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 ± 15 μmol O₂ g⁻¹ DW h⁻¹) than at high alkalinity (50 ± 27 μmol O₂ g⁻¹ DW h⁻¹), C. demersum had three times higher rates (336 ± 95 and 120 ± 31 μmol O₂ g⁻¹ DW h⁻¹), and L. major doubled its rates at low alkalinity (634 ± 114 and 322 ± 119 μmol O₂ g⁻¹ DW h⁻¹). Similar results were obtained for bicarbonate use efficiency by E. densa (136 ± 44 and 43 ± 10 μmol O₂ mequiv. L⁻¹ g⁻¹ DW h⁻¹) and L. major (244 ± 29 and 82 ± 24 μmol O₂ mequiv. L⁻¹ g⁻¹ DW h⁻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.     

Effect of zooplankton availability on the rates of photosynthesis, and tissue and skeletal growth in the scleractinian coral Stylophora pistillata

This work investigated the effect of light and feeding on tissue composition as well as on rates of photosynthesis and calcification in the zooxanthellae (zoox) scleractinian coral, Stylophora pistillata. Microcolonies were maintained at three different light levels (80, 200, 300 μmol m⁻² s⁻¹) and subjected to two feeding regimes (starved and fed) over 9 weeks. Corals were fed both natural plankton and Artemia salina nauplii four times a weeks and samplings were made after 2, 5, and 9 weeks. Results confirmed that feeding enhances coral growth rate and increases both the dark and light calcification rates. These rates were 50-75% higher in fed corals (FC; 60±20 and 200±40 nmol Ca²⁺ cm⁻² h⁻¹ for dark and light calcification, respectively) compared to control corals (CC; 30±9 and 124±23 nmol Ca²⁺ cm⁻² h⁻¹). The dark calcification rates, however, were four times lower than the rates of light calcification (independent of trophic status). After 5 weeks, chlorophyll a (chl-a) concentrations were four to seven times higher in fed corals (7-21 μg cm⁻²) than in control corals (2-5 μg cm⁻²). The amount of protein was also significantly higher in fed corals (2.11-2.50 mg cm⁻²) than in control corals (1.08-1.52 mg cm⁻²). Rates of photosynthesis in fed corals were 2-10 times higher (1.24±0.75 μmol O₂ h⁻¹ cm⁻²) than those measured in control corals (0.20±0.08 μmol O₂ h⁻¹ cm⁻²).     

Nitrogen uptake responses of Gracilaria vermiculophylla (Ohmi) Papenfuss under combined and single addition of nitrate and ammonium

The ammonium (NH₄⁺) and nitrate (NO₃⁻) uptake responses of tetrasporophyte cultures from a Portuguese population of Gracilaria vermiculophylla were studied. Thalli were incubated at 5 nitrogen (N) levels, including single (50 μM of NH₄⁺ or NO₃⁻) and combined addition of each of the N sources. For the combined additions, the experimental conditions attempted to simulate 2 environments with high N availability (450 μM NO₃⁻ + 150 μM NH₄⁺; 250 μM NO₃⁻ + 50 μM NH₄⁺) and the mean N concentrations occurring at the estuarine environment of this population (30 μM NO₃⁻ + 5 μM NH₄⁺). The uptake kinetics of NH₄⁺ and NO₃⁻ were determined during a 4 h time-course experiment with N deprived algae. The experiment was continued up to 48 h, with media exchanges every 4 h. The uptake rates and efficiency of the two N sources were calculated for each time interval. For the first 4 h, G. vermiculophylla exhibited non-saturated uptake for both N sources even for the highest concentrations used. The uptake rates and efficiency calculated for that period (V_0-4 h), respectively, increased and decreased with increasing substrate concentration. NO₃⁻ uptake rates were superior, ranging from 1.06 ± 0.1 to 9.65 ± 1.2 μM g(dw)⁻¹ h⁻¹, with efficiencies of 19% to 53%. NH₄⁺ uptake rates were lower (0.32 ± 0.0 to 5.75 ± 0.08 μM g(dw)⁻¹ h⁻¹) but G. vermiculophylla removed 63% of the initial 150 μM and 100% at all other conditions. Uptake performance of both N sources decreased throughout the duration of the experiment and with N tissue accumulation. Both N sources were taken up during dark periods though with better results for NH₄⁺. Gracilaria vermiculophylla was unable to take up NO₃⁻ at the highest concentration but compensated with a constant 27% NH₄⁺ uptake through light and dark periods. N tissue accumulation was maximal at the highest N concentration (3.9 ± 0.25% dw) and superior under NH₄⁺ (3.57 ± 0.2% dw) vs NO3 (3.06 ± 0.1% dw) enrichment. The successful proliferation of G. vermiculophylla in estuarine environments and its potential utilization as the biofilter component of Integrated Multi-Trophic Aquaculture (IMTA) are discussed.     

Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour.We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f_R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min⁻¹ while subsurface swimming, 0.78 breaths min⁻¹ after V-shaped dives and 0.57 breaths min⁻¹ after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s⁻¹, ascent 0.28±0.015 m s⁻¹) than in V-shaped dives (descent 0.10±0.008 m s⁻¹, ascent 0.12±0.012 m s⁻¹). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s⁻¹) than during the descent (0.29±0.03 strokes s⁻¹) or ascent (0.29±0.03 strokes s⁻¹). From overall f_R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.     

Influence of daylength on metabolic rate and daily water loss in the male prosimian primate Microcebus murinus

In its natural habitat, Microcebus murinus, a small malagasy prosimian primate, is exposed to seasonal shortage of water and resources. During the winter dry season, animals enter a pronounced fattening period with concurrent decrease in behavioural/physiological activities, whereas the breeding season is restricted to the rainy summer months. To determine the role of daylength on metabolic rate and water loss in this nocturnal primate, we measured body mass, oxygen consumption at 25°C (RMR), circadian water loss through urine output (UO) and evaporation (EWL) in eight males exposed to either short days (8L:16D SD) or long days (14L:10D LD), under controlled captive conditions. Exposure to SD led to a ponderal increase (maximal body mass: 125±4 g, N=8), and to significant changes in RMR and water loss, both reaching lowest values after 3 months under SD (0.84±0.04 ml O₂ h⁻¹ g⁻¹ and 38±0.3 mg H₂O g⁻¹ day⁻¹, respectively). Following exposure to LD, body mass decreased to 77±3 g (N=8), whereas both RMR and water loss, mainly through EWL, significantly increased (P<0.001), the highest value occurring after 2 months (1.51±0.08 ml O₂ h^.−1 g⁻¹ and 87±7 mgH₂O g⁻¹ day⁻¹, respectively). Moreover, independent of daylength, circadian changes in EWL were characterized by significantly reduced values during the diurnal rest. The results demonstrate that daylength variations affect the physiology of this tropical primate, allowing anticipatory adaptation to seasonal environmental constraints.     

Development of an industrial ethanol-producing yeast strain for efficient utilization of cellobiose

The BGL1 gene, encoding β-glucosidase in Saccharomycopsis fibuligera, was intracellular, secreted or cell-wall associated expressed in an industrial strain of Saccharomyces cerevisiae. The obtained recombinant strains were studied under aerobic and anaerobic conditions. The results indicated that both the wild type and recombinant strain expressing intracellular β-glucosidase cannot grow in medium using cellobiose as sole carbon source. As for the recombinant EB1 expressing secreted enzyme and WB1 expressing cell-wall associated enzyme, the maximum specific growth rates (μ_max) could reach 0.03 and 0.05 h⁻¹ under anaerobic conditions, respectively. Meanwhile, the surface-engineered S. cerevisiae utilized 5.2 g cellobiose L⁻¹ and produced 2.3 g ethanol L⁻¹ in 48 h, while S. cerevisiae secreting β-glucosidase into culture broth used 3.6 g cellobiose L⁻¹ and produced 1.5 g ethanol L⁻¹ over the same period, but no-full depletion of cellobiose were observed for both the used recombinant strains. The results suggest that S. cerevisiae used in industrial ethanol production is deficient in cellobiose transporter. However, when β-glucoside permease and β-glucosidase were co-expressed in this strain, it could uptake cellobiose and showed higher growth rate (0.11 h⁻¹) on cellobiose.     

