Laboratory Batch Cultures Research Articles

Unveiling the Cultivation of Nostoc sp. under Controlled Laboratory Conditions.

Cyanobacteria, photoautotrophic Gram-negative bacteria, play a crucial role in aquatic and terrestrial environments, contributing significantly to fundamental ecological processes and displaying potential for various biotechnological applications. It is, therefore, critical to identify viable strains for aquaculture and establish accurate culture parameters to ensure an extensive biomass supply for biotechnology purposes. This study aims to establish optimal laboratory batch culture conditions for Nostoc 136, sourced from Alga2O, Coimbra, Portugal. Preliminary investigations were conducted to identify the optimal culture parameters and to perform biomass analysis, including protein and pigment content. The highest growth was achieved with an initial inoculum concentration of 1 g.L-1, using modified BG11 supplemented with nitrogen, resulting in a Specific Growth Rate (SGR) of 0.232 ± 0.017 μ.day-1. When exposed to white, red, and blue LED light, the most favourable growth occurred under a combination of white and red LED light exhibiting an SGR of 0.142 ± 0.020 μ.day-1. The protein content was determined to be 10.80 ± 2.09%. Regarding the pigments, phycocyanin reached a concentration of 200.29 ± 30.07 µg.mL-1, phycoerythrin 148.29 ± 26.74 µg.mL-1, and allophycocyanin 10.69 ± 6.07 µg.mL-1. This study underscores the influence of light and nutrient supplementation on the growth of the Nostoc biomass.

Growth conditions impact particulate absorption and pigment concentrations in two common bloom forming cyanobacterial species

Remote sensing using satellite imagery has been promoted as a method to broaden the scale and frequency of cyanobacterial monitoring. This relies on the ability to establish relationships between the reflectance spectra of water bodies and the abundance of cyanobacteria. A challenge to achieving this comes from a limited understanding of the extent to which the optical properties of cyanobacteria vary according to their physiological state and growth environment. The aim of the present study was to determine how growth stage, nutrient status and irradiance affect pigment concentrations and absorption spectra in two common bloom forming cyanobacterial taxa: Dolichospermum lemmermannii and Microcystis aeruginosa. Each species was grown in laboratory batch culture under a full factorial design of low or high light intensity and low, medium, or high nitrate concentrations. Absorption spectra, pigment concentrations and cell density were measured throughout the growth phases. The absorption spectra were all highly distinguishable from each other, with greater interspecific than intraspecific differences, indicating that both D. lemmermannii and M. aeruginosa can be readily differentiated using hyperspectral absorption spectra. Despite this, each species exhibited different responses in the per-cell pigment concentrations with varying light intensity and nitrate exposure. Variability among treatments was considerably higher in D. lemmermannii than in M. aeruginosa, which exhibited smaller changes in pigment concentrations among the treatments. These results highlight the need to understand the physiology of the cyanobacteria and to take caution when estimating biovolumes from reflectance spectra when species composition and growth stage are unknown.

Dynamic macromolecular composition and high exudation rates in Prochlorococcus

AbstractEvery living cell is composed of macromolecules such as proteins, DNA, RNA, and pigments. The ratio between these macromolecular pools depends on the allocation of resources within the organism to different physiological requirements, and in turn affects biogeochemical cycles of elements such as carbon, nitrogen, and phosphorus. Here, we present detailed measurements of the macromolecular composition of Prochlorococcus MIT9312, a representative strain of a globally abundant marine primary producer, as it grows and declines due to nitrogen starvation in laboratory batch cultures. As cells reached stationary stage and declined, protein per cell decreased by ~ 30% whereas RNA per cell and pigments per cell decreased by ~ 75%. The decline stage was associated with the appearance of chlorotic cells, which had higher forward scatter (a proxy for cell size) but lower chlorophyll autofluorescence, as well as with changes in photosynthetic pigment composition. Specifically, during culture decline divinyl‐chlorophyll‐like pigments emerged, which were not observed during exponential growth. These divinyl‐chlorophyll‐like pigments were also observed in natural samples from the Eastern Mediterranean. Over 90% of the carbon fixed by Prochlorococcus MIT9312 (but not of a different strain, NATL2A) was released into the growth media under these laboratory conditions. Variations in RNA/protein indicate that, broadly defined, the macromolecular composition of Prochlorococcus MIT9312 is more similar to eukaryotic phytoplankton than to marine heterotrophic bacteria, possibly due to the significant investment in photosynthetic machinery of phototrophs.

