Description: Organic material entering the oceanic mesopelagic zone may either reenter the euphotic zone or settle into deeper waters. Therefore it is important to know about mechanisms and efficiency of substrate conversion in this water layer. Bacterial biomass, bacteria secondary production (BSP). extra­cellular peptidase activity (EPA) and particulate organic nitrogen (PON) were measured in vertical pro­files of the North Atlantic (46° N 18° W; 57° N 23° W) during the Joint Global Ocean Flux Study (JGOFS) cruise in May 1989. The magnitude of these parameters decreased differently with depth. The strong­est decreases were observed for bacterial production (3H-thymidine incorporation) and peptide turn­over (using the substrate analog leucine-methylcoumarinylamide). Bacterial biomass and peptidase potential activity were not reduced as much in the mesopelagic zone. Peptidase potential per unit cell biomass of mesopelagic bacteria was 2 to 3 times higher than that of bacteria in surface water. Nevertheless bacterial growth at depth was slow, due to slow actual hydrolysis. Values of theoretical PON hydrolysis were calculated from PON measurements and protein hydrolysis rates. These corre­sponded well to bacterial production rates, and the degree of correspondence increased from a factor of 0.63 (PON hydrolysis/ESP) in the mixed surface layer to 0.87 in the mesopelagic zone. Thus we hypothesized an effective coupling between particle hydrolysis and uptake of hydrolysate by bacteria, which depletes the deeper water of easily degradable substrates as hydrolysates usually are. The low enzymatic PON turnover rate of 0.04 d- 1 in the subeuphotic zone suggests that residence time of parti­cles within a depth stratum may be important for its contribution to export. storage and recycling of organic matter.

Description: Global warming is assumed to alter the trophic interactions and carbon flow patterns of aquatic food webs. The impact of temperature on phyto-bacterioplankton coupling and bacterial community composition (BCC) was the focus of the present study, in which an indoor mesocosm experiment with natural plankton communities from the western Baltic Sea was conducted. A 6°C increase in water temperature resulted, as predicted, in tighter coupling between the diatom-dominated phytoplankton and heterotrophic bacteria, accompanied by a strong increase in carbon flow into bacterioplankton during the phytoplankton bloom phase. Suppressed bacterial development at cold in situ temperatures probably reflected lowered bacterial production and grazing by protists, as the latter were less affected by low temperatures. BCC was strongly influenced by the phytoplankton bloom stage and to a lesser extent by temperature. Under both temperature regimes, Gammaproteobacteria clearly dominated during the phytoplankton peak, with Glaciecola sp. as the single most abundant taxon. However, warming induced the appearance of additional bacterial taxa belonging to Betaproteobacteria and Bacteroidetes. Our results show that warming during an early phytoplankton bloom causes a shift towards a more heterotrophic system, with the appearance of new bacterial taxa suggesting a potential for utilization of a broader substrate spectrum.

Description: Phytoplankton and bacteria are sensitive indicators of environmental change. The temporal development of these key organisms was monitored from 1988 to the end of 2007 at the time series station Boknis Eck in the western Baltic Sea. This period was characterized by the adaption of the Baltic Sea ecosystem to changes in the environmental conditions caused by the conversion of the political system in the southern and eastern border states, accompanied by the general effects of global climate change. Measured variables were chlorophyll, primary production, bacteria number, -biomass and -production, glucose turnover rate, macro-nutrients, pH, temperature and salinity. Negative trends with time were recorded for chlorophyll, bacteria number, bacterial biomass and bacterial production, nitrate, ammonia, phosphate, silicate, oxygen and salinity while temperature, pH, and the ratio between bacteria numbers and chlorophyll increased. Strongest reductions with time occurred for the annual maximum values, e.g. for chlorophyll during the spring bloom or for nitrate during winter, while the annual minimum values remained more stable. In deep water above sediment the negative trends of oxygen, nitrate, phosphate and bacterial variables as well as the positive trend of temperature were similar to those in the surface while the trends of salinity, ammonia and silicate were opposite to those in the surface. Decreasing oxygen, even in the surface layer, was of particular interest because it suggested enhanced recycling of nutrients from the deep hypoxic zones to the surface by vertical mixing. The long-term seasonal patterns of all variables correlated positively with temperature, except chlorophyll and salinity. Salinity correlated negatively with all bacterial variables (as well as precipitation) and positively with chlorophyll. Surprisingly, bacterial variables did not correlate with chlorophyll, which may be inherent with the time lag between the peaks of phytoplankton and bacteria during spring. Compared to the 20-yr averages of the environmental and microbial variables, the strongest negative deviations of corresponding annual averages were measured about ten years after political change for nitrate and bacterial secondary production (~ −60%), followed by chlorophyll (−50%) and bacterial biomass (−40%). Considering the circulation of surface currents in the Baltic Sea we interpret the observed patterns of the microbial variables at the Boknis Eck time series station as a consequence of the improved management of water resources after 1989 and – to a minor extent – the trends of the climate variables salinity and temperature.

