Production of xanthan by in-flow cultures of Xanthomonas campestris

The kinetics of xanthan formation in Xanthomonas campestris continuous and fed-batch fermentations was studied along with metabolic changes due to growth rate variation. A maximum growth rate within the range 0.11–0.12 h^–1 was obtained from the continuous culture data in defined medium, producing xanthan at rates up to 0.36 g l^–1 h^–1 corresponding to a maximum 67% glucose conversion at a dilution rate (D) of 0.05 h^–1. Comparatively, fed-batch cultivation was more efficient, producing maximum xanthan at 0.75 g l^–1 h^–1 and 63% glucose conversion at 0.1 h^–1. When reaching D=0.062 h^–1 in continuous cultures, a change was observed and the values of the specific rate of substrate consumption shifted, initiating an uncoupled growth region expressing a lack of balance of the catabolic and anabolic reactions. The deviation was not accompanied by a change in specific xanthan production indicating that xanthan metabolism was not affected by D. For fed-batch-grown X. campestris cells within the range D=0.03–0.1 h^–1, both metabolic parameters changed linearly with the growth rate showing a wide region coupled to growth. Outside that range, glucose accumulated and the specific xanthan production dropped, suggesting substrate inhibition. Correspondence to: J. C. Roseiro     

Effect of high concentration of nutrients onBacillus thuringiensis cultures

Summary Bacterial insecticide production using a strain ofBacillus thuringiensis var. kurstaki was studied in batch culture considering the influence of increasing concentration of components of a glucose — yeast extract — mineral salts medium.It was found that spore counts were increased from 1.08×10¹² spores. 1^–1 to 7.36×10¹² spores. 1^–1 and toxin level from 1.05 mg.ml^–1 to 6.85 mg.ml^–1, when the concentration of glucose was increased from 8 to 56 (g 1^–1), with the corresponding increase in the rest of medium components. Higher concentration of nutrients inhibit either spore count or toxin production.Preliminary experiments of fed-batch cultures which allows the use of high amounts of nutrients were also carried out. In this case spore counts of 1.2×10¹³ spores.1^–1 were achieved.     

Nickel toxicity inPseudomonas tabaci: Single cell and bulk sample analysis of bacteria cultured at high cation levels

Summary The growth ofPseudomonas tabaci in nutrient medium is partially inhibited in the presence of 10^–3 M added nickel (threshold toxic concentration), with complete inhibition at 10^–2 M nickel—but no effect at 10^–4 and 10^–5 M. Toxic levels of nickel affect both cell division and cell viability.Spectrophotometric determination of intracellular levels of nickel at different external concentrations showed that the highest internal values occurred with cells cultured in 10^–4M (non-toxic) nickel medium rather than in 10^–3 (toxic) medium—suggesting that nickel toxicity does not primarily relate to internal concentration.X-ray microanalysis, carried out on whole bacterial cells, showed that toxic levels of nickel in the external medium resulted in a range of ionic changes in the cell, including a decrease in the level of K (K efflux) and an increase in the levels of Mn, Fe, Ni, and Cu (transition metal cation influx). Other changes induced by nickel toxicity included an increase in the level of soluble S (with a decrease in insoluble S), an increased cell dry mass, and a conspicuous plasmolysis—which was observed both in whole cells and in ultrathin sections.The results obtained support a primary toxic effect of nickel at the cell surface—possibly directly affecting the transport activity of the plasmalemma. The resulting changes, particularly involving the influx of a range of cations, may lead to secondary toxic activities affecting the whole metabolism, leading to plasmolysis and inhibition of division.     

The production of cyclopiazonic acid by Penicillium commune and cyclopiazonic acid and aflatoxins by Aspergillus flavus as affected by water activity and temperature on maize grains

The combined effects of water activity (a_w) and temperature on mycotoxin production by Penicilium commune (cyclopiazonic acid — CPA) and Aspergillus flavus (CPA and aflatoxins — AF) were studied on maize over a 14-day period using a statistical experimental design. Analysis of variance showed a highly significant interaction (P 0.001) between these factors and mycotoxin production. The minimum a_w/temperature for CPA production (2264 ng g^–1 P. commune, 709 ng g^–1 A. flavus) was 0.90 a_w/30 °C while greatest production (7678 ng g^–1 P. commune, 1876 ng g^–1 A. flavus) was produced at 0.98 a_w/20 °C. Least AF (411 ng g^–1) was produced at 0.90 a_w/20 °C and most (3096 ng g^–1) at 0.98 a_w/30 °C.     

