RESPONSE OF MICROALGAL EPIPHYTE COMMUNITIES TO NITRATE ENRICHMENT IN AN EELGRASS (ZOSTERA MARINA) MEADOW1

The community structure and productivity of epiphytic microalgae on field populations of eelgrass (Zostera marina L.) from a high flow regime were characterized under water-column nitrate enrichment over a 30–d period during the autumn growing season for the macrophyte. Epiphyte communities in replicate low-nitrogen sites (LOW-N, median water-column nitrate concentrations below detection) were compared to communities in replicate N-enriched sites wherein nitrate was leached from clay pots filled with enriched agar (N-ENRICH, median concentration ca. 6 μM NO₃^?_-N; pots replaced at 8– to 12–d intervals). In experimental chambers, total epiphyte community productivity as ¹⁴C-bicarbonate uptake was determined from short-term (3–h) laboratory assays. Track light microscope-autoradiography enabled estimates of species-specific productivity for abundant algal taxa. After 6 d in the LOW-N and N-ENRICH communities, the crustose adnate red alga Sahlingia subintegra (Rosenvinge) Kornmann was dominant in terms of cell number and codominant in biovolume. Photosynthetic dinoflagellates, not previously reported as abundant in eelgrass epiphyte communities, were dominant in biovolume contribution after both 6 and 30 d in LOW-N communities. Nitrate enrichment stimulated the adnate monoraphid diatom Cocconeis placentula Ehr. but apparently inhibited dinoflagellates and the diatom Melosira sp. Total productivity of the epiphyte communities remained comparable in both the LOW-N and N-ENRICH sites. Shifts in community structure and species-specific productivity, however, indicated a controlling influence of nitrate supply on microalgal epiphytes in the field eelgrass community.     

Ecosystem Structure and Function Still Altered Two Decades After Short-Term Fertilization of a Seagrass Meadow

An oligotrophic phosphorus (P) limited seagrass ecosystem in Florida Bay was experimentally fertilized in a unique way. Perches were installed to encourage seabirds to roost and deliver an external source of nutrients via defecation. Two treatments were examined: (1) a chronic 23-year fertilization and (2) an earlier 28-month fertilization that was discontinued when the chronic treatment was initiated. Because of the low mobility of P in carbonate sediments, we hypothesized long-term changes to ecosystem structure and function in both treatments. Structural changes in the chronic treatment included a shift in the dominant seagrass species from Thalassia testudinum to Halodule wrightii, large increases in epiphytic biomass and sediment chlorophyll-a, and a decline in species richness. Functional changes included increased benthic metabolism and quantum efficiency. Initial changes in the 28-month fertilization were similar, but after 23 years of nutrient depuration T. testudinum has reestablished itself as the dominant species. However, P remains elevated in the sediment and H. wrightii has maintained a presence. Functionally the discontinued treatment remains altered. Biomass exceeds that in the chronic treatment and indices of productivity, elevated relative to control, are not different from the chronic fertilization. Cessation of nutrient loading has resulted in a superficial return to the pre-disturbance character of the community, but due to the nature of P cycles functional changes persist.     

Capture of proteins from mammalian cells in pilot scale using different STREAMLINE adsorbents

This presentation compares three different expanded bed matrices. STREAMLINE rProtein A, STREAMLINE SP-XL and STREAMLINE Chelating were monitored in respect to their ability to clarify the broth, to concentrate and to purify the distinct target protein. The capture of a mouse IgG₁ and a recombinant prothrombin (PT) was carried out in pilot scale using a 100-l bioreactor and STREAMLINE 100 and 200 columns, respectively. The robustness of the process was also estimated monitoring the expansion behaviour and the cell and debris concentrations during the load and in the eluat. In all cases the capture of the target proteins was comparable to conventional chromatographic systems. The purification success was mainly dependent on the selectivity of the ligand used. The affinity process resulted in a highly purified product. The ion exchanger and chelating material mainly concentrated the product. In all three cases 100 l of cell broth were successfully processed in one run. The robustness of the ion exchanger process was poor, because of strong cell matrix interaction. However, for the chelating and especially for the affinity matrix a highly reproducible process was obtained.     

Energetics of photosynthesis in Zea mays. II. Studies of the flash-induced electrochromic shift and fluorescence induction in mesophyll chloroplasts

Patterns of electron transfer in isolated mesophyll chloroplasts of maize (Zea mays L.) were studied in the presence of the physiological substrates, oxaloacetate, 3-phosphoglycerate and pyruvate. Flash-induced absorbance changes due to the electrochromic pigment band-shift (P-518) were used to estimate relative electron flow rates through the cyclic and non-cyclic pathways of electron transport. Further information on the redox state of electron carriers and the activity of coupled electron flow was obtained from measurements of fluorescence induction and of actinic-light-induced fluorescence changes. The results demonstrate the importance of correct redox poising for optimal rates of photosynthesis and are discussed in relation to the operation and regulation of photosynthesis in the C₄ system.     

