Search

To suppress the occurrence of phytoplankton blooms dominated by cyanobacteria, control measures were implemented during the bottleneck stages of algal succession, overwintering and pre-recruitment, using a combination of chemical and biological algicides. First, water and sediment samples were incubated in the laboratory to determine the threshold temperature for cyanobacteria recruitment. Second, the functional characteristics of candidate algicides were screened. Third, an in situ pilot experiment was conducted to test the feasibility of this method. Our results indicated that (1) the recruitment of cyanophytes was initiated at 15°C, (2) H202 and rice straw were the optimum algicides and their optimal concentrations were 10 mg/L and 1 g/L, respectively, and (3) following the combined application of H202 and rice straw during overwintering and pre-recruitment, the biomass of cyanobacteria decreased by 27.1% during recruitment and by 53.2% during the first algal bloom. These results suggested that the combined application of H202 and rice straw, during the bottleneck stages of algal cycling, suppressed the recruitment of cyanobacteria and decreased the magnitude of algal blooms, thus offering a promising choice for prevention of cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Thirty Microcystis colonies, belonging to three species (Microcystis aeruginosa, Microcystis flos-aquae, and Microcystis wesenbergii) were isolated from Lake Taihu and Lake Chaohu in China. Bacterial communities associated with the single Micro cystis colonies were investigated using a seminested polymerase chain reaction-amplification along with denaturing gradient gel electrophoresis (DGGE). The bacterial communities of most colonies of the same Microcystis species in each lake tended to be similar. This indicates that species-specific associations may exist between colony-associated bacteria and Microcystis spp. Sequence analysis of dominant DGGE bands revealed that the dominant bacterial groups associated with Microcystis colonies were Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, Deinococcus-Thermus, and Gemmatimonadetes. Phylotypes related to Pseudomonas sp., Serratia sp., and Flexibacteraceae were dominant in colonies of M wesenbergii, M flos-aquae, and M aeruginosa, respectively. [ABSTRACT FROM AUTHOR]

Fourteen bacteria were isolated from a natural bloom of Microcystis aeruginosa colonies collected from Lake Taihu. According to 16S rDNA sequence analysis, seven isolates were related to Alphaproteobacteria including the genera Erythromicrobium, Porphyrobacter, Sphingomonas, Sandarakinorhabdus, Afipia, and two unclassified genera. Six isolates were affiliated with the genera Aquimonas, Pseudomonas, Acinetobacter, and Stenotrophomonas of the Gammaproteobacteria group. One isolate was related to Sphingomonadales (Betaproteobacteria). In subsequent assays, the bacterial isolates variously affected the growth of M. aeruginosa (i.e., positively or negatively). All bacterial isolates were able to grow in a medium in which the only carbon source was filtrate of the M. aeruginosa culture, indicating that these bacteria may be associated with M. aeruginosa not only as a substrate for colonization but also as energy source. [ABSTRACT FROM AUTHOR]

The effects of pyrophosphate and polyphosphate on the growth of Microcystis aeruginosa and Chiorella pyrenoidosa were studied in unialgal cultures and in cultures separated by a dialysis membrane. M. aeruginosa and C. pyrenoidosa were able to similarly utilize pyrophosphate and polyphosphate, but their growth rates and cell densities were low in comparison with those in the orthophosphate controls. C. pyrenoidosa had a higher growth rate than M. aeruginosa in both unialgal and the separated cultures; moreover, C. pyrenoidosa had a greater ability to utilize phosphorus than M. qeruginosa. But because the C. pyrenoidosa population developed early but then declined, M. aeruginosa eventually became dominant in the separated cultures. Therefore, the interaction between M aeruginosa and C. aeruginosa might be complex because of an allelopathy effect, and nutrient competition is not the only factor determining species dominance in the phytoplankton assemblage. [ABSTRACT FROM AUTHOR]

We assessed the response of Chiorella pyrenoidosa to substance(s) from the rotifer Brachionus calyciflorus using flow cytometry and PHYTO-PAM fluorometry. The cell density of C. pyrenoidosa in the rotifer water treatment was significantly higher than that in the control, suggesting that substance(s) from the rotifer stimulated the alga to grow faster. Additionally, the cell size of C. pyrenoidosa in the rotifer water treatment was consistently smaller than that in the control. Esterase activity and chlorophyll fluorescence of C. pyrenoidosa cells in the rotifer water treatment increased and were higher than those in the control but were not significantly different. The maximal efficiency of PSII (Fv/Fm) and the effective quantum yield of PSII (ΦPSII) of C. pyrenoidosa in the rotifer water were also consistently higher than those in the control, although these differences also were not significant. The pattern, however, does seem to support the idea that C. pyrenoidosa responded to infochemical produced by the rotifer. [ABSTRACT FROM AUTHOR]

