Process development with nitrogenase-producing Escherichia coli C-M74 (pUS1) CellS

A process for the continuous fermentation of the genetically modified, nitrogenase-producing Escherichia coli C-M74 (pUS1)-strain has been developed. This strain, which is able to fix molecular nitrogen, has the nifgenes of the bacterium Klebsiella pneumoniae. Cell growth and nitrogenase activity of the enzyme have been optimized both in batch and continuous fermentations. For the fermentations, trial runs were performed by cultivating the E. coli cells in 50-ml culture bottles. The medium composition was varied in order to provide high biomass production and nitrogenase activity. For an effective fermentation control, an on-line analysis was built up for the substrates ammonium and glucose. Other medium components such as ampicillin, citric acid, acetic acid, nitrogenase activity, and protein were measured by using different off-line methods. Modern optical methods like in-line microfluorometry for monitoring the culture fluorescence and laser flow cytometry for the estimation of DNA and protein content were also employed. Plasmid stability was also determined.     

Effect of photobioreactor inclination on the biomass productivity of an outdoor algal culture

The profiles of photon flux density incidented on a tubularloop photobioreactor in the day could be altered by inclining the bioreactor at an angle with the horizontal. The photon flux density at noon decreased with increasing angle of inclination, whereas the photon flux density in the early morning and late afternoon increased with increasing angle of inclination. The overall photosynthetic radiance received by the bioreactor inclined at 0, 25, 45, and 80 degrees was 1:0.89:0.77:0.62. Regardless of the angle of bioreactor inclination, the overall biomass output rate of a fed-batch culture over an 8-h/day period was comparable (26-36 g-biomass m(-2) bioreactor surface area day(-1)). As a bioreactor inclined at an angle occupied smaller land area, and daily biomass output rate per land area of a bioreactor inclined at 80 degrees (130 g-biomass m(-2) land) was about six times of that obtainable at horizontal position (21-g biomass m(-2) land). The bioenergetics growth yield from the absorbed photosynthetic radiance was not a constant but an inverse function of the photon flux density. The quasi-steady state chlorophyll content of the Chlorella cells varied between 36 and 63 mg g(-1) cells. Photoinhibition of the maximum photosynthetic capacity was not observed in this study.     

Ultrastructural and biochemical aspects of cell wall reconstitution in recalcitrant (grapevine) and regenerating (tobacco) leaf protoplasts

Summary To identify possible reasons that may contribute to recalcitrance in plant protoplasts, the time course of new cell wall deposition was studied by scanning electron microscopy in protoplasts of a recalcitrant species, the grapevine. Results showed that microfibrils were developed after 2 days of culture, that complete cell wall formation occurred on Day 6 to 7 of protoplast culture, and its ultrastructural appearance was identical to that of grapevine leaf-derived callus cells. In addition, a comparative study was undertaken on [U-¹⁴C]glucose uptake and incorporation in ethanol-soluble, cellulosic, and noncellulosic polysaccharide fractions in protoplasts of grapevine and of a readily regenerating species, tobacco, during culture. There was a significantly higher [U-¹⁴C]glucose uptake by tobacco than by grapevine protoplasts. The label distribution in the ethanol-soluble, cellulosic, and noncellulosic fractions of newly synthesized cell walls differed quantitatively between the two species. In particular, the labeled glucose incorporated in the noncellulosic cell wall fraction was threefold greater in tobacco than in grapevine protoplasts. Differences were also revealed in the monosaccharide composition of this fraction between the two species. Addition of dimethyl sulfoxide to the culture medium resulted in a dramatic increase in [U-¹⁴C]glucose uptake by grapevine protoplasts, whereas it exhibited a limited effect in tobacco protoplasts. It showed no effect on the ultrastructural characteristics of new cell wall nor on the incorporation rate of labeled glucose in the cellulosic and noncellulosic cell wall fractions.     

Fecundity,reproductive effort,and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 g egg^–1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.     

