Effect of oxygen transfer and carbon source composition on the growth of Corynebacterium melassecola

Corynebacterium melassecola, a glutamate producing bacteria, has been cultivated in a 4-l batch aerated fermentor with glucose and fructose mixtures of various proportions as carbon sources and mineral ammonium as nitrogen source. Experimental results are analysed in order to obtain the specific rates and the conversion yields. A data reconciliation technique is used to manage with the experiments performed in similar conditions. The redundant experimental informations are used to test the carbon, nitrogen, available electrons, phosphorus and protons balances. The measurement of dissolved oxygen tension and volumetric oxygen transfer coefficient indicates that oxygen was never a limiting substrate in the experimental device though the oxygen demand was up to 70 mmoles/l.h and the heterogeneity of the liquid phase. The highest specific growth rate (0.59 h^?1) and the highest biomass production yield (0.48 gX/gS) are obtained with glucose as the sole carbon source. These two parameters progressively decrease with the increase of the proportion of fructose in the medium down to 0.43 h^?1 and 0.38 gX/gS on fructose so that the specific carbon uptake rate remains constant and equal to 0.04 C-mole/gX h. From a metabolic point of view, this decrease of the carbon conversion efficiency into cellular material is correlated to a lower carbon flux through the pentose pathway as the fructose proportion is increased. This is correlated with an accumulation of fructose 1,6-biphosphate which further activates the lactate deshydrogenase resulting to lactate production though the metabolism remains strictly aerobic.     

Widespread formation of intracellular calcium carbonates by the bloom-forming cyanobacterium Microcystis

The formation of intracellular amorphous calcium carbonates (iACC) has been recently observed in a few cultured strains of Microcystis, a potentially toxic bloom-forming cyanobacterium found worldwide in freshwater ecosystems. If iACC-forming Microcystis are abundant within blooms, they may represent a significant amount of particulate Ca. Here, we investigate the significance of iACC biomineralization by Microcystis. First, the presence of iACC-forming Microcystis cells has been detected in several eutrophic lakes, indicating that this phenomenon occurs under environmental conditions. Second, some genotypic (presence/absence of ccyA, a marker gene of iACC biomineralization) and phenotypic (presence/absence of iACC) diversity have been detected within a collection of strains isolated from one single lake. This illustrates that this trait is frequent but also variable within Microcystis even at a single locality. Finally, one-third of publicly available genomes of Microcystis were shown to contain the ccyA gene, revealing a wide geographic and phylogenetic distribution within the genus. Overall, the present work shows that the formation of iACC by Microcystis is common under environmental conditions. While its biological function remains undetermined, this process should be further considered regarding the biology of Microcystis and implications on the Ca geochemical cycle in freshwater environments.     

Bioguided Fractionation and Isolation of an Antiplasmodial Saponin from the Roots of Nauclea xanthoxylon (A.Chev.) Aubrév. (Rubiaceae)

The root extract of Nauclea xanthoxylon (A.Chev.) Aubrév. displayed significant 50 % inhibition concentration (IC₅₀s) of 0.57 and 1.26 μg/mL against chloroquine resistant and sensitive Plasmodium falciparum (Pf) Dd2 and 3D7 strains, respectively. Bio-guided fractionation led to an ethyl acetate fraction with IC₅₀s of 2.68 and 1.85 μg/mL and subsequently, to the new quinovic acid saponin named xanthoxyloside ( 1 ) with IC₅₀s of 0.33 and 1.30 μM, respectively against the tested strains. Further compounds obtained from ethyl acetate and hexane fractions were the known clethric acid ( 2 ), ursolic acid ( 3 ), quafrinoic acid ( 4 ), quinovic acid ( 5 ), quinovic acid 3-O-β-D-fucopyranoside ( 6 ), oleanolic acid ( 7 ), oleanolic acid 3-acetate ( 8 ), friedelin ( 9 ), β-sitosterol ( 10a ), stigmasterol ( 10b ) and stigmasterol 3-O-β-D-glucopyranoside ( 11 ). Their structures were characterised with the aid of comprehensive spectroscopic methods (1 and 2D NMR, Mass). Bio-assays were performed using nucleic acid gel stain (SYBR green I)-based fluorescence assay with chloroquine as reference. Extracts and compounds exhibited good selectivity indices (SIs) of >10. Significant antiplasmodial activities measured for the crude extract, the ethyl acetate fraction and xanthoxyloside ( 1 ) from that fraction can justify the use of the root of N. xanthoxylon in ethnomedicine to treat malaria.     

