Enhancement of algicidal activity by immobilization of algicidal bacteria antagonistic to Stephanodiscus hantzschii (Bacillariophyceae)

AIMS: Enhancement of algicidal activity by immobilization of algicidal bacteria antagonistic to Stephanodiscus hantzschii. METHODS AND RESULTS: In laboratory studies, A diatom-lysing bacterium, Pseudomonas fluorescens HYK0210-SK09 showed strong algicidal activity against S. hantzschii, but a natural mesocosm study revealed that this bacterium failed to fully control natural blooms of Stephanodiscus at the low water temperatures that favour these blooms. Here, we sought to develop an effective immobilization strategy for enhancing the algicidal activity of HYK0210-SK09 in the natural setting. Bacterium HYK0210-SK09 was immobilized with various carriers including agar, alginate, polyurethane and cellulose sponge. The bacterial cells immobilized with cellulose sponge (CIS) induced more rapid and complete lysis of S. hantzschii than other carriers, and had a higher packing ability than polyurethane. Furthermore, CIS-immobilized cells showed higher lysis of S. hantzschii at the same concentrations as that of free cells (< or =1 x 10(7) cells ml(-1)), and had especially strong algicidal activity at the low temperatures (<10 degrees C). Based on these laboratory studies, we assessed the possible application of HYK0210-SK09 cells in the field by performing a mesocosm study during the winter season. The CIS-immobilized cells with species-specific activity towards the genera Stephanodiscus showed extremely high algicidal activity (up to 95%) against a bloom of Stephanodiscus hantzschii even at low water temperatures, because of high cell packing and subsequent cell protection against low temperatures and predators, whereas free cells showed negligible algicidal activities under these conditions. CONCLUSION: Immobilizing cells of HYK0210-SK09 in CIS foam, rather than in the other matrices tested, could achieve more efficient control of Stephanodiscus blooms and showed a significant algicidal activity on in vitro and in vivo blooms, even at low water temperature. SIGNIFICANCE AND IMPACT OF THE STUDY: Collectively, these results indicate that CIS of algicidal bacteria may form an important strategy for effective management of Stephanodiscus blooms at low water temperatures.     

Pseudomonas fluorescens HYK0210-SK09 offers species-specific biological control of winter algal blooms caused by freshwater diatom Stephanodiscus hantzschii

Aims:  The study of an algicidal activity and mechanism of the isolated Pseudomonas fluorescens HYK0210-SK09 (SK09) against a winter bloomed harmful diatom, Stephanodiscus hantzschii.
Methods and Results:  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 × 10⁶ 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.
Conclusions:  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.
Significance and Impact of the Study:  The bacterium enabled us to develop a new strategy, to understand the interaction for anthropogenic control of harmful algal blooms in nature.     

62 An updated checklist of the seaweeds and seagrasses of oregon

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.     

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 17505^T. HYK0512-SK12, HYK0512-PK04 and HYY0512-PK05 showed high homology with Variovorax paradoxus IAM 12373^T (98.9%), Hydrogenophaga palleronii ATCC 49743^T (98.8%) and Pseudomonas plecoglossicida ATCC 700383^T (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.     

Biological control of Stephanodiscus hantzschii (Bacillariophyceae) blooms in a field mesocosm by the immobilized algicidal bacterium Pseudomonas fluorescens HYK0210-SK09

The aim of the study was to determine the activity of an immobilized algicidal bacterium, Pseudomonas fluorescens HYK0210-SK09 (SK09), against blooms of the diatom Stephanodiscus hantzschii and to characterize its effect in an ecosystem. To this end, SK09 cells that had been immobilized using an activated carbon polyvinyl alcohol sponge (APVAS) were tested in a field mesocosm in the Nakdong River, South Korea. Immobilized SK09 cells showed species-specific activity toward S. hantzschii throughout the study, whereby up to 72 % of the population of this species was killed. The APVAS carrier absorbed nutrients in the mesocosms effectively, which reduced the free concentrations of nutrients. Other phytoplankton species, such as Cryptomonas ovata, did not show any fluctuation in abundance. The abundance of heterotrophic protists, such as heterotrophic flagellates and ciliates, increased significantly owing to the utilization of SK09 as a food source. The high level of algicidal activity of SK09 against S. hantzschii was sustained by the release of these algicidal cells from the carrier. Thus, the immobilization of algicidal bacteria has various advantages, which include high packing ability, enhancement of bacterial growth, protection from bacterial predators, effective nutrient removal, and improved algicidal activity. The present study demonstrates that immobilized SK09 is an effective biocontrol agent for natural S. hantzschii blooms. Taken together, the findings of this study clearly demonstrate that SK09 cells immobilized in APVAS can improve the water quality in mesocosm ecosystems without producing any ecological disturbance.     