Metabolomics-derived marker metabolites to characterize Phaeocystis pouchetii physiology in natural plankton communities

Phaeocystis pouchetii (Hariot) Lagerheim, 1893 regularly dominates phytoplankton blooms in higher latitudes spanning from the English Channel to the Arctic. Through zooplankton grazing and microbial activity, it is considered to be a key resource for the entire marine food web, but the actual relevance of biomass transfer to higher trophic levels is still under discussion. Cell physiology and algal nutritional state are suggested to be major factors controlling the observed variability in zooplankton grazing. However, no data have so far yielded insights into the metabolic state of Phaeocystis populations that would allow testing this hypothesis. Therefore, endometabolic markers of different growth phases were determined in laboratory batch cultures using comparative metabolomics and quantified in different phytoplankton blooms in the field. Metabolites, produced during exponential, early and late stationary growth of P. pouchetii, were profiled using gas chromatography-mass spectrometry. Then, metabolites were characterized that correlate with the growth phases using multivariate statistical analysis. Free amino acids characterized the exponential growth, whereas the early stationary phase was correlated with sugar alcohols, mono- and disaccharides. In the late stationary phase, free fatty acids, sterols and terpenes increased. These marker metabolites were then traced in Phaeocystis blooms during a cruise in the Barents Sea and North Norwegian fjords. About 50 endometabolites of P. pouchetii were detected in natural phytoplankton communities. Mannitol, scyllo-inositol, 24-methylcholesta-5,22-dien-3β-ol, and several free fatty acids were characteristic for Phaeocystis-dominated blooms but showed variability between them. Distinct metabolic profiles were detected in the nutrient-depleted community in the inner Porsangerfjord (< 0.5 µM NO3−, < 0.1 µM PO43−), with high relative amounts of free mono- and disaccharides indicative for a limited culture. This study thereby shows how the variable physiology of phytoplankton can alter the metabolic landscape of entire plankton communities.

Salinity and growth effects on dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas of Skeletonema costatum, Phaeocystis globosa and Heterocapsa triquetra

The effects of growth stage and salinity on dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cellular content were investigated in laboratory batch cultures of three phytoplankton species (Skeletonema costatum, Phaeocystis globosa and Heterocapsa triquetra). DMSP and DMSO cell quotas of the three microalgae were measured at three salinities (20, 27, 35) and in three growth phases at salinity 35. DMSP and DMSO cell quotas varied along the growth for all species with an increase of DMSP for S. costatum and a decrease of the DMSP to DMSO ratio (DMSP/DMSO) for P. globosa and H. triquetra in late exponential-stationary phase. We hypothesized that the oxidative stress caused by light and/or nutrients limitation induced the oxidation of DMS or DMSP to DMSO. DMSP cell quotas increased with salinity, mostly in S. costatum and H. triquetra, for which DMSP is supposed to be an osmoregulator. In H. triquetra, DMSO cell quotas stayed constant with increasing salinity. DMSO was near detection limits in S. costatum experiments. In P. globosa, DMSP and DMSO concentrations increased at low and high salinity. DMSO showed higher increase at low salinity presumably as the result of a salinity-induced oxidative stress which caused DMSP oxidation into DMSO in hyposaline conditions. We concluded that DMSP acts as an osmoregulator for the three studied species and DMSO acts as an antioxidant for P. globosa at low salinity. In P. globosa and H. triquetra, DMSP/DMSO increase with salinity in response to salinity stress.

