper briefly introduced the classification of algae and the role they played in ecological system and focused on the influence which included temperature,illumination,nitrogen,phosphorus and pH on the growth and competition of algal.In the end,the author proposed key questions which were still needed to be studied in order to know more about the relationship between environment effects and growth and competition of algae.Therefore,people could better improve the community structure of algae and water ecological environment,and improve water primary productivity.

Nutritional value of domesticated duckweed variety DW2602 and its feeding effects on the growth performance and digestive activities of tilapia fingerlings

Duckweed are a family of fast-growing aquatic plants,in which wild plants of many species have been tested in animal feed.We domesticated a duckweed variety,Spirodela polyrhiza DW2602,which had 44.5%protein and 2.6% lysine and was grown on a large scale.The effects of DW2602 on the growth performance and the digestive enzyme activities of tilapia variety GIFT(Genetic Improvement of Farmed Tilapia,Oreochromis niloticus)fingerlings were evaluated.The dry powder of DW2602 was added to conventional tilapia feed at six inclusion levels of 0%,10%,15%,20%,25%,and 30%.The diets were fed to tilapia fingerlings with an initial weight of 2.0±0.15 g for 60 d.Results showed that DW2602 improved the growth performance and digestive enzyme activities significantly.The feeding effect was the best when the inclusion rate was 20%,in which the body weight increased to 37.24±1.21 g in 60 d,18.15%higher than the control(P<0.05).The weight gain rate,the specific growth rate,the condition factor,and the hepatosomatic index of the fish were all significantly higher than the control(P<0.05),and the amylase,protease,and lipase activities in the digestive system were all promoted by DW2602(P<0.05).Therefore,the duckweed variety DW2602 has great application prospect in tilapia culture.

Beneficial roles of nutrients as immunostimulants in aquaculture:A review

Protein deficiency is a major difficulty for human needs in the past few decades,while different types of aquatic species are rich in high quality protein.Therefore,aquaculture is considered as the main developing food production sector globally.Bacterial infections are the main problem for aquaculture,and their outbreaks have a great impact on productivity,and previously indiscriminate use of antibiotics to control them.However,the emergence of multidrug-resistant pathogens might lead to sudden infectious disease outbreaks resulting in serious economic loss.Immunostimulants application is an effective technique to protect and enhance the immune system of aquatic animals and therefore improve aquaculture production.Nutrient immunostimulants such as essential fatty acids,amino acids,vitamins,and minerals are the most important responsibility to improve aquaculture production,as well as the cost of this method,which is effective,non-toxic,and environment friendly.These nutrient immunostimulants are supportive to increase the immune system,antioxidant,anti-inflammatory,and infection resistance of aquatic animals.In addition,nutritional feed additives improved feed palatability and the excellence of aquatic products and also enhance gut functions.Some information is available on nutrient immunostimulants in aquaculture applications,and this review provides information on different kinds of nutritional administration used in aquaculture to enhance positive impacts on aquatic animals’health as well as feed quality development.This review will provide theoretical references for the application of nutrient immunostimulants in aquatic feeds.

Morphological changes and allometric growth in hatcheryreared Chinese loach Paramisgurnus dabryanus(Dabry de Thiersant, 1872)

The length-weight relationship and allometric growth patterns of hatchery-reared Chinese loach, Paramisgurnus dabryanus(Dabry de Thiersant, 1872), were determined from hatching to 60 days after hatching. A best power model was estimated for the length-weight relationship during the early life stages. Positive allometric growth for the head segment, trunk length, tail length and eye diameter was also found in the early life stages, while body depth, tail depth, tail fi n length, pectoral fi n length and barbel length displayed a negative coeffi cient. During the subsequent early developmental stage, the growth coeffi cients showed a clear and common tendency towards isometry for all measured body ratios. The allometric growth changes in Chinese loach during the early stage are possibly the result of selective organogenesis directed towards survival priorities.