Hydrogen accumulation by H2-uptake negative strains of Rhizobium

Summary Hydrogen evolution from root nodules has been reported to decrease the efficiency of the nitrogen fixing system. Mutants ofRhizobium meliloti andRhizobium leguminosarum were selected which were deficient in H₂-uptake capacity (Hup^–). The relative efficiency of the nitrogen fixation for both species assessed with C₂H₂ reduction was 0.66.The hydrogen production was monitored using a simple root incubation method. As such, hydrogen production up to 3.83 and 15.57 ml.day^–1.g^–1 plant dry weight were recorded forPisum sativum — Rhizobium leguminosarum 4.20 Hup^– andMedicago sativa — Rhizobium meliloti 1.5 Hup^– respectively. In a closed container (250 ml), hydrogen concentrations up to 20% (v/v) could be reached in the root phase ofMedicago sativa in a time period of 320 hours.     

Effect of riparian land use on contributions of terrestrial invertebrates to streams

Since terrestrial invertebrates are often consumed by stream fishes, land-use practices that influence the input of terrestrial invertebrates to streams are predicted to have consequences for fish production. We studied the effect of riparian land-use regime on terrestrial invertebrate inputs by estimating the biomass, abundance and taxonomic richness of terrestrial invertebrate drift from 15 streams draining catchments with three different riparian land-use regimes and vegetation types: intensive grazing — exotic pasture grasses (4 streams), extensive grazing — native tussock grasses (6 streams), reserve — native forest (5 streams). Terrestrial invertebrate drift was sampled from replicated stream reaches enclosed by two 1 mm mesh drift nets that spanned the entire channel. The mean biomass of terrestrial invertebrates that entered tussock grassland (12 mg ash-free dry mass m^–2 d^–1) and forest streams (6 mg AFDM m^–2 d^–1) was not significantly different (p > 0.05). However, biomass estimated for tussock grassland and forest streams was significantly higher than biomass that entered pasture streams (1 mg AFDM m^–2 d^–1). Mean abundance and richness of drifting terrestrial invertebrates was not significantly different among land-use types. Winged insects contributed more biomass than wingless invertebrates to both pasture and tussock grassland streams. Winged and wingless invertebrates contributed equally to biomass entering forest streams. Land use was a useful variable explaining landscape-level patterns of terrestrial invertebrate input for New Zealand streams. Evidence from this study suggests that riparian land-use regime will have important influences on the availability of terrestrial invertebrates to stream fishes.     

Release of sedimentary nitrogen and phosphorus in polder ditches of a low-moor peat area

The release of N and P from the sediment of two ditches, one (A) dominated by filamentous algae and the other (B) by water-lilies, was estimated by core and enclosure experiments. The release rates for ditch A tended to be higher than those for ditch B. Sediment cores covered by a filamentous algae layer released about 1.5 times more N and P than those from which the layer had been removed. During the incubation of the cores in the dark at 20°C for 2–3 weeks, about 10% of the N in the filamentous algae layer was mineralized. The mineralization could be described as a first-order reaction with a rate constant of about 0.2 d^–1. On average the cores of ditches A and B released about 40 mg mineral N and 3 mg.m^–2.d^–1 soluble reactive phosphorus. Defining the release from the sediment in the enclosures as the net increase of N and P in the water phase and in the vegetation minus the input, a negative net release,i.e. net accumulation of N and P in the sediment, was found over the summer half of the year. The negative values were due to the significant N and P input, resulting from pumping ditch water into the enclosures in order to compensate for downward seepage. From the enclosure experiments a downward seepage rate of 14 mm.d^–1 and an external load of about 6 g.m^–2 total N and 0.6 g.m^–2 total P during the summer half of the year —i.e. 33 mg.m^–2.d^–1 N and 3 mg.m^–2.d^–1 P. respectively — was calculated for the ditches. Tentative gross release rates — based on the sum of the positive net release of N and P into the water phase over 1–2 weeks intervals and the net increase of N and P in the vegetation — converted to 20°C and allowing for underestimation of the primary production by a factor of 5, amounted to 58 mg mineral N and 7 mg.m^–2.d^–1 soluble reactive phosphorus during the summer half of the year. Combining the rates estimated by cores and enclosures and converting them to rates at the mean water temperature during the summer half of the year, the release of mineral N and soluble reactive phosphorus roughly amounted to 40 and 4 mg.m^–2.d^–1, respectively. The release rates as well as the external load indicated a relatively low eutrophication of the ditches.     

