[Critical collapse pressure of gas vesicles in six strains of cyanobacteria].

Two methods including filtration (vacuity is 0.02 MPa) and centrifugation ( < 500 r/min) were applied to concentrate algal biomass, and capillary compression tube and the concentrated algae suspensions, critical pressure distribution of gas vesicles in six cyanobacteria were also investigated. The results showed that unicellular Microcystis aeruginosa cells couldn't be concentrated effectively by filtration or centrifugation, but colony of Microcystis wesenbergii and Microcystis flosaquae, and filament of Planktothrix mougeotii could be concentrated by centrifugation and filtration respectively. Both filtration and centrifugation had a negligibly impact on gas vesicles content of cells, and the loss of gas vesicles was lower than 7%. The mean critical pressure values of five strains Microcystis were very close, which ranged from 0.64 to 0.67 MPa, and the mean critical pressure of P. mougeotii was 0.715 MPa. All of the six cyanobacteria were isolated from three shallow lakes, and their mean critical pressure values were lower than those cyanobacteria that inhabit in deep lakes or reservoirs. At the same condition of illumination density and temperature, turgor pressures of two unicellular Microcystis were higher than those of colonial Microcystis.

[Effects of EDTA and iron on growth and competition of Microcystis aeruginosa and Scenedesmus quadricauda].

Not only population density of phytoplankton but also its community structure were influenced by iron limitation. The growth and competition of a cyanobacterium Microcystis aeruginosa and a green alga Scenedesmus quadricauda at different iron and EDTA concentrations were investigated using batch cultures. The results showed that the growth of M. aeruginosa was significantly inhibited whereas S. quadricauda wasn't when EDTA at high concentrations (> or = 13.5 micromol/L), and consequently, it favored the dominance of S. quadricauda. Moreover, increasing iron concentration from 3 micromol/L to 18 micromol/L could greatly alleviate the growth inhibition of M. aeruginosa while increasing concentration of other microelements e.g. B, Mn, Zn, Cu, Mo didn't. These results suggest that high EDTA concentration decreases iron availability for M. aeruginosa, but not for S. quadricauda. The reason that the two algae respond to high EDTA concentrations differently is that their adsorption strategies for iron should be different.