Control Of Harmful Algal Blooms Research Articles

Pseudomonas fluorescensHYK0210-SK09 offers species-specific biological control of winter algal blooms caused by freshwater diatomStephanodiscus hantzschii

The study of an algicidal activity and mechanism of the isolated Pseudomonas fluorescens HYK0210-SK09 (SK09) against a winter bloomed harmful diatom, Stephanodiscus hantzschii. SK09 was isolated from the Paldang reservoir, Korea and used to biological control of S. hantzschii. The inoculation of SK09 at the final density of 5 x 10(6) cells ml(-1) caused degradation of >90% of S. hantzschii cells within 5 days. The algal cell lysis was achieved by a direct attack of the bacteria to the diatom cells, and the algicidal compound was located in the cytoplasm of the cell. As SK09 did not suppress Microcystis aeruginosa, Anabaena cylindrica, Coelastrum astroideum or Cyclotella meneghiniana, it appeared to attack S. hantzschii in a species-specific manner. Testing in an indoor mesocosms confirmed that SK09 effectively reduced S. hantzschii cells by 88% within 9 days. This bacterium is useful in regulating blooms of S. hantzschii. However, it should be studied in the future that their impact in shaping phytoplankton community and their activity in natural environments. The bacterium enabled us to develop a new strategy, to understand the interaction for anthropogenic control of harmful algal blooms in nature.

Isolation, identification and characterization of algicidal bacteria against Stephanodiscus hantzschii and Peridinium bipes for the control of freshwater winter algal blooms

Five strains (HYY0510-SK04, HYY0511-SK09, HYK0512-SK12, HYK0512-PK04 and HYY0512-PK05) of algicidal bacteria against the harmful bloom forming diatom Stephanodiscus hantzschii and dinoflagellate Peridinium bipes, were isolated. Among these strains, HYY0510-SK04, HYY0511-SK09 and HYK0512-SK12 have an effective algicidal activity for S. hantzschii, while HYK0512-PK04 and HYY0512-PK05 have an algicidal effect against P. bipes. Sequence analysis of 16S rDNA showed that HYY0510-SK04 and HYY0511-SK09 were closely related to Acidovorax delafieldii ATCC 17505T. HYK0512-SK12, HYK0512-PK04 and HYY0512-PK05 showed high homology with Variovorax paradoxus IAM 12373T (98.9%), Hydrogenophaga palleronii ATCC 49743T (98.8%) and Pseudomonas plecoglossicida ATCC 700383T (98.3%), respectively. HYY0510-SK04, HYY0511-SK09 and HYK0512-SK12 degraded S. hantzschii cells within two weeks when those bacteria were inoculated at densities of ≥107cells mL−1 to the lag or logarithmic growth phase of the algal culture. HYK0512-PK04 and HYY0512-PK05 degraded more than 90% of P. bipes cells within 14 and 8 days, respectively, when these bacteria were inoculated at densities of ≥107cells mL−1. Among the five bacterial strains, HYK0512-SK12 and HYY0512-PK05 showed the most effective growth inhibition of all the algae and cyanobacteria tested. Biochemical assays revealed that the main algicidal substance from all isolates were likely to be extracellular substances. These results indicate that the bacterial strains isolated for this study are potential agents for the control of harmful algal blooms in eutrophic reservoirs.

Isolation and Structure Determination of Algicidal Compounds fromUlva fasciata

Thirty-seven species of seaweeds including 10 Chlorophyta, 13 Phaeophyta, and 14 Rhodophyta collected from the coast of Nagasaki Prefecture, Japan, were screened for algicidal activity against the red-tide phytoplankton Heterosigma akashiwo. The green alga Ulva fasciata (Ulvaceae, Chlorophyta) showed the strongest algicidal activity among the seaweeds tested. Bioassay-guided fractionation of the methanol extract of U. fasciata led to isolation of three algicidal compounds whose structures were determined to be hexadeca-4,7,10,13-tetraenoic acid (HDTA), octadeca-6,9,12,15-tetraenoic acid (ODTA), and alpha-linolenic acid on the basis of spectroscopic information. These polyunsaturated fatty acids (PUFAs) showed potent algicidal activity against H. akashiwo (LC(50) 1.35 microg/ml, 0.83 microg/ml, and 1.13 microg/ml for HDTA, ODTA, and alpha-linolenic acid, respectively), and the result demonstrated the potential of these PUFAs for practical harmful algal bloom control.