A review of the hydrobiology of Lake Khubsugul (Mongolia)

Lake Khubsugul phytoplankton is dominated by Diatoms and Chlorococcales. Its algal flora is rather peculiar, but lacks Baikalian endemics.Primary production ranges from 2 to 5 mg C m^–3 d^–1. Total bacteria in the open water is 150–200 × 10³ cells ml^–1.Predominant in numbers and biomass throughout the year are two pelagial species of Copepoda — the endemic Mixodiaptomus kozhovi Step., and Cyclops abyssorum Sars.The bottom fauna consists of cold stenothermic invertebrates, mostly Chironomidae. In biomass, they rank only third, however, after Gammaridae and Mollusca. The average zoobenthos biomass of the lake is 5.5g m^–2.     

Primary production by benthic microalgae in nearshore marine sediments of Signy Island,Antarctica

Summary During the austral summer of 1987/1988, three 24 h in situ primary productivity measurements were made at a nearshore sublittoral site on the east coast of Signy Island, Antarctica. The first experiment in December, coincided with the peak of the benthic algal bloom as shown by benthic chlorophyll measurements and a primary productivity rate of 700.9 mg carbon m^–2 day^–1. In January, the experiment was undertaken during the peak of the phytoplankton bloom when light intensities reaching the benthos were greatly reduced. A rate of 313.4 mg carbon m^–2 day^–1 was measured, half that of the previous month. In March the phytoplankton bloom had died off, benthic light intensities had increased and production was 391.8 mg m^–2 day^–1. The experiments indicate changes in benthic microalgal activity during the summer, linked to changes in the benthic light climate. Compared with previous measurements of phytoplanktonic activity at Signy, the microphytobenthos seems to be an important source of primary production. A production estimate of 100.9 mg carbon m^–2, for the ice-free summer period, lies within the range of values of results from other polar studies.     

The soil fauna of a beech forest on limestone: trophic structure and energy budget

Summary The soil fauna of a mull beech forest on lime-stone in southern Lower Saxony (West Germany) was sampled quantitatively. Biomass estimates, trophic characteristics, and measurement and calculation of the energetic parameters of the constituent animal populations were used to construct an energy budget of the total heterotrophic subsystem of the forest. Mean annual zoomass amounted to about 15 g d wt m^–2; earthworms (about 10 g d wt m^–2) and other groups of the macrofauna were dominant. Protozoa constituted about 1.5 g d wt m^–2. Relative distribution of zoomass among the trophic categories was 50% macrosaprophages, 30% microsaprophages, 12% microphytophages, and 4% zoophages. Total annual consumption rate of the saprophagous and microphytophagous soil fauna (6328 and 4096 kJ m^–2 yr^–1, respectively) was of the same order of magnitude as annual litter fall (canopy leaves 6124 kJ m^–2 yr^–1, flowers and fruits 944 kJ m^–2 yr^–1, herbs 1839 kJ m^–2 yr^–1, fine woody material 870 kJ m^–2 yr^–1, tree roots 3404 kJ m^–2 yr^–1, without coarse woody litter). Primary decomposers (macrosaprophages) were the key group for litter comminution and translocation onto and into the soil, thus contributing to the high decomposition rate (k=0.8) for leaf litter. Consumption rates of the other trophic groups were (values as kJ m^–2 yr^–1): bacteriophages 2954, micromycophages 416, zoophages 153. Grazing pressure of macrophytophages (including rhizophages) was low. Faeces input from the canopy layer was not significant. Grazing pressure on soil microflora almost equalled microbial biomass; hence, a large fraction of microbial production is channelled into the animal component. Predator pressure on soil animals is high, as a comparison between consumption rates by zoophages and production by potential prey — mainly microsaprophages, microphytophages and zoophages — demonstrated. Soil animals contributed only about 11% to heterotrophic respiration. However, there is evidence that animals are important driving variables for matter and energy transfer: key processes are the transformation of dead organic material and grazing on the microflora. It is hypothesized that the soil macrosaprophages are donor-limited.     