Effects of fertilization and afforestation on community structure of traditionally managed hay meadows in western Norway

The aims of this paper were to find the effects of artificial fertilizer, intensive cultivation and abandonment with afforestation on species composition of traditional meadows at a broad scale, and to describe the ecological variation of different meadow communities. The flora of 21 traditionally managed hay meadows was compared with that of 52 artificially fertilized hay meadows, 28 intensively cultivated grasslands and 29 afforested grasslands by means of classification. Predictors for differences in species composition were tested using multiple regression analyses with associated Monte Carlo permutation tests. Habitat diversity and Ellenberg N were the most important predictors for differences in species composition of traditional meadows. High habitat diversity was associated with maximum occurrences of all kinds of meadow species (high-productive, generalist, low-productive, habitat specialist, regionally rare, vulnerable and orchid species). These meadows are therefore of high conservation value. Traditional meadows contained also some nitrophilous species that dominate artificially fertilized meadows, but in small populations. Artificially fertilized meadows supported the generalist and productive subset of the species from traditional meadows. Thus, artificially fertilized meadows are of low conservation value. As regionally rare and vulnerable species were only recorded at sites with no use of artificial fertilizer, its application should be avoided whenever the aim is to recreate or maintain semi-natural grasslands of high conservation value. Regionally rare and vulnerable meadow species were not recorded in afforested sites, suggesting that afforestation of traditional meadows may have similar negative effects for the traditional meadow flora as the use of artificial fertilizer.     

Fluorescent study of tobacco mosaic virus protein

The synthesis of two new variants of gramicidin is described. It is shown that the changes in the aromatic side groups do not influence the single channel conductivity. Experiments in which solutions having different molarities on the two sides of the bilayer lipid membrane are described and their results compared with a rate theory analysis. It is concluded that the gramicidin pore contains approximately 10 equal potential maxima.     

Binding proteins for adenosine 3′:5′-cyclic monophosphate in bovine adrenal cortex

Five peaks of cyclic AMP-binding activity could be resolved by DEAE-cellulose chromatography of bovine adrenal-cortex cytosol. Two of the binding peaks co-chromatographed with the catalytic activities of cyclic AMP-dependent protein kinases (ATP-protein phosphotransferase, EC 2.7.1.37) of type I or type II respectively. A third binding protein was eluted between the two kinases, and appeared to be the free regulatory moiety of protein kinase I. Two of the binding proteins for cyclic AMP, sedimenting at 9S in sucrose gradients, could also bind adenosine. They bound cyclic AMP with an apparent equilibrium dissociation constant (K(d)) of about 0.1mum, and showed an increased binding capacity for cyclic AMP after preincubation in the presence of K(+), Mg(2+) and ATP. The two binding proteins differed in their apparent affinities for adenosine. The isolated regulatory moiety of protein kinase I had a very high affinity for cyclic AMP (K(d)<0.1nm). At low ionic strength or in the presence of MgATP, the high-affinity binding of cyclic AMP to the regulatory subunit of protein kinase I was decreased by the catalytic subunit. At high ionic strength and in the absence of MgATP the high-affinity binding to the regulatory subunit was not affected by the presence of catalytic subunit. Under all experimental conditions tested, dissociation of protein kinase I was accompanied by an increased affinity for cyclic AMP. To gain some insight into the mechanism by which cyclic AMP activates protein kinase, the interaction between basic proteins, salt and the cyclic nucleotide in activating the kinase was studied.     

Pi Ecincinnati: A new alpha1-antitrypsin allele in three negro families

Summary Serum specimens of three unrelated black males had an unusual alpha-1-antitrypsin phenotype, designated Pi Ecincinnati because of its electrophoretic mobility. Family studies indicated that the new phenotype was the expression of an alpha-1-antitrypsin allele, labeled Pi ^Ecincinnati