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1.
The impacts of varying algal growth rates on the bacterial load in the cultures were studied for six marine microalgae: Skeletonema costatum ,Chaetoceros mülleri (Bacillariophyceae), Nannochloropsis oculata (Eustigmatophyceae), Isochrysis galbana, Pavlova lutheri (Haptophyceae), and Tetraselmis sp. (Prasinophyceae). Samples were taken in batch cultures during early exponential phase and in stationary phase when the growth rate was below 5% of maximum growth rate (µmax). Except for C. mülleri and N. oculata, the microalgae were thereafter grown semi-continuously at dilution rates of 20% and 60% of µmax and samples taken during a period of 10 days.Higher bacterial levels were associated with slow-growing microalgae on a per volume basis. Per algal cell, variations in the bacterial load were more related to species. Relatively high bacterial densities (5.7–16.4 CFU algal cell–1) with large proportions of opportunistic and haemolytic species were associated with the Bacillariophyceae. For the other species, the bacterial density was 0.2–4.3 CFU algal cell–1. Bacterial levels were in general lower and not affected to the same extent by algal growth conditions in Tetraselmis sp. and P. lutheri. No or very low levels of presumptive Vibrio spp. were observed, except in semi-continuous cultures of P. lutheri. Cultures of Tetraselmis sp. had low levels of opportunistic bacteria at all growth conditions.  相似文献   

2.
Vibrio spp. are the most common and harmful shrimp pathogenic bacteria; however, microalgae and cyanobacteria have the ability to produce antimicrobial substances against these species. In this study, the organic and aqueous extracts of 28 species of marine microalgae and cyanobacteria were screened against Vibrio campbellii M1. Two of these phytoplankton species with antibacterial activity in aqueous extracts (Dunaliella tertiolecta and Skeletonema costatum) and nontoxic to brine shrimp Artemia franciscana nauplii were used to evaluate their anti‐Vibrio effect when used as green‐water cultures in Vibrio‐challenged white shrimp Litopenaeus vannamei cultures. No differences in mortality of juvenile L. vannamei were observed between treatments tested, suggesting that the pathogenicity of V. campbellii could be related to the growth stage of shrimp. The proximal composition of D. tertiolecta and S. costatum was in the recommended range for penaeid shrimp nutrition, allowing shrimp supplemented with these microalgae to have significantly greater total length and weight than control shrimp. Shrimp supplemented with S. costatum presented the highest values of organic mass (11.48 mg/organism) and growth rate (0.31 mg/d) in comparison to D. tertiolecta. These results indicate that microalgae are not only capable of producing antibacterial compounds against Vibrio but can also help shrimp nutrition.  相似文献   

3.
The effect of Microbacterium sp. strain 8L and Exiguobacterium mexicanum strain 8N was evaluated in the diet of Artemia under xenic conditions. Viable cultures of bacteria were provided to xenic cultures of Artemia in combination with Sacharomyces cerevisiae, cornflour or Spirulina, and the effect on the survival and growth was recorded. The use of these bacterial strains improves significantly the survival of Artemia independently of the used food (P < 0.05), and variable results were observed in the growth.  相似文献   

4.
This study identified phytase-producing bacteria that were previously isolated from the gastrointestinal tract of Atlantic cod, Gadus morhua and determined its effect on head kidney leukocytes. Out of the 216 bacterial strains tested, the two phytase producers were identified as Pseudomonas sp. and Psychrobacter sp. based on their 16S rDNA sequence. Crude phytase from these two bacterial strains was produced employing the shake flask method. Even though the total protein of the crude phytase was not significantly different for the two bacteria, the phytase activity of the crude enzyme produced by Pseudomonas sp. (97.1 ± 16.7 U) was significantly higher than that of the enzyme from Psychrobacter sp. (75.9 ± 2.4 U). When cod head kidney leukocytes were incubated with the crude phytase (50 μg ml−1), it resulted in enhanced cell proliferation, higher myeloperoxidase, and acid phosphatase activities. Extracellular responses—respiratory burst activity and hydrogen peroxide production were not enhanced by the crude enzyme. As a consequence, the growth of two pathogenic bacteria Aeromonas salmonicida and Vibrio anguillarum was not suppressed by the supernatants obtained from head kidney leukocytes incubated with the crude bacterial phytase. Thus, the enzyme from phytase-producing intestinal bacteria of Atlantic cod can stimulate intracellular head kidney leukocyte activities but not the production of extracellular substances that are involved in antibacterial response. These have implications on the potential use of bacterial phytase as feed supplement to boost cellular immune response of the fish and could be employed as a health management strategy in culture systems.  相似文献   

