Modeling of biomass productivity in tubular photobioreactors for microalgal cultures: effects of dilution rate, tube diameter, and solar irradiance

A macromodel is developed for estimating the year-long biomass productivity of outdoor cultures of microalga in tubular photobioreactors. The model evaluates the solar irradiance on the culture surface as a function of day of the year and the geographic location. In a second step, the geometry of the system is taken into account in estimating the average irradiance to which the cells are exposed. Finally, the growth rate is estimated as a function of irradiance, taking into account photoinhibition and photolimitation. The model interconnects solar irradiance (an environmental variable), tube diameter (a design variable), and dilution rate (an operating variable). Continuous cultures in two different tubular photobioreactors were analyzed using the macromodel. The biomass productivity ranged from 0.50 to 2.04 g L-1 d-1, and from 1.08 to 2. 76 g L-1 d-1, for the larger and the smaller tube diameter photobioreactors, respectively. The quantum yield ranged from 1.1 to 2.2 g E-1; the higher the incident solar radiation, the lower the quantum yield. Simultaneous photolimitation and photoinhibition of outdoor cultures was observed. The model reproduced the experimental results with less than 20% error. If photoinhibition was neglected, and a growth model that considered only photolimitation was used to fit the data, the error increased to 45%, thus reflecting the inadequacy of previous outdoor growth models that disregard photoinhibition. Copyright 1998 John Wiley & Sons, Inc.     

Diel thermoregulation of the crawfish Procambarus Clarkii (crustacea, cambaridae)

1. 1. In a diel cycle Procambarus clarkii has two preferred temperatures: 24.0 ± 0.15 SEM °C during the day and 26.7 ± 0.13 SEM °C at night.

2. 2. The preferred temperatures are independent from the weight of the organisms.

3. 3. In the photophase the animals are dispersed, in the scotophase they congregate.

4. 4. The crawfish seem to feed during the thermal interphases.

5. 5. Animals in a constantly dark condition maintain a diel preferendum of temperature.

In Vitro Studies on the Biosynthesis of the Surface Glycoprotein of Trypanosoma congolense1,2

Tritiated leucine, glucosamine, mannose, and galactose were incorporated into the variant specific surface glycoprotein (VSG) of Trypanosoma congolense in vitro. The uptake of the precursors is shown by SDS-polyacrylamide electrophoresis and fluorography, by assay of the radioactivity in immunoprecipitates obtained with specific antisera, and by the isolation of the labeled antigens by affinity chromatography on concanavalin A-sepharose and isoelectric focusing. The in vitro labeled VSG exhibits the same degree of microheterogeneity as that observed in the VSG isolated from trypanosomes grown in animals. Analysis of the incorporated sugars after hydrolysis of the glycoprotein showed that glucosamine and mannose were utilized in biosynthesis of the carbohydrate moiety directly whereas galactose was converted possibly to other intermediates before being incorporated into the antigen. Tunicamycin completely prevented the incorporation of the radiolabeled sugars into the surface glycoprotein. The unglycosylated VSG with a molecular weight of 47 kDa had completely lost its size heterogeneity.     

Evidence for manganese(III) binding to the mangano superoxide dismutase from a higher plant (Pisum sativum L.)

Homogenous preparations of a manganese superoxide dismutase from a higher plant (Pisum sativum L.) were studied by epr and optical spectroscopies. The visible spectrum of manganese superoxide dismutase shows a weak and broad band in the range 350–700 nm with two shoulders at about 480 and 600 nm. Reduction with dithionite brought about a considerable disappearance of the visible component of the spectrum. The epr spectra of the native and dithionite-treated enzyme did not show any signal attributable to Mn(II) that only was visible after acid hydrolysis of the protein. The lack of epr signal both in the native and reduced superoxide dismutase can be attributed to the presence of Mn(III) in the former and of Mn(II) strongly bound to the protein in the latter. The results obtained with the manganese superoxide dismutase from leaves of the higher plant Pisum sativum are consistent with the general catalytic mechanism of action postulated for superoxide dismutases from other sources studied so far.     

Cloning and characterization of a 2-Cys peroxiredoxin from Pisum sativum

A cDNA sequence coding for a pea (Pisum sativum L.) 2-Cys peroxiredoxin (2-Cys Prx) has been cloned. The deduced amino acid sequence showed a high sequence homology to the 2-Cys Prx enzymes of Phaseolus vulgaris (86%), Arabidopsis thaliana (75%), and Spinacia oleracea (75%), and contained a chloroplast target sequence at its N-terminus. The mature enzyme, without the transit peptide, has a molecular mass of 22 kDa as well as two cysteine residues (Cys-53 and Cys-175) which are well conserved among proteins of this group. The protein was expressed in a heterologous system using the expression vector pET3d, and was purified to homogeneity by three sequential chromatographic steps. The enzyme exhibits peroxidase activity on hydrogen peroxide (H(2)O(2)) and t-butyl hydroperoxide (TBHP) with DTT as reducing agent. Although both pea Trxs f and m reduce oxidized 2-Cys Prx, Trx m is more efficient. The precise conditions for oligomerization of 2-Cys Prx through extensive gel filtration studies are also reported. The transition dimer-decamer produced in vitro between pH 7.5 and 8.0 and the influence of DTT suggest that a great change in the enzyme quaternary structure of 2-Cys Prx may take place in the chloroplast during the dark-light transition. In addition, the cyclophilin-dependent reduction of chloroplast 2-Cys Prx is shown.     