Description: An vier Tidenzyklus-Stationen von 21 bis 36 Std. Dauer wurde auf einem Längsschnitt von Hamburg bis zur Außenelbe untersucht, welchen Anteil die Bakterien am Abbau der organischen Substanz haben. Der Gesamt-Abbau durch die planktische Organismengemeinschaft wurde aus dem Sauerstoffverbrauch mit einem angenommenen Respirationsquotienten von 0,85 bestimmt. Der bakterielle Abbau wurde über die Biomasse-Produktion und die Wachstums-Effizienz der Bakterien ermittelt. Die Tidenzyklus-Stationen mit einer hohen zeitlichen Auflösung zeigten eine große Variabilität der Abbauprozesse während der Gezeiten. Die Mittelwerte ergaben, dass der Gesamt-Abbau im oberen noch limnischen Bereich 10,2 μg C l-1 h-1 betrug mit einem bakteriellen Anteil von 82%. Flussabwärts ging der Gesamt-Abbau auf 2,7 μg C l-1 h-1 zurück und der bakterielle Anteil belief sich auf rd. 50 %. Der Längsschnitt von Hamburg bis Neuwerk mit einer hohen räumlichen Auflösung zeigte eine grundsätzlich ähnliche regionale Verteilung. Der hohe Anteil des bakteriellen Abbaus in dem oberen limnischen Ästuarbereich geht darauf zurück, dass das hier aus dem Mittellauf der Elbe eingeschwemmte Phytoplankton infolge Lichtmangels größtenteils abstirbt. Die Ursachen liegen in der großen Wassertiefe des Hamburger Hafengebietes und der starken Gezeitendurchmischung der Wassersäule. Dadurch vermindert sich die Respiration des Phytoplanktons und die Abbautätigkeit ist daher im Wesentlichen auf die Bakterien und das Zooplankton beschränkt. Von diesen beiden verbleibenden Hauptkomponenten des Flussplanktons spielen die Bakterien die wichtigere Rolle beim Abbau der organischen Substanz im Elbe-Ästuar.

Description: Der Nord-Ostsee-Kanal ist ein Brackwasserbiotop, der sich durch einen relativ hohen Salzgehalt in seinem östlichen Teil, einem fast ausgesüßten mittleren Bereich und einem leichten Salzgehaltsanstieg auf den letzten westlichen Kilometern auszeichnet. In seiner westlichen Hälfte ist die Wassertrübung deutlich höher als in der östlichen. Die Bakterienzahl lag nahe der Schleuse Kiel-Holtenau zwischen 3,6 und 7,9 x 10 hoch 9 l hoch -1 Zellen, von denen 0 bis 9,5 % an Partikeln angeheftet waren. In Richtung Westen nahmen die Bakterienzahl und der Prozentsatz der partikelgebundenen Bakterien fast linear zu und erreichten in der Nähe der Schleuse Brunsbüttel mit 11,5 bis 18,0 x 10 hoch 9 l hoch -1 Zellen und 80-94 % partikelgebundenen Bakterien ihre Maxima. Trübungsgehalt, Bakterienzahl und Prozentsatz der partikelgebundenen Bakterien waren hoch signifikant miteinander korreliert. Die Mittelwerte der bakteriellen Aktivität (gemessen als Leucin-Inkorporation), die zwischen 45 pmol l hoch -1 h hoch -1 im Januar und 383 pmol l hoch -1 h hoch -1 im Juli lagen, zeigten den großen Einfluss der sommerlichen Temperaturzunahme. Die maximalen Werte der spezifischen Leucin-Inkorporation erreichten rd. 80 pmol h hoch -1 10 hoch -9 Bakterien. Die Umsatzraten von Acetat, das als Repräsentant für die niedermolekularen gelösten organischen Verbindungen verwendet wurde, beliefen sich auf Werte zwischen 7 und 34,1 % h-1 (Mittelwerte über den gesamten NOK). Die Erneuerungszeit für den Acetat-"Pool" lag demnach zwischen rund 14 h (Januar) und 3 h (April).