5.
The present study investigated the immunomodulatory activities of alginic acid and fucoidan, both derived from brown seaweeds, on selected cellular immune responses and antibacterial activity of head kidney (HK) leukocytes of cod, Gadus morhua. Primary cultures of HK leukocytes were incubated with either 10 or 100 μg ml−1 of the substances and the effects on respiratory burst, cellular proliferation, acid and alkaline phosphatase activity and cellular myeloperoxidase were measured at 3- and 24-h post-incubation. The antibacterial activity of the supernatants collected from the cell cultures incubated with 100 μg ml−1 of the substances were tested against Vibrio anguillarum and Aeromonas salmonicida. Respiratory burst was significantly elevated in cells incubated with either alginic acid or fucoidan in a dose-dependent manner. Incubation with a higher dose of alginic acid and fucoidan resulted in lower cellular proliferation at 3- and 24-h, respectively. Both acid and alkaline phosphatase activities of HK leukocytes were not significantly modulated, except for a slight elevation of acid phosphatase in cells incubated with 100 μg ml−1 of alginic acid for 24-h. Fucoidan, but not alginic acid significantly increased cellular myeloperoxidase activity at a concentration of 100 μg ml−1. The growth of the bacteria in both the treated and control supernatants was significantly lower than what was observed in the bacterial culture medium. However, the supernatants from the treated cells had significantly higher bacterial growth compared with supernatants of the control cells. Taken together, these results showed that at the tested concentrations, both alginic acid and fucoidan are able to differentially stimulate some cellular immune responses of cod HK leukocytes in vitro and the respiratory burst activity was significantly stimulated by these brown algal derivatives. These substances could be tested as potential immunostimulants in future in vivo studies.  相似文献   

6.
To control harmful algal blooms (HABs), in particular dinoflagellate Noctiluca scintillans, which causes damage to shrimp production, algicidal bacteria were isolated from shrimp pond water and screened for their killing effect against N. scintillans under laboratory condition. Among 260 bacterial isolates, 10 showed killing effects on N. scintillans. Out of 5 strains showing relatively stronger killing activity, 4 strains belonged to the Gammaproteobacteria group. Among these, strain BS2 (identified as Marinobacteria salsuginis) showed the strongest Noctiluca-killing activity. In the present study, we also investigated bacterial effects against growth of other phytoplankton species. Strain BS2 killed only N. scintillans but not any other phytoplankton (Heterosigma akashiwo NIES-6, Chatonella antique NIES-1, Chaetoceros ceratosporum, Prorocentrum lima, and Dunaliella sp.). Results of the present study lead us to expect prevention of damage by HABs, in particular dinoflagellate N. scintillans, in shrimp farming and mitigation for shrimp production in ponds using Noctiluca-killing bacteria.  相似文献   

7.
Lactic acid bacteria (LAB) were isolated from rotifer cultures in a marine hatchery to search for potential probiotics for marine animals. Fifteen strains were first selected among a total of 55, according to antibacterial activity against Vibrio sp. Among eight strains identified as Lactobacillus casei, four were highly adhesive, suggesting some ability for surface colonization. The other strains were identified as Lactobacillus plantarum, Lactobacillus dextrinicus, and Leuconostoc sp. To validate probiotic potential, Artemia were challenged against pathogenic Vibrio alginolyticus, with or without one of six selected LAB strains. The six strains protected Artemia against the pathogen, to some extent on condition that nutrient enrichment was provided. La. casei BR51 and X2 were preferred, as they were efficient even in the absence of nutrient supply. La. casei X2 was finally selected as candidate probiotic, due to the best growth performances of Artemia, with or without the pathogen.  相似文献   

8.
The antibacterial activities of essential oils and herbal extracts have been demonstrated against a range of bacterial species. In this study, the antibacterial effects of a new combination of essential oils from the herbs Thymus vulgaris, Salvia officinalis, Eucalyptus globulus and Mentha piperita were assayed against common bacterial isolates (Staphylococcus aureus, Escherichia coli and Pseudomonas aeroginosa) and fifteen novel marine bacteria isolates. The sensitivity of different isolates to antibacterial activity of the essential oils was determined using well diffusion assays. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were quantified by micro dilution assays. The data demonstrate that the combination of essential oils had potent antibacterial effects and marine bacteria were more sensitive to growth inhibition (P < 0.05). MIC rates were 0.77–6.18 mg/ml, and MBC rates were 1.67–12.30 mg/ml. This indicates that the combined essential oils (CEO) can be a new source of antibacterial agents for use in marine aquaculture.  相似文献   

