Abundance of picophytoplankton in the halocline of a meromictic lake, Lake Suigetsu, Japan

Abstract

Numerous (0.5 to 4.8 × 10 5 cells/ml), small phytoplankton (smaller than 0.5-1 × 1-2 µm in cell size, picophytoplankton) were distributed in the halocline (depth 2-12 m, 4-14 practical salinity units) of the saline meromictic lake, Lake Suigetsu (35°35′ N, 135°52′ E), located in the central part of the coast of Wakasa Bay along the Japan Sea in Fukui Prefecture, Japan. Vertical distribution of phytoplankton revealed that the maximum number of picophytoplankton was always observed near or a little deeper than the oxic-anoxic boundary layer (depth 5-6 m); they were dominant phytoplankton in the water layer deeper than the oxic-anoxic boundary from July to late September 2005. Spectral analysis of autofl uorescence emitted from the particle fractions smaller than 5 µm measured with a spectrofl uorometer and from individual cells measured with a microscope photodiode array detector revealed that the major component of picophytoplankton was phycoerythrinrich, unicellular cyanobacteria (picocyanobacteria). Eukaryotic phytoplankton about 2.5 µm in diameter were also found, but the numbers were low. Fluorescence intensity of chlorophyll a at 685 nm (room temperature) emitted from the particle fractions smaller than 5 µm was increased by the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. These observations indicated that at least some picophytoplankton had a functional photosystem II in the halocline where sulfi de, the potential inhibitor of oxygenic photosynthesis, was always present. The large abundance together with their physiological potency suggest that picophytoplankton are one of the important primary producers in the halocline of Lake Suigetsu.Electronic supplementary material Supplementary material is available in the online version of this article at http://dx.

Comprehensive Detection of Phototrophic Sulfur Bacteria Using PCR Primers That Target Reverse Dissimilatory Sulfite Reductase Gene

“…Green sulfur bacteria of Prostecochloris, Pelodictyon, and Chlorobium have been detected previously mainly in or just below the oxycline of Lake Suigetsu by denaturing gradient gel electrophoresis (DGGE) (17). A recent study found bacteriochlorophylls e and d in the water in and around the oxycline of Lake Suigetsu (23). These results were consistent with our results in the clone library analysis of dsrA.…”

“…Purple sulfur bacteria were occasionally detected at the chemocline of Lake Kaiike, a small saline meromictic lake in Japan similar to Lake Suigetsu (8), while no purple sulfur bacteria were detected in Lake Suigetsu either by DGGE (17) or in photopigment analyses (23). Sequencing of clones derived from our phototrophic sulfur bacterial dsrA-specific PCR, however, showed the presence of purple sulfur bacteria in the waters of Lake Suigetsu.…”

“…The primers were tested using water samples from a meromictic lake, where phototrophic sulfur bacteria often form dense blooms in and/or just below the oxycline during the summer (17,23).…”

“…We used samples of anoxic water from the meromictic Lake Suigetsu, characterized by a permanent large of oxycline at a depth of between 3 and 8 m separating the aerobic freshwater epilimnion from the anaerobic, saline, sulfidogenic hypolimnion (10), since both sulfate-reducing bacteria and phototrophic sulfur bacteria were present in the anaerobic layers of the lake (13,14,17,23). To provide final confirmation of the specificity of the primers, we sequenced 79 clones (38 clones from a depth of 7 m and 41 clones from 10 m) derived from anoxic water samples of Lake Suigetsu amplified using the primers.…”

Abundance and size structure of planktonic protist communities in a Neotropical floodplain: effects of top-down and bottom-up controls

“…A filter set that provided blue excitation (450 to 490 nm) was used to detect chlorophyll a, while green excitation (546 nm) was used to detect phycoerythrin and phycocyanin pigments of some cyanobacteria (Waterbury et al,1986). 30 fields/100 cells were counted to estimate the abundance (Okada et al, 2007) and 50 cells of each sample were measured in length and width to estimate the biovolume (Waterbury et al,1986).…”