Ectoenzyme activity and bacterial secondary production in nutrient-impoverished and nutrient-enriched freshwater mesocosms.

This report presents results on relationships between the kinetics (Vmax and Km) of ß-glucosidase (GLCase) and aminopeptidase (AMPase) activity, and dissolved organic carbon (DOC) and bacterial secondary production in freshwater mesocosms of differing degrees of eutrophication. These relationships varied in different mesocosms and depended on the trophic status of water and the exudation rates of organic carbon (EOC) by phytoplankton. Close coupling of bacterial production to Vmax of GLCase activity was observed only in nutrient-enriched mesocosms. The relationship between GLCase and DOC content was also significant in enriched water. There was no correlation between the Vmax, of GLCase and DOC and bacterial production in nutrient-impoverished and control (mesotrophic) enclosures. However, the Vmax of AMPase correlated well to DOC and bacterial production in these mesocosms. AMPase activity did not correlate with DOC and bacterial production in nutrient-impoverished mesocosms. There was no relationship between bacterial biomass and enzyme activity in all studied mesocosms. Comparison of the rates of phytoplankton production of EOC and rates of the bacterial organic carbon demand (BOCD) in nutrient-impoverished mesocosms showed that EOC flux constituted, on average, 90% of BOCD. However, in nutrient-enriched mesocosms EOC contributed only, on average, 27% to the BOCD; thus, in these mesocosms, bacteria were probably organic-carbon limited. It is hypothesized that to bypass substrate limitation, bacteria produced GLCase and AMPase. These enzymes had a high specific activity and high affinity to their substrates and efficiently hydrolyzed polysaccharides and proteins, thereby supplying microorganisms with readily utilizable products of enzyme catalysis.

Kinetics of alkaline phosphatase activity and phosphorus availability for phytoplankton and bacterioplankton in lake plu\see (North German Eutrophic Lake).

Annual studies of kinetics of alkaline phosphatase (APA) activity and phosphorus availability for microplankton in the photic zone of an eutrophic lake are reported. The total APA activity of microplankton varied strongly. Vmax was highest during summer P depletion, and in autumn and winter total APA activity was low. The total APA specific activity of the microplankton was also highest (average 3.55 pmole PO4 (3-) ng ATP(-1) min(-1)) when ambient orthophosphate concentrations were very low. Both Vmax and specific APA activity were not dependent on the biomass of microplankton; they were strongly affected by P available for microplankton. A differential filtration technique was used for separation of microplankton into two size classes, i.e., algal, larger than 3µm, and bacterial fraction with size 0.2-3.0µm. The algal size fraction had lower specific APA activity (average 1.224 pmole PO4 (3-) ng ATP(-1) min(-1)) and higher KM values (38.8µmole × liter(-1)) than microorganisms which were smaller than 3µm (2.011 pmole PO4 (3-) ng ATP(-1) min(-1) and 25.4µmole liter(-1), respectively). The KM values of free, dissolved APA (36.8µmole liter(-1)) indicated that free APA was probably released by algae. Phytoplankton were major APA activity producers in the photic zone of the lake from March to November, and their activity constituted, on the average, 48.6% of the total APA activity in the water. Bacteria were the dominant APA activity producers in winter (41.3-44.9%); however, during other periods they contributed significantly (average 21.7%) to total APA activity. When surplus constituted less than 10% of particulate P in seston, phytoplankton produced high specific APA activity, and when surplus P was higher than 15%, the specific APA activity of phytoplankton size fraction rapidly decreased. APA of the bacterial size fraction of the seston was not affected by P concentrations. Orthophosphate was a competitive inhibitor of APA produced by microorganisms of the size fraction larger than 3.0µm, and increasing concentrations of inorganic phosphate caused an increase in KM values. The hypothetical metabolic-coupling between phytoplankton and bacterioplankton in the phosphorus cycle in conjunction with carbon metabolism in the lake is discussed.

Plankton photosynthesis, extracellular release and bacterial utilization of released dissolved organic carbon (RDOC) in lakes of different trophy.

The major objective of these studies was to assess the extent of the flow of released dissolved organic carbon (RDOC) from phytoplankton to heterotrophic bacteria. The second aim was to test Nalewajko and Schindler's (1976) hypothesis that the percentage of extracellular release (PER) of RDOC by phytoplankton is higher in oligotrophic than eutrophic waters. The studies on the relationship between the bacterial assimilation of RDOC and productivity of phytoplankton in the lakes of different trophy have shown a direct correlation. It was observed that higher utilization rate of phytoplankton RDOC occurred in lakes with higher primary production. The inverse relationship between productivity of lakes, i.e. trophy of waters, and amount of RDOC or PER is closely dependent on the heterotrophic activity of bacteria in waters.

Molecular weight fractionation of dissolved organic matter (DOM) released by phytoplankton.

The application of an ultrafiltration procedure for fractionation of molecular weight of dissolved organic matter (DOM) extracellularly released by phytoplankton is described. Seven ultrafiltration membranes Diaflo (Amicon Corp. USA), with range 500--300,000 molecular weight (MW), were used for separation of different molecular weight compounds released by phytoplankton in Rhode River estuary of Chesapeake Bay, and their composition was determined. Percentage of extracellular release of DOM by phytoplankton varied from 3.92--68.07% of total carbon fixed in photosynthesis. The composition of algal extracellular products varied with different phytoplankton populations. However, two fractions of molecular weight compounds dominated in the composition of DOM released, i.e. a low molecular weight fraction of less than 1,000 MW and the fraction between 10,000--30,000 MW. The ultrafiltration procedure is effective for studying the composition of DOM released by phytoplankton in natural waters.

