Low Inorganic Carbon Research Articles

Cyanobakterielle Toxine — von der Biosynthese zur Funktion

Cyanobacteria are infamous for the production of potent toxins, among them the widespread hepatotoxins microcystin and nodularin. The recent assignment of biosynthetic pathways to these cyclic peptides has allowed detailed investigations into evolution, regulation, and function of these toxins. Knowledge on the biosynthetic genes provides a basis for the advancement of detection techniques for toxic cyanobacteria. Inter — disciplinary approaches support the idea of an important intracellular role of the toxin in oxidative stress acclimation and low inorganic carbon adaptation.

Nitrifying bacterial community structures and their nitrification performance under sufficient and limited inorganic carbon conditions

This study examined the hypothesis that different inorganic carbon (IC) conditions enrich different ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) populations by operating two laboratory-scale continuous-flow bioreactors fed with 15 and 100mg IC/L, respectively. During this study, both bioreactors maintained satisfactory nitrification performance and stably oxidized 250mg N/L of influent ammonium without nitrite accumulation. Based on results of cloning/sequencing and terminal restriction fragment length polymorphism targeting on the ammonia monooxygenase subunit A (amoA) gene, Nitrosomonas nitrosa lineage was identified as the dominant AOB population in the high-IC bioreactor, while Nitrosomonas europaea and Nitrosomonas nitrosa lineage AOB were dominant in the low-IC bioreactor. Results of real-time polymerase chain reactions for Nitrobacter and Nitrospira 16S rRNA genes indicated that Nitrospira was the predominant NOB population in the high-IC bioreactor, while Nitrobacter was the dominant NOB in the low-IC bioreactor. Furthermore, batch experiment results suggest that N. europaea and Nitrobacter populations are proliferated in the low-IC bioreactor due to their higher rates under low IC conditions despite the fact that these two populations have been identified as weak competitors, compared with N. nitrosa and Nitrospira, under low ammonium/nitrite environments. This study revealed that in addition to ammonium/nitrite concentrations, limited IC conditions may also be important in selecting dominant AOB/NOB communities of nitrifying bioreactors.

Comparison of CO2 and bicarbonate as inorganic carbon sources for triacylglycerol and starch accumulation in Chlamydomonas reinhardtii

Microalgae are capable of accumulating high levels of lipids and starch as carbon storage compounds. Investigation into the metabolic activities involved in the synthesis of these compounds has escalated since these compounds can be used as precursors for food and fuel. Here, we detail the results of a comprehensive analysis of Chlamydomonas reinhardtii using high or low inorganic carbon concentrations and speciation between carbon dioxide and bicarbonate, and the effects these have on inducing lipid and starch accumulation during nitrogen depletion. High concentrations of CO(2) (5%; v/v) produced the highest amount of biofuel precursors, transesterified to fatty acid methyl esters, but exhibited rapid accumulation and degradation characteristics. Low CO(2) (0.04%; v/v) caused carbon limitation and minimized triacylglycerol (TAG) and starch accumulation. High bicarbonate caused a cessation of cell cycling and accumulation of both TAG and starch that was more stable than the other experimental conditions. Starch accumulated prior to TAG and then degraded as maximum TAG was reached. This suggests carbon reallocation from starch-based to TAG-based carbon storage.

Operon flv4-flv2 Provides Cyanobacterial Photosystem II with Flexibility of Electron Transfer

Synechocystis sp PCC 6803 has four genes encoding flavodiiron proteins (FDPs; Flv1 to Flv4). Here, we investigated the flv4-flv2 operon encoding the Flv4, Sll0218, and Flv2 proteins, which are strongly expressed under low inorganic carbon conditions (i.e., air level of CO(2)) but become repressed at elevated CO(2) conditions. Different from FDP homodimers in anaerobic microbes, Synechocystis Flv2 and Flv4 form a heterodimer. It is located in cytoplasm but also has a high affinity to membrane in the presence of cations. Sll0218, on the contrary, resides in the thylakoid membrane in association with a high molecular mass protein complex. Sll0218 operates partially independently of Flv2/Flv4. It stabilizes the photosystem II (PSII) dimers, and according to biophysical measurements opens up a novel electron transfer pathway to the Flv2/Flv4 heterodimer from PSII. Constructed homology models suggest efficient electron transfer in heterodimeric Flv2/Flv4. It is suggested that Flv2/Flv4 binds to thylakoids in light, mediates electron transfer from PSII, and concomitantly regulates the association of phycobilisomes with PSII. The function of the flv4-flv2 operon provides many β-cyanobacteria with a so far unknown photoprotection mechanism that evolved in parallel with oxygen-evolving PSII.