The formation of DNA sugar radicals from photoexcitation of guanine cation radicals

In this investigation of radical formation and reaction in gamma- irradiated DNA and model compounds, we report the conversion of the guanine cation radical (one-electron oxidized guanine, G(.+)) to the C1' sugar radical and another sugar radical at the C3' or C4' position (designated C3'(.)/C4'(.)) by visible and UV photolysis. Electron spin resonance (ESR) spectroscopic investigations were performed on salmon testes DNA as well as 5'-dGMP, 3'-dGMP, 2'-deoxyguanosine and other nucleosides/nucleotides as model systems. DNA samples (25- 150 mg/ml D(2)O) were prepared with Tl(3+) or Fe(CN)(3-)(6) as electron scavengers. Upon gamma irradiation of such samples at 77 K, the electron-gain path in the DNA is strongly suppressed and predominantly G(.+) is found; after UV or visible photolysis, the fraction of the C1' sugar radical increases with a concomitant reduction in the fraction of G(.+). In model systems, 3'- dGMP(+.) and 5'-dGMP(+.) were produced by attack of Cl(.-)(2) on the parent nucleotide in 7 M LiCl glass. Subsequent visible photolysis of the 3'-dGMP(+.) (77 K) results predominantly in formation of C1'(.) whereas photolysis of 5'-dGMP(+.) results predominantly in formation of C3'(.)/C4'(.). We propose that sugar radical formation is a result of delocalization of the hole in the electronically excited base cation radical into the sugar ring, followed by deprotonation at specific sites on the sugar.     

Formation of 8-oxo-7,8-dihydroguanine-radicals in gamma-irradiated DNA by multiple one-electron oxidations

Electron spin resonance (ESR) studies of radicals formed by radiation-induced multiple one-electron oxidations of guanine moieties in DNA are reported in this work. Annealing of gamma-irradiated DNA from 77 to 235 K results in the hydration of one electron oxidized guanine (G^•+) to form the 8-hydroxy-7,8-dihydroguanin-7-yl-radical (•GOH) having one β-proton coupling of 17–28 G and an anisotropic nitrogen coupling, A_‖, of ~20 G, A = 0 with g_‖ = 2.0026 and g = 2.0037. Further annealing to 258 K results in the formation of a sharp singlet at g = 2.0048 with line-width of 5.3 G that is identified as the 8-oxo-7,8-dihydroguanine one-electron-oxidized radical (8-oxo-G^•+). This species is formed via two one-electron oxidations of •GOH. These two one-electron oxidation steps leading to the formation of 8-oxo-G^•+ from •GOH in DNA, are in accordance with the expected ease of oxidation of •GOH and 8-oxo-G. The incorporation of oxygen from water in G^•+ leading to •GOH and to 8-oxo-G^•+ is verified by ESR studies employing ¹⁷O isotopically enriched water, which provide unambiguous evidence for the formation of both radicals. ESR analysis of irradiated-DNA in the presence of the electron scavenger, Tl³⁺, demonstrates that the cationic pathway leads to the formation of the 8-oxo-G^•+. In irradiated DNA–Tl³⁺ samples, Tl³⁺ captures electrons. Tl²⁺ thus produced is a strong oxidant (2.2 V), which is metastable at 77 K and is observed to increase the formation of G^•+ and subsequently of 8-oxo-G^•+ upon annealing. We find that in the absence of the electron scavenger the yield of 8-oxo-G^•+ is substantially reduced as a result of electron recombinations with G^•+ and possible reaction with •GOH.     

Folding kinetics of phage 434 Cro protein

Folding kinetics for phage 434 Cro protein are examined and compared with those reported for lambda(6-85), the N-terminal domain of the repressor of phage lambda. The two proteins have similar all-helical structures consisting of five helices but different stabilities. In contrast to lambda(6-85), sharp and distinct aromatic (1)H NMR signals without exchange broadening characterize the native and urea-denatured 434 Cro forms at equilibrium at 20 degrees C, indicating slow interconversion on the NMR time scale. Stopped-flow fluorescence data using the single 434 Cro tryptophan indicate strongly urea-dependent refolding rates and smaller urea dependencies of the unfolding rates, suggesting a native-like transition state ensemble. Refolding rates are slower and unfolding rates considerably faster at pH 4 than at pH 6. This accounts for the lower stability of 434 Cro at pH 4 and suggests the existence of pH-dependent, possibly salt bridge interactions that are more stabilizing at pH 6. At <2 M urea, decreased folding amplitudes and nonlinear urea dependencies that are apparent at pH 6 indicate deviation from two-state behavior and suggest the formation of an early folding intermediate. The folding behavior of 434 Cro and why it folds 2 orders of magnitude slower than lambda(6-85) are rationalized in terms of the lower intrinsic helix stabilities and putative charge interactions in 434 Cro.     

Virus-induced diabetes in a transgenic model: role of cross-reacting viruses and quantitation of effector T cells needed to cause disease

Virus-specific cytotoxic T lymphocytes (CTL) at frequencies of >1/1, 000 are sufficient to cause insulin-dependent diabetes mellitus (IDDM) in transgenic mice whose pancreatic beta cells express as "self" antigen a protein from a virus later used to initiate infection. The inability to generate sufficient effector CTL for other cross-reacting viruses that fail to cause IDDM could be mapped to point mutations in the CTL epitope or its COO(-) flanking region. These data indicate that IDDM and likely other autoimmune diseases are caused by a quantifiable number of T cells, that neither standard epidemiologic markers nor molecular analysis with nucleic acid probes reliably distinguishes between viruses that do or do not cause diabetes, and that a single-amino-acid change flanking a CTL epitope can interfere with antigen presentation and development of autoimmune disease in vivo.