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.     

Testing addition of <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> HYK0210-SK09 to mitigate blooms of the diatom <Emphasis Type="Italic">Stephanodiscus hantzschii</Emphasis> in small- and large-scale mesocosms

An algicidal bacterium Pseudomonas fluorescens HYK0210-SK09 (SK09) was applied to a natural bloom of Stephanodiscus hantzschii using a small-scale mesocosm (SM) and a large-scale mesocosm (LM) to clarify the algicidal effects and evaluate the response of the planktonic community and environments. When SK09 cells were inoculated at a final concentration of 5 × 10⁶ cells mL⁻¹, the abundance of S. hantzschii decreased significantly by 95% in SM and 85% in LM. The microcosm in the laboratory revealed that the abundance of Pseudomonas increased rapidly after inoculation with a corresponding decrease in the S. hantzschii population. Nutrient concentrations increased following the decline in the diatom cells. The abundances of nondominant species such as Chlamydomonas, Cryptomonas, and Navicula increased slightly with increased nutrient concentrations. The abundance of heterotrophic protists also increased significantly due to utilization of SK09 as food. The present study demonstrates that SK09 is an effective biocontrol agent for natural S. hantzschii bloom, and grazing pressure plays a crucial role in the successful application of algicidal bacteria to natural environments.     

滇池中溶藻细菌的分离鉴定及其溶藻效应

【背景】藻类水华或赤潮在世界范围内频发,带来各种危害,亟需找到有效途径控制水华或赤潮。溶藻细菌具有杀死藻类控制藻类生物量的能力,可以作为防治水华和赤潮的有效工具。【目的】分离并鉴定滇池中的铜绿微囊藻(Microcystisaeruginosa)及其溶藻细菌,对溶藻菌作用于铜绿微囊藻的溶藻效应进行研究,初步了解其溶藻特性与溶藻机制。【方法】采用LB平板稀释涂布,再经多次划线分离纯化细菌,测定16SrRNA基因序列以鉴定细菌种类;采用毛细管分离的方法分离铜绿微囊藻,并测定其cpcBA基因序列以鉴定蓝藻种类;采用热乙醇法提取叶绿素a,从而计算溶藻效率;基于过氧化氢酶(CAT)、还原型谷胱甘肽(GSH)和丙二醛(MDA)探究藻细胞在溶藻菌处理下的抗氧化系统响应。【结果】共分离获得11株微囊藻和17株针对铜绿微囊藻的高效溶藻菌。选取其中一株生长速度最快的铜绿微囊藻DCM4和一株溶藻效果最好的溶藻菌Sp37 (Bacillus siamensis)进行后续研究。Sp37对DCM4的4 d溶藻率达到92.4%±1.5%,且对微囊藻属的水华微囊藻(M. flos-aquae)和惠氏微囊藻(M.wesenbergii)均有溶藻效果,而对绿藻没有溶藻效果。Sp37的原菌液和无菌滤液对DCM4的4d溶藻率分别为86.8%±4.3%和81.1%±2.2%,两者没有显著差异(P0.05)。Sp37菌体对DCM4的溶藻率为25.4%±7.3%。Sp37无菌滤液经不同温度和pH处理之后的溶藻率与未经处理的无菌滤液的溶藻率无明显差异。Sp37无菌滤液处理藻细胞会使藻细胞的CAT、GSH和MDA含量发生变化。【结论】菌株Sp37对铜绿微囊藻DCM4具有高效的溶藻作用,而且对微囊藻属具有一定的溶藻特异性。Sp37是通过分泌胞外物质间接溶藻,且溶藻物质具有热稳定性和酸碱稳定性。Sp37无菌滤液处理藻细胞会触发藻细胞抗氧化系统,并且会损伤藻细胞膜。Sp37无菌滤液很可能是通过对藻细胞造成氧化胁迫,最终导致藻细胞死亡的。     