The seasonality of monsoonal primary productivity in Sri Lanka

The relationship between phytoplankton primary production and seasonality of physico-chemical parameters were examined for five man-made lakes in the dry-zone of Sri Lanka. Sri Lanka experiences two monsoons dividing the year into four meteorological seasons: — the North East (October–December) and South West (April–June) monsoons and the two inter-monsoons. A significant log linear relationship was found between Secchi disc depth and the depth of the euphotic zone which was lowest during the NE monsoon. Maximum mean photosynthetic rate ranged from 0.935 ± 0.067 SE to 0.479 mg O₂l^–1 h^–1 ± 0.115. Gross primary productivity which ranged from 0.378 g O₂ m^–2 h^–1 in the NE monsoon to 0.980 g O₂ m^–2 h^–1 in the SW monsoon showed significant season variation. This is shown to be determined either directly or indirectly by the light regime.     

Disruption of sulfur cycling and acid neutralization in lakes at low pH

Experimental acidification of a softwater lake to below pH 5 fundamentally changed the sulfur cycle and lowered internal alkalinity generation (IAG). Prior to reaching pH 4.5, the balance of sulfur reduction and oxidation reactions within the lake was in favour of reduction, and the lake was a net sink for sulfate. In the four years at pH 4.5 the balance of reduction and oxidation reactions was in favour of oxidation, and there was a net production of sulfate (SO₄ ^2–) within the lake. Evidence indicating a decrease in net SO₄ ^2– reduction at pH 4.5 was also obtained in an anthropogenically acidified lake that had been acidified for many decades. In both lakes, the decrease in net SO₄ ^2– reduction appeared to be linked not to a simple inhibition of SO₄ ^2– reduction but rather to changes in benthic ecosystem structure, especially the development of metaphytic filamentous green algae, which altered the balance between SO₄ ^2– reduction and sulfur oxidation.At pH's above 4.5, net SO₄ ^2– reduction was the major contributor to IAG in the experimental lake, as it is in many previously studied lakes at pH 5 and above. At pH 4.5, the change in net annual SO₄ ^2– reduction (a decrease of 110%) resulted in a 38% decrease in total IAG. Because of the important role of net SO₄ ^2– reduction in acid neutralization in softwater lakes, models for predicting acidification and recovery of lakes may need to be modified for lakes acidified to pH <5.     

Plankton and primary productivity of Lake Manzala,Egypt

Primary production and distribution and abundance of phyto- and zooplankton of lake Manzala were investigated from June 1985 to June 1986.Primary production varied from 4.1 to 28.7 g O₂ m^–2 d^–1 with the highest values 24.2 and 28.7 g O₂ m^–2 d^–1 recorded in the eastern and southern sectors and the lowest value 4.1 g O₂ m^–2 d^–1 recorded in the northern sector. The seasonal mean production for the lake was estimated at 13.3 g O₂ m^–2 d^–1.Mean phytoplankton abundance ranged from 32.7 10⁷ to 76.1 10⁷ cells m^–3 with a mean value of 48.10⁷ cells m^–3. Diatoms were the dominant phytoplankton group comprising 52 to 90 % by number. The greatest relative abundance (87 to 90%) was recorded in the southern sector.Mean zooplankton abundance ranged from 30.1 10³ to 44.4 10³ organisms m^–3 in the eastern sector to 5.5.10³ in the northern sector. In response of eutrophication, the species composition changed significantly over the last 20 years. Cladocerans represented less than 1% of zooplankton during 1959/60, but 75% in 1985/86. Rotifers constituted 40% in 1959/60, and only 1% in 1985/86. Cirriped larvae declined from 21% to 1%.     