Ionic and osmotic regulation capabilities of juvenile Gulf of Mexico sturgeon, Acipenser oxyrinchusde sotoi

The salinity tolerance, and hydromineral regulation capabilities of three size groups (small 110–170 g; medium 230–290 g, large 460–700 g; n=48 for each group) of 13-month-old juvenile Gulf of Mexico sturgeon were investigated. Fish (n=6 for each salinity) were transferred directly from freshwater (FW) to a series of experimental salinity treatments (0, 5, 10, 15, 20, 25, 30, and 35 parts per thousand (ppt)). Fish were also acclimated in brackish water (20 ppt) for 2 weeks and transferred to a salinity of 34 ppt. In this condition juvenile Gulf of Mexico sturgeon adapted to saltwater (SW) and maintained their hydromineral balance. FW adapted sturgeon (n=6) had an average blood hemotocrit of 28.2±0.8%, plasma osmolality of 260.7±1.6 mOsm kg⁻¹ H₂O, and plasma ion concentrations of 135.7±1.2 mM l⁻¹ Na⁺, 106.9±1.9 mEq l⁻¹ Cl⁻, and 2.9±0.1 mM l⁻¹ K⁺. In SW adapted sturgeon (n=8) blood parameters averaged 26.9±0.7% for hematocrit, 294.2±2.3 mOsm kg⁻¹ H₂O for osmolality, 152.0±1.7 mM l⁻¹ Na⁺, 149.2±1.4 mEq l⁻¹ for Cl⁻, and 3.1±0.1 mM l⁻¹ K⁺. The method of transfer (abrupt or slow acclimation) directly affected fish survival and the time they took to achieve ionic and osmotic regulation. This SW adaptation appears to be related to body size, the larger the fish the easier the adaptation process. A threshold size of about 170 g was apparent for the fish to adapt to saltwater after 2 weeks of acclimation. Chloride cells were present in both FW and SW adapted sturgeon with SW and brackish water fish having chloride cells significantly (P<0.05) more numerous (561±53 and 598±45 cells mm⁻²) and larger in size (41.0±3.85 and 34.2±4.49 μm²) than FW adapted sturgeon (10±1.0 cells mm⁻² and 22±2.53 μm²). Few chloride cells were observed in the opercular membrane, however, none were found in the pseudobranch and spiracle.     

Reduction of perchlorate by salt tolerant bacterial consortia

Two perchlorate-reducing bacterial consortia (PRBC) were obtained by enrichment cultures from polluted marine sediments. Non-salt-tolerant PRBC (N-PRBC) was enriched without the addition of NaCl, and salt tolerant-PRBC (ST-PRBC) was enriched with 30 g-NaCl L⁻¹. Although the perchlorate reduction rates decreased with increasing NaCl concentration, ST-PRBC (resp., N-PRBC) could reduce perchlorate until 75 g-NaCl L⁻¹ (resp., 30 g-NaCl L⁻¹). The reduction yield (1.34 ± 0.05 mg-perchlorate per mg-acetate) and maximum perchlorate reduction rate (86 mg-perchlorate L⁻¹ h⁻¹) of ST-PRBC was higher than those (1.16 ± 0.03 mg-perchlorate per mg-acetate and 48 mg-perchlorate L⁻¹ h⁻¹) of N-PRBC. Kinetic analysis showed that NaCl acted as an uncompetitive inhibitor against both PRBCs. The inhibition constants were 25 and 41 mg-NaCl L⁻¹ for N-PRBC and ST-PRBC, respectively.     

Impact of natural metazooplankton assemblage on planktonic microbial communities in a newly flooded reservoir

The grazing impact of a natural assemblage of metazoan zooplankton on pigmented flagellates (PF), heterotrophic nanoflagellates (HNF), ciliates, and non-flagellate algae and microcyanobacteria (NFAM) was measured in situ during the period of thermal stratification in a newly flooded reservoir (Reservoir de la Sep, France). Experiments were conducted with diffusion chambers in the meta- and epilimnion over a period of 7 h. The mean mortalities of PF in the epi- and metalimnion (0.08 0.02 and 0.06 ± 0.03 h^-1, respectively), of HNF (0.04 ± 0.02 and 0.05 ± 0.02 h^-1) and ciliates (0.09 ± 0.04 and 0.11 ± 0.04 h^-1) demonstrate the impact of the metazoan zooplankton, and particularly of the rotifer Asplanchna priodonta, on the components of the microbial loop. The mortality of NFAM, accounting for 14 and 18% of total mortality, remained low throughout the study. The taxa with the highest mortality were pigmented flagellates of 4-19 m, HNF, and small-sized ciliates such as Halteria sp. (0.10 ± 0.02 h^-1 at 1 m and 0.30 ± 0.38 h^-1 at 7 m) and Urotricha furcata (0.11 ± 0.05 h^-1 at 1 m and 0.12 ± 0.06 h^-1 at 7 m). Large-sized ciliates (Paradileptus elephantinus) and sessile ciliates (Suctorida, Vorticella sp.) had a very low mortality (>0.04 h^-1). After reservoir flooding, the organisms in the microbial trophic loop, favoured by the high quantities of allochthonous organic matter, are subject to a higher mortality than the phytoplankton.      