Optimization of microalgae growth for biofuel production using a new empirical dynamic model

This study involves modeling the growth of Tetradesmus sp. in a laboratory batch culture chamber under red, blue and magenta lights at intensities of 1000 to 5000 lux as well as under artificial white light and sunlight (at natural intensities). The growth, which is determined by measuring the optical density at 680 nm, is found to be highest at 5000 lux with values of 0.997 (Magenta), 0.793 (blue) and 0.777 (red) which are compared to 0.799 (sunlight) and 0.815 (artificial white light). Furthermore, an empirical dynamic model is developed for the estimation of the microalgae growth and implemented with Matlab Simulink. The model is validated by calculating mean absolute percentage error (MAPE), correlation coefficient (R), root mean square error (RMSE), mean square error (MSE), and mean absolute error (MAE) and comparing the values with those of some existing (Logistic and Monod) models. The values of R are found to be 0.9834 (new model), 0.7119 (Logistic model) and 0.8177 (Monod model), showing that the new model has the highest correlation with the experimental data. Thus, the growth of microalgae (Tetradesmus sp.) is greatly enhanced by high intensity magenta light and is best described by the new empirical model.

Joint effects of five environmental factors on the growth of cyanobacterium Microcystis aeruginosa

Abstract In many lakes and reservoirs, Microcystis aeruginosa is one of the dominant bloom species. Five environmental factors, including nutrients and physical factors, were selected to evaluate their effects and interactions on the growth of M. aeruginosa (FACHB-905) by joint analysis in a laboratory batch culture. The results indicated that all five factors affected the growth rate alone or in combination, and that their interactions were complex. This cyanobacterium strain preferred higher water temperature and alkaline conditions, while not requiring high illumination or high concentrations of nitrogen and phosphorus. Owing to these features the bloom of this cyanobacterium appears easily in nature. The form of nitrogen (nitrate or ammonium) also affected the assessment of M. aeruginosa bloom. The possibility of M. aeruginosa bloom would still exist even if the phosphorus concentration in the water column was very low. The result provided a good basis for the analysis and prediction of M. aeruginosa blooms in terms of environmental assessment, because the joint analysis of multiple factors would offer more valuable information than a univariate analysis. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).

Effect of temperature rise and ocean acidification on growth of calcifying tubeworm shells (&amp;lt;i&amp;gt;Spirorbis spirorbis&amp;lt;/i&amp;gt;): an in situ benthocosm approach

Abstract. The calcareous tubeworm Spirorbis spirorbis is a widespread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbis shell growth we carried out four seasonal experiments in the Kiel Outdoor Benthocosms at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbis was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favoured selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.

Evolutionary Engineering in Chemostat Cultures for Improved Maltotriose Fermentation Kinetics in Saccharomyces pastorianus Lager Brewing Yeast

The lager brewing yeast Saccharomyces pastorianus, an interspecies hybrid of S. eubayanus and S. cerevisiae, ferments maltotriose, maltose, sucrose, glucose and fructose in wort to ethanol and carbon dioxide. Complete and timely conversion (“attenuation”) of maltotriose by industrial S. pastorianus strains is a key requirement for process intensification. This study explores a new evolutionary engineering strategy for improving maltotriose fermentation kinetics. Prolonged carbon-limited, anaerobic chemostat cultivation of the reference strain S. pastorianus CBS1483 on a maltotriose-enriched sugar mixture was used to select for spontaneous mutants with improved affinity for maltotriose. Evolved populations exhibited an up to 5-fold lower residual maltotriose concentration and a higher ethanol concentration than the parental strain. Uptake studies with 14C-labeled sugars revealed an up to 4.75-fold higher transport capacity for maltotriose in evolved strains. In laboratory batch cultures on wort, evolved strains showed improved attenuation and higher ethanol concentrations. These improvements were also observed in pilot fermentations at 1,000-L scale with high-gravity wort. Although the evolved strain exhibited multiple chromosomal copy number changes, analysis of beer made from pilot fermentations showed no negative effects on flavor compound profiles. These results demonstrate the potential of evolutionary engineering for strain improvement of hybrid, alloploid brewing strains.

