Browsing by Subject "Heterotrophic"
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Item Bioassay for ichthyocidal activity of Pfiesteria piscicida: Characterization of a culture flask assay format(Springer, 2002) Quesenberry, MS; Saito, Keiko; Krupatkina, Danara N; Robledo, Jose A Fernandez; Drgon, Tomas; Pecher, Wolf T; O'Leary, Nuala; Alavi, Mohammad Reza; Miller, Todd; Schneider, RE; Belas, R; Deeds, Jonathan R; Place, Allen R; Zohar, Y; Vasta, Gerardo RThe description of the heterotrophic dinoflagellate Pfiesteriapiscicida as the causative agent of fish lesions and deaths along the mid-Atlantic estuaries has revealed the need for bioassays to assess its potential toxigenicity. We designed a bioassay in which fish are exposed to clonal dinoflagellate strains or environmental consortia (e.g. environmental water or sediment samples) in 750-mL culture flasks, and examined the relationships among dinoflagellate proliferation profiles, the presence ofP. piscicida and fish deaths. Assay development and characterization were accomplished with dinoflagellate clonal cultures(P. piscicida, Karlodinium micrum,Prorocentrum minimum, CCMP1828, CCMP1829, and CCMP1834)co-incubated with sets of two young adult sheepshead minnows(Cyprinodon variegatus). Variables characterized included water quality (pH, dissolved oxygen, ammonia, nitrate and nitrite concentrations), the effect of the presence of fish on the proliferation and compositions of protist (dinoflagellate, protozoa, diatom) and bacterial populations, and time of fish death. The presence of fish in experimental flasks induced proliferation of P. piscicida and Cryptoperidiniopsis sp. (but not K.micrum or P. minimum) with populations rising between days 6 and 10, and declining 4 to 5 days later. Some fish deaths occurred when or soon after P. piscicida cell numbers were maximal. We conclude that this assay enables the assessment of acute effects of ichthyocidal dinoflagellates on fish during the first 10 days (StageA) of the experimental course. Fish deaths during the subsequent 10 to 20 days(Stage B) may be attributed to the proliferation of ichthyocidaldinoflagellates, pathogenic bacteria and/or deteriorating water quality,where as those beyond a period of approximately three weeks (Stage C) can be most certainly attributed to deteriorated water quality. Application of the flask assay to environmental samples [n=53] yielded fish deaths in all three stages:A, 78%; B, 11%, and C, 2%, with fish still living in 9% of the sample waters tested at the conclusion of the experiment beyond three weeks. The majority of samples that resulted in fish death in stage A tested positive for P.piscicida by PCR. If implemented with cautious interpretation, this assay should prove useful in monitoring blooms for the presence of P.piscicida and other dinoflagellate s pecies potentially harmful to fish.Item IMPROVING HAEMATOCOCCUS PLUVIALIS GROWTH AND ASTAXANTHIN PRODUCTION THROUGH CHEMICAL MUTAGENESIS(2019-01-01) Ramarui, KyariiRamarui, Kyarii; Li, Yantao; Biological Sciences; Biological SciencesAstaxanthin is a keto-carotenoid known for its strong antioxidant activity. It is widely used in the aquaculture and nutraceutical industries. Haematococcus pluvialis has long been used as a natural source of astaxanthin, however, its slow growth rate creates a production bottleneck. To overcome this bottleneck, Haematococcus mutants with improved growth rate under heterotrophic culture conditions were generated. This was achieved through screening for mutants with improved acetate catabolic rates. An ethyl methanesulfonate based chemical mutagenesis approach was used to generate Haematococcus mutants. Two mutants, YLEMS 3L-33 and KREMS 23D-3, were identified after three rounds of screening, which showed 75% and 21% higher biomass concentrations than the wild type under heterotrophic growth conditions, respectively. Interestingly, when grown under high light to induce astaxanthin biosyntheses, the biomass concentrations of YLEMS 3L-33 and KREMS 23D-3 were 46% and 65% higher than the wild type, respectively. It was hypothesized that these mutants may exhibit a higher acetate catabolism rate under heterotrophic conditions. Acetate metabolism produces acetyl-CoA, which is an integral intermediate in various biosynthetic pathways related to growth and astaxanthin biosyntheses. Therefore, the acetate consumption rate, lipid content, and astaxanthin content of YLEMS 3L-33 and KREMS 23D-3 mutants were comparatively analyzed against the wild type. Our data showed the acetate consumption rate in both mutants was about 60% higher than the wild type. Additionally, the final astaxanthin contents of YLEMS 3L-33 and KREMS 23D-3 were 86% and 66% higher than the wild type, respectively. The astaxanthin productivities of both mutants were about 2.7-fold higher than the wild type.