Flow cytometry (FC) was used to determine effects of tetrabromobisphenol A (TBBPA) on the green alga Chlorella pyrenoidosa (C. pyrenoidosa) by evaluating esterase activity, membrane integrity, concentrations of intracellular reactive oxygen species (ROS) and chlorophyll a (Chl-a) auto-fluorescence. TBBPA can inhibit esterase activity. Esterase activity was inversely proportional with TBBPA with a 24 h EC50 value of 3.13 mg TBBPA/L. After 48 h of exposure to TBBPA intracellular ROS was significantly greater than in the unexposed cells. TBBPA inhibited Chl-a fluorescence after 168 h. Concentrations of ROS were directly proportional to both magnitude and duration of exposure and was inversely proportional to cellular Chl-a. FC was useful as an integrated, ecologically relevant, measure of a functional response of the algae. The possible action pathway of TBBPA in C. pyrenoidosa is that TBBPA can cause toxic effects on esterase activity. As concentrations and exposure time increased, TBBPA change the ROS level in the internal. The role of anti-oxidative action is marked and significant at the duration of 48 h exposure, compared to the control. This suggested there was a redox cycle. TBBPA changes physiological status of cells, further decreased Chl-a fluorescence indicating inhibition. [ABSTRACT FROM AUTHOR]

Variations of δ13C and δ15N in dissolved organic matter and size-fractionated plankton, ranging from 0.7 to 200 μm, were studied in Taihu Lake on two occasions during a cyanobacterial bloom. Paired-sample t-tests indicated that stable isotope ratios of samples collected did not significantly differ from each other on the two sampling dates. The overall correlation between δ13C and δ15N of forty taxa of the plankton community was weak (r2=0.227, N=40), indicating a non-trophic enrichment effect in δ13C. The δ15N values increased along with plankton size. We used δ15N as an index of the trophic level and demonstrated that logarithmic organism size was positively and significantly related to trophic level, indicating that a size-dependent approach is preferable in the analysis of trophic isotope enrichment in microplankton food webs. [ABSTRACT FROM AUTHOR]

The effect of darkness on the cyanobacterium Microcystis aeruginosa and the green alga Chlorella pyrenoidosa were observed. Cell growth, metabolic activity, chlorophyll a fluorescence, cell size, and maximum quantum yield (Fv : Fm) were determined. M aeruginosa and C. pyrenoidosa both maintained their initial cell abundances while in the dark, but they showed distinctly different physiological responses to darkness. During the dark period metabolic activity decreased slightly, cell size and Fv : Fm decreased significantly, and chlorophyll a increased markedly in M. aeruginosa cells. However, metabolic activity, cell size, and Fv : Fm decreased dramatically, and chlorophyll a decreased trivially in C. pyrenoidosa cells. After re-illumination, metabolic activity, cell size, and Fv : Fm of M aeruginosa and metabolic activity, chlorophyll a, and Fv : Fm of C. pyrenoidosa recovered significantly. No recovery was found in either chlorophyll a of M aeruginosa or cell size of C. pyrenoidosa. Compared with C. pyrenoidosa, M. aeruginosa is more capable of withstanding the dark circumstances, which are unfavorable to the growth of alga but usually exists in water and sediment of eutrophic lakes. Its greater tolerance of darkness may be one of the reasons that M. aeruginosa is commonly the dominant species in eutrophic lakes. [ABSTRACT FROM AUTHOR]

Lake water, which contained an abundance of zooplankton, was passed through a 0.15 μm membrane filter, and 20 ml were immediately added to 80 ml Suspensions of Microcystis aeruginosa in either exponential or late stationary growth phase. In the control system, 20 ml of BG-11 medium were added. After two days, colony formation was observed in the treatment of the exponential growth phase M. aeruginosa, whereas no colonies were formed in the control. The mean number of cells per unit of M. aeruginosa increased significantly compared with that in the control (P<0.05). However, late stationary phase M. aeruginosa populations, both in the control and in the treatment, were strongly dominated by unicells and paired cells, and no colonies were formed. As a consequence, no significant difference in the mean number of cells per unit was detected between the control and the treatment (P>0.05). However, no significant difference in the growth rate was detected between the control and the treatment (P>0.05), regardless of growth phase. These results indicated that any chemicals released from zooplankton had no influence on the growth of M. aeruginosa, and the inducible colony formation in M. aeruginosa was related to physiological phase. [ABSTRACT FROM AUTHOR]