Dynamics of cyanophage-like particles and algicidal bacteria causing Microcystis aeruginosa mortality

The dynamics of cyanophage-like particles and algicidal bacteria that infect the bloom-forming cyanobacterium Microcystis aeruginosa was followed in a hyper-eutrophic pond from September 1998 to August 1999. The densities of M. aeruginosa ranged between 4.0 × 10⁵ and 1.9 × 10⁷ cells ml⁻¹, whereas those of algicidal bacteria were between 4.0 and 5.1 × 10² plaque-forming units (PFU) ml⁻¹ and those of cyanophage-like particles were between <5.0 × 10² and 7.1 × 10³ PFU ml⁻¹. A significant relationship was found between the densities of algicidal bacteria and M. aeruginosa (r = 0.81, n = 69, P < 0.001), suggesting that the dynamics of the algicidal bacteria may regulate the abundance of M. aeruginosa. Occasional peaks of density of cyanophage-like particles were detected in October, June, and August, when sharp declines in M. aeruginosa cell densities were also observed. The densities of cyanophage-like particles became undetectable when the abundance of M. aeruginosa was low, suggesting the density-dependent infection of M. aeruginosa by cyanophage-like particles. Thus, we suggest that infections of both algicidal bacteria and cyanophage-like particles are important biological agents that decompose blooms of M. aeruginosa in freshwater environments. Received: August 31, 2000 / Accepted: December 6, 2000     

DIFFERENTIAL EFFECTS OF SEDIMENTS ON SURVIVAL AND GROWTH OF FUCUS SERRATUS EMBRYOS (FUCALES,PHAEOPHYCEAE)1

Recruitment of seaweeds through small reproductive stages is limited on sediment inundated rocky shores and largely unsuccessful in soft sediment environments. Burial in sediment has several potentially negative effects for seaweed propagules, and these effects were differentiated in a laboratory experiment. We investigated how light deprivation, sediment type (grain size, organic content, and origin), and sediment chemistry (oxygen presence and toxicity through hydrogen sulfide) affected survivorship and growth of Fucus serratus L. embryos. Presence of hydrogen sulfide had overriding negative impacts on both survivorship and growth of Fucus embryos, independently of sediment type and light availability. In contrast, simple anaerobiosis generally did not impair survival or growth of the embryos. Fine sediments, 3 mm thick, significantly reduced embryo survivorship, presumably through accumulation of metabolic waste products in the immediate vicinity of the embryos as a consequence of constrained diffusion. This effect was equally pronounced in the presence of a 1‐mm layer of organically rich biodeposits. Irradiance levels did not affect survival of embryos but influenced growth. Decreasing thickness and increasing coarseness of sediments together represented a gradient of enhanced light penetration and diffusion. Growth of embryos increased along this gradient. In nature, soft sediment environments with organically enriched muds (e.g. tidal flats and salt marshes) represent habitats least favorable for colonization through small reproductive stages of seaweeds.     

Effect of five chinese traditional medicines on the biological activity of a red-tide causing alga—Alexandrium tamarense

The activity of algal cells plays an important role in the development of a red tide. Thus, when mass sedimentation of algae occurs, the scale of the red tide is reduced to some degree. Using cell suspension ability as an indicator, we studied the inhibitory effect of five Chinese traditional medicines/Chinese herbs on the activity of the red tide causing alga, Alexandrium tamarense, strain DH01. The results showed that among the five herbs, golden thread (Rhizoma coptidis Huang Lian) and areca seed (Semen arecae Bing Lang) had the best inhibitory effect, followed by indigowoad (Isatis tinctoria L.), and the least effect was found in lightyellow sophora (Sophora flavescens Ait.) and chameleon plant (Houttuynia cordata Thunb.). The 1hLC₅₀ of golden thread and areca seed was 0.054% (w/v) and 0.074% (w/v), respectively. Moreover, the higher the concentration of the herbs, the higher the inhibitory rate (IR), and the shorter reaction time needed. Combination of two herbs improved, to some extent, the inhibitory effect on the algae. A mixture of golden thread and areca seed was the most effective treatment against cell mobility of this red tide alga, and the 1 h inhibitory rate was 70.7%. Next most effective was the combination of indigowoad root and lightyellow sophora. The best inhibition results in the experiments using absorbents were golden thread and indigowoad with aloe (Aloe vera L. var. chinensis (Haw.) Berg.); followed by areca seed with aloe, and golden thread and areca seed with kelp (Laminaria japonica). In general, the zeolite based algal inhibitors were less effective. The inhibitory rates of the algal inhibitors LA, LI, KG, KA and KG were all above 90%, and remained high for 72 h. Our research results showed that the red tide inhibitors made with Chinese herbs, such as golden thread and areca seed, had the merits of low concentration, fast reaction time, and demonstrated a promising future for use in the control of red tides.     