Copper toxicity in gibel carp Carassius auratus gibelio: Importance of sodium and glycogen

In general, copper is primarily an osmoregulatory toxicant to fish and Cu toxicity is thought to be related to the rate of sodium loss. Looking at a previous research it is striking that gibel carp, Carassius auratus gibelio, do not seem so susceptible to the first ionoregulatory shock phase of Cu exposure, but rather build up physiological disturbances slowly until mortality occurs. Since it was noted that gibel carp experience severe hypoxia under Cu exposure, we hypothesised that, besides the Na loss, the slow depletion of liver glycogen stores contributed equally to the collapse of physiological integrity. It is clear from our results that glycogen stores are being depleted in Cu exposed fish and that dead fish suffered more extensive glycogen losses compared to surviving fish, with liver glycogen levels of 125 ± 8 mg g⁻¹ in dead fish compared to 230 ± 13 mg g⁻¹ in surviving fish. However, changes in liver glycogen did not contribute significantly to mortality, while changes in whole body sodium and the rate of sodium loss did. Whole body Na levels dropped from 1111 ± 48 μg g⁻¹ dry weight in control fish to 850 ± 54 μg g⁻¹ in surviving fish and to 607 ± 24 μg g^− 1 in fish that had died resulting in Na loss rates of 1.25 ± 0.22 μg g^− 1 h^− 1 and 3.39 ± 0.19 μg g^− 1 h^− 1 in surviving and dead fish respectively. Our results support the finding that the rate of Na loss largely determines Cu toxicity in fish, even in resistant species.     

Nitrogen nutrition of Canna indica: Effects of ammonium versus nitrate on growth, biomass allocation, photosynthesis, nitrate reductase activity and N uptake rates

The effects of inorganic nitrogen (N) source (NH₄⁺, NO₃⁻ or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g⁻¹ d⁻¹), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH₄⁺ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO₃⁻ fed plants suggesting a slight advantage of NH₄⁺ nutrition. The NO₃⁻ fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m⁻² s⁻¹) than NH₄⁺ and NH₄⁺/NO₃⁻ fed plants (24.4-25.6 μmol m⁻² s⁻¹) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (V_max) of NO₃⁻ did not differ between treatments (24-35 μmol N g⁻¹ root DW h⁻¹), but V_max for NH₄⁺ was highest in NH₄⁺ fed plants (81 μmol N g⁻¹ root DW h⁻¹), intermediate in the NH₄NO₃ fed plants (52 μmol N g⁻¹ root DW h⁻¹), and lowest in the NO₃⁻ fed plants (28 μmol N g⁻¹ root DW h⁻¹). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO₃⁻ in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO₃⁻ had high NRA (22 and 8 μmol NO₂⁻ g⁻¹ DW h⁻¹ in leaves and roots, respectively) whereas NRA in NH₄⁺ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO₃⁻ in the presence of NH₄⁺. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands.     

Physiological properties of Cellulomonas fermentans,a mesophilic cellulolytic bacterium

