The depth distribution of sulphate-reducing bacteria (SRB) in the water column of a meromictic lake, Lake Suigetsu, Fukui, Japan was investigated using quantitative competitive PCR targeting the gene coding for portions of the α-subunit of dissimilatory sulphite reductase (dsrA). The total bacterial cell density (DAPI count) was 5−13×106 cells mL−1 in the water column of the lake with maximum abundance occurring at the oxic-anoxic interface layer. SRB were not detected in oxic surface water using competitive PCR. SRB were found in the anoxic waters below the oxycline ranging from 104 to 105 cells mL−1, accounting for 0.3–8.9% of the total bacteria. The SRB cell densities were higher than previously estimated using the most-probable-number (MPN) method. Sequencing of the cloned PCR product of dsrA showed the existence of different SRB groups in the anoxic water. The majority of the dsrA sequences were associated with the Desulfosarcina-Desulfococcus-Desulfonema group and members of the Desulfobulbaceae family. Other dsrA clones belonged to the Desulfomicrobium and Desulfovibrio species as well as to a deeply branched group in the dsrA tree with no representatives from previously isolated SRB groups. These SRB species appear to be important for the sulphur and carbon cycle in the anoxic waters of Lake Suigetsu.
The stable isotope approach to dietary reconstructions is based on the consistent isotopic fractionation between diet and consumer. Despite the rapidly increasing use of stable isotopes in studies on bivalves, classical fractionation values (0–1‰ for δ13C and 3–4‰ for δ15N) are used in the literature irrespective of the tissue analyzed and of the sample preparation method. We measured δ13C and δ15N for lipid-removed and lipid-containing tissues (adductor muscle, foot, mantle lobe, siphon, labial palp, gill lamella, midgut gland, and male and female gonad) of three suspension feeding bivalves (Crassostrea gigas, Cyclina sinensis and Ruditapes philippinarum) to provide an essential calibration for the diet-tissue fractionation. There were similar tissue-specific patterns in the δ13C and δ15N, which rank adductor muscle>other tissues>midgut gland or female gonad. Removal of lipids raised the δ13C and δ15N for all tissues of the three species. Acid treatment of the total soft tissues of R. philippinarum had no significant effects on the isotopic compositions. Diet-tissue fractionations for R. philippinarum were estimated based on the known fractionation values for the lipid-containing total soft tissues. Lipid removal and associated rinsing raised not only the 13C fractionation by 0.4–1.5‰ but also the 15N fractionation by 0–0.8‰, resulting in large fractionation values outside of the range of currently accepted 13C and 15N fractionation. The present study demonstrates that isotopic analyses are affected by the choice of tissue type and sample preparation method.
Oblea acanthocysta of the diplopsalid group is described as a new species from Omura Bay, West Japan. The motile cells are subspherical, have a large sulcal list at the left margin, and are characterized by the plate formula, Po, X, 3′, 1a, 6″, 3c+t, 6s?, 5‴, 2″″. The species resembles Oblea torta in shape and plate distribution, but is smaller and differs in the shape of plate 1′ and position of plate 1a. Resting cysts of O. acanthocysta are spherical and pale brown in color, possess many hollow acuminate spines, and have a theropylic archeopyle. In the SSU rRNA gene sequences of three cells of O. acanthocysta and two cells of O. torta, no intraspecific base substitutions were detected within either species. Based on phylogenetic analyses, the O. acanthocysta clade is included in the diplopsalids clade together with other diplopsalid species such as O. torta, Diplopsalis lebourae, Diplopsalopsis bomba and Gotoius excentricus. The sequences of O. acanthocysta are different from those of O. torta in 154 base pair substitutions, but O. acanthocysta and O. torta have a very close phylogenetic relationship.
Iron is an especially essential element for the growth of phytoplankton and its deficiency is well known to suppress primary productivity in both freshwater and marine ecosystems. We discovered iron-complexing ligands secreted by a freshwater eukaryotic phytoplankton, Closterium aciculare in an iron-deficient chemically defined medium. To investigate the character of the siderophore-like substance secreted from C. aciculare, growth experiments were carried out for several phytoplankton species using the culture filtrate (<0.4 μm) of C. aciculare after incubation under iron-deficient conditions. Addition of the culture filtrate of C. aciculare enhanced growth in the green algae C. aciculare, Pediastrum simplex, Staurastrum paradoxum and the diatom Aulacoseria granulata. However, addition of the filtrate suppressed that of the green alga Cosmocladium constrictum, and did not affect growth in the cyanobacteria Anabaena spiroides or Microcystis wesenbergii. These results suggest that the substances secreted from C. aciculare have species-specific growth-promoting effects and may control phytoplankton growth under iron-deficient conditions.
The distribution of sea anemones on the rocky intertidal zone at 12 stations in Mutsu Bay and at 7 stations at a 5-km scale was investigated. Seven species of sea anemone were noted at sampling stations: Anthopleura japonica, A. fuscoviridis, A. pacifica, A. atodai, Cnidopus japonicus, Haliplanella lineata, and Actinia equina. In Anthopleura, the appearance frequencies of A. japonica (spawner) were higher than those of other anemones that occurred at each station, while A. atodai (brooder) showed a limited distribution. C. japonicus, C. japonicus, and A. equina were very rare. Sea anemones and sympatric benthic organisms occurred at the same stations, and no significant relationship between the number of sea anemones and the coverages of mussels which might be strong competitors for space was found. We show that the reproductive mode and sympatric organisms of sea anemones may be included among the factors that determine the distribution of sea anemones in Mutsu Bay, Japan. However, we need to further examine the environmental factors in this area, as well as intra- and interspecific relationships among anemones.
Glass plates were immersed in the surface layer (1 m) in Gokasho Bay during a 7 day period every month over an annual cycle to allow periodic collection of epilithic microalgae and to analyze their year-round stable carbon and nitrogen isotope ratios. The bulk of the attached material was diatoms throughout the year. The δ13C and δ15N of epilithic microalgae varied seasonally, ranging from −22.0 to −14.6‰ and from 3.6 to 10.2‰, respectively. The δ13C increased during a period from August to November when large microalgal biomasses were found, while the δ15N decreased after November through January in the next year. Such seasonal variations are discussed from the viewpoints of the algal growth and ambient nutrient concentrations. Comparison of the δ13C (yearly mean=−19.8‰) and δ15N (7.7‰) for epilithic microalgae with the previously reported values for primary producers and organic matter in Gokasho Bay shows that the overlap of the δ13C with marine phytoplankton (−20.4‰), which will result in poor resolution of sources.
We evaluated the suitability of ELF-based assay (ELF: Enzyme-Labeled Fluorescence, Molecular Probes) as a tool for specific-detection of alkaline phosphatase (AP) activity in individual species of marine phytoplankton. Among 4 species of marine phytoplankton tested in the present culture experiments, the ELF-labeled cells of Karenia mikimotoi (Dinophyceae) and Skeletonema costatum (Bacillariophyceae) were simultaneously found with AP activity that was determined by using 4-methylumbelliferyl phosphate under the phosphorus-starved state but not found under the phosphorus-replete state. There were significant positive correlations between the percentage of ELF-labeled cells and AP activity of K. mikimotoi and of S. costatum. In contrast for Chattonella antiqua and Heterosigma akashiwo (Raphidophyceae) which do not produce AP, no ELF-labeled cells were found even under the phosphorus-starved state. Thus, ELF-based assay is considered to be useful for specific-detection of AP activity.