A survey of epiphytic dinoflagellates from the coastal waters of the island of Hawai‘i

Three hundred and sixty-nine macroalgal and non-algal samples were collected from six coastal sites around the island of Hawai‘i on a biweekly basis over a 1-year period to ascertain (1) the presence of potentially toxigenic benthic dinoflagellates, and (2) substrate and environmental preferences of the dinoflagellates. Twenty-six genera/species of dinoflagellates were encountered including the (potentially) toxigenic species Amphidinium sp., Coolia monotis, Gambierdiscus sp., Ostreopsis ovata, Prorocentrum concavum, Prorocentrum hoffmannianum, Prorocentrum lima, and Prorocentrum mexicanum. Twenty of the species are being reported for the first time as present in Hawaiian coastal waters. There was some evidence of macroalgal host preference (e.g., C. monotis on Tolypiocladia glomerulata), although host morphology preferences was greater (e.g., Gambierdiscus sp., and P. lima on filamentous turfs; O. sp. 1 on sheet-like macroblades). While some dinoflagellate groups were significantly correlated with nutrient concentrations (e.g., total dinoflagellates with nitrate + nitrite and phosphate concentrations), others were not (e.g., Gambierdiscus sp., Prorocentrum emarginatum, P. lima, and Sinophysis microcephalus). The presence of several potentially toxigenic dinoflagellate species in Hawai‘i merits future study on possible impacts of these dinoflagellates on coastal food webs and human health.     

Eukaryotic Sequences in the 16SrRNA Metagenomic Dataset of Algal–bacterial Consortia of the White Sea Coastal Zone

The libraries of bacterial 16SrRNA gene fragment from algal–bacterial consortia of the White Sea coastal zone are analyzed. Up to 3% of the reads have revealed to correspond to eukaryotic rRNA. They related to following main eukaryotic clades: Discoba, Stramenopiles, Ciliata, Amoebozoa, and Nucletmycea. Amoebae, especially Vermamoeba, were present in all samples. In one sample, heterolobose amoeba Paravahlkampfia was detected. These microorganisms are parasites of microalgae, which can induce significant damage to industrial cultures. However, the data on their physiology and distribution are scarce. This study provides new evidence about the diversity of herbivorous eukaryotic microorganisms in natural algal‐containing consortia.     

Composition of phytobenthos in “lab-lab”, a periphyton-based extensive aquaculture technology for milkfish in brackishwater ponds during dry and wet seasons

The study compared the species composition of phytoperiphyton (“lab-lab”) present in ponds when gradually filled with water weekly to depths of 5, 10, 15 and 30 cm between the wet and dry seasons, for one month before the stocking of fish was studied. This was done during the dry season (March–April, 2003) and wet season (June–July, 2002). Periphyton was allowed to grow on 24 artificial substrates set at equal distances in a 1000 m² pond. “Lab-lab” that colonized the artificial substrates and that on the pond surrounding the substrates were scraped off from a measured surface area. Simultaneously, water was collected for the analysis of physical, chemical and biological parameters. Sampling was done bi-weekly coinciding with 2 and 7 days submergence at a desired depth before adjusting the water level. The major algae consisted of the diatoms (Bacilliarophyta), the blue green algae (Cyanobacteria), and the green algae (Chlorophyta). The diatoms were dominant during the dry season while the cyanobacteria dominated during the wet season. Twenty eight genera were observed during the dry season and 25 genera were noted in the wet season. Variation in genera and density that were observed every sampling period, was influenced by environmental conditions and the incoming water. The total algal density ranged from 100.7 × 10⁸ – 855.1 × 10⁸ and to 24.7 × 10⁸ – 83.9 × 10⁸ organisms.m⁻² during the dry and wet seasons, respectively. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Heat resistance of Paecilomyces variotii in sauce and juice

It has been demonstrated that some anamorphic fungi ( Paecilomyces variotii, Fusarium sp) could cause spoilage of food products after pasteurisation. Four food-borne and one clinical isolate of P. variotii were cultivated on one solid medium and three liquid media. Their survival after heating at 80–100˚C for 0.25–15 min in sterile distilled water and curry sauce or fruit juice was investigated. Heat resistance was determined by the thermal death method in a thermostatically-controlled oil bath. The most resistant spores of P. variotii from curry sauce cultivated on malt extract agar survived 100˚C for 0.5 min in sauce; cultivated in curry sauce survived 100˚C for 15 min in water and cultivated in malt broth survived 100˚C for 5 min in water and sauce. The most resistant spores of P. variotii from juice cultivated on malt extract agar were able to survive 100˚C for 15 min in water; cultivated in juice survived 100˚C for 0.5 min in juice and suspensions from cultivation in malt broth survived 100˚C for 1.5 min in juice. Spores of the clinical strain of P. variotiifrom malt extract agar survived 95˚C for 0.33 min in water, and orange juice cultures survived 96˚C for 10 min in orange juice. It was thus found that P. variotii strains cultivated in food were better adapted to heat stress, suggesting that fungal biomass suspensions were able to survive the higher temperatures for longer time intervals than spore suspensions. Journal of Industrial Microbiology & Biotechnology (2000) 24, 227–230. Received 02 June 1999/ Accepted in revised form 05 December 1999     

Effects of nutrient recycling by zooplankton and fish on phytoplankton communities

In laboratory experiments we tested the hypothesis that nutrients supplied by fish and zooplankton affect the structure and dynamics of phytoplankton communities. As expected from their body size differences, fish released nutrients at lower mass-specific rates than Daphnia. On average, these consumers released nutrients at similar N:P ratios, although the ratios released by Daphnia were more variable than those released by fish. Nutrient supply by both fish and Daphnia reduced species richness and diversity of phytoplankton communities and increased algal biomass and dominance. However, nutrient recycling by fish supported a more diverse phytoplankton community than nutrient recycling by Daphnia. We conclude that nutrient recycling by zooplankton and fish have different effects on phytoplankton community structure due to differences in the quality of nutrients released. Received: 21 December 1998 / Accepted: 31 May 1999     

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.