Primary productivity and related parameters in three different types of inland waters in Sri Lanka

Gross and net primary production together with chlorophyll-a biomass were investigated with respect to depth and diurnal changes in three categories of inland waters (reservoirs, temporary ponds, brackish water lagoons) in Sri Lanka. Ten field sites, in both the dry and wet zones of the island, were investigated. Bimodal productivity profiles were recorded in two of the three reservoirs studied. The diel pattern of net photosynthetic rate varied between sites although peak photosynthetic efficiency occurred at solar noon. Surface photoinhibition was characteristic of the reservoirs and brackish water lagoons but not of the temporary ponds. Mean gross primary production was 3.02 g C m^–2 d^–1 but was higher in the temporary ponds than in the reservoirs. The gross primary production in the brackish water Koggala Lagoon at 0.08 g C m^–2 d^–1 is a record low for tropical lagoons and was 2.5 times less than the two other lagoons investigated. Variability in net primary production between sites was similar to the variation in gross production with a relatively low mean value for tropical inland waters of 0.495 C m^–2 d^–1. Mean maximum photosynthetic rate was 0.30 mg C m^–3 h^–1 but was lower in the reservoirs than in the temporary ponds and lagoons.     

Production of planktonic Rotatoria in Ormajärvi,an eutrophicated lake in southern Finland

The production of planktonic rotifers was studied in eutrophic Lake Ormajärvi. Of the total annual production of rotifers (2.9 g org. C m^–2 or 231 mg dry weight m^–3) 49% was achieved during one month (July) and 88% during 3 months of summer. The most important producers were Keratella cochlearis (1.2 g C m^–2), Asplanchna priodonta (0.8 g C m^–2) and Conochilus unicornis (0.6 g C m^–2). The P/B ratio for the total rotifer community during the growing season (7 months) was 25.0; monthly P/ B values varied between 0.3 and 5.2. The daily P/ B values were highest among species of Collotheca. The relationships of rotifers to some biotic and abiotic factors (invertebrate predators — Mesocyclops, Cladocera, planktonic Protozoa and temperature) are briefly discussed.     

Benthic community metabolism of three Austrian pre-alpine lakes of different trophic conditions and its oxygen dependency

Benthic community respiration rates of profundal sediments of Fuschlsee (37.6 mg · O₂ · m^–2 · h^–1 — eutrophic), Mondsee (40.19 mg · O₂ · m^–2 · h^–1 — eutrophic) and Attersee (11.5 mg · O₂ · m^–2 · h^–1 — oligo-mesotrophic) were measuredin situ, and in cores. By exposing the sediments to different oxygen levels in the laboratory it was found that benthic community metabolism reduced with decreasing oxygen concentrations. The slope of the regression lines, relating oxygen uptake rates to oxygen concentrations, differed significantly for the different sites investigated. These results were closely related to the trophic conditions of the lakes.     

Human urine is an excellent liquid waste for the culture of fish food organism, Moina micrura

With a view to converting human urine into bio-wealth in the form of zooplankton, the nutrient potentials of liquid wastes (0.11 mL L⁻¹)—(i) human urine (♂), (ii) cow urine, (iii) human–cow mixed urine or some solid wastes (0.11 g L⁻¹): (iv) vermi-compost, (v) cow dung, (vi) poultry droppings and (vii) mixed wastes (vermi-cow-poultry)—were evaluated for the mass culture of zooplankton Moina micrura in 24 outdoor tanks (4500 L) in triplicate treatments using life table as indicator during the period of October–December, 2005. Neonates of Moina micrura held in the treatment with human urine started reproduction at least 4 days earlier than other solid wastes tested. Total number of Moina micrura enumerated in the culture tank, related with offspring production per life span, was maximum in case of human urine treatment, followed by human–cow mixed urine, cow urine, vermin-compost, poultry droppings, mixed wastes (vermin–cow–poultry), cow dung and control treatments. The relationship between the total offspring production per female per life span and the nitrogen content of water in different treatments implied that human urine was an excellent liquid waste that can be used for the mass production of zooplankton Moina micrura required for larval and post larval rearing of commercial fishes.     