Extracellular release in Chlorella vulgaris culture and the role of bacteria accompanying - algae in this process.

The effect of different concentrations of nitrogen and phosphorus on extracellular release was investigated. Phosphorus induced the enhanced extracellular release of metabolites by Chlorella vulgaris. No influence of nitrogen on extracellular release was observed. In the initial stages of C. vulgaris culture the algae release was observed. In the initial stages of C. vulgaris culture the algae release compounds readily assimilated by the accompanying bacteria, hence the observed drop of percentage of extracellular release (PER) in culture medium caused by the bacteria. Both, the glycolic acid and the products of photoassimilation released to the environment in the first stages of cultivation were assimilated by the bacteria accompanying-algae at a similar rate. The ageing of C. vulgaris culture resulted in the accumulation of extracellularly released metabolites and increase of PER. These products were not assimilated by the bacteria present in the algal culture.

Primary production and extracellular release by phytoplankton in some lakes of the Masurian Lake District, Poland.

The primary production and extracellular release by phytoplankton were measured at different depths of Mikolajskie Lake, Rynskie Lake and Beldany Lake (Masurian Lake District, Poland). The release of dissolved organic compounds was found to be related to the rates of primary production. The percentage of extracellular release (PER) of organic matter in the photic zone showed an inverse relationship with particulate production and chlorophyll alpha concentration. The highest PER was determined in the epilimnion of the studied lakes, where also increased release was observed. The higher release of algal products of photosynthesis in the photic zone than in the profundal is probably caused by the inhibition of physiological activity of bacteria by antibacterial substances produced by algae. The substances released by algae in the profundal are taken up by aquatic bacteria which explains the lower release and PER measured.

Some factors affecting the heterotrophic activity of bacteria in lake.

The heterotrophic activity of aquatic bacteria was measured by incorporation of 3H-thymidine, uptake of 14C-sodium acetate and mineralization of 14C-acetate. The temperature of water, oxygen content and concentration of chlorophyll a were also measured in the studied lakes. The obtained results of the studied processes in the surface layer and epilimnion were distinguished by negative correlation coefficients. A distinctive feature is the relation between chlorophyll a concentration in the water bodies and heterotrophic activity of bacteria. This indicates a negative dependence between these processes and phytoplankton activity in the photic zone. In contrast a positive relationship between phytoplankton activity and heterotrophic activity of bacteria was found in the metalimnion and hypolimnion of the studied lakes.

The estimation of extracellular release by phytoplankton and heterotrophic activity of aquatic bacteria.

The actual extracellular release of organic matter by algae was determined in water samples in which the heterotrophic activity of bacteria was inhibited by gentamycin. Gentamycin rapidly and efficiently inhibited the activity of aquatic bacteria without affecting phytoplankton metabolism. Aquatic bacteria utilized the products of algal extracellular release. The amount of algal photosynthetic products metabolized by bacteria can be taken as a measure of their heterotrophic activity in waters.

Extracellular release of organic products and growth of bacteria in Anabaena cylindrica (blue-green alga) culture.

The studies were made with stationary cultures of Anabaena cylindrica (blue-green alga). The bacterial microflora accompanying blue-green algae is subject to succession and elimination in the course of growth. The bacteria are able to utilize organic products released by the blue-green algae. The products released by A. cylindrica to the environment are peptide-like compounds.

Degradation of urea by bacteria and algae in mass algal cultures.

Studies were conducted to determine the role of bacteria and algae in the degradation of urea in industrial waste waters. The microflora accompanying algae in continuous cultures on waste waters from the nitrogen fertilizers industry was found to include bacteria capable of intensive degradation of urea. Urea hydrolyzing bacteria are with time eliminated from the algal culture. This elimination can be attributed to algal metabolites which inhibit the development of sensitive bacteria. The Chlorella vulgaris strain used in the treatment of wast waters from the nitrogen fertilizers industry did not hydrolyse urea.

Inhibitors produced by algae as an ecological factor affecting bacteria in water. II. Antibacterial activity of algae during blooms.

It has been found that during algal blooms in an eutrophic lake occurs elimination and selection of bacteria. In this period a strong decrease in number of bacteria in the water was observed. The effect of the antibacterial substances produced by algae on the growth and respiration of bacteria isolated from the lake was investigated. The bloom forming algae were found to produce substances inhibiting the growth and respiration of Gram positive bacteria. Gram negative rods were resistant to the action of these substances. The algal substances inhibited also degradation of organic matter in the lake but only in the euphotic zone.

Inhibitors produced by algae as an ecological factor affecting bacteria in water ecosystems. I. Dependence between phytoplankton and bacteria development.

Studies were conducted on the eutrophic Mikolajskie Lake in the Mazurian Lake District. Over the period of investigation three maxima of the development of phytoplankton were observed: in the spring, summer and autumn. During the algal blooms the total number of bacteria in the lake strongly decreased and was between several and a dozen time smaller than between blooms. The decrease in the total number of bacteria in water and the elimination of gram positive bacteria during the algal blooms is most probably caused by the production by the algae of substances inhibiting bacterial development.