We applied different types of fluorescent markers to natural bacterioplankton from different aquatic systems to investigate microscopically the percentage of viable bacteria. To characterise viable bacteria, cell-specific respiration was measured by cyanoditolyltetrazolium chloride (CTC) reduction. Membrane integrity was investigated with 3 'dead cell' stains (SYTOX ® Green, propidium iodide and ethidium homodimer-2). Cellular enzyme activity was detected by artificial substrate analogs with a high cell retention (CellTracker™ Green CMFDA for cellular esterase and 7-amino-4-chloromethylcoumarin L-leucine amide, hydrochloride [CMAC-Leu] for cellular peptidase). The percentage of impermeable, i.e. morphologically intact, cells accounted for 22 to 81% of the total cell number at all locations. Although up to 48% of all bacteria were respiring, they averaged between 10 and 14% in freshwater, estuarine waters and in the Baltic Sea. The portion of esterase-positive cells correlated significantly with the concentrations of dissolved (DOC) and particulate organic carbon (POC) as well as with chlorophyll a (chl a) content. Cellular esterase was shown by this labelling technique in only 9% of freshwater, 12% of estuarine and 5% of Baltic Sea bacteria, . The percentages of bacteria with cellular peptidase were even lower with 6, 5 and 3%, respectively. The different amounts of intact and respiring bacteria as well as those with cellular hydrolytic enzyme activities require not only correct operational definitions of active and viable bacteria, but also the appropriate choice of fluorescent markers regarding the goals of investigation. Fluorescent labels for cellular hydrolytic enzymes will also provide a new tool to localise active cells in aggregates or on sediment particles, where, besides the respiration of organic carbon, hydrolysis of organic substances is an important conversion process.

Exposed to over 30 yr of continuous eutrophication, the Darß-Zingst bodden chain, a shallow tideless estuary accumulated large amounts of particulate organic matter (POM). We sampled along the eutrophication gradient throughout the vegetation period 1996, in order to assess POM properties. Besides parameters describing the chemical composition, such as C/N ratio, protein content and protein:carbohydrate ratio, particles were microscopically analysed. From the volumes of non-transparent, nucleic acid-containing (fluorescently labelled by propidium iodide) and organic particles (stained with DTAF), the percentages of detrital and transparent mucoid material were derived. Ten to 63% of particulate organic carbon (POC) in the bodden system consisted of carbon from bacteria, phytoplankton and protozoans. Of the total organic particle volume, up to 46% were microorganisms. Although detritus volume averaged 14%, maximum values of 68% could be determined. Most of the organic particle volume consisted to 64% of transparent mucoid matter, which is an important carbon compartment in material cycling (e.g. settling substrate). At higher POC concentrations the chemically unidentified material as well as the mucoid matter were quantitatively more important compared to the mesotrophic Baltic Sea station, where the portion of detritus (62% on average) was much higher. The microscopically derived quantification of detrital and mucoid matter provides additional information on the suitability of seston as settling substrate, its age, origin and physical properties. Since the riverine water input into the bodden system is small and its POC concentration lower compared to the bodden itself, most of the estuarine POM was obviously produced locally. Detritus from submersed macrophytes did not occur before the end of the vegetation period in October and thus cannot contribute significantly to the POM analysed in this study. The high amounts of POM in the bodden system probably originate mainly from pelagic primary production. The sedimentation of POM, its processing in and frequent resuspension from the several mm-thick flocculent sediment layers, seems to be the main source for the high amount of mucoid particles.