Enhanced antibody production associated with altered amino acid metabolism in a hybridoma high-density perfusion culture established by gravity separation

A high density hybridoma perfusion culture was established by separating and recycling cells from the product stream to the reactor using a simple external sedimentation-based separator — an inclined modified Erlenmeyer flask. After 3 weeks, when the optimal perfusion rate of 1.0 day^–1 had been reached, viable cell density stabilized at around 10×10⁶ cells ml^–1, a level five times that obtained by simple batch culture. The efficiency of the separator was enhanced by cell flocculation. Specific antibody productivity, which was initially 0.4 g 1×10⁶ cells^–1 h^–1, decreased to half that value while cell density was increasing, but recovered to the initial level when the culture finally stabilized at a high cell density. During the final phase, when viable cell density and specific antibody production were high, there was a marked shift in metabolism. Consumption of the two most important substrates for energy generation, glucose and glutamine, caused their broth concentrations to decrease to 1.5 mM and 1 mM, respectively, from input medium concentrations of 25 mM and 10 mM, respectively. At the same time there was an increase in the specific production of glycine and aspartate, their broth concentrations reaching 1.5 mM and 0.02 mM, respectively. We suggest that this shift in metabolism results in enhanced production of ATP from glutamine. The specific glucose consumption and lactate production also indicate that there is a shift to more energy efficient metabolism. The mechanism whereby this leads to enhanced specific antibody production remains to be elucidated. Nevertheless, the combination of high cell density and enhanced productivity obtained with the present perfusion culture resulted in a high monoclonal antibody production –100 mg l^–1 d^–1.     

Secondary production of Rhyacophila minora,Ameletus sp., and Isonychia bicolor from streams of low and circumneutral pH in the Appalachian Mountains of West Virginia

We estimated the secondary production of Rhyacophila minora, Ameletus sp., and Isonychia bicolor in three acidic streams and one circumneutral stream in Randolph County, West Virginia. Quantitative benthic samples were collected monthly from these second-order streams from November 1990 to October 1991. Mean pH values in the acidic streams were 4.5, 4.8, and 4.8, and mean pH in the circumneutral stream was 6.7. Production estimates for Rhyacophia minora in the acidic streams were 49.6, 19.2, and 15.8 mg m^–2 y^–1. Production of R. minora in the circumneutral stream was 1.0 mg m^–2 y^–1. Ameletus sp. production estimates for the acidic streams were 144.8, 176.8, and 208.3 mg m^–2 y^–1. Ameletus sp. production in the circumneutral stream was 7.4 mg m^–2 y^–1. Secondary production of I. bicolor in the circumneutral stream was 116.6 mg m^–2 y^–1. No Isonychia were collected from the acidic streams. The higher production of R. minora and Ameletus sp. in the acidic streams may be associated with differences in macroinvertebrate community structure.     

Oxidative Stress and Taxol Production Induced by Fungal Elicitor in Cell Suspension Cultures of Taxus Chinensis

Treatment of Taxus chinensis cell suspension cultures with fungal elicitor resulted in an oxidative stress characterized by H₂O₂ production, malondiadehyde (MDA) accumulation and cell death. This oxidative stress was dependent on the concentration of elicitor. Cells exposed to elicitor accumulated taxol, however, not proportional to elicitor concentration. High production of taxol occurred in cells treated with the suitable elicitor concentration. We concluded that oxidative stress had the deleterious effect on taxol production. Simultaneous treatment with elicitor and ascorbic acid (ASA) changed the oxidative stress and taxol production. Production of taxol in cells treated with 200 mg dm^–3 elicitor and ASA was enhanced compared with that in cells treated with only 200 mg dm^–3 elicitor, while production of taxol in cells treated with 100 and 50 mg dm^–3 elicitor and ASA was decreased compared with that in cells treated with 100 and 50 mg dm^–3 elicitor.