Effect of culture conditions on growth, fatty acid composition and DHA/EPA ratio of Phaeodactylum tricornutum

The effect of growth phase and environmental factors on growth, fatty acid composition and DHA/EPA ratio of Phaeodactylum tricornutum Bohlin was studied. Microalgae were grown in laboratory batch cultures in f/2 medium. Cultures were grown at different salinities (15, 20, 28, and 35ppt), nitrogen (N) concentrations (1.24, 12.35, 24.70 and 49.40mgL−1), light intensities (50, 100 and 150μmolm−2s−1; 14:10h light:dark cycle) and temperatures (15, 20 and 25°C), and sampled at different points of the respective growth phases (inoculums, early-linear, middle-linear and late-linear phases). Samples were analyzed for biomass weight, fatty acid composition and total fatty acid content (TFAC). The main fatty acids in all culture conditions were C14:0 (5.25%–6.04%), C16:0 (13.96%–14.78%), C16:1n-7 (19.09%–35.73%), C18:1n-9 (5.56%–9.01%) and eicosapentaenoic acid (EPA, 22.81%–30.72%). The percentage of polyunsaturated fatty acids (PUFAs) was reduced while that of monounsaturated fatty acid acids (MUFAs) and TFACs increased with culture time. Salinity had no serious effect on fatty acid composition, however, a significant decline of TFAC was observed at the lowest salinity (p<0.05). Significant (p<0.05) increases of the relative contents of SFAs and MUFAs and a decrease of PUFAs were observed under N-limitation condition. The percentage of docosahexaenoic acid (DHA) was significantly enhanced with increasing light intensity (p<0.05), while that of DHA, EPA and PUFA decreased significantly with increasing temperature (p<0.05). DHA/EPA ratio tended to rise initially and fall later with increasing growth time, and reached the highest level with the lowest salinity, and the lowest temperature and initial N concentration, revealing a possible cell response to the stress brought from the unfavorable conditions. In conclusion, this study demonstrates the variation of growth, fatty acid composition and DHA/EPA ratio with growth phase and environmental factors in P. tricornutum, benefiting the production of PUFA-rich microalgae, with a DHA/EPA ratio optimal for aquaculture live food. Statement of relevanceWe conducted detailed analysis on the effect of the culture conditions on growth, fatty acid composition and DHA/EPA ratio in Phaeodactylum tricornutum, a widely used microalga for aquaculture feedstuff in China. We found that the environmental stress conditions increased DHA/EPA ratio. The research will benefit the production of PUFA-rich and DHA/EPA-ratio-optimal microalgae for aquaculture feedstuff.

An experimentally validated nitrate–ammonium–phytoplankton model including effects of starvation length and ammonium inhibition on nitrate uptake

Nitrate and ammonium are the two most important ionic forms of inorganic nitrogen driving biomass production in marine and freshwater aquatic systems. The performance of plants and algae often changes when reared with either of these two forms of nitrogen individually, as well as when they are both present, or when cells have experienced previous periods of nitrogen starvation. Current functional responses quantifying how ambient nitrogen drives changes in population density are unable to capture interacting and transient effects of nitrate and ammonium. Hence, in this paper we formulate, calibrate, and test a new nitrate–ammonium quota model that accounts for nitrate and ammonium uptake, as well as the effects of nitrogen starvation length and ammonium-induced nitrate uptake inhibition. We fit the model with several time-series from the green alga Chlorella sp. reared in laboratory batch cultures under multiple initial conditions. We show that a single set of calibrated model parameters can capture time-series collected from experiments inoculated at 12 different initial concentrations of nitrate, ammonium, and biomass. The model also performed well when validated against time-series from two novel initial conditions withheld from model calibration. Our model therefore provides a framework for evaluating the potential broader ecological and environmental consequences of ambient nitrate and ammonium regimes for phytoplankton communities in nature and aquaculture.

Cadmium accumulation and toxicity in the unicellular alga Pseudokirchneriella subcapitata: Influence of metal-binding exudates and exposure time.