NH4-N Removal Through Nitrification and Hydrogenotrophic Denitrification in Simple Attached Growth Reactors

To provide good quality of drinking water, a biological system to remove ammonium-nitrogen (NH4-N) from groundwater was studied in this research. The NH4-N removal system consists of two attached growth reactors: one for nitrification and the other for hydrogenotrophic denitrification (H. denitrification). The nitrification reactor, fed by the NH4-N contained water, could remove NH4-N without any need of aeration. The nitrification efficiency was increased by reactor length; the highest efficiency of 92 % was achieved at the longest reactor of 100 cm. A high Fe in groundwater affected the reactor performance by decreasing the efficiency, while a low inorganic carbon (IC) had no effects. Despite of good efficiency in terms of NH4-N removal, the nitrification reactor increased the concentration of NO3-N in its effluent. To treat the NO3-N, a H. denitrification reactor was set up after the nitrification reactor. Efficiency of the H. denitrification reactor was enhanced by increasing H2 flow rates. The efficiencies were 3, 27, and 90 % for 30, 50, and 70 mL/min of H2 flow rates, respectively. It was also found that the NO3-N contained water (water from the nitrification reactor) had to supply IC (i.e., NaHCO3 or CO2) for efficient H. denitrification; however, an on-site reactor showed that it can be achieved even without IC addition. The treated water contained low NH4-N and NO3-N of <1.5 and <11.3 mg/L, respectively, which comply with drinking water standards. The good performance of the reactors in terms of high efficiency, no aeration need, and low H2 supply indicated appropriateness of the system for groundwater treatment.

Development of an attached growth reactor for NH4–N removal at a drinking water supply system in Kathmandu Valley, Nepal

Higher concentrations of ammonium (NH4–N) and iron (Fe) than a standard for drinking are typical characteristics of groundwater in the study area. To remove NH4–N and Fe, the drinking water supply system in this study consists of a series of treatment units (i.e., aeration and sedimentation, filtration, and chlorination); however, NH4−N in treated water is higher than a standard for drinking (i.e., <1.5 mg NH4–N/L). The objective of this study, therefore, is to develop an attached growth system containing a fiber carrier for reducing NH4–N concentration within a safe level in the treated water. To avoid the need of air supply for nitrification, groundwater was continuously dripped through the reactor. It made the system simple operation and energy efficient. Effects of reactor design (reactor length and carrier area) were studied to achieve a high NH4−N removal efficiency. In accordance with raw groundwater characteristics in the area, effects of low inorganic carbon (IC) and phosphate (PO4–P) and high Fe on the removal efficiency were also investigated. The results showed a significant increase in NH4–N removal efficiency with reactor length and carrier area. A low IC and PO4–P had no effect on NH4–N removal, whereas a high Fe decreased the efficiency significantly. The first 550 days operation of a pilot−scale reactor installed in the drinking water supply system showed a gradual increase in the efficiency, reaching to 95−100%, and stability in the performance even with increased flow rate from 210 to 860 L/day. The high efficiency of the present work was indicated because only less than 1 mg of NH4−N/L was left over in the treated water.