Field assessment of the potential of algicidal bacteria against diatom blooms

The possible use of algicidal bacteria for the efficient termination of natural freshwater diatom blooms with minimal adverse effects on the freshwater ecosystem was assessed under laboratory and field conditions. A field mesocosm (150 L) was dosed with a single application of isolate SK09, and monitored at Samnang jin in the lower part of the Nakdong River (South Korea) over 12 days of the winter season. We found that the tested bacterium acted against some species of Stephanodiscus- and Aulacoseira-like structures on in vitro and in vivo diatom blooms. However, this bacterium failed to fully control in vivo natural blooms of Stephanodiscus due to the low water temperatures of less than 10°C and predation activity of protozooplankton (heterotrophic nanoflagellates and ciliates). In addition, its selective inhibition indirectly affected the decrease of dissolved oxygen levels, the dramatic regeneration of N and P by the large-scale Stephanodiscus-lysing process, and a great increase in algal biomass of genera Chlamydomonas. This strongly suggests the necessity of developing an effective strategy for enhancing the activity of algicidal bacteria, and for mitigating some drawbacks to effectively and safely regulate natural diatom blooms.     

A bacterium that inhibits the growth of Pfiesteria piscicida and other dinoflagellates

Toxic dinoflagellate blooms have increased in estuaries of the east coast of the United States in recent years, and the discovery of Pfiesteria piscicida has brought renewed attention to the problem of harmful algal blooms (HAB) in general. Many bacteria and viruses have been isolated that have algicidal or algistatic effects on phytoplankton, including HAB species. Twenty-two bacterial isolates from the Delaware Inland Bays were screened for algicidal activity. One isolate (Shewanella IRI-160) had a growth-inhibiting effect on all three dinoflagellate species tested, including P. piscicida (potentially toxic zoospores), Prorocentrum minimum, and Gyrodinium uncatenum. This bacterium did not have a negative effect on the growth of any of the other four common estuarine non-dinoflagellate species tested, and in fact had a slight stimulatory effect on a diatom, a prasinophyte, a cryptophyte, and a raphidophyte. Shewanella IRI-160 is the first non-microzooplankton example of a microbe with the ability to control and inhibit the growth of P. piscicida, suggesting that bacteria in the natural environment could play a role in controlling the growth and abundance of P. piscicida and other dinoflagellates. Such bacteria could also potentially be used as management tools to prevent the proliferation of potentially harmful dinoflagellates in estuaries and coastal waters.     

Isolation,identification, and algicidal activity of marine bacteria against <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis>

The aim of this study was to isolate and identify algicidal bacteria against the dinoflagellate Cochlodinium polykrikoides, and to determine the algicidal activity and algicidal range. During the declining period of C. polykrikoides blooms, seven algicidal bacteria were isolated. The algicidal bacteria against C. polykrikoides were enumerated using the most probable number (MPN) method. The number of algicidal bacteria was high (3.7 × 10³ mL⁻¹). Algicidal bacteria were identified on the basis of biochemical and chemotaxonomic characteristics, and analysis of 16S rDNA sequences. Seven algicidal bacteria isolated in this study belonged to the genera Bacillus, Dietzia, Janibacter, and Micrococcus. The most algicidal bacterium, designated Micrococcus luteus SY-13, is assumed to produce secondary metabolites. When 5% culture filtrate of this strain was applied to C. polykrikoides cultures, over 90% of C. polykrikoides cells were destroyed within 6 h. M. luteus SY-13 showed significant algicidal activities against C. polykrikoides and a wide algicidal range against various harmful algal bloom (HAB) species. Taken together, our results suggest that M. luteus SY-13 could be a candidate for controlling HABs.     