Summary The fermentation of cellobiose, glucose and cellulose MN 300 by Cellulomonas fermentans was studied. The molar growth yields (i.e. grams of cells per mole of hexose equivalent) were similar on cellobiose and cellulose at low sugar consumption levels (47.8 and 46.5 respectively), but was lower on glucose (38.0). The occurrence of cellobiose phosphorylase activity, detected in cellobiose- and cellulose-grown cells, might explain this result. The specific growth rates measured in cultures on cellobiose, glucose and cellulose were 0.055 h^-1, 0.040 h^-1 and 0.013 h^-1 respectively. Growth inhibition was observed, and a drop in Y_H occurred after relatively low but different quantities of hexose were consumed (2.2 mM, 5 mM and 8 mM hexose equivalent with cellulose, glucose and cellobiose respectively), which coincided with a change in the fermentative metabolism from a typical mixed acid metabolism (1 ethanol, 1 acetate and 2 formate synthesized by consumed hexose) to a more ethanolic fermentation. When growth ceased in cellulose cultures, consumption of cellulose continued, as did production of ethanol.Molar growth yields of C. fermentans were similar in anaerobic and aerobic cellobiose cultures (47.8 g/mol and 42.2 g/mol respectively). Specific growth rates were also quite similar under both culture conditions (0.055±0.013 h^-1 and 0.070±0.007 h^-1 respectively). Aerobic metabolism was studied using ¹⁴C glucose. During the exponential growth phase, acetate, succinate and nonidentified compound(s) accumulated in the supernatant, but no ¹⁴CO₂ was produced. During the stationary phase, acetate was oxidized and ¹⁴CO₂ produced, but without any further biomass synthesis. It seems that a blocking of metabolite oxidation may have occurred in C. fermentans except in the case of acetate, but acetate oxidation was apparently not coupled with production of energy utilizable in biosynthesis.     

Biomass-specific respiration rates of benthic meiofauna: Demonstrating a novel oxygen micro-respiration system

Meiofauna (small-sized Metazoa and Foraminifera) may constitute a significant part of seafloor biomass and potentially play an important role in benthic metabolism. However, respiration measurements are limited and the methods used are diverse together complicating comparison or upscaling. Here we describe a novel glass micro-respiration chamber used to perform non-invasive measurements (built-in oxygen-sensitive fluorogenic membrane and stirrer) and together with direct organic carbon measurements report initial biomass-specific respiration rates of common intertidal meiofauna. Results indicate large differences between respiration rates of different taxa (biomass 0.7-5.2 µg C per individual) but very similar organic carbon biomass-specific respiration rates (1.6-2.5 µl O₂ h^− 1 mgC^− 1 or on average 2.0 ± 0.3 µl O₂ h^− 1 mgC^− 1). This new, rapid and accurate method allows the study of metabolic allometry of the different small-sized taxa and determining their functional role in benthic metabolism.     

The Soil Flagellate Heteromita globosa Accelerates Bacterial Degradation of Alkylbenzenes through Grazing and Acetate Excretion in Batch Culture

The impact of grazing by soil flagellates Heteromita globosa on aerobic biodegradation of benzene by Pseudomonas strain PS+ was examined in batch culture. Growth of H. globosa on these bacteria obeyed Monod kinetics (_max, 0.17 ± 0.03 h^–1; K_s, 1.1 ± 0.2 × 10⁷ bacteria mL^–1) and was optimal at a bacteria/ flagellate ratio of 2000. Carbon mass balance showed that 5.2% of total [ring-U-¹⁴C]benzene fed to bacteria was subsequently incorporated into flagellate biomass. Growth-inhibiting concentrations (IC₅₀) of alkylbenzenes (benzene, toluene, ethylbenzene) were inversely related with their octanol/ water partitioning coefficients, and benzene was least toxic for bacteria and flagellates with IC₅₀ values of 4392 (± 167) M and 2770 (± 653) M, respectively. The first-order rate constant for benzene degradation (k₁, 0.48 ± 0.12 day^–1) was unaffected by the presence or absence of flagellates in cultures. However, the rate of benzene degradation by individual bacteria averaged three times higher in the presence of flagellates (0.73 ± 0.13 fmol cell^–1 h^–1) than in their absence (0.26 ± 0.03 fmol cell^–1 h^–1). Benzene degradation also coincided with higher levels of dissolved oxygen and a higher rate of nitrate reduction in the presence of flagellates (p < 0.02). Grazing by flagellates may have increased the availability of dissolved oxygen to a smaller surviving population of bacteria engaged in the aerobic reactions initiating benzene degradation. In addition, flagellates may also have increased the rate of nitrate reduction through the excretion of acetate as an additional electron donor for these bacteria. Indeed, acetate was shown to progressively accumulate in cultures where flagellates grazed on heat-killed bacteria. This study provided evidence that grazing flagellates stimulate bacterial degradation of alkylbenzenes and provide a link for carbon cycling to consumers at higher trophic levels. This may have important implications for bioremediation processes.     