Description: Of 45 bacterial isolates from healthy tips of Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann, 29% were identified as 'conditional inducers' of an apical necrosis. That is, the isolates induced necrotic tips in G. conferta within 16 h after elimination of most of the resident microflora from the alga. Several disinfectants and antibiotics were screened for their ability to induce algal susceptibility to the bacteria and to suppress uncontrolled appearance of tip necrosis. Treatment with 100 mg L-1 Cefotaxim + 100 mg L-1 Vancomycin over three days was the least damaging and most efficient. Tip necrosis was related to isolates of the Corynebacterium-Arthrobacter-group and to the Flavobacterium-Cytophaga-group. The damaging effect occurred due to the bacterial excretion of active agents and was not correlated with a capability to degrade agar. The damaging influence of four Cytophaga-like strains was inhibited by 20 of 40 isolates. This protective effect was caused by very different organisms. In five of six cases examined further, the effect was not cellbound, but due to the excretion of agents. These were not antimicrobially active, but inactivated necrosis-inducing excretions. These results indicate that epiphytic bacterial degradation or inactivation of damaging agents is a protecting factor in Gracilaria, which prevents the alga from being harmed by epiphytes.

Description: Gracilaria conferta (Schousboe ex Montagne) J. ct G, Feldmann responded with an oxidative burst and rapid increases in respiration and halogenating activity when agar, agarose, or the agarose degradation products neoagarotetraose and neoagarohexaose were added to the growth medium, In contrast, carrageenan, oligocarrageenans, neoagarobiose, L-galactose, D-galactose, and several other mono- and oligosaccharides did not have any effect, Sixfold increases in respiration were observed 3 min after addition of neoagarohexaose. The response could only be induced in species of the genera Gracilaria and Gracilariopsis. Neoagarohexaose also elicited a release of hydrogen peroxide in less than 15 min, resulting in an immediate increase in algal brominating activity. Bleached thallus tips appeared a few hours after the addition of neoagarohexaose. This effect was dependent on the release of hydrogen peroxide and exposure to light, Exposure to light and oligosaccharide elicitors increased the production of reactive oxygen species, which reached destructive concentrations when both mechanisms were simultaneously active. Concentrations of 0.1 to 3.3 mu M agarose or agars were sufficient to trigger an increase in respiration, an oxidative burst response, and tip bleaching. However, higher concentrations of neoagarohexaose and neoagarotetraose were necessary to elicit the responses, indicating that the alga is more sensitive to oligoagars with degrees of biose-polymerization 〉 3, The extremely short reaction time and high specificity indicate that intermediates of agar degradation are recognized by Gracilaria as messengers when microbial degradation of its cell wall occurs, The physiological responses may represent the early stages of algal defense mechanisms involved in repression of pathogen ingress.

Description: This study deals with large spatial scale differences in the ratios between bacterial leucine incorporation (TLi: protein synthesis) and thymidine incorporation (TTi: DNA synthesis) in oligotrophic offshore and comparatively more mesotrophic inshore (sub)tropical regions of the Atlantic Ocean. Observations were derived from 2 RV ‘Polarstern’ cruises, one of which traversed a meridional mid-ocean transect while the other followed the African coast line. Average values (from 42°N to 35°S) of TLi, TTi and chlorophyll a (chl a) concentration were 40.3 pmol leucine l–1 h–1, 1.32 pmol thymidine l–1 h–1 and 0.18 µg chl a l–1 along the offshore transect, compared to 51.8 pmol leucine l–1 h–1, 2.72 pmol thymidine l–1 h–1 and 0.29 µg chl a l–1 along the inshore transect. Mean values of the TLi:TTi ratio (which defines bacterial growth characteristics) were 32.4 in offshore waters and 20.5 in inshore waters. Offshore ratios of TLi:chl a or TTi:chl a (proxy for bacterial substrate) were 274.1 and 8.5, compared to inshore ratios of 198.7 and 10.0, respectively. This means that, per unit of chl a, considerably higher bacterial protein synthesis was supported in water farther from the coast than near the coast, whereas bacterial DNA synthesis per unit chl a was slightly higher in the latter. Because temperature variability along the cruise tracts was rather similar (except in the Benguela upwelling region), we assume that substrate supply was mainly responsible for the observed significant differences in bacterial growth characteristics. In addition, the potential different contributions of picocyanobacteria to leucine uptake (TLi) must be considered. We conclude that the different TLi:TTi ratios in (sub)tropical offshore and inshore waters reflect reactions of the relevant bacterial communities to prevailing environmental conditions. Therefore, we did not interpret our results in the context of the currently used terms ‘balanced’ or ‘unbalanced’ growth. Bacterial community growth may be balanced in both regions of study, but at different levels of the TLi:TTi ratio.

