David Wynne

HOT WATER EXTRACTABLE PHOSPHORUS—AN INDICATOR OF NUTRITIONAL STATUS OF PERIDINIUM CINCTUM (DINOPHYCEAE) FROM LAKE KINNERET (ISRAEL)?1

The intracellular levels of hot water extractable and total phosphorus were determined in the dinoflagellate Peridinium cinctum. f. westii (Lemm.) Lef. for natural samples from the bloom in Lake Kinneret and from laboratory cultures. Amounts of phosphorus (P) in the hot water fraction, relative to total cellular phosphorus, were similar in lake Peridinium and in cells grown in high ambient orthophosphate (Pi) media (3–6 mg P · l−1). The absolute amounts of hot water extractable P in natural cell and those cultured at lower Pi concentrations (0.02–0.05 mg P · 1−1) were similar, although average Pi in lake water were 4 μg · l−1. Under most growth conditions the hot water extract contained approximately equal amounts of molybdate reactive phosphorus (MRP) and non‐MRP. Short chain (6–9 units) polyphosphates (mol wt 630–950) probably constituted the bulk of the non‐MRP pool, which was hydrolysable by alkaline phosphatase and may serve as a precursor for a more permanent P store. Intracellular P levels and distribution were not directly dependent on external Pi concentrations but may be determined by the N:P atomic ratio or overall external ionic milieu. Peridinium grown in low ambient Pi released significant amounts of non‐MRP compounds. In Lake Kinneret, for at least most of the bloom period, Peridinium does not appear to be limited by P supply.

ANTIOXIDATIVE PROTECTION OF PERIDINIUM GATUNENSE IN LAKE KINNERET: SEASONAL AND DAILY VARIATION1

A comprehensive antioxidative mechanism was found in the freshwater dinoflagellate Peridinium gatunense Lemm. during the spring bloom in Lake Kinneret. Ascorbate was present throughout the bloom period and was responsible, together with catalase, for the elimination of photosynthetically produced H2O2. As glutathione concentrations and ascorbate regenerative enzymes were negligible during mid‐spring, ascorbate was presumably biosynthesized during the photosynthetically active period. Antioxidative activity increased overall at the end of the spring in conjunction with elevated ambient stress conditions, for example high light. Under such circumstances, ascorbate was regenerated. Ascorbate levels doubled when cells were exposed to an increase in irradiance from 60 to 600 μmol photons·m−2·s−1, and on addition of H2O2, concentrations increased a further 20‐fold. Significant antioxidative activity was also noted in the dark, although this was dependent on the presence of H2O2. Diurnal changes in antioxidants and their regenerative enzymes were observed. The activities of mono‐dehydroascorbate reductase, glutathione reductase, and ascorbate concentrations showed ultraradian periodicity and were completely in phase throughout the day/night period. Dehydroascorbate reductase activity and glutathione concentrations were also in phase but showed aperiodic variation, as did ascorbate peroxidase activity. Superoxide dismutase and catalase activities were generally out of phase during the 24‐h period but did show ultraradian periodicity. Lake samples entrained under constant light revealed an inate 12‐h rhythm for catalase activity, during at least 36 h.

Phosphatases revisited : analysis of particle-associated enzyme activities in aquatic systems

A modified assay for alkaline or acid phosphatases associated with microorganisms in aquatic environments has been developed. This is based on collecting microplankton on filters and subsequently determining the enzyme activities spectrophotometrically or fluorometrically, using p-nitrophenyl-phosphate or 4-methylumbelliferyl phosphate, respectively as substrates. The assay is simple and rapid, and has the further advantage of permitting phosphatase activities to be assigned to specific size fractions of the natural microplankton. In samples taken from Lake Kinneret and a nearby reservoir, a consistently high proportion of the total alkaline or acid phosphatase activity was associated with the size fraction < 0.8 µm > 0.2 µm indicating the potentially high contribution of bacteria to these activities. This approach can also be used to examine the enzymatic potential of microplankton to release orthophosphate from other organo-phosphate substrates.

SUPEROXIDE DISMUTASE ACTIVITY IN PERIDINIUM GATUNENSE IN LAKE KINNERET: EFFECT OF LIGHT REGIME AND CARBON DIOXIDE CONCENTRATION1

The activity of superoxide dismutase (EC 1.15.1.1, superoxide: superoxide oxidoreductase) (SOD) was determined in Peridinium gatunense Lemm. under natural and controlled conditions. SOD activity increased toward the end of the spring algal bloom in Lake Kinneret simultaneously with maximal photosynthetic activity and conditions of elevated ambient stress such as high irradiance. Activity staining of native polyacrylamide gel electrophoresis gels of bloom samples showed a similar pattern to the spectrophotometrically measured SOD. Both Mn SOD and CuZn SOD were present, however no Fe SOD was found in Peridinium. One of three isoenzymes of Mn SOD showed marked differential regulation of activity under stress. An increase in the quantity of the 32‐kDa Mn SOD polypeptide during the bloom was found to be unrelated to senescence; it was assumed that this polypeptide was induced by stress. Thus, SOD in Peridinium undergoes physiological and molecular acclimation to seasonal environmental changes. When Peridinium was exposed to various O2 and CO2 concentrations in culture, CuZn SOD significantly increased under high C02 concentrations and normoxic conditions (20% O2). However, at high irradiances, Peridinium cultures exposed to low and high CO2 concentrations also had similar CuZn SOD activity. It was concluded that stressful irradiance is the overriding cause of increased SOD activity in both lake samples and in cultures of Peridinium.