Producing mechanism of an algicidal compound against red tide phytoplankton in a marine bacterium γ-proteobacterium

Strain MS-02-063, γ-proteobacterium, isolated from a coast area of Nagasaki, Japan, produced a red pigment which belongs to prodigiosin members. This pigment, PG-L-1, showed potent algicidal activity against various red tide phytoplanktons in a concentration-dependent manner. An understanding of a mechanism of PG-L-1 production by this marine bacterium may yield important new insights and strategies for preventing blooms of harmful flagellate algae in natural marine environments. Therefore, we analyzed the mechanisms of PG-L-1 production. In our previous study, the pigment production by this marine bacterium was completely inhibited at 1.56 μg/ml of erythromycin or 3.13 μg/ml of chloramphenicol, while minimal inhibitory concentrations for cell growth of erythromycin and chloramphenicol against this bacterium were >100 and 25 μg/ml, respectively. It is interesting to note that the ability of the pigment production in erythromycin-treated bacterium recovered by an addition of homoserine lactone. In fact, the pigment production was inhibited by β-cyclodextrin that inhibits autoinducer activities by a complex with N-acyl homoserine lactones. N-acyl homoserine lactones with autoinducer activities are ubiquitous bacterial signaling molecules that regulate gene expression in a cell density dependent process known as quorum sensing. Therefore, it was suggested that PG-L-1 produced by strain MS-02-063 is controlled by the homoserine lactone quorum sensing. It is speculated that this quorum sensing is involved in the production of algicidal agents of other marine bacteria. This bacterium and other algicidal bacteria might be concerned in regulating the blooms of harmful flagellate algae through the quorum sensing system.     

溶藻细菌FS1的溶藻效果与机制初探

近年来,由水体富营养化引发的蓝藻水华频繁暴发,对水体生态系统平衡产生了重大影响,给人类健康也带来严重威胁。生物法除藻具有高效性、环境友好等优点,因此,如果能获得具有较高溶藻效率的溶藻细菌,选择生物法除藻更为理想。从菏泽一富营养化池塘分离得到1株溶藻细菌FS1,经16S rDNA测序分析鉴定为芽胞杆菌属。实验以铜绿微囊藻为研究对象,采用血球计数板法计算反应前后藻细胞的浓度,对不同生长阶段溶藻细菌FS1的溶藻效果进行了探究。停滞期、对数期、稳定期和衰亡期的除藻率分别为7.1%、24.3%、57.0%和45.5%,结果表明,处于稳定期的FS1对铜绿微囊藻的去除效果最佳。细菌溶藻方式的研究结果表明,溶藻细菌是通过分泌溶藻物质间接溶解藻细胞。     

Novel algicidal evidence of a bacterium Bacillus sp. LP-10 killing Phaeocystis globosa,a harmful algal bloom causing species

While searching for effective bio-agents to control harmful algal blooms (HABs), the bacterial strain LP-10, which has strong algicidal activity against Phaeocystis globosa (Prymnesiophyceae), was isolated from surface seawater samples taken from the East China Sea. 16S rDNA sequence analysis and morphological characteristics revealed the strain LP-10 belonged to the genus Bacillus. The lytic effect of Bacillus sp. LP-10 against P. globosa was both concentration- and time-dependent. Algicidal activities of different growth stages of the bacterial culture varied significantly. The lytic effect of different parts of the bacterial cultures indicated that the algal cells were lysed by algicidal active compounds in the cell-free filtrate. Analysis of the properties of the active compounds showed that they had a molecular weight of less than 1000 Da and that the active compounds were stable between −80 and 121 °C. The algicidal range assay indicated that five other algal species were also suppressed by strain LP-10, including: Alexandrium catenella, A. tamarense, A. minutum, Prorocentrum micans and Asterionella japonica. Our results suggested that the algicidal bacterium Bacillus sp. LP-10 could be a potential bio-agent to control the blooms of harmful algal species.     

Algicidal Effects of a Novel Marine Actinomycete on the Toxic Dinoflagellate <Emphasis Type="Italic">Alexandrium tamarense</Emphasis>

A marine actinomycete strain BS01 with algicidal activity to the toxic dinoflagellate, Alexandrium tamarense, was isolated from Xiamen Bay, China. Sequence analysis of 16S rDNA demonstrates that BS01 is closely related to the genus Brevibacterium of Actinomycetales. BS01 exhibited algicidal activity in an indirect manner. Additional organic nutrients, but not algal-derived dissolved organic matter, were necessary for the synthesis of yet unidentified algicidal compounds (molecular weight less than 100), which were heat tolerant, a stable in acidic or alkali conditions, and exhibited a wide range of algicidal activity. This is the first report of an actinomycete algicide to the toxic dinoflagellate A. tamarense. Our results indicate that BS01 could be a potential bio-agent for controlling harmful algal blooms.     