Bicarbonate use in three aquatic plants

Our study aimed to test the ability of aquatic plants to use bicarbonate when acclimated to three different bicarbonate concentrations. To this end, we performed experiments with the three species Ceratophyllum demersum, Egeria densa, Lagarosiphon major to determine photosynthetic rates under varying bicarbonate concentrations. We measured bicarbonate use efficiency, photosynthetic performance and respiration. For all species, our results revealed that photosynthetic rates were highest in replicates grown at low alkalinity. Thus, E. densa had approx. five times higher rates at low (264±15μmolO2g−1DWh−1) than at high alkalinity (50±27μmolO2g−1DWh−1), C. demersum had three times higher rates (336±95 and 120±31μmolO2g−1DWh−1), and L. major doubled its rates at low alkalinity (634±114 and 322±119μmolO2g−1DWh−1). Similar results were obtained for bicarbonate use efficiency by E. densa (136±44 and 43±10μmolO2mequiv.L−1g−1DWh−1) and L. major (244±29 and 82±24μmolO2mequiv.L−1g−1DWh−1). As to C. demersum, efficiency was high but unaffected by alkalinity, indicating high adaptation ability to varied alkalinities. A pH drift experiment supported these results. Overall, our results suggest that the three globally widespread worldwide species of our study adapt to low inorganic carbon availability by increasing their efficiency of bicarbonate use.

Low-carbon acclimation in carboxysome-less and photorespiratory mutants of the cyanobacterium Synechocystis sp. strain PCC 6803

Using metabolic and transcriptomic phenotyping, we studied acclimation of cyanobacteria to low inorganic carbon (LC) conditions and the requirements for coordinated alteration of metabolism and gene expression. To analyse possible metabolic signals for LC sensing and compensating reactions, the carboxysome-less mutant ΔccmM and the photorespiratory mutant ΔglcD1/D2 were compared with wild-type (WT) Synechocystis. Metabolic phenotyping revealed accumulation of 2-phosphoglycolate (2PG) in ΔccmM and of glycolate in ΔglcD1/D2 in LC- but also in high inorganic carbon (HC)-grown mutant cells. The accumulation of photorespiratory metabolites provided evidence for the oxygenase activity of RubisCO at HC. The global gene expression patterns of HC-grown ΔccmM and ΔglcD1/D2 showed differential expression of many genes involved in photosynthesis, high-light stress and N assimilation. In contrast, the transcripts of LC-specific genes, such as those for inorganic carbon transporters and components of the carbon-concentrating mechanism (CCM), remained unchanged in HC cells. After a shift to LC, ΔglcD1/D2 and WT cells displayed induction of many of the LC-inducible genes, whereas ΔccmM lacked similar changes in expression. From the coincidence of the presence of 2PG in ΔccmM without CCM induction and of glycolate in ΔglcD1/D2 with CCM induction, we regard a direct role for 2PG as a metabolic signal for the induction of CCM during LC acclimation as less likely. Instead, our data suggest a potential role for glycolate as a signal molecule for enhanced expression of CCM genes.

Physiological characterization and light response of the CO2-concentrating mechanism in the filamentous cyanobacterium Leptolyngbya sp. CPCC 696

We studied the interactions of the CO(2)-concentrating mechanism and variable light in the filamentous cyanobacterium Leptolyngbya sp. CPCC 696 acclimated to low light (15 μmol m(-2) s(-1) PPFD) and low inorganic carbon (50 μM Ci). Mass spectrometric and polarographic analysis revealed that mediated CO(2) uptake along with both active Na(+)-independent and Na(+)-dependent HCO(3)(-) transport, likely through Na(+)/HCO(3)(-) symport, were employed to concentrate Ci internally. Combined transport of CO(2) and HCO(3)(-) required about 30 kJ mol(-1) of energy from photosynthetic electron transport to support an intracellular Ci accumulation 550-fold greater than the external Ci. Initially, Leptolyngbya rapidly induced oxygen evolution and Ci transport to reach 40-50% of maximum values by 50 μmol m(-2) s(-1) PPFD. Thereafter, photosynthesis and Ci transport increased gradually to saturation around 1,800 μmol m(-2) s(-1) PPFD. Leptolyngbya showed a low intrinsic susceptibility to photoinhibition of oxygen evolution up to PPFD of 3,000 μmol m(-2) s(-1). Intracellular Ci accumulation showed a lag under low light but then peaked at about 500 μmol photons m(-2) s(-1) and remained high thereafter. Ci influx was accompanied by a simultaneous, light-dependent, outward flux of CO(2) and by internal CO(2)/HCO(3)(-) cycling. The high-affinity and high-capacity CCM of Leptolyngbya responded dynamically to fluctuating PPFD and used excitation energy in excess of the needs of CO(2) fixation by increasing Ci transport, accumulation and Ci cycling. This capacity may allow Leptolyngbya to tolerate periodic exposure to excess high light by consuming electron equivalents and keeping PSII open.

