Microbial biostabilization in fine sediments

Microbial biostabilization has increasingly received attention over the last years due to its significance for the dynamics of fine sediments in fluvial and coastal systems with implications for ecology, economy and human-health. This habilitation thesis highlights the contributions of the applicant and her team to this multi-disciplinary research area and is based on eight core publications that are presented in seven chapters. First, the topic of biofilm and biostabilization is introduced and second, the materials and methods applied are presented before own research findings are discussed. To start with, the stabilization potential of heterotrophic bacterial assemblages has been emphasised as well as the adhesive properties of the protein moieties within the EPS (extracellular polymeric substances) that are more significant than previously thought. Furthermore, the engineering potential of estuarine prokaryotic and eukaryotic assemblages has been studied separately and combined to reveal the effective cooperation of mixed biofilm that resulted in highest substratum stabilization although the effects were not clearly synergistic (=more than additive). The significance of biostabilization could be evidenced as well for freshwaters where highest adhesive capacity and sediment stability occurred during spring. Microbial community composition differed accordingly to result in mechanically highly diverse biofilm. Moreover, the importance of two of the most influential abiotic conditions, light intensity and hydrodynamics, was shown for biofilm growth, species composition and functionality - here biostabilization. In order to test adhesive properties at the relevant mesoscale (mm-cm) but non-destructively and highly sensitive, MagPI (Magnetic Particle Induction) has been applied. The last chapter concerns technical aspects to further improve its performance while demonstrating the impact of material and geometry and the importance of both, magnetic field strength and field gradient for the physics of the MagPI approach

Vertical migration of phytoplankton in coastal waters with different UVR transparency

Background: The vertical migration of phytoplankton was investigated in natural waters using in situ fluorescence profiling, chlorophyll a concentrations and life counts at two study sites differing in coloured dissolved organic matter (cDOM) concentrations. The data from the corresponding water depths (50-cm intervals down to 10 m) and times (hourly, before dawn to sunset, several days) were related to the highly resolved (2 nm) underwater ultraviolet radiation (UVR)/photosynthetic active radiation (PAR) transparency (290 to 700 nm). Results: Chlorophyll a maxima of mainly motile dinoflagellates were observed in situ at all days and at both study sites (open marine, brackish waters), independent on prevailing weather conditions or cDOM concentrations. Phytoplankton migration was triggered solely by irradiance in the 400- to 700-nm wavelength range (PAR) at the particular water depth, irrespective of PAR/UVR ratios and surface UVR (290 to 400 nm), after an illumination period of about 40 min. Interestingly, the PAR tolerance levels of the phytoplankton, which have been lower in cDOM-rich waters, matched their light acclimation values determined by parallel PAM measurements. Conclusions: The response of the phytoplankton to PAR is not a sufficient protection strategy versus increasing UVR levels, which might have wide ecological implications beyond the level of primary producers to impact important ecosystem functions such as the delicate trophic interactions

Nutrient mass balance of the seagrass Posidonia oceanica: the importance of nutrient retranslocation

The seasonal nutrient mass balance of the dominant seagrass of the Mediterranean, Posidonia oceanica (L.) Delde, was evaluated in NE Spain in order to test the hypothesis that the effect of seasonal nutrient imbalance can be reduced by the reutilization of internal nutrient pools. To this end we investigated the seasonal and age-dependent variability of nitrogen and phosphorus concentration of the leaves, inferring from these data values of seasonal nitrogen and phosphorus incorporation, uptake, losses and retranslocation. Incorporation of nitrogen and phosphorus in leaves peaked in June and was lowest in September, thus following the seasonal growth pattern of the plant. Retranslocation of nitrogen and phosphorus was high from May to September and close to zero during the rest of the year. Losses of nitrogen and phosphorus were highest at the end of summer, associated with the major biomass losses. Nitrogen uptake by leaves reached maximum values in winter and was lowest during August-September, while phosphorus uptake was highest in spring and lowest in August-September. On an annual basis nitrogen and phosphorus uptake accounted for 60 and 41 % of the total nutrient incorporation, respectively, while retranslocation of nutrients from old tissues accounted for the remaining 40 and 59%. Although roots and rhizomes function as sources of nutrients at the beginning of the summer, their contribution to the seasonal nutrient budget seemed to be minor.This work was supported by grant STEP-0063-C of the ECC.Peer reviewe

Interdisciplinary reservoir management : a tool for sustainable water resources management