9.
In the present study a microtitre plate assay was used to evaluate antagonistic activity of 157 intestinal bacteria belonging to Carnobacterium isolated from Arctic charr (Salvelinus alpinus L.), Atlantic salmon (Salmo salar L.) and wolf fish (Anarhichas lupus L.) against fish pathogenic bacteria. One hundred and forty‐nine strains isolated from Arctic charr fed; (a) different lipid levels and (b) different fatty acids were screened for their ability to inhibit growth of the fish pathogen Aeromonas salmonicida ssp. salmonicida strain AL 2020 (the causative agent of furunculosis). Carnobacterium maltaromaticum and Carnobacterium mobile isolated from fish fed a low‐lipid diet inhibited growth of the pathogen, while none of the Carnobacterium divergens isolated from fish fed the high‐lipid diet had this ability. When Arctic charr was fed different fatty acids, was the frequency of antibacterial ability of C. maltaromaticum highest in strains isolated from fish fed 4%α‐linolenic acid (18:3 n‐3) and lowest in strains isolated from fish fed 4% linoleic acid (18:2 n‐6). Extracellular growth inhibitory compounds harvested in exponential and stationary growth phase from eight carnobacteria strains isolated from three fish species were tested for their ability to inhibit growth of six fish pathogens [A. salmonicida, Vibrio splendidus strain VS11, Vibrio salmonicida strain LFI 315, Vibrio anguillarum strain LFI 317, Moritella (Vibrio) viscosa strain LFI 5000 and C. maltaromaticum (piscicola) CCUG 34645]. The highest antibacterial activity was found when cellular extracts of the producer isolate were harvested in stationary growth phase. Scanning electron microscopy (SEM) investigations of A. salmonicida showed that cell morphology was affected by the inhibitory substance produce by strain 8M851, a Carnobacterium inhibens‐like bacteria.  相似文献   

10.
Seaweed production represents one of the rising activities in the aquaculture industry. This study explores the impact of bacteria associated with the growth of Ulva clathrata, a promising alga in the field of food and bioremediation. Fifty‐six bacteria isolated from four seaweed (Caulerpa sp., Gracilaria sp., Ulva lactuca and U. clathrata) were tested to evaluate their effect on U. clathrata growth. Eight of them showed a significant growth‐promoting effect (p < .05). Isolates Ul‐11 and Ul‐12 from U. lactuca induced an increase of 73 and 81% of growth respectively. They were classified as Reugeria sp. and Alteromonas sp. based on 16S DNA sequencing (>95.0% sequence identity). Multiple combinations of the growth‐promoting bacteria were also tested on U. clathrata, and the best result was achieved by combining Ca‐3/Uc‐18/Ul‐12 isolates with a significant increase in seaweed growth of up to 76%; however, no synergistic effect was observed compared to Ul‐12 alone. Scanning electron microscopy revealed no alteration in the cell wall of U. clathrata when inoculated with selected bacteria, showing an average increase of bacterial density on U. clathrata.  相似文献   

11.
The present study evaluated the effects of five bacterial isolates from the microalga Muriellopsis sp. on the microalgal biomass concentration (g/L), specific growth rate (K), photosynthetic quantum yield (QY), non‐photochemical quenching (NPQ), maximum relative electron transport rates (rETR max) and levels of nutritional components such as carbohydrates, lipids, proteins and carotenoids in Muriellopsis sp. cultivated in seawater under indoor and outdoor conditions. The bacterial strains were Microbacterium sp. Dom 1; Pseudomonas sp. Dom2; Microbacterium sp. Dom 3; Rhizobium sp. Dom 4; and Dietzia sp. Dom 5, as well as the Pseudoalteromonas sp. (SLP1), a bacterium known to promote the growth of microalgae. At the laboratory level, inoculation of the strains SLP1, Dom 1, Dom 3 and Dom 5 resulted in higher specific growth rates and biomass of the microalga. Subsequently, the best results were obtained with a combination of the selected bacterial strains (Dom1, Dom 3, Dom5 and SLP1) under outdoor culture conditions improved the biomass, proteins, carbohydrates and total carotenoids in 22.12%, 48.28%, 19,25% and 48.27%, respectively, compared to cultures without the incorporation of the selected bacteria (control), while no effects were observed on the photosynthetic parameters. Thus, it was demonstrated that positive associations of the selected bacterial strains played an important role in the production of Muriellopsis sp. acclimatized to grow in seawater. This is of crucial importance, especially in desert areas, where solar radiation is high and freshwater is a limited resource.  相似文献   