A novel marine bacterium algicidal to the toxic dinoflagellate Alexandrium tamarense

Aims: This work is aiming at investigating algicidal characterization of a bacterium isolate DHQ25 against harmful alga Alexandrium tamarense. Methods and Results: 16S rDNA sequence analysis showed that the most probable affiliation of DHQ25 belongs to the γ‐proteobacteria subclass and the genus Vibrio. Bacterial isolate DHQ25 showed algicidal activity through an indirect attack. Xenic culture of A. tamarense was susceptible to the culture filtrate of DHQ25 by algicidal activity assay. Algicidal process demonstrated that the alga cell lysed and cellular substances released under the visual field of microscope. DHQ25 was a challenge controller of A. tamarense by the above characterizations of algicidal activity assay and algicidal process. Conclusion: Interactions between bacteria and harmful algal bloom (HAB) species proved to be an important factor regulating the population of these algae. Significance and Impact of Study: This is the first report of a Vibrio sp. bacterium algicidal to the toxic dinoflagellate A. tamarense. The findings increase our knowledge of the role of bacteria in algal–bacterial interaction.     

Isolation and characterization of a marine algicidal bacterium against the toxic dinoflagellate Alexandrium tamarense

Interactions between bacteria and harmful algal bloom (HAB) species have been acknowledged as an important factor regulating both the population dynamics and toxin production of these algae. A marine bacterium SP48 with algicidal activity to the toxic dinoflagellate, Alexandrium tamarense, was isolated from the Donghai Sea area, China. Genetic identification was achieved by polymerase chain reaction amplification and sequence analysis of 16S rDNA. Sequence analysis showed that the most probable affiliation of SP48 was to the γ-proteobacteria subclass and the genus Pseudoalteromonas. Bacterial isolate SP48 showed algicidal activity through an indirect attack. Additional organic nutrients but not algal-derived DOM was necessary for the synthesis of unidentified algicidal compounds but β-glucosidase was not responsible for the algicidal activity. The algicidal compounds produced by bacterium SP48 were heat tolerant, unstable in acidic condition and could be easily synthesized regardless of variation in temperature, salinity or initial pH for bacterial growth. This is the first report of a bacterium algicidal to the toxic dinoflagellate A. tamarense and the findings increase our knowledge of bacterial–algal interactions and the role of bacteria during the population dynamics of HABs.     

溶微囊藻细菌的富集筛选及其菌群结构特征

利用铜绿微囊藻(Microcystis aeruginosa)作为溶藻对象富集、筛选, 获得一个稳定的溶藻菌群。采用叶绿素、PCR和变性梯度凝胶电泳(DGGE)方法研究溶藻过程及其细菌种群结构的变化。结果显示, 富集的溶藻菌经1×10-5稀释后仍有显著溶藻效果。Rubritepida菌C1、假单胞菌C2和鞘氨醇单胞菌C3是存在于铜绿微囊藻中的3种伴生细菌。加入富集的溶藻菌群后, 菌群结构发生明显的变化, Rubritepida菌C1、假单胞菌C2消失, 混合菌群包含未培养黄杆菌A2、鞘氨醇单胞菌C3和噬氢     

Algicidal Effects of a Novel Marine Pseudoalteromonas Isolate (Class Proteobacteria,Gamma Subdivision) on Harmful Algal Bloom Species of the Genera Chattonella,Gymnodinium, and Heterosigma