Reservoirs are a common way to store and retain water serving for a multitude of purposes like storage of drinking and irrigation water, recreation, flood protection, navigation, and hydropower production, and have been built since centuries. Today, few reservoirs serve only one purpose, which requires management of present demands and interests. Since each reservoir project will cause negative impacts alongside desired advantages both on a local, regional and global scale, it is even more urgent to develop a common management framework in an attempt to mitigate negative impacts, incorporate different demands and make them visible within the discourse in order to avoid conflicts from early on. The scientific publications on reservoirs are manifold, yet a comprehensive and integrative holistic tool about management of this infrastructure is not available. Therefore, a comprehensive and integrated conceptual tool was developed and proposed by the authors of this paper that can contribute to the sustainable management of existing reservoirs. The tool presented herein is based on the results from the interdisciplinary CHARM (CHAllenges of Reservoir Management) project as well as the condensed outcome of relevant literature to aid and enhance knowledge of reservoir management. The incorporated results are based on field, laboratory and empirical social research. The project CHARM focused on five different aspects related to existing reservoirs in southern Germany (Schwarzenbachtalsperre, Franconian Lake District), namely: sedimentation of reservoirs, biostabilisation of fine sediments, toxic cyanobacteria(l) (blooms), greenhouse gas emissions from reservoirs and social contestation, respectively consent. These five research foci contributed to the topics and setup of a conceptual tool, put together by the research consortium via delphi questioning, which can be found alongside this publication to provide insights for experts and laymen. Conceptualising and analysing the management in combination with quantitative and qualitative data in one descriptive tool presents a novelty for the case studies and area of research. The distribution within the scientific community and interested public will possibly make a positive contribution to the goal of sustainable water resources management in the future.Ministerium für Wissenschaft, Forschung und Kunst Baden-Württember

An advanced technique for Immuno-labelling of microcystins in cryosectioned cells of <em>Microcystis aeruginosa</em> PCC 7806 (Cyanobacteria): implementations of an experiment with varying light scenarios and culture densities

The intracellular localisation of cyanobacterial toxins might well indicate production sites and possible shifts to destination points, thus giving information on possible functions of these toxins within algal cells or at the ecological level beyond. By preparing cells of Microcystis aeruginosa PCC 7806 by cryofixation/cryosectioning and using purified high quality antibodies for immunogold-localisation, excellent ultrastructural integrity and labelling of microcystins was shown. Compared to conventional techniques, including organic solvents, possible dislocation/extraction was significantly minimised, hence, the labelling density was enhanced and the labelling pattern changed. The microcystins were mainly localised within the inner nucleoplasmic area and accumulations of epitopes could be detected around / within intracellular inclusions, such as polyphosphate bodies and carboxysomes. Photosynthetic active radiation (PAR) had a significant effect on microcystin biosynthesis, and the medium light intensity of 25 mu E m(-2) s(-1) induced the highest intracellular microcystin contents (up to 160 epitopes per cell and 26 epitopes per pm 2). The restriction of the full light spectrum to blue (400-500 nm) or red (&gt; 610 nm) wavelengths did not result in any significant effect on microcystin production. However, the subcultures harvested at higher optical densities (&gt; 0.5) revealed significantly higher microcystin labelling compared to the less dense cell cultures (OD &lt; 0.5). Altogether, the possibility was discussed whether microcystin might function as an inhibitor of RUBISCO under conditions of C-limitations. The effects of light intensity and cell suspension density on intracellular microcystin shown by immuno-detection matched the pattern of microcystin concentrations determined in parallel by HPLC and ELISA. (c) 2005 Elsevier Ltd. All rights reserved.</p

Microphytobenthic primary production in the Bodden estuaries, southern Baltic Sea, at two study sites differing in trophic status

Eutrophication in coastal areas has stimulated phytoplankton growth, sustaining a high biomass and leading to a shift in the underwater light field. With the significance of the microphytobenthos for oxygen supply and carbon budget of both benthic and pelagic habitats in mind, the possible effects of reduced light availability were investigated in the estuarine Bodden area (southern Baltic Sea) at 2 sites differing in trophic status-the eutrophic Kirr Bucht (KB) and the mesotrophic Rassower Strom (RS). Using for the first time microsensors in Bodden sediments, it was possible to visualize small-scale heterogeneity in the light regime, photosynthetic activity and oxygen penetration with high spatial and temporal resolution. Hence, differences at the 2 sites related to sediment characteristics (KB sandy, RS muddy), and photoautotrophic biomass (benthic chlorophyll a in the upper 1 cm, mu g cm(-3) = 11 to 48 at KB and 13 to 17 at RS) could be ruled out. Calculations of benthic primary production based solely on microelectrode measurements revealed substantial oxygen fluxes and carbon fixation rates at in situ light intensities at both study sites (e.g. gross primary production, GPP, mg C m(-2) h(-1) = 28 to 80 at KB and 3 to 36 at RS). The different combinations of water transparency (pelagic chlorophyll a, mu g l(-1) = 12 to 33 at KB and 1.3 to 4.5 at RS), light attenuation k (3.17 m(-1) at KB, 0.61 m(-1) at RS) and water depth (0.6 m at KB, 3.4 m at RA) have led to a similar light availability for benthic algae on the sediment surface at both study sites. Consequently, the benthic algae had comparable productivity at both sites, with maximum primary production, P-max(B) (mg C mg(-1) chlorophyll a h(-1)) of 0.29 to 1.46 at KB and 0.17 to 1.63 at RS; and were adapted to rather low light conditions, with light saturation, E-k (mu E m(-2) s(-1)) of 22 to 152 at KB and 10 to 116 at RS). Varying with season, microphytobenthic photosynthetic activity accounted for 26 to 59 and 2 to 53 % to the total primary production at the KB and RS, respectively, with the highest contribution in spring coincident with the most favourable light conditions at the sediment surface. With an annual average of about 37 and 30 % (KB and RS, respectively), the contribution of the microphytobenthos to total production was significant and comparable at both study sites. Nevertheless, the higher trophic status at KB resulted in a change in the benthic microalgal community towards sedimentated phytoplankton species and had a negative impact on microphytobenthic primary production rates. This was estimated by calculating the gross primary production for varying water depths on the basis of the different water transparency at the 2 sites.</p