Various freshwater, estuarine and coastal stations of the Southern Baltic Sea were comparatively studied to evaluate pelagic bacterial performance. Inner coastal waters (so-called bodden or lagoons) are highly productive systems and dominate the coast of the Southern Baltic Sea. Due to high nutrient loads up to the 1990s in combination with an enhanced primary production, increased amounts of particulate (POC) and dissolved organic carbon (DOC) accumulated in these waters. In the Darß-Zingst bodden chain, POC < 16 and DOC < 13 mg C l -1 , and C:N ratios of 9 to 11 in particulate matter were measured in winter and spring samples. Due to high POC concentrations, the average ratio of DOC:POC was 1.1:1, which is very low compared to other aquatic systems. Bacterial abundance and activities were rather high and reached 24 × 10 6 ml -1 and 18 µg C l -1 h -1 , respectively. Although 2 of the 3 investigated freshwater systems were classified as eutrophic, the highest measured POC concentrations, bacterial abundance and production were much lower (1.6 mg C l -1 , 11 × 10 6 bacteria ml ) than in the bodden. In contrast to that, the DOC load was as high as in these inner coastal waters (<12 mg C l -1 ). The coastal stations of the Baltic Sea, classified as mesotrophic, were not severely loaded with organic matter and bacteria (POC < 0.8, DOC < 5.5 mg C l -1 , bacteria < 3 × 10 6 ml -1). Bacterial production again was lower than at all other stations; however, levels did reach an exceptional 4.6 µg C l -1 h -1, which is comparable to values of the freshwater systems. Compared to the other investigated marine and freshwater systems, the bodden were heavily loaded with organic matter, especially particulate organic matter (POM). The origin of this material is assumed to be mainly autochthonous as it is known not to be transported by rivers into these estuaries. Although dissolved inorganic nitrogen (DIN) concentrations were high at least in winter, POM was of poor quality; this was reflected by high C:N ratios and a low contribution of phytoplankton carbon to POC. However, this is particularly surprising, because nitrogen should be readily available at all bodden sites by resuspension from the sediment caused by frequent winds in these very shallow systems of < 2 m depth. KEY WORDS: Organic matter · Bacterial production · Hydrolytic enzymes · Marine systems · Brackish systems · Freshwater systems Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 32: [121][122][123][124][125][126][127][128][129][130][131][132][133][134][135] 2003 organic matter input and decomposition, and subsequently reveal the most important regulating factors of bacterial activity.Besides nutrient availability, grazing as a top down control factor regulates bacterial biomass and species composition (e.g. Berninger et al. 1991). Protozoa, especially heterotrophic nanoflagellates, are an important, or often the dominating, loss factor for bacterial standing stock in pelagic systems (e.g. Jürgens et a...

The Darß-Zingst Boddens (DZB) represents the typical bodden coasts of northern Germany, which stretch from the Fischland-Darß-Zingst peninsula via the islands of Hiddensee, Rügen and Usedom to the Polish island of Wolin. The "double coasts" show the typical features of level coasts at the seashore while, at the back, the indented boddens and lagoons are inner seawaters that are subject to a progressive phytogenic silting-up.The "jointed" structure of the DZB is also found in the Northern Rügener Bodden and at the mouth of the river Schlei ( Fig. 3.1), and these areas are therefore considered together here. Investigations into the DZB were sporadic at first (Gessner 1937;Hupfer 1959Hupfer , 1960Fukarek 1961;Schwarz 1961aSchwarz , 1961bSchwarz , 1964Brosin 1965aBrosin , 1965bHoppe and Pankow 1968;Hübel 1969). This changed fundamentally in the mid-1960s. The DZB has become the main area of investigation under the new focus on ecology and marine biology at Rostock University. Darß-Zingst Boddens Environmental CharacteristicsThe climate of the Baltic coast is determined by the "Ostseeklima". According to Kliewe (1951) and Hurtig (1957), a coastal area stretching 20-30 km landwards is basically involved. The "Ostseeklima" is identified by a transitional character with a relatively constant temperature, and by a delay in the start of the spring and summer seasons followed by mild autumns and relatively short winters. There is only little rain (405-790 mm per year), falling usually during autumn and winter. The mean annual air temperature is 9. 1°C (1995-2004). The number of frosty days is around 75-80 (Niedermeyer et al. 1987). The main wind direction is southwest/ west, with 80% of all winds reaching an average speed of 1.3-5 m s

Plants are settled by epiphytic bacteriae able to convert tryptophan to IAA. This bacterial activity is abolished by chloramphenicol and streptomycin but not by penicillin. Tryptophan conversion to IAA by plant parts or enzyme preparations is far more intensive in non-sterile conditions than in sterile ones. This is true for all investigated objects: Helianthus annuus, Phaseolus vulgaris, Pisum sativum, Triticum vulgare, Zea mays, Enteromorpha compressa, Fucus vesiculosus, Furcellaria fastigiata. From pea plants, 58 strains of IAA producing bacteriae were isolated and partly identified.While non-sterile plants (Pisum, Zea) contain considerable amounts of IAA (extraction, thin layer chromatography, biotest), hardly any traceable auxin can be extracted of sterile plants. But sterile plants re-infected with mixtures or single strains of suitable bacteriae again contain considerable amounts of extractable IAA.