Deposition and Decomposition of Turtlegrass Leaves

In coastal zones where prevailing winds are onshore, seagrasses are regularly deposited at the shoreline, often forming large accumulations. We have compared the rates of output of dry matter, organic carbon, and nitrogen for turtlegrass (Thalassia testudinum) when it decays at the shoreline or continuously submerged nearby. Output rates were either delayed (by 30 days or more) or were significantly slower for decay under submerged conditions.     

Fluidized bed ion exchange for improving purification of lactic acid from fermentation

A strong anionic exchange resin was used to recover lactic acid directly from fermentation in an upflow fluidized bed column, resulting in 0.18 g lactic acid/g resin bound with a subsequent elution of 94%. When the culture broth was heated and adjusted pH to 8.0, 0.4 g lactic acid was bound per g resin, with a subsequent elution of 90%. L(+) and D(–) lactic acid isomers distribution was analyzed in the elution product resulting in an increase of L(+) isomer concentration. The resin did not alter its binding capacity after 23 cycles.     

Development of cyanobacterial build-up and evolution of river bed morphology in the chalk stream Eaulne (Upper-Normandy, France)

In some hardwater rivers of the Seine basin (France), the development ofan encrusting cyanobacterial microflora may gradually lead to a cementation ofriver bed sediments, to a reduction of spawning ground areas and to a loss ofbenthic floral and faunal diversity. Current methods for build-up management arebased on mechanical dredging of the stream bed. In the short term, the habitatdiversity and microfaunal diversity are improved, but in 1–3years the cyanobacterial growth resumes and the bed sediments arecemented again. The early growth stages of stromatolitic structures on newlyavailable substrata were studied for three years in the river Eaulne(Upper-Normandy, France) in relation with microfloral development, sedimentaryprocesses and water quality. Seasonal current velocity variations appeared tocontrol the construction process (colonization dynamics and dependency ofstromatolite growth to mat extension) through substratum availability andnutrient renewal. Under the conditions allowing an optimal microfloraldevelopment, the carbonate precipitation rates were inversely correlated withsubstratum grain size, i.e. the maximal encrusting biomass was hosted bygravels. Homogeneous substrata showed the highest short-term potentialities forhigh sediment cementation rate, whereas heterogeneous, mixed grain size had thehighest potentialities for long-term colonization by the encrusting microflora.     

Preparative scale enantioseparation of a chiral epoxide: Comparison of liquid chromatography and simulated moving bed adsorption technology

The feasibility of using simulated moving bed technology (SMB) for chiral separation on cellulose triacetate is demonstrated on the preparative scale: 1 kg of a chiral epoxide has been separated. On comparing SMB technology with conventional liquid chromatography it turns out that the main advantage of SMB lies in the significant reduction of mobile phase consumption. The process design for SMB is made theoretically and the predictions are confirmed by our pilot study. © 1993 Wiley-Liss, Inc.     

Purification of horse radish peroxidase by metal affinity chromatography in an expanded bed system

Immobilised metal chelate affinity chromatography (IMAC) in an expanded bed mode was used for the purification of horse radish peroxidase. Recovery of horse radish peroxidase varied between 85 and 72% starting from the crude homogenate. When a pure peroxidase was passed through the purification protocol a recovery of about 95% was achieved.     

The effect of environmental stability on hyporheic community structure

Interstitial water samples were collected from two well depths (30 and 60 cm) from 8 rivers in the Cass-Craigieburn region, South Island (New Zealand) during January 1998 to assess the hyporheos in streams of differing stability. Hyporheic water chemistry was more similar to surface water chemistry at unstable sites than at stable sites. The greatest diversity of both epigean and hypogean animals occurred at intermediate levels of disturbance; however, invertebrate density declined with increasing bed movement. Abundance of epigean animals also increased with declining environmental stability (i.e., increasing bed movement). Water chemistry was most like the river channel at unstable sites, probably because less stable substrates had increased interstitial flow facilitating a greater supply of water from the surface channel. In contrast, stable sites were spring fed and groundwater had a greater influence. Thus, substrate stability may influence hyporheic water chemistry and porosity by changing the interaction between ground and surface waters. Epigean taxa may be less abundant at stable sites because the chemical nature of the water is least like the river channel (e.g. low dissolved oxygen, higher temperature and higher conductivity), while the abundance of hypogean animals is greater, as these taxa are more tolerant of this water chemistry, and are thus capable of persisting in the stable substrates.