Efficiencies and costs of larval growth in different food environments (Asteroidea: Asterina miniata)

The ocean is a nutritionally heterogeneous environment. For feeding larval forms, food variability has significant consequences for growth and later recruitment success. In this study, the physiological and biochemical responses to a range of different food concentrations (unfed, 4, 20, and 40 algal cells μl^− 1) were examined in larvae of the asteroid, Asterina miniata. Measurements of growth, protein synthesis rates, and the energetic cost of protein synthesis were made. Under conditions of rapid growth, protein comprised a larger percent (66%) of a larva's organic biomass compared to similar-aged, slower-growing larvae (26%). Larvae fed at the highest food concentration tested (40 algal cells μl^− 1) had a protein depositional efficiency of 80% (± 16%), a value 3-fold higher than larvae fed 20 algal cells μl^− 1 (28% ± 11%). Also, faster-growing larvae required 3-fold less energy per unit mass of protein growth. Larvae fed 40 algal cells μl^− 1 deposited protein at a respiratory cost of 65 ± 11 pmol O₂ h^− 1 (μg protein)^− 1; larvae fed 20 algal cells μl^− 1 had a cost of 192 ± 47 pmol O₂ h^− 1 (μg protein)^− 1. While there were differences in the cost to deposit protein (i.e., protein growth, the balance of synthesis and degradation), there were no differences in the energetic cost of protein synthesis for all food concentrations tested. The energetic cost of protein synthesis was fixed at 13.8 (± 0.92) Joules (mg protein synthesized)^− 1 and was independent of developmental stage, growth rates, and large changes (58-fold) in protein synthesis rates. A major conclusion from this study is that larvae grown in high-food environments not only grew faster, but did so for considerably less energy. Defining the complex relationships of food availability and metabolic efficiency will provide more accurate predictions of larval growth under variable food conditions in the ocean.     

Oxygen consumption of Astyanax fasciatus (Characidae,Pisces): a comparison of epigean and hypogean populations

Synopsis The standard and routine oxygen consumptions of Astyanax fasciatus from one surface population (Rio Teapao) and three cave populations (Chica, Micos and Pachon caves: sAnoptichthys jordani, the Micosfish and Anoptichthys antrobius) were determined individually over 24 hours by the use of a flow-through respirometer and polarographic oxygen electrodes. The phylogenetically oldest Pachon fish had a significantly lower standard metabolic rate (0.230 ± 0.036 mg O₂ g^-1 h^-1) than the epigean Teapao fish, the hybrid Chica fish and the phylogenetically younger Micos fish (0.314 ± 0.081 mg O₂g-^-1h^-1, 0.284 ± 0.048 mg O₂g^-1h^-1, 0.277 ± 0.063 mg O₂g^-1h^-1). No significant differences could be determined among the latter three populations. A significant difference in routine metabolic rate existed only between the Pachon fish (0.309 ± 0.0.56 mg O₂g^-1h^-1) and the Teapao fish (0.415 ± 0.071 mg O₂g^-1h^-1). The Chica fish (0.356 ± 0.084 mg O₂g^-1h^-1) and the Micos fish (0.355 ± 0.080 mg O₂ g^-1h^-1) could not be separated from either the Teapao or the Pachon fish, but a decreasing trend from the surface population through the Chica and the Micos to the Pachon population was obvious. During a starvation period of 29 days the metabolic rate of epigean Teapao and hypogean Pachon fish decreased significantly by 32.5% and 34.8% (standard oxygen consumption rate) and 27.5% and 28.2% (routine oxygen consumption rate), respectively. Body mass loss during the starvation period was 16.3% for the Teapao fish and 9.5% for the Pachon fish.     

