Jürgen Overbeck

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 PO43− 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 PO43− ng ATP−1 min−1) and higher KM values (38.8μmole × liter−1) than microorganisms which were smaller than 3μm (2.011 pmole PO43− 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.

Microbial ecology of Lake Plußsee

Lake Plusssee is a small eutrophic kettle lake in northern Germany. Because it is sheltered and has no inflow from rivers, the Plusssee exhibits stable stratification and is especially suitable for limnological studies. This book presents the results of extensive research conducted on the ecophysiology of micro-organisms - principally bacteria - at the Plusssee over the past several decades. It begins with three chapters on the general limnological state of the lake: physical factors, inorganic nutrients, plankton composition and succession, fish fauna, etc. These chapters are followed by discussions of dissolved organic matter and photosynthetic production of organic matter by phytoplankton. The remainder of the book addresses the dynamics of structure, function and metabolism of the micro-organisms in the Plusssee.

Growth of Scenedesmus obliquus in relation to the supply of iron.

Equal amounts of iron in the form of iron citrate or Fe-EDTA were added to the mineral media. The effect of the two salts upon cell-, substance-and chlorophyll-production of Scenedesmus obliquus cultivated in light-dark-regimes of 15:9 hours was studied.In bubbling cultures at 75 000 Lux the number of cells and the dry substance increased by a factor of about 16-19 with Fe-EDTA and by a factor of 10-12 with iron citrate. With both salts it was possible to get a production of daughter cells twice within one light-dark-cycle of 24 hours.The chlorophyll content of cells and substance cultivated in Fe-EDTA-medium was smaller than that of those cultivated in iron citrate-medium. The possible relations between the amount of chlorphyll and the production of substance are discussed.SummaryEqual amounts of iron in the form of iron citrate or Fe-EDTA were added to the mineral media. The effect of the two salts upon cell-, substance-and chlorophyll-production of Scenedesmus obliquus cultivated in light-dark-regimes of 15:9 hours was studied.In bubbling cultures at 75 000 Lux the number of cells and the dry substance increased by a factor of about 16–19 with Fe-EDTA and by a factor of 10–12 with iron citrate. With both salts it was possible to get a production of daughter cells twice within one light-dark-cycle of 24 hours.The chlorophyll content of cells and substance cultivated in Fe-EDTA-medium was smaller than that of those cultivated in iron citrate-medium. The possible relations between the amount of chlorphyll and the production of substance are discussed.ZusammenfassungGleiche Eisenmengen in Form von Eisencitrat und Fe-EDTA wurden Nährmedien zugesetzt und ihre Wirkung auf Zell-, Substanz-und Chlorophyllproduktion von Scenedesmus obliquus im Licht-Dunkel-Wechsel untersucht.In Durchlüftungskulturen bei 75 000 Lux wurde mit Fe-EDTA eine 16–19fache, mit Eisencitrat eine 10–12fache Substanz- und Zellver-mehrung erzielt. — Mit Fe-EDTA und mit Eisencitrat war eine zweimalige Autosporenproduktion innerhalb eines Licht-Dunkel-Wechsels von 24 Std möglich.Der Chlorophyllgehalt der Trockensubstanz war bei Fe-EDTA-Zusatz geringer als in Eisencitrat-Lösungen. Die möglichen Zusammen-hänge zwischen Chlorophyllgehalt und Substanzproduktion werden diskutiert.

Introduction: Aims, Problems, and Solutions in Aquatic Microbial Ecology

The ultimate aim of ecology is to understand the relationships of all organisms to their environment. Thus, in very general terms, the duty of the ecologist is to examine a particular environment, estimate the abundance of individuals of each species that make up the populations, recognize the communities, and determine their activities and their interactions with both related species and the rest of the community. Stated this way, the problems of the microbial ecologist are obvious and difficult. Semantic problems often arise when a group of botanists, zoologists, and microbiologists try to discuss general ecological theory. Macroecological studies always start by defining the species composition and then proceed to draw certain conclusions on the role of these species in the ecosystem. However, the taxonomic name of the individual isolate of an aquatic bacterium (if any name can be given to it) in only a few instances gives us any indication of its role in the ecosystem. The uncertain state of microbial and especially bacterial classical taxonomy (based on isolation techniques and determination of morphology and in vitro biochemical characteristics of isolates) makes determination of each species of aquatic bacteria almost impossible, except in a few, well-defined instances. As a result, the microbial ecologist has had to rely on methods that have attempted to measure the biomass or activity of a very large conglomerate of coexisting microbial taxa in the aquatic environment. For a long time this has caused the very slow development of microbial ecology concepts and application of a general ecological theory to the microbial ecology.