Predicting metal availability and toxicity for chronic (several hours or days) metal exposure scenarios, even for unicellular algae, is a major challenge to existing toxicity models. This is because several factors affecting metal uptake and toxicity, such as the release of metal-binding exudates, changes in the kinetics of metal uptake and toxicity over time, and algal physiological acclimation to internalized metals, are still poorly understood. The present study assessed the influence of these factors on Cd uptake and toxicity in laboratory batch cultures of the freshwater alga Pseudokirchneriella subcapitata. To do so, changes in the free Cd(2+) concentrations caused by the release of metal-binding algal exudates were monitored, (109)Cd accumulation in algal cells was measured, and Cd-induced inhibition of algal growth as a function of exposure time (from 12 h to 96 h) was followed. Results indicate that metal-binding exudates may decrease the proportion of the free Cd(2+) ion in solution up to 2-fold, a decrease that affects Cd uptake and toxicity. Pseudokirchneriella subcapitata has the capacity to decrease net Cd uptake rate on short time scales (<24 h), but this reduction in the Cd uptake rate disappeared after 24 h, and Cd toxicity occurred at relatively high Cd concentrations in solution. These data illustrate some of the pitfalls of standard algal toxicity assays, which were designed for acute exposures, and suggest how robust chronic bioassays might be developed.

Photosynthetic and cellular toxicity of cadmium in Chlorella vulgaris

The toxic effects of cadmium (Cd) on the green alga Chlorella vulgaris were investigated by following the response to Cd of various toxicity endpoints (cell growth, cell size, photochemical efficiency of PSII in the light or Φ(PSII), maximal photochemical efficiency or Fv/Fm, chlorophyll a fluorescence, esterase activity, and cell viability). These toxicity endpoints were studied in laboratory batch cultures of C. vulgaris over a long-term 96-h exposure to different Cd concentrations using flow cytometry and pulse amplitude modulated fluorometry. The sequence of sensitivity of these toxicity endpoints was: cell yield >> Φ(PSII) ≈ esterase activity > Fv/Fm > chlorophyll a fluorescence ≈ cell viability. It is shown that cell apoptosis or cell death only accounted for a minor part of the reduction in cell yield even at very high algistatic free Cd²⁺ concentrations, and other mechanisms such as blocked cell divisions are major contributors to cell yield inhibition. Furthermore, cadmium may affect both the electron donors and acceptors of the electron transport chain at high free Cd²⁺ concentration. Finally, the resistance of cells to cell death was size-dependent; medium-sized cells had the highest toxicity threshold. The present study brings new insights into the toxicity mechanisms of Cd in C. vulgaris and provides a detailed comparison of the sensitivity of various Cd toxicity endpoints.

Actinobacteria—An Ancient Phylum Active in Volcanic Rock Weathering

A molecular biological analysis of Icelandic volcanic rocks of different compositions and glassiness revealed the presence of Actinobacteria as an abundant phylum. In outcrops of basaltic glass they were the dominant bacterial phylum. A diversity of Actinobacteria were cultured from the rocks on rock-agar plates showing that they are capable of growing on rock-derived nutrient sources and that many of the taxa identified by molecular methods are viable, potentially active members of the community. Laboratory batch-culture experiments using a Streptomyces isolate showed that it was capable of enhancing the release of major elements from volcanic rocks, including weathered basaltic glass, crystalline basalt and komatiite, when provided with a carbon source. Actinobacteria of a variety of other sub-orders were also capable of enhancing volcanic rock weathering, measured as Si release. However, most strains did not significantly increase the weathering of the silica-rich rock, obsidian. These data show that Actinobacteria can contribute to volcanic rock weathering and, therefore, the carbonate-silicate cycle. Given their ancient lineage, it is likely they have played a role in rock weathering for over two billion years.