Microphytobenthic primary production in the Bodden estuaries, southern Baltic Sea, at two study sites differing in trophic status

Eutrophication in coastal areas has stimulated phytoplankton growth, sustaining a high biomass and leading to a shift in the underwater light field. With the significance of the microphytobenthos for oxygen supply and carbon budget of both benthic and pelagic habitats in mind, the possible effects of reduced light availability were investigated in the estuarine Bodden area (southern Baltic Sea) at 2 sites differing in trophic status-the eutrophic Kirr Bucht (KB) and the mesotrophic Rassower Strom (RS). Using for the first time microsensors in Bodden sediments, it was possible to visualize small-scale heterogeneity in the light regime, photosynthetic activity and oxygen penetration with high spatial and temporal resolution. Hence, differences at the 2 sites related to sediment characteristics (KB sandy, RS muddy), and photoautotrophic biomass (benthic chlorophyll a in the upper 1 cm, mu g cm(-3) = 11 to 48 at KB and 13 to 17 at RS) could be ruled out. Calculations of benthic primary production based solely on microelectrode measurements revealed substantial oxygen fluxes and carbon fixation rates at in situ light intensities at both study sites (e.g. gross primary production, GPP, mg C m(-2) h(-1) = 28 to 80 at KB and 3 to 36 at RS). The different combinations of water transparency (pelagic chlorophyll a, mu g l(-1) = 12 to 33 at KB and 1.3 to 4.5 at RS), light attenuation k (3.17 m(-1) at KB, 0.61 m(-1) at RS) and water depth (0.6 m at KB, 3.4 m at RA) have led to a similar light availability for benthic algae on the sediment surface at both study sites. Consequently, the benthic algae had comparable productivity at both sites, with maximum primary production, P-max(B) (mg C mg(-1) chlorophyll a h(-1)) of 0.29 to 1.46 at KB and 0.17 to 1.63 at RS; and were adapted to rather low light conditions, with light saturation, E-k (mu E m(-2) s(-1)) of 22 to 152 at KB and 10 to 116 at RS). Varying with season, microphytobenthic photosynthetic activity accounted for 26 to 59 and 2 to 53 % to the total primary production at the KB and RS, respectively, with the highest contribution in spring coincident with the most favourable light conditions at the sediment surface. With an annual average of about 37 and 30 % (KB and RS, respectively), the contribution of the microphytobenthos to total production was significant and comparable at both study sites. Nevertheless, the higher trophic status at KB resulted in a change in the benthic microalgal community towards sedimentated phytoplankton species and had a negative impact on microphytobenthic primary production rates. This was estimated by calculating the gross primary production for varying water depths on the basis of the different water transparency at the 2 sites.</p

An advanced technique for Immuno-labelling of microcystins in cryosectioned cells of <em>Microcystis aeruginosa</em> PCC 7806 (Cyanobacteria): implementations of an experiment with varying light scenarios and culture densities

The intracellular localisation of cyanobacterial toxins might well indicate production sites and possible shifts to destination points, thus giving information on possible functions of these toxins within algal cells or at the ecological level beyond. By preparing cells of Microcystis aeruginosa PCC 7806 by cryofixation/cryosectioning and using purified high quality antibodies for immunogold-localisation, excellent ultrastructural integrity and labelling of microcystins was shown. Compared to conventional techniques, including organic solvents, possible dislocation/extraction was significantly minimised, hence, the labelling density was enhanced and the labelling pattern changed. The microcystins were mainly localised within the inner nucleoplasmic area and accumulations of epitopes could be detected around / within intracellular inclusions, such as polyphosphate bodies and carboxysomes. Photosynthetic active radiation (PAR) had a significant effect on microcystin biosynthesis, and the medium light intensity of 25 mu E m(-2) s(-1) induced the highest intracellular microcystin contents (up to 160 epitopes per cell and 26 epitopes per pm 2). The restriction of the full light spectrum to blue (400-500 nm) or red (&gt; 610 nm) wavelengths did not result in any significant effect on microcystin production. However, the subcultures harvested at higher optical densities (&gt; 0.5) revealed significantly higher microcystin labelling compared to the less dense cell cultures (OD &lt; 0.5). Altogether, the possibility was discussed whether microcystin might function as an inhibitor of RUBISCO under conditions of C-limitations. The effects of light intensity and cell suspension density on intracellular microcystin shown by immuno-detection matched the pattern of microcystin concentrations determined in parallel by HPLC and ELISA. (c) 2005 Elsevier Ltd. All rights reserved.</p