Effects of acid wastes from titanium dioxide production on biomass and species richness of benthic algae

Titanium dioxide wastes are suspected to be toxic to rocky shore communities in an estuary in southeast Norway. An experimental project lasting two years examined whether titanium dioxide wastes affected recolonization by rocky shore organisms. The experiments were performed in situ in six tanks (each with 9 m³ brackish water) at two different levels of salinity. Three different concentrations of industrial waste water were used. The growth season in 1986 was dry and sunny compared to 1987, causing reduction of growth on exposed granite chips compared to controls. At the two highest waste concentrations in the tanks, Fucus serratus was observed with necrotic tissue both years, and in 1986 benthic diatoms were scarce.     

Biomass and photosynthesis of size-fractionated phytoplankton in Canadian Shield lakes

Both in situ primary production and biomass (chlorophyll ) of fractionated phytoplankton (<64,µ, <25 µm and < 10 µm) were studied in 10 Canadian Shield lakes to elucidate the spatial and temporal variability of the contribution of size fractions to the biomass and primary production of the phytoplankton community. Mean summer biomass and production of each size fraction varied significantly between lakes. Within lakes, temporal variation was low for biomass but great for production. However, temporal variation can be considered of minor importance during the sampling period, as compared to the spatial variation between lakes. Algae from the < 10 µm size fraction were the most important in biomass (41–65 %) and production (23–69%). The temporal trends for both phytoplankton variables thus generally followed closely that of the < 10 µm size fraction. Among the physical, chemical and morphometric variables of the studied lakes, water transparency (Secchi disk), total phosphorus, lake volume, lake area, and mean depth gave the best correlations with phytoplankton variables.Contribution number 354 from the Groupe de recherches en Ecologie des Eaux douces, Limnological Research Group, Université de Montréal.     

Seasonal coupling between phyto- and bacterioplankton in a sand pit lake (Créteil lake,France)

Phyto- and bacterioplankton biomass and activity were simultaneously measured during the course of one year in the shallow Créteil Lake (France).Phytoplankton was dominated, during the whole year, by small-sized organisms (10 to 25 µm). Bacteria were in a majority small coccoids (<0.3 µm). Phyto -and bacterioplankton abundances averaged respectively 3.3 × 10⁶ cells l^–1 and 6 × 10⁹ cells l^–1.The phasing of the activity and biomass periods suggest a close coupling between phyto- and bacterioplankton. There were two distinct periods of high activity and biomass. Maximal values were observed in summer but an early increase occurred also in winter. Low or undetectable phytoplankton excretion rates, when heterotrophic activity was maximum, indicated a bacterial uptake of up to 100% of the released algal products during the incubation period. Heterotrophic uptake measurements with both glucose and amino acids revealed a seasonal change of the substrates in the lake, glucose uptake being associated more with the maximum activity of the algae, while the amino acids uptake was relatively higher during their decline.The maximal photosynthetic rate averaged 21.5 mgC m^–3 h^–1 and mean Vmax values were 0.056 and 0.050 mgC m^–3 h^–1 respectively for glucose and amino acids uptake.     

Size-frequency estimates of secondary production byMysis relicta in Lakes Michigan and Huron

Data from five Great Lakes studies ofMysis relicta populations were reanalyzed to calculate secondary production estimates using the size-frequency method. Production estimates (P) ranged from 0.25 to 3.2 g dry weight m^–2 yr^–1. Average annual biomass {xxB} and mean annual density (xxD) were 0.11–1.11 g dry weight/ m² and 25–434 animals/ m², respectively. P:{xxB} ratios varied only between 2.2 and 3.3. Maximum and minimum biomass values within a study varied by a factor of 519 for one study but by less than 17 for the others. Highest estimates of P, {xxB} and {xxD} were calculated for collections from a 50-m station in Lake Michigan despite the larger populations suspected to be present at greater depths sampled in the other studies. These conservative estimates provide a basis for scaling trophic interactions involvingM. relicta and emphasize findings by previous workers that night-time sampling with vertical net hauls is the best available technique for quantitative studies ofM. relicta populations in the Great Lakes.