Description: In order to examine the effects of warming and diversity changes on primary productivity, we conducted a meta-analysis on six independent indoor mesocosm experiments with a natural plankton community from the Baltic Sea. Temperature effects on primary productivity changed with light intensity and zooplankton density and analysed pathways between temperature, diversity and productivity, elucidating direct and indirect effects of warming on primary productivity during the spring phytoplankton bloom. Our findings indicate that warming directly increased carbon specific primary productivity, which was more pronounced under low grazing pressure. On the other hand, primary productivity per unit water volume did not respond to increased temperature, because of a negative temperature effect on phytoplankton biomass. Moreover, primary productivity response to temperature changes depended on light limitation. Using path analysis, we tested whether temperature effects were direct or mediated by warming effects on phytoplankton diversity. Although phytoplankton species richness had a positive impact on both net primary productivity and carbon specific primary productivity – and evenness had a negative effect on net primary productivity – both richness and evenness were not affected by temperature. Thus, we suggest that diversity effects on primary productivity depended mainly on other factors than temperature like grazing, sinking or nutrient limitation, which themselves are temperature dependent. Highlights ► Impact of warming on primary productivity and diversity–productivity relationship. ► Meta-analysis on indoor mesocosm experiments with a natural plankton community. ► Temperature has a direct impact on specific productivity, not on net productivity. ► Species richness increases and evenness decreases net primary productivity. ► Temperature does not directly affect diversity–productivity relationship.

Description: Heterotrophe Bakterien sind auf die Versorgung mit organischem Material zur Deckung ihres Kohlenstoff- und Energiebedarfs angewiesen. In Gewässern kann dieses Material durch die Primärproduktion des Phytoplanktons und Phytobenthos autochthon erzeugt werden oder allochthoner Herkunft sein. Auf drei Stationen, zwei in der inneren Schlei (Schleswig-Holstein) und eine im Oderhaff (Mecklenburg-Vorpommern), wurde durch Probenahmen in kurzen Abständen versucht, eine von der Primärproduktion des Phytoplanktons gesteuerte Tagesperiodik der Bakterienaktivität nachzuweisen. Beide Gewässer sind stark eutrophiert und haben eine Jahresprimärproduktion von 600 bis 800 g C m-2. An den Untersuchungstagen (Anfang Juni in der Schlei und Ende August im Oderhaff) lag die Primärproduktion zwischen rd. 2,5 und 3,0 g C m-2 pro Tag. Die Maximalwerte der Thymidin- und Leucin-Aufnahme beliefen sich auf 0,346 bzw. 4,01 nmol l-1 h-1und die höchsten Umsatzraten von Glucose und Acetat als Vertreter der niedermolekularen organischen Verbindungen betrugen 99 bzw. 67 % h-1. Statistisch signifikante Unterschiede zwischen den Mittelwerten der Tages- bzw. Nachtmessungen konnten bei keinem Parameter nachgewiesen werden. Der einzige Hinweis auf eine eventuelle Tagesrhythmik fand sich bei der in der ersten Nachthälfte deutlich geringeren Umsatzrate von Glucose. Ein mehrtägiges Laborexperiment mit einer Vergleichsprobe aus der Schlei, die unter kontrollierten Bedingungen im Lichtinkubator gehalten wurde, bestätigte das Fehlen eines Tag-Nacht-Rhythmus. Aus diesen Befunden wird gefolgert, dass einerseits die Versorgung der Bakterien mit organischem Material allochthoner Herkunft groß ist und dass andererseits tageszeitlich nicht gebundene Prozesse wie Zooplanktonfraß oder Hydrolyse in diesen hypertrophen Systemen eine so bedeutende Rolle spielen, dass die Primärproduktion trotz ihrer absoluten Höhe keine messbaren, an die Tageszeit gebundenen Rhythmen der Bakterien hervorruft.