12.
Carps are the most diversified freshwater fish belonging to family Cyprinidae. Numerous probiotic and pathogenic lactic acid bacteria (LAB) have been characterized from carps. However, the diversity of these ecologically important bacteria is entirely unknown in freshwater fish of Pakistan. The present study aimed to characterize and identify the lactic acid bacteria from two carps viz. Laboe rohita and Cirrhinus mrigala and determine their antagonistic activity. Seventeen bacterial isolates were purified from the gastrointestinal tract and gills of these fish and characterized morphologically. Initially, seven isolates were screened as LAB using agar supplemented with CaCO3. Subsequently, only two isolates CILB2 and RIL10 were selected as LAB after high‐performance liquid chromatography analysis for lactic acid production. Isolates CILB2 and RIL10 were genetically identified as Enterococcus faecalis and Weissella sp., respectively after 16S rRNA gene sequence analysis. Both strains exhibited significant antagonistic activity against common fish pathogens Streptococcus agalactiae, Staphylococcus aureus and Escherichia coli. Enterococcus faecalis CILB2 and Weissella sp. RIL10 were also found negative for haemolysis and gelatinase activities and were sensitive to ampicillin, amoxicillin, doxycycline, erythromycin, chloramphenicol and co‐trimoxazole antibiotics. The identified LAB strains may further be investigated for their potential probiotic application in fish feed and food preservation techniques.  相似文献   

13.
The antimicrobial activity and mode of action of chitosan were evaluated against Streptococcus iniae, a pathogenic Gram‐positive bacterium of fish worldwide. Cell proliferation kinetics were examined following exposure to varying concentrations of chitosan. The action of chitosan on S. iniae was also investigated by measuring agglutination activity, conductivity, and extracellular and intracellular bacterial adenosine triphosphate (ATP) levels. Chitosan exhibited antibacterial activity against S. iniae at concentrations of 0.1% and above and was lethal at a concentration of 0.4% and higher. The mechanism of antibacterial activity of chitosan at the inhibitory level of bacterial growth appears to hinge upon the interaction between chitosan and the oppositely charged bacterial surface. This interplay causes agglutination, which was readily observed grossly and microscopically. After interacting with the cell surface via adsorption, an efflux of intracellular ATP was documented, which suggests that chitosan disrupts the bacterial cell causing leakage of cytosolic contents and ultimately cell death. Results suggest chitosan may be worth evaluating as a natural alternative to antibiotic against S. iniae infection of fish.  相似文献   

14.
Columnaris disease, caused by the bacterium Flavobacterium columnare, is currently the most frequently reported bacterial disease affecting farm‐raised channel catfish in the USA. Common treatments against the disease include the use of medicated feed that has led to emergent antibiotic resistant strains of F. columnare. Nigella sativa (Black cumin) is a medicinal herb commonly used by many cultures as a natural remedy for numerous disorders. Recently, we have discovered the antibacterial activity of N. sativa and its oil extract against F. columnare. In this study, we showed N. sativa oil (NSO) strongly inhibited the growth of all of the strains of F. columnare tested and yielded significantly larger zones of inhibition than those produced by oxytetracyclin. We tested the protective effect against columnaris disease in vivo by incorporating NSO (5%) or N. sativa seeds (NSS) (5%) into fish feeds. Fishes (Ictalurus punctatus and Danio rerio) fed amended diets displayed significantly lower mortality than those fed control diets. Per cent mortalities in control groups ranged from 77% to 44% and from 70% to 18% in zebrafish and channel catfish, respectively. A dose study using different NSS concentrations showed that 5% NSS offered the most protection against columnaris disease in channel catfish.  相似文献   

15.
Microbiological conditions in 200 L cultures of microalgae Chlorella minutissima in polyethylene sleeves were examined. The influence of addition of antibiotic (nitrofurantoin) was studied. Samples were taken 2, 5, 9, and 14 d after inoculation and were spread on solid Zobell medium and on thiosulfate citrate bile salts sucrose agar for the enumeration of total numbers of bacteria and numbers of presumptive Vibrio bacteria, respectively. Microalgae grew well in the cultures and high numbers of culturable bacteria (about 107 bacteria/mL) were present in all microalgae cultures. Addition of antibiotic in 200‐L cultures of C. minutissima did not result in a significant decrease of total counts of bacteria per unit volume (P > 0.05), while the numbers of presumptive Vibrio were higher in cultures added antibiotic compared with the control treatment (P < 0.05). The numbers of presumptive Vibrio per unit volume and the percentage of fast‐growing bacteria were higher in microalgae supernatant than in noncentrifuged samples. Representative colonies were taken from all samples and in total 649 bacterial strains were isolated during this study. A range of phylotypes was identified by amplification and sequencing of the 16S rDNA gene and phylogenetic trees were constructed. Several members of the Roseobacter clade were dominant among the culturable isolates.  相似文献   