Algicidal bacteria in the sea and their impact on algal blooms.

Over the past two decades, many reports have revealed the existence of bacteria capable of killing phytoplankton. These algicidal bacteria sometimes increase in abundance concurrently with the decline of algal blooms, suggesting that they may affect algal bloom dynamics. Here, we synthesize the existing knowledge on algicidal bacteria interactions with marine eukaryotic microalgae. We discuss the effectiveness of the current methods to characterize the algicidal phenotype in an ecosystem context. We briefly consider the literature on the phylogenetic identification of algicidal bacteria, their interaction with their algal prey, the characterization of algicidal molecules, and the enumeration of algicidal bacteria during algal blooms. We conclude that, due to limitations of current methods, the evidence for algicidal bacteria causing algal bloom decline is circumstantial. New methods and an ecosystem approach are needed to test hypotheses on the impact of algicidal bacteria in algal bloom dynamics. This will require enlarging the scope of inquiry from its current focus on the potential utility of algicidal bacteria in the control of harmful algal blooms. We suggest conceptualizing bacterial algicidy within the general problem of bacterial regulation of algal community structure in the ocean.

60 Identification of diatom‐lytic bacterium sk‐02 and its capability to degrade stephanodiscus hantzschii

In order to control harmful algal blooms, many biological approaches have been tried. Specially, there have recently been discussions concerning the roles of bacteria in algal bloom dynamics. Then, algicidal bacteria are expected as an agent considerate for harmful algal blooms control. Development of these organisms as biological control agents involves isolation from environmental samples. With the aim of develop eco‐technology controlling water blooms in fresh waters, we isolated the diatom‐lysing bacteria from the sediments of Lake Seokchon and Pal¡¯tang River‐Reservoir. A soft agar‐overlay technique was used to isolate the diatom lytic bacteria. The SK‐02 showed a diatom lytic activity against Stephanodiscus hantzschii. Taxonomic identification including 16S rDNA base sequencing, and phylogenetic analysis indicated that the isolate SK‐02 had a 99.20% homology in its 16S rDNA base sequence with Pseudomonas putida. The nature of these diatom‐lying components is still under investigation. These results suggest that the indigenous bacteria isolated from the sediments may have a potential in the application and development of eco‐technology controlling harmful water blooms in the fresh water environments.

Evidence for multiple species within the endoparasitic dinoflagellate Amoebophrya ceratii as based on 18S rRNA gene-sequence analysis.

Parasitism within the group of dinoflagellates is a widespread phenomenon. Whether the parasitic dinoflagellates exhibit specificity in their infection is not well known, but this possibility has become an important issue in the development of biological control of harmful algal blooms. The 18S rDNA sequences from the parasite Amoebophrya sp. and its dinoflagellate host Dinophysis norvegica were determined and compared with the published sequence of Amoebophrya sp. infecting Gymnodinium sanguineum and other dinoflagellates. The results showed that the sequence from the parasite within D. norvegica was clustered with that of the one from G. sanguineum with 100% bootstrap support in a maximum-likelihood analysis. The observed identity between these two sequences was 93%, which indicates that they are not identical species. The two sequences from Amoebophrya sp. were deeply branched within the group of dinoflagellate sequences and represent the earliest diverging dinoflagellates. The sequence from the parasite Parvilucifera infectans, also infecting D. norvegica, was not closely related to the Amoebophrya sp. sequences. The sequence from D. norvegica appeared as a sister group to a cluster containing Prorocentrum lima and Alexandrium spp. without significant bootstrap support. The data presented herein support the hypothesis that A. ceratii comprises more than one species, and this opens the possibility that infections of harmful algal species might involve more than one Amoebophrya species.

ANNA – Artificial Neural Network model for predicting species abundance and succession of blue-green algae

Predictive potential of deductive and inductivephytoplankton models are compared regarding theirusefulness for forecasting and control of harmfulalgal blooms. While applications of deductive modelsstill seem to be restricted by lack of knowledge, ad hocinductive models sometimes prove to bestraightforward and useful. The inductive neuralnetwork model ANNA is documented by means of anapplication to Lake Kasumigaura, Japan. ANNA wasvalidated for five blue-green algae species wherepredictive accuracy has improved with increased eventand time resolution of training data. A scenarioanalysis on species succession has demonstrated thepotential of ANNA for hypothesis testing. Finally,implications for use of ANNA for operational algalbloom control are discussed.