Silicon limitation on primary production and its destiny in Jiaozhou Bay,China V:Silicon deficit process

Silicon is a necessary nutrient for diatoms, silicon uptake in diatom reproduction decreased sea- water silicon content. This paper clarified the characteristics of silicon transferring in the sea, which plays an important role in phytoplankton growth, zooplankton graze and marine ecosystem. Analysis revealed that silicate is supplied by terrestrial sources, through plankton uptake, death, and eventually deposits to the sea bottom, and cannot diffuse upward. This is a general silicon deficit process. Many global marine waters showed the same silicon transfer route: land→silicon biogeochemical process→sea bottom. River flow brings abundant silicate into marine waters, silicate concentration in the waters decreased in the distance away from the river estuaries. In discussion of silicon characteristics and its transfer route, it was considered that the main factor controlling the mechanism of diatom and non-diatom red tides occurrence is silicon, and the changes in silicon source. Human activities, such as sea-route cutting by building embankment and dam, and silicon supplement by the sea, such as sandstorm, rainstorm and storm tide, have largely impaired the earth ecosystem and hugely threatened the human existence. It is suggested in this paper that man should resume the original face of the Si input into the sea to keep natural ecosystem in sustainable pattern.

Silicon limitation on primary production and its destiny in Jiaozhou Bay, China Ⅳ: Study on cross-bay transect from estuary to ocean

The authors analyzed the data collected in the Ecological Station Jiaozhou Bay from May 1991 to November 1994, including 12 seasonal investigations, to determine the characteristics, dynamic cycles and variation trends of the silicate in the bay. The results indicated that the rivers around Jiaozhou Bay provided abundant supply of silicate to the bay. The silicate concentration there depended on river flow variation. The horizontal variation of silicate concentration on the transect showed that the silicate concentration decreased with distance from shorelines. The vertical variation of it showed that silicate sank and deposited on the sea bottom by phytoplankton uptake and death, and zooplankton excretion. In this way, silicon would endlessly be transferred from terrestrial sources to the sea bottom. The silicon took up by phytoplankton and by other biogeochemical processes led to insufficient silicon supply for phytoplankton growth. In this paper, a 2D dynamic model of river flow versus silicate concentration was established by which silicate concentrations of 0.028–0.062 μmol/L in seawater was yielded by inputting certain seasonal unit river flows (m3/s), or in other words, the silicate supply rate; and when the unit river flow was set to zero, meaning no river input, the silicate concentrations were between 0.05 –0.69 μmol/L in the bay. In terms of the silicate supply rate, Jiaozhou Bay was divided into three parts. The division shows a given river flow could generate several different silicon levels in corresponding regions, so as to the silicon-limitation levels to the phytoplankton in these regions. Another dynamic model of river flow versus primary production was set up by which the phytoplankton primary production of 5.21–15.55(mgC/m2·d)/(m3/s) were obtained in our case at unit river flow values via silicate concentration or primary production conversion rate. Similarly, the values of primary production of 121.98–195.33 (mgC/m2·d) were achieved at zero unit river flow condition. A primary production conversion rate reflects the sensitivity to silicon depletion so as to different phytoplankton primary production and silicon requirements by different phytoplankton assemblages in different marine areas. In addition, the authors differentiated two equations (Eqs.1 and 2) in the models to obtain the river flow variation that determines the silicate concentration variation, and in turn, the variation of primary production. These results proved further that nutrient silicon is a limiting factor for phytoplankton growth.

The teleconnection between marine silicon supply and desertification in China

Desertification has been notably expanding in China in the recent decade, especially in North China where dust/sand storm （DSS） frequently assaulted local communities. Analyses in marine ecology found that the earth ecosystem could be able to complement nutrient silicon for keeping sustainable development of marine ecosystem, and decreasing CO2 concentration in the atmosphere; as a result, the area of desertification would be enlarged. Modem human being activities have resulted in constant changes in the amount of silicon transport from land into sea, leading to oversupply of nitrogen and phosphorus but silicon in seawater. The proportion of nitrogen, phosphorus and silicon was seriously imbalanced and the limitation of silicon for phytoplankton growth has become more serious. The silicon deficiency has damaged the marine ecosystem in coastal regions and slowed down the carbon sedimentation in the atmosphere of the world. The authors believe that the continual discharge of CO2 into the atmosphere is the cause for the global warming including marine water temperature rise. Consequently, the earth ecosystem would have to trigger its complementary action to resume to the silicon balance by algae bloom in seawater for reducing air and water temperatures. In order to complement nutrient silicon into the sea, the ecosystem would transport silicon via the atmosphere; therefore, the desertification in the inner land is a natural reaction. As marine phytoplankton booming can reduce the CO2 concentration in the atmosphere and further ease the green-house effect, during this process, a large amount of silicon are demanded by the ecosystem, which human being are unable to stop desertification from happening but slow down the progress and ease the risk. Therefore, as an important role in earth ecosystem, people should reduce the CO2 discharge into the atmosphere first; then, the normal function of river transporting silicon must be restored. In this way, the CO2 in the atmosphere can be kept in balance, the global warming slowed down, marine ecosystem development sustained, the drought in inner land eased, and the desert gradually under-controlled.