16.
As adhesion and translocation through fish gut enterocytes of the pathogen Vibrio (Listonella) anguillarum are not well investigated, the effective cause of disease and mortality outbreaks in larval sea bass, Dicentrarchus labrax, suffering from vibriosis is unknown. We detected V. anguillarum within the gut of experimentally infected gnotobiotic sea bass larvae using transmission electron microscopy and immunogold labelling. Intact bacteria were observed in close contact with the apical brush border in the gut lumen. Enterocytes contained lysosomes positive for protein A‐gold particles suggesting intracellular elimination of bacterial fragments. Shed intestinal cells were regularly visualized in the gut lumen in late stages of exposure. Some of the luminal cells showed invagination and putative engulfment of bacterial structures by pseudopod‐like formations. The engulfed structures were positive for protein A‐colloidal gold indicating that these structures were V. anguillarum. Immunogold positive thread‐like structures secreted by V. anguillarum suggested the presence of outer membrane vesicles (MVs) hypothesizing that MVs are potent transporters of active virulence factors to sea bass gut cells suggestive for a substantial role in biofilm formation and pathogenesis. We put forward the hypothesis that MVs are important in the pathogenesis of V. anguillarum in sea bass larvae.  相似文献   

17.
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18.
《水生生物资源》1999,12(5):343-350
Haemocytes of Mytilus edulis, allowed to attach to the plastic surface of a tissue culture plate in the presence of haemolymph, were observed by time-lapse video recording. When bacteria were added at concentrations of 10 or 50 bacteria per haemocyte, certain bacterial strains caused rounding of the cells within 2–3 h. Haemolymph was necessary for the rounding to occur; if bacteria were added in sterile seawater there was no significant difference in the number of rounded cells between control and bacteria-treated cultures for up to 4 h. The haemolymph factor required for this activity was active at 1/64 dilution in seawater, was sensitive to trypsin treatment, and activity was halved on heating at 56 or 100 °C for 30 min. For the most toxic bacteria tested, Vibrio alginolyticus NCMB 1339 and Vibrio anguillarum A7, haemocyte cell rounding appeared to be induced by a very small number of bacterial cells. Bacteria-free culture supernatant of V. anguillarum 2981 induced rounding of haemocytes in a dose-dependent manner, with 50 % of cells being rounded at a dilution of approximately 1/500 of the culture supernatant. In a survey of 226 bacterial isolates, those isolated from incidents of disease in a bivalve hatchery were significantly more toxic towards haemocytes than bacteria isolated from hatcheries without disease or from turbot hatcheries.  相似文献   

19.
Intestinal bacteria in marine fish may produce antimicrobial substances which inhibit pathogenic bacteria. The aim of this study was to determine the influence of a change of fish diet on the antimicrobial activity of the culturable aerobic gut microflora of Senegalese sole, Solea senegalensis. Pre‐adult 15‐month‐old fish previously fed on an artificial diet, were fed polychaetes (Hediste diversicolor), which form part of the natural diet of Senegalese sole. Samples were taken0, 3 and 6 weeks after start of the experiment from the stomach, small and large intestine of the fish. The bacterial strains isolated from these samples were sub‐cultured to pure cultures and stored at ?80°C. Several biochemical tests were run to obtain some basic phenotypic characteristics of the isolated strains. Amplification and sequencing of 16S rDNA fragments were used to identify the majority of the bacterial strains isolated. The identification by use of this molecular approach gave results in agreement to the phenotypic characterization. Feeding with polychaetes significantly increased (P<0.05) the numbers of presumptive Vibrio isolates in the gut. The number of bacterial strains with antimicrobial activity, as determined by two in vitro approaches, was significantly (P<0.05) increased by feeding with polychaetes.  相似文献   

20.
There are few reports in the literature about the isolation of bacteria from whale intestine. In this report, we counted colony-forming units in the feces obtained from three female common minke whales (Balaenoptera acutorostrata). The number of colony-forming units ranged from (2.2 ± 0.4) × 105 to (8.9 ± 2.0) × 108 per gram (wet weight) of excrement. 16S rRNA gene sequences of 141 isolates were determined. These strains were identified as Enterococcus faecalis, Enterococcus sp., Enterobacter cloacae, Enterobacter sp., Escherichia coli, Edwardsiella ictaluri or Clostridium sp. The data suggested that the facultative anaerobic population of the intestinal bacterial flora of the minke whale was similar to that of ground mammals.  相似文献   

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