During a bacterial survey of the Huon Estuary in southern Tasmania, Australia, we isolated a yellow-pigmented Pseudoalteromonas strain (class Proteobacteria, gamma subdivision), designated strain Y, that had potent algicidal effects on harmful algal bloom species. This organism was identified by 16S rRNA sequencing as a strain with close affinities to Pseudoalteromonas peptidysin. This bacterium caused rapid cell lysis and death (within 3 h) of gymnodinoids (including Gymnodinium catenatum) and raphidophytes (Chattonella marina and Heterosigma akashiwo). It caused ecdysis of armored dinoflagellates (e.g., Alexandrium catenella, Alexandrium minutum, and Prorocentrum mexicanum), but the algal cultures then recovered over the subsequent 24 h. Strain Y had no effect on a cryptomonad (Chroomonas sp.), a diatom (Skeletonema sp.), a cyanobacterium (Oscillatoria sp.), and two aplastidic protozoans. The algicidal principle of strain Y was excreted into the seawater medium and lost its efficacy after heating. Another common bacterial species, Pseudoalteromonas carrageenovora, was isolated at the same time and did not have these algicidal effects. The minimum concentrations of strain Y required to kill G. catenatum were higher than the mean concentrations found in nature under nonbloom conditions. However, the new bacterium showed a chemotactic, swarming behavior that resulted in localized high concentrations around target organisms. These observations imply that certain bacteria could play an important role in regulating the onset and development of harmful algal blooms.Historically, the dynamics of marine bacterial and algal populations have been studied largely in isolation. Increasing evidence is now pointing toward a close spatial and temporal association between the two and recently attention has been focused on phagocytosis of bacteria by photosynthetic flagellates (21, 28, 30). In contrast, the importance of inhibitory or predatory bacteria in regulating populations of different algal species has received relatively little attention (9, 11). Some bacteria may selectively promote bloom formation by algal species (13), while other bacteria have algicidal effects and are involved in the termination and decomposition of algal blooms (12). The latter finding has raised the possibility of bacterial control of harmful algal blooms (19). There is little data on the occurrence of marine algicidal bacteria outside Japan, where toxic blooms are frequent events (20), and algicidal bacteria have been isolated during toxic blooms of naked dinoflagellates and raphidophytes (9).Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) is thought to have been introduced into southern Tasmania via ballast water after 1973, and in some years it has a severe negative impact on the shellfish industry (16). Previous efforts to understand and predict the seasonal and interannual variability of harmful algal blooms have largely focused on the environmental factors that affect dinoflagellate growth in the water column, notably water temperature, rainfall, and water column stability (16). Rainfall and estuarine flow patterns also largely determine the allochthonous input of dissolved organic matter (DOM), which is a source of organic carbon for bacteria (27) and is possibly involved in micronutrient dynamics that promote G. catenatum growth (3, 6). As part of a study investigating DOM, bacteria, and algal interactions in the Huon Estuary (24), we isolated two bacterial strains that we tested for possible alga-bacterium interactions by using cultures of G. catenatum. Both bacteria appeared to be Pseudoalteromonas species, which are extremely common, slightly halophilic, gram-negative bacteria found in many marine ecosystems. Preliminary observations indicated that one of the strains was extremely toxic towards G. catenatum, while the other was more benign. The aims of this study were (i) to determine the taxonomic identity of the bacteria, (ii) to document by light microscopy the sequence of algal cell lysis after exposure to an algicidal Pseudoalteromonas strain and compare this lysis to the effect of the more benign Pseudoalteromonas species, (iii) to define the minimum bacterial concentrations required for algicidal effects and compare these concentrations to concentrations in natural water samples, and (iv) to investigate the range of potential target organisms for the bacterium.     

一种快速检测分离溶藻细菌方法的初探

传统的细菌培养基对铜绿微囊藻具有毒性作用。会大大影响溶藻细菌的筛选效率和准确性。通过基本培养基各成分对铜绿微囊藻DS的作用研究发现,培养基中的葡萄糖成分对藻有抑制作用,并且这种抑制作用与培养基中的葡萄糖浓度密切相关,当培养基中葡萄糖的浓度在0．1～0．4g/L时,藻细胞生长受到抑制,当用柠檬酸三钠取代葡萄糖后,铜绿微囊藻在改良后的培养基中生长正常,与对照组相比无显著性差异(P＜0．05)。用改良的培养基富集水样中的溶藻微生物,并用此培养液直接感染宿主藻,一周内即可初步快速检测是否含有溶藻细菌。此种方法既排除了培养基的干扰因素,又迅速增加了溶藻细菌的生物量,并可大量收集细菌分泌的胞外物质,为溶藻细菌尤其以分泌物质溶藻的细菌的初步筛选提供了一条快捷、有效的途径。