Phosphatase Activities in Lake Kinneret Phytoplankton

Aquatic microorganisms (phytoplankton, bacteria) require a constant supply of nutrients in order to grow and divide and to carry out the multitude of metabolic processes occurring in the cell. The inorganic forms of macronutrients such as P and N are generally the only compounds that can be directly taken up and utilized by algae although, it has been shown that both organo-P and organo-N compounds can be used as indirect sources of nutrients (Antia et al., 1975; Cembella et al., 1984a; 1984b).

Seasonal and environmental influences on antioxidative protection inPeridinium gatunense in Lake Kinneret

As the only freshwater lake in Israel, Lake Kinneret serves a number of important functions which directly rely upon the viability of the water. The annual outbreak of a dinoflagellate bloom strictly governs the nature of the macro and micro food web and ultimately determines water quality.The freshwater dinoflagellatePeridinium gatunense is subject to a wide range of environmental stresses throughout the spring bloom period. It was confirmed that SOD played an important antioxidative maintainance role throughout the bloom, especially during periods of relatively high photosynthetic activity (820 mg C m−2 day−1), when activity reached ≈500 Units SOD mg protein−1. In addition, high light stress (>300 μmol photons m−2 s−1) induced SOD activity, despite the low dissolved inorganic carbon (DIC) concentrations at the end of the bloom (1.3 mM). Catalase activity was only significant at the end of the bloom, peaking at 120 μmol O2 mg protein−1 min−1, when induced by photorespiratory activity.A series of experiments withPeridinium cultures showed that 2 × 10−4 M ascorbate inhibited catalase activity >50% within 15 min incubation, bothin vivo andin vitro. It is suggested that the high concentrations of ascorbate, found previously inPeridinium during early and mid-bloom (0.2–1.6 mM), not only eliminate H2O2 build-up, but also prevent (directly or indirectly) the induction of catalase.

THE SPATIAL DISTRIBUTION OF ENTERIC BACTERIA IN THE JORDAN RIVER–LAKE KINNERET CONTACT ZONE

Lake Kinneret, in the north of Israel, is the only freshwater body in the country. It supports many activities, including recreation, tourism, and a commercial fishing industry, but its prime function is to supply water to other parts of the country. Consequently, maintaining a high water quality of the lake is of prime importance. The major part (some 90%) of the annual runoff of water enters Lake Kinneret from the north via the Jordan River during the autumn–winter floods. During this period, the river carries sediments, toxic agricultural chemicals, and allochthonous organisms, including pathogenic bacteria, into the lake. The Jordan River–Lake Kinneret contact zone is characterized by a rapid transformation from a riverine to a lacustrine water mass within 700 m from the river mouth, with very high spatial gradients of practically all hydrodynamic, hydrophysical, hydrochemical, and microbiological parameters. Previous measurements have shown that the distribution of enteric bacteria in the river–lake contact zone is related to the attenuation of river current flows. The aim of this study was to determine whether the change in the number of enteric bacteria (fecal coliforms, Escherichia coli, and Klebsiella spp.) in the water of the River Jordan–Lake Kinneret contact zone was due to sedimentation or to dilution. The data were then utilized to build a conceptual model explaining the distribution of biological pollutants (bacteria) in the river–lake contact zone of a shallow tropical lake, using the microbial communities of the River Jordan–Lake Kinneret contact zone, as an example.

Physiological variability within a Peridinium gatunense (Dinoflagellate) population during its patchy bloom in Lake Kinneret

Patchy blooms of dinoflagellates are a universal phenomenon frequently observed in marine and freshwater environments. In Lake Kinneret (Sea o f Galilee ), Israel, the spring bloom of the dinoflagellate Peridinium gatunense is characterized by a spatial heterogeneity, concomitant with a diurnal vertical migration of the population (POLLINGHER 1988). This migration was attributed to active movement toward the layer with optimum light intensity ( during periods o f daylight and calm) and wind-created shear mixing ( dominate in the evenings) that vertically disperses the accumulated population. Rapid population growth, supported by local supply o f nutrients on one hand and physical processes on the other hand, are major factors governing the formation and persistence o f the patchy population. In an effort to distinguish between physical driving forces and biological processes involved in the patchy phenomenon, we determined the vertical and horizontal distribution of Peridinium population and assessed the physiological status ofthe population at different sites by analyzing pigment and fatty acid composition.