Growth and energy production in Bacteroides amylophilus

The molar growth yield (Y _m) of Bacteroides amylophilus strain WP91 on maltose was 68±2 g/mol when determined from batch cultures at the peaks of maximal growth. Continued incubation led to considerable cell lysis. When calculated from batch cultures in exponential phase (specific growth rate, =0.57 h^-1) Y _m was 101 g/mol. The maximum value of Y _m in maltose-limited chemostat cultures at the maximum dilution rate (D) attainable (D==0.39 h^-1) was about 79 g/mol. Ammonia-Fmited chemostat cultures metabolized maltose with a much reduced efficiency and this was associated with a difference in morphology and chemical composition of the cells. The theoretical maximum molar growth yields (Y _m ^max ) were 55 and 114 g/mol for ammonia- and maltose-limited growth respectively. However, if account was taken of extracellular nitrogen-containing material in ammonia-limited cultures, Y _m ^max became 60. The maintenance coefficient (m _s), estimated from the lines relating the specific rate of maltose consumption (q _m) and D (where m _s=q _m at D=0), was 7.4±0.6×10^-4 mol maltose/g x h for both nutrient limitations. A difference in maintenance energy demand, independent of growth-rate, could not account, therefore, for the observed differences in Y _m between ammonia- and maltose-limited growth.     

Substrate recognition and hydrolysis by a fungal xyloglucan-specific family 12 hydrolase

Biochemical studies to elucidate the structural basis for xyloglucan specificity among GH12 xyloglucanases are lacking. Accordingly, the substrate specificity of a GH12 xyloglucanase from Aspergillus niger (AnXEG12A) was investigated using pea xyloglucan and 12 xylogluco-oligosaccharides, and data were compared to a structural model of the enzyme. The specific activity of AnXEG12A with pea xyloglucan was 113 μmol min⁻¹ mg⁻¹, and apparent k_cat and K_m values were 49 s⁻¹ and 0.54 mg mL⁻¹, respectively. These values are similar to previously published results using xyloglucan from tamarind seed, and suggest that substrate fucosylation does not affect the specific activity of this enzyme. AnXEG12A preferred xylogluco-oligosaccharides containing more than six glucose units, and with xylose substitution at the −3 and +1 subsites. The specific activities of AnXEG12A on 100 μM XXXGXXXG and 100 μM XLLGXLLG were 60 ± 4 and 72 ± 9 μmol min⁻¹ mg⁻¹, respectively. AnXEG12A did not hydrolyze XXXXXXXG, consistent with other data that demonstrate the requirement for an unbranched glucose residue for hydrolysis by this enzyme.     

Performance and macrokinetic analysis of biofiltration of toluene and p-xylene mixtures in a conventional biofilter packed with inert material

Interactions of toluene and p-xylene in air treatment biofilters packed with an inert filter media were studied. The effect of the inlet load of toluene, p-xylene and mixtures of both compounds on the biodegradation rate was analyzed in three lab-scale biofilters. A maximum elimination capacity (EC) of 26.5 and 40.3 g C m⁻³ h⁻¹ for an inlet load (IL) of 65.6 and 57.8 g C m⁻³ h⁻¹ was obtained for p-xylene and toluene biofilters, respectively. Inhibition of p-xylene biodegradation by the presence of toluene took place when the mixture was treated, whereas the presence of p-xylene had an enhancing effect on the toluene removal efficiency. Specific growth rates (μ) from 0.019 to 0.068 h⁻¹ were calculated in the mixed biofilter, where the highest values were similar to mixtures with lower p-xylene levels (IL_p-Xyl 8.84 ± 0.29 g C m⁻³ h⁻¹). Michaelis-Menten and Haldane type models were fitted to experimental EC for p-xylene and toluene biofilters, respectively.     

Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth,morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO₃⁻, NH₄⁺, or both at equimolar concentrations (500 μM). Plants supplied with only NO₃⁻ had lower growth rates (0.17 ± 0.01 g g⁻¹ d⁻¹), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH₄⁺ alone or in combination with NO₃⁻ (RGR = 0.28 ± 0.01 g g⁻¹ d⁻¹). Ammonium was the preferred form of N taken up. The maximal rate of NH₄⁺ uptake (V_max) was 6–14 times higher than the maximal uptake rate of NO₃⁻ and the minimum concentration for uptake (C_min) was lower for NH₄⁺ than for NO₃⁻. Plants supplied with NO₃⁻ had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO₃⁻ was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO₂⁻ g⁻¹ DW h⁻¹). Under natural growth conditions NH₄⁺ is probably the main N source for S. natans, but plants probably also exploit NO₃⁻ when NH₄⁺ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH₄⁺ levels in the water, even though the uptake capacity for NO₃⁻ is reduced under these conditions.