Modulation of the Major Paths of Carbon in Photorespiratory Mutants of Synechocystis

BackgroundRecent studies using transcript and metabolite profiles of wild-type and gene deletion mutants revealed that photorespiratory pathways are essential for the growth of Synechocystis sp. PCC 6803 under atmospheric conditions. Pool size changes of primary metabolites, such as glycine and glycolate, indicated a link to photorespiration.Methodology/Principal FindingsThe 13C labelling kinetics of primary metabolites were analysed in photoautotrophically grown cultures of Synechocystis sp. PCC 6803 by gas chromatography-mass spectrometry (GC-MS) to demonstrate the link with photorespiration. Cells pre-acclimated to high CO2 (5%, HC) or limited CO2 (0.035%, LC) conditions were pulse-labelled under very high (2% w/w) 13C-NaHCO3 (VHC) conditions followed by treatment with ambient 12C at HC and LC conditions, respectively. The 13C enrichment, relative changes in pool size, and 13C flux of selected metabolites were evaluated. We demonstrate two major paths of CO2 assimilation via Rubisco in Synechocystis, i.e., from 3PGA via PEP to aspartate, malate and citrate or, to a lesser extent, from 3PGA via glucose-6-phosphate to sucrose. The results reveal evidence of carbon channelling from 3PGA to the PEP pool. Furthermore, 13C labelling of glycolate was observed under conditions thought to suppress photorespiration. Using the glycolate-accumulating ΔglcD1 mutant, we demonstrate enhanced 13C partitioning into the glycolate pool under conditions favouring photorespiration and enhanced 13C partitioning into the glycine pool of the glycine-accumulating ΔgcvT mutant. Under LC conditions, the photorespiratory mutants ΔglcD1 and ΔgcvT showed enhanced activity of the additional carbon-fixing PEP carboxylase pathway.Conclusions/SignificanceWith our approach of non-steady-state 13C labelling and analysis of metabolite pool sizes with respective 13C enrichments, we identify the use and modulation of major pathways of carbon assimilation in Synechocystis in the presence of high and low inorganic carbon supplies.

Nutrient limitation of phytoplankton in a naturally acidic lake (Lake Caviahue, Argentina)

As a result of a low pH, the inorganic carbon of acidic lakes is present as CO2 at air-equilibrium concentration and is substantially lower than the inorganic carbon concentration in higher-pH waters with bicarbonate. This situation is quite common in artificially acidified lakes and where inorganic carbon is considered the limiting factor in phytoplankton growth. Apart from low inorganic carbon content, Lake Caviahue in Argentina has low nitrogen and high phosphorus content. The aim of this work was to assess the importance of inorganic carbon, phosphorus, and nitrogen, relating data on lake nutrients to phytoplankton species requirements. Lake samples taken in the 2004–2006 period did not show any particular trend in the vertical distribution of the water column of ammonium, inorganic carbon, and phosphorus with reference to either seasonality or depth. A decrease of some 15% in the lake’s phosphorus concentration was observed over the same period. Although the total phytoplankton biomass in Lake Caviahue was similar throughout the period, a seasonal variation was observed. Lab bioassays were carried out with solutions of bicarbonates, ammonium, nitrates, and phosphate. We worked with three species separately, namely, two chlorophytes, Keratococcus rhaphidioides and Watanabea sp.; and one euglenophyte, Euglena mutabilis. Answers to specific nutrient requirements differed for each algal species: both chlorophytes prefer ammonium or nitrates added on their own, whereas the euglenophyte registered a higher growth rate with the joint addition of ammonium and phosphorus. Even when the limiting nutrient(s) for phytoplankton yield and rate varied between species, we observed a tendency for nitrogen limitation in Lake Caviahue.

