EXTRACELLULAR ENZYMES OF THE MICROCYSTIS AERUGINOSA PCC 7813 STRAIN ARE INHIBITED IN THE PRESENCE OF HYDROQUINONE AND PYROGALLOL, ALLELOCHEMICALS PRODUCED BY AQUATIC PLANTS(1).

Several cyanobacterial species have a high potential to dominate in marine environments and freshwater reservoirs, and the ecological and physiological reasons for this phenomenon are not understood comprehensively. In this study, the ability of a Microcystis aeruginosa Kütz. strain to produce free dissolved enzymes was documented. We have observed that this highly toxic strain releases alkaline phosphatase, leucine aminopeptidase, and ß-glucosidase into the ambient environment. Additionally, the inhibitory activity of selected phenols produced by aquatic plants on the activity of these enzymes was analyzed. The investigated compounds, pyrogallol and, to a lesser degree, hydroquinone, decreased the activity of extracellular enzymes produced by M. aeruginosa, with leucine aminopeptidase being the most sensitive to the inhibitors. The noncompetitive character of enzymatic inhibition suggests that the polyphenols produced by aquatic plants are able to influence the activity of different extracellular or membrane-bound enzymes.

Degradation of microcystin-LR by ozone in the presence of Fenton reagent.

In this study the effectiveness and feasibility of the degradation of microcystin-LR (MC-LR) using a combined method ozone/Fenton reagent was investigated. The decomposition of the toxin was determined by the chromatographic technique. The effect of the Fenton reaction on the ozonation was observed at various concentrations of ozone at pH 3.0 and 6.8. A low concentration of ozone (0.01 mg/L) given simultaneously with Fenton reagent was more effective in MC-LR degradation than ozone or Fenton reagent treatment individually regardless of the pH. At higher concentrations of ozone the use together with Fenton reagent at pH 6.8 was less efficient in MC-LR degradation than treatment with ozone alone, whereas at pH 3.0 Fenton process turned out to be more effective. The mixture of ozone and hydrogen peroxide was more striking than using ozone with Fenton reagent regardless of the pH. The complete degradation of MC-LR was achieved using ozone alone at a concentration of 0.10 mg/L, whereas the same result using ozonation with Fenton reagent required a dose of ozone of 0.20 mg/L at pH 6.8. In acidic pH the total removal of MC-LR was achieved using ozone alone at a concentration of 0.20 mg/L and the same result was obtained for the combined method of ozone/Fenton reagent.

The alteration of Microcystis aeruginosa biomass and dissolved microcystin-LR concentration following exposure to plant-producing phenols.

Plant-producing phenols could strongly inhibit the growth of toxic cyanobacteria genera, but the ecological consequences of this action are still unknown. In this work, the activity of selected phenols in relation to the strain Microcystis aeruginosa was investigated. We have found that the mechanism of the growth inhibition could involve both the inhibition of the photosynthetic system and the alkaline phosphatase activity. The excretion of a high amount of microcystin-LR to the environment was observed as a final result of the application of phenols to the cyanobacterial culture. This finding suggests that first of all an algicidal effect of phenols was probably the reason of the cyanobacterial biomass decreasing.

THE EFFECT OF ABSCISIC ACID AND FUSICOCCIN ON MALIC ACID CONCENTRATION IN PULVINI OF PHASEOLUS COCCINEUS L.

Fusicoccin and abscisic acid can modify the movements of some nyctinastic plants. This paper reports the effects of these two compounds on the concentrations of malic acid in pulvini of Phaseolus coccineus L. in the transition period of two phases of the circadian rhythm. The concentrations of malic acid in the two parts of the pulvinus, extensor and flexor, depend upon the phase of leaf movements. Abscisic acid and fusicoccin significantly affected the content of malic acid in leaves compared with the control. In the two phases of the diurnal cycle investigated, abscisic acid markedly reduced the production of malic acid in the flexor and extensor regions of the pulvinus, and treatment with fusicoccin produced small but distinct increases in the concentration of malic acid in the same regions. The results are discussed with particular reference to the effect of abscisic acid and fusicoccin on the activity of the H+ pump associated with the control of turgor in cells.