Physiological response of Nannochloropsis sp. to saline stress in laboratory batch cultures

In the present paper, we investigated the physiological response of the marine microalga Nannochloropsis sp. to salt stress (13, 27, 54, and 81 g L−1 NaCl). Increasing the sodium chloride concentration caused up to a 70 % decrease in the chlorophyll a concentration, cell growth, and net photosynthesis rate. The chlorophyll a fluorescence measurements indicated a strong reduction in the effective quantum yield of photosystem II (−60 %) and an increase in nonphotochemical quenching when the cells were exposed to NaCl concentrations greater than 27 g L−1 (control). In contrast, the specific lipid content increased up to 80 % when the sodium chloride concentration was increased from 27 to 54–81 g L−1. These results are relevant for the outdoor cultivation of this microalga using open photobioreactors, in which microalgae are subjected to strong changes in salinity concentration caused by water evaporation.

Nitrogen isotope ratio of cyanobacterial chlorophyll: Chemostat vs. batch culture

Nitrogen isotope records of chloropigments can be used to reconstruct photic zone processes. However, the 15N offset between chlorophyll and biomass (εpor=δ15Nbiomass−δ15Nchlorophyll) of cyanobacteria and eukaryotes grown in laboratory batch cultures differs significantly and the cause of the difference remains unknown. Here, in four experiments with Synechocystis sp. PCC 6803, values of εpor were statistically invariant when cultures were maintained at pH 6.5–9.5 under constant growth conditions in a chemostat. The results suggest that the negative values of εpor observed for freshwater cyanobacteria are not artifacts of batch culturing.

Comment on “Measuring primary production rates in the ocean: Enigmatic results between incubation and non‐incubation methods at Station ALOHA” by P. D. Quay et al.

[1] Quay et al. [2010, paragraph 52] state that “...an absolute standard for [primary production] does not exist [therefore] the accuracy of any method cannot be verified.” Further, after diminishing possible errors in their nonincubation methods (paragraph 53 in Quay et al. [2010]), they say that the difference they note with incubation methods “raises a cautionary flag about incubation-based [estimates]” of ocean primary production. [2] Here, I take issue with these statements, arguing (1) from current understanding of phytoplankton and photosynthetic physiology, and (2) from previous comparisons of in situ and incubation estimates of primary production, evidence that Quay et al. [2010] ignore. [3] That there is no “absolute standard” for the accuracy of any primary production method is true in the analytical sense, in that creation of a standard or calibration curve is not possible. However, there is substantial empirical, and strong theoretical, evidence for the limits of photosynthesis with regard to both the supply of irradiance, and with regard to the temperature at which metabolism proceeds. [4] Photochemical reactions in photosynthesis require 8 quanta to produce 1 molecule of O2 from the splitting of the water molecule, a quantum yield of 1/8 or 0.125. Measurements to support the theory are done under low irradiance where efficiency will be highest. Although difficult to confirm, it is generally accepted that a quantum yield for photosynthesis of 0.10 cannot be exceeded [Bannister and Wiedemann, 1984]. Falkowski [1981] extended these ideas to consider the limitations to photosynthesis under high irradiance. Falkowski argues from the actions of the photosynthetic unit in algal chloroplasts. The photosynthetic unit consists of antenna pigments to absorb irradiance, proteins, and a reaction center. The photosynthetic reaction center serves to stabilize, momentarily, the energy delivered from absorption of irradiance at the antenna in the form of electrons, and before those electrons are transferred along a chain of reactions leading to chemical energy. At high irradiance, electron transfer becomes saturated. A turnover of the photosynthetic unit can then be defined, representing the limit at which photochemistry can proceed. The number of photosynthetic units is proportional to the quantity of chlorophyll-a in the phytoplankton cell. The maximum rate of photosynthesis can be scaled, therefore, to the quantity of chlorophyll, and this is called the assimilation number. Falkowski [1981] concluded that 1 mg chlorophyll-a would correspond with fixing up to 25 mg C h . In the 30 years since that publication, I cannot recall data exceeding an assimilation number of 25 mg C (mg chlorophyll-a) 1 h 1 without there being serious questions. [5] The above limits to photosynthesis occur at the subcellular level, at the components of the photosynthetic units. At the cellular level, ambient temperature will ultimately limit the growth rate in phytoplankton, when light and nutrients are in abundance. Eppley [1972] compiled laboratory batch culture experiments conducted over a range of temperatures from near 0 C to >30 C. He found he could enclose virtually all the growth rate data with the equation,

