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G Goma

Publications and source records attributed to G Goma.

28 records · Page 2Linked to original sources
PubMed1990

A non-passive mechanism of butyrate excretion operates during acidogenic fermentation of methanol by Eubacterium limosum.

The inhibitory effects of organic acids produced as fermentation end-products during methylotrophic growth of the acidogenic anaerobe, Eubacterium limosum have been investigated. Precise quantification of the intracellular concentrations of acetate and butyrate, together with delta pH measurements indicate that butyrate efflux cannot be explained by a process of passive diffusion. Intracellular concentrations of butyrate were significantly lower than those of the culture broth. It is argued that growth inhibition by butyrate is due to energetic limitations resulting from the energy drain associated with this non-passive efflux mechanism.

Adenosine Triphosphate↗
PubMed1990

Effects of Partial O(2) Pressure, Partial CO(2) Pressure, and Agitation on Growth Kinetics of Azospirillum lipoferum under Fermentor Conditions.

Azospirillum lipoferum crt1 was grown in batch cultures under standard conditions at 85% saturation of dissolved oxygen (DO) and 30-g/liter glucose concentrations. Kinetic studies revealed nutritional limitations of growth and the presence of an initial lag phase prior to consumption of glucose. The influences of various gaseous environments and shear stress on growth, i.e., various conditions of agitation-aeration, were characterized. Faster growth in the first stages of the culture and shorter duration of the lag phase were observed at DO concentrations of <30% saturation. The possible influences of dissolved CO(2) concentration or shear stress or both were discounted, and we confirmed the detrimental effect of high DO levels (up to 80% saturation) and the favorable influence of low DO concentrations (lower than 30% saturation) on growth. It was concluded that the gaseous environment, i.e., the DO concentration, needs to be considered as an operating parameter and be accurately controlled to ensure optimal growth of Azospirillum cells.

Journal Article↗
PubMed1990

Purification and characterization of acidolysin, an acidic metalloprotease produced by Clostridium acetobutylicum ATCC 824.

Acidolysin an extracellular protease produced by Clostridium acetobutylicum ATCC 824 was purified to homogeneity by anion-exchange chromatography with a recovery of 91%. The enzyme was a monomeric protein with a molecular weight of 44,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an acidic isoelectric point of 3.3. Acidolysin was very sensitive to metal-chelating agents and phosphoramidon and was unaffected by sulfhydryl reagents. It was shown to be a calcium- and zinc-containing protease. It exhibited optimal activity against Azocoll at pH 5 and 45 degrees C. It was stable at low pH and heat labile above 50 degrees C. It exhibited specificity toward peptide bonds formed by the amino group of hydrophobic amino acids (isoleucine, leucine, and phenylalanine) and its NH2-terminal amino acid sequence showed a high degree of similarity with that of Bacillus subtilis neutral metalloprotease A. Acidolysin is the first phosphoramidon-sensitive, acidic zinc metalloprotease reported.

Amino Acid Sequence↗
PubMed1989

Enhancement of oxygen transfer rates in fermentation using oxygen-vectors.

Oxygen transfer is one of the bottlenecks in conventional fermentation technology and it has so far been almost totally overlooked with regards to high cell densities and immobilized cells. This review presents some new concepts to improve oxygen supply in aerobic fermentations, especially the use of oxygen-vectors. The oxygen-vectors generally used are liquids which are insoluble in the fermentation media. Their utilization in an emulsified form can significantly increase the oxygen transfer coefficient between gas and aqueous phases. It seems that the vector acts as an active intermediate in the oxygen transport from gas bubbles to aqueous phase, but the mechanisms involved in this unconventional technique of aeration are not yet known.

Journal Article↗
PubMedDate not supplied

Glutamate excretion triggering mechanism: a reinvestigation of the surfactant-induced modification of cell lipids.

Lipid alterations induced by surfactants to trigger glutamate excretion were investigated with an industrial strain of Corynebacterium glutamicum. The lipid composition of this strain was determined for cultures in a synthetic medium and in a complex medium. A distribution of complex lipids between the cell wall and the cell membrane is proposed. Depending on growth conditions, 70-85% of the cell fatty acids had saturated chains in cells grown with surfactants. In the synthetic medium up to 80% of the straight-chain fatty acids may have come from the acylated surfactant added to the induce excretion. In industrial fermentation, the maximal excretion rate corresponded to the highest saturated fatty acid content of cells. It was shown by radioactive labelling in the synthetic medium that the addition of the acylated surfactant induced the degradation of more than 50% of the phospholipids. Some phospholipid synthesis occurred at that time using the surfactant (saturated) fatty acids, but the membrane did nor recover its previous phospholipid content. A model is proposed to explain the mechanism of glutamate excretion triggering by surfactants.

Cell Membrane↗
PubMedDate not supplied

Production of 2-phenylethyl alcohol by Kluyveromyces marxianus.

Among the numerous yeasts able to produce flavor compounds, several strains of Kluyveromyces species are known for the synthesis of large amounts of aromatic compounds. In particular, the accumulation of 2-phenylethyl alcohol in liquid cultures of Kluyveromyces marxianus was observed after incubation on a semisynthetic medium at 30 degrees C, 125 rpm. Changes in the carbon sources led to a significant modification of the amount of this aromatic compound; moreover, the variations in the level of DL-phenylalanine and the exclusive use of a precursor isomer (L) also affected the synthesis of 2-phenylethyl alcohol. Finally, this study revealed the growth inhibition of K. marxianus when the concentration of 2-phenylethyl alcohol reached a critical value near 1.4 g/L; the use of an exponential model allowed the inhibition constant ki to be determined (ki = 0.35 g/L).

Carbon↗