Biochemisch-oekologische Studien zum Phosphathaushalt vonAzotobacter chroococcum

The influence of different phosphate-compounds, especially of NaH2PO4×2 H2O and fructose-1,6-diphosphate, on nitrogen fixation was studied in three tribes ofAzotobacter chroococcum. In stagnant nonaerated cultures a phosphate-optimum exists for the nitrogenfixation of 90 µg P/ml. Using fructose-1,6-diphosphate the same quantity of nitrogen is fixed with only 50 µg P/ml. In aerated cultures the differences between inorganic phosphate and fructose-1,6-diphosphate (regarding their influence on the nitrogen-fixation) disappear. The quotient: used up C/fixed N also depends on aeration. In stagnant cultures containing organic phosphate-compounds, the C/N-quotient is lower than in those containing inorganic phosphate. In aerated cultures, however, the C/N-quotient is lowest with orthophosphate. The experiments indicate that the phosphate-esters are incorporated into the cell immediately without splitting up on the cell surface. These incorporated phosphateesters in non-aerated cultures, lacking an extensive oxidative phosphorylation, are apparently important for the economy of nitrogen fixation. The ecological role of the incorporation of phosphate-esters is discussed in relation to the fact that a great part of phosphorus in the natural environment is not inorganic but organic phosphate.Zusammenfassung1. Zur Untersuchung der Frage, ob der StickstoffbinderAzotobacter chroococcum organische Phosphorverbindungen verwerten kann, werden Na2HPO4 × 2H2O und Fructose-1,6-diphosphat in ihrer Wirkung auf die Stickstoffbindung und den Zuckerverbrauch des Bakteriums verglichen.2. Es zeigte sich, daß Fructose-1,6-diphosphat einen spezifischen Einfluß auf die Stickstoffbindung ausübt. Denn unter stagnierenden Kulturbedingungen ergibt der Phosphatester eine ökonomischere Stickstoffbindung als anorganisches Orthophosphat, das heißt, es wird mehr Stickstoff je Kohlenstoffmenge gebunden (Abb. 6). Bei Belüftung verschwindet der fördernde Einfluß des Fructose-1,6-diphosphats auf die Stickstoffbindung.3. Die durch Fructose-1,6-diphosphat in unbelüfteten Kulturen gesteigerte Stickstoffausbeute wird dadurch erklärt, daß Phosphatesterbindungen in die Zelle aufgenommen und dem Stoffwechsel zur Verfügung gestellt werden. Bei Belüftung sind Phosphatbindungen dagegen im Zusammenhang mit verstärkten Phosphorylierungen im Überschuß vorhanden. Ein zusätzliches Angebot exogener Phosphatbindungen ist in diesem Falle für den Stoffwechsel bedeutungslos.4. Da am natürlichen Standort Phosphate häufig nicht frei, sondern gebunden vorliegen, wird die ökologische Bedeutung der Befunde diskutiert.

Primary Production, Photosynthesis, and Chlorophylla in the Plußsee

The numerous naturally eutrophic baltic lakes of the East-Holstein district have similar origins but differ in morphometry and trophic levels. Plussee, a small wind-sheltered forest lake (Utermohl 1925), is notable because of its surface area/depth ratio and resulting stable summer stratification (Krambeck 1974). These features in particular have led to numerous and comprehensive studies, among which chlorophyll and primary production have been examined (Ohle 1962, 1964, Overbeck 1979) along with the vertical distribution of chlorophyll (Rai 1975, Krambeck 1981).

Bacterial Life in the Plußsee: General Remarks on Aquatic Microbial Ecology

Until recently it was thought that heterotrophic bacteria in aquatic ecosystems played only a trivial role in organic fluxes and in the functioning of the ecosystem. It was commonly accepted that phytoplankton primary production was utilized predominantly by herbivores (mainly zooplankton) and passed on to the organisms that comprise the grazing food chain. Even in recently published, widely distributed books on limnology, bacteria are still treated as only remineralizers and/or decomposers of organic matter in the energy and organic matter fluxes throughout a lake ecosystem (Wetzel 1983, Cole 1988, Schwoerbel 1987, Sommer 1989, Lampert and Sommer 1993). Very little attention has been directed to further implications of bacterial dynamics for the trophic relationships between these microorganisms and higher trophic levels and the functioning of the lake ecosystem. This notion has changed significantly during the last decade with results from new methods of measuring bacterial production, biomass and activity of bacteria, and their in situ growth rates. In an ecosystem context, these new findings portray bacteria as a very dynamic metabolic and trophic component representing a major pathway for organic matter and energy flux in the aquatic food web (Sherr and Sherr 1988, Ducklow and Carlson 1992, Simon et al. 1992, Chrost 1992).

Methodology for studies of carbon dynamics between phytoplankton primary production and heterotrophic bacterial secondary production

The SCENTO-System was used to study the carbon dynamics between phytoplankton primary production and heterotrophic bacterial secondary production. Most of the methods used nowadays in situ for limnological synecology studies were applied. Primary production measurement showed an increasing tendency with increasing content of chlorophylla. It provided a true photosynthetic rate lying within the range of eutrophic lakes. Net EOC released from the algae ranged from 8.5 to 27.5 μg C l−1(6h)−1. Accompanying the algal products the number of bacteria increased from 1.475 ×109 to 8.074×109 cells l−1. The bacterial mean cell volume was small, between 0.0315 and 0.0548μm3. Bacterial carbon production from direct growth estimates was compared with independent calculations of bacterial growth from EOC uptake and3H-thymidine incorporation. Direct estimates were 2.97–10.0 μg Cl−1 (24h)−1 with the exception of a zero-growth on the third day. EOC uptake was 123.5–191.0 μg Cl−1 (6h)−1. That calculated from3H-thymidine incorporation was 0.2–0.5 μg Cl−1 (6h)−1.14C-glucose dark uptake ran parallel to the increasing bacterial biomass. The respiration of glucose was 6.5% (avg.) of the gross uptake. Since the system operated without grazing pressure, a real carbon flow from primary production to bacterial secondary production could be observed.

CO2-Uptake as a Measure of Bacterial Production

Autotrophic and heterotrophic processes are the basic components of the carbon cycle in aquatic ecosystems. We know rather well the uniform, biochemical basis of autotrophy—photosynthesis. The reverse process however, decomposition and heterotrophic utilization of orgenic substances, is very complex and cannot be measured with only one method—e.g. Steemann-Nielsen technique— as in the case of autotrophy.