SigC sigma factor is involved in acclimation to low inorganic carbon at high temperature in Synechocystis sp. PCC 6803

Inactivation of the sigC gene (sll0184), encoding the group 2 sigma factor SigC, leads to a heat-sensitive phenotype of Synechocystis sp. PCC 6803. Cells of the DeltasigC strain grew poorly at 43 degrees C at pH 7.5 under ambient CO(2) conditions. Addition of inorganic carbon in the form of 3 % CO(2) or use of an alkaline growth medium (pH 8.3) restored the growth of the DeltasigC strain at 43 degrees C. These treatments compensate for the low concentration of inorganic carbon at high temperature. However, addition of organic carbon as glucose, pyruvate, succinate or 2-oxoglutarate did not restore growth of the DeltasigC strain at 43 degrees C. In the control strain, the amount of the SigC factor diminished after prolonged incubation at 43 degrees C if the pH of the growth medium was 7.5 or 6.7. Under alkaline conditions, the amount of the SigC factor remained constant at 43 degrees C and cells of the control strain grew better than at pH 7.5 or pH 6.7. The pH dependence of high-temperature growth was associated with changes in photosynthetic activity, indicating that the SigC factor is involved in adjustment of photosynthesis according to the amount of available inorganic carbon. Our results indicate that acclimation to low inorganic carbon is a part of acclimation to prolonged high temperature and that the SigC factor has a central role in this acclimation.

Metabolism and resources of spherical colonies of Nostoc zetterstedtii

Constraints imposed by the spherical form and gelatinous matrix of centimeter‐thick colonies of the cyanobacterium Nostoc zetterstedtii on its functional properties were tested by examining the scaling of its composition, light absorption, photosynthesis, and respiration to individual size. In three summer experiments with colonies collected from the bottom of oligotrophic lakes of low inorganic carbon concentrations (dissolved inorganic C, DIC), metabolism and pigment density of colonies were scaled to their surface area as most algal filaments were confined to a 2‐mm‐thick outer shell. Nostoc absorbed 96% of incident light from the surface to the center because of high areal pigment density, but absorbed photons were used with low quantum efficiency (11–38 mmol O2 mol−1 photon) and photosynthesis was low relative to dark respiration (2.0–5.4). Therefore, N. zetterstedtii is threatened by reduced light availability and only extended to lake depths receiving about 12% of surface irradiance, whereas mosses, characeans, and angiosperms with thin photosynthetic tissues grew deeper (3.1–7.5% of surface irradiance). Nostoc ameliorated the restrictions of low lake DIC and long diffusion paths by active transport that could extract most external DIC, accumulate DIC in the colony 150–fold above external concentrations, and retain respiratory CO2. The energy cost of solute transport and gel formation in Nostoc colonies and extensive self shading restrict their potential growth, whereas colony formation should prevent grazing and increase longevity and nutrient recirculation. Nostoc zetterstedtii has become one of rarest freshwater macroalgae because of widespread lake eutrophication reducing water transparency and increasing competition from taller and faster‐growing stands of filamentous algae and higher plants.

Use of sediment CO2 by submersed rooted plants.

Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO(2) availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana and Hydrocotyle verticillata) are able to support photosynthesis supplied by uptake of CO(2) from the sediment. Gross photosynthesis was measured in two-compartment split chambers with low inorganic carbon availability in leaf compartments and variable CO(2) availability (0 to >8 mmol L(-1)) in root compartments. Photosynthetic rates based on root-supplied CO(2) were compared with maximum rates obtained at saturating leaf CO(2) availability, and (14)C experiments were conducted for two species to localize bottlenecks for utilization of sediment CO(2). All species except Hydrocotyle were able to use sediment CO(2), however, with variable efficiency, and with the isoetid, Lobelia, as clearly the most effective and the elodeid, Ludwigia, as the least efficient. At a water column CO(2) concentration in equilibrium with air, Lobelia, Lilaeopsis and Vallisneria covered >75% of their CO(2) requirements by sediment uptake, and sediment CO(2) contributed substantially to photosynthesis at water CO(2) concentrations up to 1000 micromol L(-1). For all species except Ludwigia, the shoot to root ratio on an areal basis was the single factor best explaining variability in the importance of sediment CO(2). For Ludwigia, diffusion barriers limited uptake or transport from roots to stems and transport from stems to leaves. Submersed plants other than isoetids can utilize sediment CO(2), and small and medium sized elodeids with high root to shoot area in particular may benefit substantially from uptake of sediment CO(2) in low alkaline lakes.