Changing patterns of carbon allocation in lake phytoplankton: an FTIR analysis

Fourier transform infra-red (FTIR) spectroscopy was used to assess carbon allocation in selected phytoplankton (Pediastrum duplex, Ceratium hirundinella, Anabaena flos-aquae) in a eutrophic lake. In contrast to bulk-analysis techniques, FTIR spectroscopy can provide information on carbon allocation at the species level within natural mixed populations. Carbon allocation was determined using lipid/protein (L/P) and carbohydrate/protein (C/P) ratios and multivariate analysis of complete spectra and showed considerable intraspecific heterogeneity within samples dates, and clear seasonal changes in the spectra of Pediastrum and Anabaena, with both alga showing increased L/P and C/P ratios on selected sampling dates. Although increased ratios can indicate nutrient deficiency, the alga were not nutrient deficient during these periods, as indicated by continued population growth and high (>0.1%) internal phosphorus concentrations. FTIR spectra from Ceratium did not show any clear seasonal change. In all three algae, the transition from population growth to decline was not accompanied by any significant change in ratios, nor were low epilimnetic nutrients correlated with increased ratios, marking a significant contrast to laboratory batch cultures (previous studies) where low nutrients and the transition to stationary phase led to marked spectral changes.

Nitrogen and phosphorus removal through laboratory batch cultures of microalga Chlorella vulgaris and cyanobacterium Planktothrix isothrix grown as monoalgal and as co-cultures

Batch cultures of the green microalga Chlorella vulgaris and cyanobacterium Planktothrix isothrix and their corresponding co-cultures were grown in municipal wastewater in order to study their growth as well as the nitrogen (NH4–N) and phosphorus (PO43−–P) removal. The cultures were grown under two irradiances of 20 and 60 μmol photons m−2 s−1 in shaken and unshaken conditions. The co-culture of unshaken Chlorella and Planktothrix showed the greatest growth under both irradiances. The monoalgal Planktotrix cultures showed better growth when unshaken than when shaken, whereas Chlorella cultures grew better when mixed, but only at the higher irradiance. The highest percentage of nitrogen removal (up to 80%) was attained by the unshaken co-cultures of Chlorella and Planktothrix. The amount of nitrogen recycled in the biomass reached up to 85% of that removed. Shaken monoalgal cultures of Chlorella showed phosphorus removal under both irradiances. They completely removed the initial phosphorus concentration (7.47 ± 0.17 mg L−1) within 96 and 48 h under 20 and 60 μmol photons m−2 s−1, respectively.

Investigation of mircroorganisms colonising activated zeolites during anaerobic biogas production from grass silage

The colonisation of activated zeolites (i.e. clinoptilolites) as carriers for microorganisms involved in the biogas process was investigated. Zeolite particle sizes of 1.0–2.5 mm were introduced to anaerobic laboratory batch-cultures and to continuously operated bioreactors during biogas production from grass silage. Incubation over 5–84 days led to the colonisation of zeolite surfaces in small batch-cultures (500 ml) and even in larger scaled and flow-through disturbed bioreactors (28 l). Morphological insights were obtained by using scanning electron microscopy (SEM). Single strand conformation polymorphism (SSCP) analysis based on amplification of bacterial and archaeal 16S rRNA fragments demonstrated structurally distinct populations preferring zeolite as operational environment. via sequence analysis conspicuous bands from SSCP patterns were identified. Populations immobilised on zeolite (e.g. Ruminofilibacter xylanolyticum) showed pronounced hydrolytic enzyme activity (xylanase) shortly after re-incubation in sterilised sludge on model substrate. In addition, the presence of methanogenic archaea on zeolite particles was demonstrated.