The Streptococcus agalactiae Ribose Binding Protein B (RbsB) Mediates Quorum Sensing Signal Uptake via Interaction with Autoinducer-2 Signals

Understanding aquatic pathogen in sediments or aquacultural water is crucial to protect public health from soilborne and waterborne diseases.Quorum sensing(QS)was increasingly reported in biological wastewater treatment processes because of their inherent roles in biofilm development,bacterial aggregation and so on.The widely QS signals was Antoinducer-2(AI-2),primarily involved to allow the possibility of interspecies communication.However,the cellular components that mediate the response of Streptococcus agalactiae to AI-2 have not been fully characterized.Analysis of the complete genome sequence of S.agalactiae indi-cated that its RbsB protein has similarity to Escherichia coli LsrB and Aggregatibacter actinomycetemcomitans RbsB proteins that bind AI-2.We hypothesized that RbsB protein mediates quorum sensing signal uptake via interaction with AI-2.To evaluate the regulatory effect of RbsB on QS system,the recombinant plasmid pGEX-6p-1-RbsB was constructed and RbsB protein was purified with GST-tag.To further elucidate the role of RbsB protein binding to DPD(AI-2 precursor dihydroxypentanedione),the systemati-cally throughput circular dichroism(CD)spectroscopy,isothermal titration calorimetry200(ITC200)and molecular docking methods were employed.The high expression of soluble RbsB protein with molecular weight of 33 kDa was obtained.The thermodynamics results(ΔH<0,ΔS<0,ΔG<0)with ITC determination indicated that the binding process between DPD and RbsB was exothermic and spontaneous,with hydrogen bonds and van der Waals forces as the main binding forces.Obviously,DPD can be more easily combined with RbsB in a dose-dependent manner,suggesting that RbsB was changed in the microenvironment of DPD when the DPD concentration was between 0.8-1.0mmolL−1 and reaching the maximum binding amount.According to molecular docking,3 hydrophobic residues involved in DPD and RbsB protein stable binding were be found,and also hydrogen bonding plays a key role in the formation of the new complex.RbsB efficiently inhibited V.harveyi bioluminescence induced by both S.agalactiae AI-2 and V.harveyi AI-2 in a dose-dependent manner.However,our results suggest that RbsB may play a role in the response of S.agalactiace to AI-2.

Carnobacteria in fish

Carnobacterium is a genus of Gram-positive bacteria,within family Carnobacteriaceae,and they are catalase-and oxidase-negative,non-sporing bacteria with properties such as CO_(2)and L(+)-lactic acid production from glucose,but they are not able to grow on acetate agar.They are ubiquitous lactic acid bacteria and have been isolated from both cold and temperate environments,and they are identified as components of the microbiota in the gastrointestinal(GI)tract of salmonids and several other fish species of which Carnobacterium(piscicola)maltaromaticum,Carnobacterium mobile,Carnobacterium divergens,Carnobacterium alterfunitum,and Carnobacterium inhibens are reported.During the last two decades several studies have revealed that carnobacteria can act as probiotics to promote health benefits of fish,as well as they in ex vivo studies to some extent can out-compete pathogens.In addition to beneficial effects,information is available that some carnobacteria species causing fish disease.The aim of the present review is to present an updated overview of Carnobacterium in fish,with focus on their presence in the GI tract,their use as probiotic supplement and general information on pathogenic carnobacteria.