Lactobacillus plantarum response to inorganic carbon concentrations: PyrR2-dependent and -independent transcription regulation of genes involved in arginine and nucleotide metabolism

Lactobacillus plantarum susbp. plantarum is a capnophilic Gram-positive heterotroph with optimal growth in 4 % CO(2)-enriched air. At low inorganic carbon (C(i)) concentrations, the pyr genes encoding the enzymes of the pyrimidine biosynthetic pathway were overexpressed, in agreement with a previous study showing that these genes are regulated at the transcription level in response to C(i) via a PyrR(2)-mediated mechanism. A previous study of high-CO(2)-requiring (HCR) mutants revealed an unknown genetic link between arginine regulation and C(i)-dependent nutritional needs. To better understand L. plantarum's adaptation to C(i) availability, additional C(i)-responsive genes were sought in the arginine biosynthetic pathway (arg and car genes) using slot-blot hybridization and a proteomic differential 2D gel electrophoresis (DIGE) global approach. Besides the nine pyr-encoded proteins, 16 new Icr (inorganic-carbon-regulated) proteins accumulated differentially in response to C(i) availability, suggesting that the C(i) response involves several metabolic pathways and adaptation processes. Among these Icr proteins only argininosuccinate lyase, encoded by argH, was involved in arginine biosynthesis. Three proteins involved in the purine biosynthetic pathway and nucleotide conversion, adenylate kinase (Adk), GMP synthase (GuaA), and IMP dehydrogenase (GuaB), accumulated differentially in response to changes in C(i) levels. Expression of the Icr protein-encoding genes argH and guaB was regulated at the transcription level or by RNA stability in response to C(i) availability, as previously demonstrated for the pyr genes. However, PyrR(2) was not essential for the C(i)-regulated transcription of argH and guaB, demonstrating that PyrR(2) modulates only a subset of C(i)-regulated genes. These results suggest that the C(i) response may involve at least two regulatory mechanisms in L. plantarum.

Growth limitation due to high pH and low inorganic carbon concentrations in temperate species of the dinoflagellate genus Ceratium

The effects of high pH and low DIC (dissolved inorganic carbon) concentrations on growth rates of the dinoflagellate Ceratium were studied using 2 different approaches: (1) pH drift experiments, in which both pH and DIC change during the experiment, and (2) constant pH and DIC experiments at a range of fixed pH and DIC levels. The upper pH limits for growth were between 8.7 and 9.1 for the 3 species tested (C. furca, C. tripos and C. fusus) and thus within an environmentally relevant pH range. Hence, for Ceratium spp. and other dinoflagellates with upper pH tolerances for growth below or around 9, high pH will most likely periodically be a limiting factor in coastal areas. Different upper pH limits for growth were found using either the pH drift or the constant pH methods for the larger Ceratium species, but, for the smaller species, the 2 methods provided similar results. The results therefore suggest a combined pH/DIC limitation for large species such as C. tripos and C. furca in natural waters.

Facies distribution of post‐impact sediments in the Ordovician Lockne and Tvären impact craters: Indications for unique impact‐generated environments

Abstract— The Lockne and Tvären craters formed in the Late Ordovician Baltoscandian epicontinental sea. Both craters demonstrate similarities concerning near‐synchronous age, target seabed, and succeeding resurge deposits; however, the water depths at the impact sites and the sizes of the craters were not alike. The post‐impact sedimentary succession of carbonates, i.e., the Dalby Limestone, deposited on top of the resurge sediments in the two craters, is nevertheless similar. At least three main facies of the Dalby Limestone were established in the Lockne crater, depending on sea‐floor topography, location with respect to the crater, and local water currents. The dominating nodular argillaceous facies, showing low values of inorganic carbon (IC), was distributed foremost in the deeper and quiet areas of the crater floor and depressions. At the crater rim, consisting of crushed crystalline basement ejecta, a rim facies with a reef‐like fauna was established, most certainly due to topographical highs and substrate‐derived nutrients. Between these facies are occurrences of a relatively thick‐bedded calcilutite rich in cephalopods (cephalopod facies).In Tvären, the lower part of the succession consists of an analogous argillaceous facies, also showing similar low IC values as in Lockne, followed by calcareous mudstones with an increase of IC. Occasionally biocalcarenites with a distinctive fauna occur in the Tvären succession, probably originating as detritus from a facies developed on the rim. They are evident as peaks in IC and lows in organic carbon (Corg). The fauna in these biocalcarenites corresponds very well with those of erratic boulders derived from Tvären; moreover, they correspond to the rim facies of Lockne except for the inclusion of photosynthesizing algae, indicating shallower water at Tvären than Lockne. Consequently, we suggest equivalent distribution patterns for the carbonates of the Dalby Limestone in Lockne and Tvären.

FtsH protease is required for induction of inorganic carbon acquisition complexes in Synechocystis sp. PCC 6803

Cyanobacteria possess a complex CO(2)-concentrating mechanism (CCM), which is induced by low inorganic carbon conditions. To investigate the involvement of proteases in the processes of induction and degradation of the CCM complexes, we studied the FtsH2 (DeltaSlr0228) and Deg-G (DeltaSlr1204/DeltaSll1679/DeltaSll1427) protease mutants of Synechocystis sp. PCC 6803. WT and protease mutant cells were grown under high CO(2) and then shifted to low CO(2), followed by a proteome analysis of the membrane protein complexes. Interestingly, in the FtsH2 protease mutant, inducible CCM complexes were not detected upon shift to low CO(2), whereas the Deg-G mutant behaved like WT. Also the transcripts of the inducible CCM genes and their regulator ndhR failed to accumulate upon shift of FtsH2 mutant cells from high to low CO(2), indicating that the regulation by the FtsH2 protease is upstream of NdhR. Moreover, functional photosynthesis was shown a prerequisite for induction of CCM in WT at low CO(2), possibly via generation of oxidative stress, which was shown here to enhance the expression of inducible CCM genes even at high CO(2) conditions. Once synthesized, the CCM complexes were not subject to proteolytic degradation, even when dispensable upon a shift of cells to high CO(2).

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat ( Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha −1 year −1 were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing ∼19 g kg −1 of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha −1 year −1 exhibited thick sola with low inorganic carbon content (mean 3 g kg −1) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.

Modelling vegetative growth, gamete production and encystment of dinoflagellates in batch culture

An intriguing case of encystment of the dinoflagellate Scrippsiella lachrymosa in culture has recently been presented: cyst concentrations still increased after the abundance of the vegetative cells had decreased to very low numbers. To account for this apparent time lag, and using a model with an encystment rate equation in which vegetative growth and encystment rates were coupled, the calculated growth and encystment rates had to be 8 to 12 d -1 , values which were considered 'not biologically meaningful'. Here a new model of dinoflagellate growth and encystment is presented in which the mitotic cycle (vegetative growth) is coupled quantitatively to the sexual cycle (cyst forma- tion) by having 4 gametes emanate from 1 vegetative cell, but without directly coupling the rates of vegetative growth and encystment. Calibrated on literature data of S. lachrymosa cultured in f/4 medium, this model satisfactorily describes motile cell (vegetative cells and gametes) and cyst devel- opment with correlations between log-transformed model and experimental data of r 2 = 0.80 (motile cells) and r 2 = 0.94 (cysts) and with typical maximum rates in the exponential growth phase of μcell = 0.55 d -1 (gross vegetative cell rate), μgamete+cell = 0.38 d -1 (net motile cell growth rate), e = 0.42 d -1 (encystment rate). All these rates declined in the stationary growth phase. Sample sonication is sug- gested as the cause for low motile cell concentrations in the original experiment when cyst produc- tion was high. Inorganic carbon limitation due to low inorganic carbon to nitrogen concentrations in the growth media is probably the reason why cysts in f/4 medium stopped making calcite covers in later stages of the experiment and why cyst yield in f/2 medium was not double the yield in f/4. A new method for measuring in situ encystment rates of dinoflagellate populations with a phased sexual cycle is proposed.