Nabil Nancib

The effect of supplementation by different nitrogen sources on the production of lactic acid from date juice by Lactobacillus casei subsp. rhamnosus

Production of lactic acid from date juice by fermentation has been studied using Lactobacillus casei subsp. rhamnosus as the producer organism. The optimum substrate concentration, expressed in its glucose content, was 60 g l(-1). Various nitrogen sources were compared with yeast extract in terms of their efficiency for lactic acid production. None of these nitrogen sources gave lactic acid concentrations as high as that obtained with yeast extract. As yeast extract supplementation was not economically attractive, different proportions of (NH4)2SO4 and yeast extract were used. When the elemental nitrogen ratio of(NH4)2SO4 to yeast extract was 4:1, the substrate use and efficiency of lactic acid production were the same as in date juice supplemented with 20 g l(-1) yeast extract (0:5).

Use of waste date products in the fermentative formation of baker's yeast biomass by Saccharomyces cerevisiae

Abstract This work was an approach to waste date products valorization through biomass production with the yeast Saccharomyces cerevisiae. The carbon and nitrogen sources of a semi-synthetic fermentation medium were substituted by date-coat (fleshy part) sugar extract, date-seed hydrolysate, and ammonium nitrate. This modified medium was enriched with date-seed ash and date-seed lipid. Date-coat sugar extract as a carbon source was found to be satisfactory at a concentration of 25 g/l (expressed as its glucose concentration) and date-seed hydrolysate as a nitrogen source was equally suitable at 25 g/l. The addition to the medium of 1·0 g/l ammonium nitrate increased the efficiency of yeast biomass formation, as did phosphorus, which produced a maximum when the medium was supplemented with about 6·0 g/l KH 2 PO 4 . The presence of 1 g/l date-seed lipid in the medium also increased the efficiency of biomass formation. Finally, the addition of date-seed ash (0·6 g/l), as a mineral source, to the fermentation medium could substitute for MgSO 4 and CaCl 2 of the semi-synthetic medium.

Metabolic roles of peptone and yeast extract for the culture of a recombinant strain of Escherichia coli.

SummaryThe influence of complex compounds on the growth of a recombinant strain ofEscherichia coli containing the gene encoding glyceraldehyde 3-phosphate dehydrogenase, as well as the production of this enzyme have been studied. Batchwise cultures led to an accumulation of acetate, which was not utilized in a yeast extract-free medium. After glucose exhaustion, growth stopped and enzyme activity decreased. Whereas yeast extract allowed acetate assimilation and growth, peptone stabilized the enzymatic activity. The addition of both compounds resulted in optimal performances for enzyme production.

Use of date products in production of the thermophilic dairy starter strain Streptococcus thermophilus

Date-coat sugar extract and date-seed hydrolysate were utilized as the main constituents of a medium for the production of a thermophilic dairy starter strain. Date-coat sugar extract was used as the carbon source, while date-seed hydrolysate was used as the nitrogen source. A suitable concentration of date-coat sugar was in the range of 50 mg sugar/ml. Addition of various amounts of date-seed hydrolysate as the sole nitrogen source in the medium showed that, in spite of a nitrogen insufficiency found in the hydrolysate, the production of the starter strain increased with date-seed hydrolysate (nitrogen) concentration, but the maximum production of biomass was less than that observed with other nitrogen sources. Therefore, various amounts of urea were added and a mixture of urea (6 mg/ml) and of date-seed hydrolysate (4.0 mg/ml) allowed an increase in the concentration of the biomass. The addition of date-seed ash as a mineral source, at a concentration of 1.0 mg/ml in the medium containing date-coat sugar extract, date-seed hydrolysate, and urea could substitute for MgSO4, and MnSO4 of the usual medium. This medium gave the maximum production of the thermophilic lactic acid bacteria (0.57 mg/ml) and lactic acid (2 mg/ml), very close to what was obtained with the Elliker broth medium.

Effect of growth rate on stability and gene expression of a recombinant plasmid during continuous culture ofEscherichia coli in a non-selective medium

SummaryExperimental results were obtained withEscherichia coli C600 galK (GAPDH), a genetically engineered strain that synthetizes a large quantity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), (80 % of the soluble proteins). Data concerning the stability of plasmid-containing cells and gene expression as a function of dilution rate have been obtained in continuous cultures. Contrary to other studies, our results show a clear indication that the rate of the recombinant activity was dependent on dilution rate. The results support the finding that the apparent stability of the plasmid decreases with dilution rate.

Modelling of batch fermentation of a recombinant Escherichia coli producing glyceraldehyde-3-phosphate dehydrogenase on a complex selective medium

Abstract The kinetics of growth, substrate consumption and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) production by Escherichia coli C600 galK (GAPDH) have been studied. Using the corresponding observations, an unstructured physiological model has allowed description of the behaviour of the recombinant strain in batch culture on a selective complex medium. This model is characterized by two physiological states (glucose and acetic acid consumption) and is based on the Monod equation applied to the growth rate combined with inhibition by acetate. Since the strain used is genetically engineered, it also incorporates the probability of plasmid loss which has been modelled previously. The model has been applied to a set of batch cultures at varying initial glucose concentrations. According to the simulation results, the model provides an excellent fit to the experimental results.

Production of glyceraldehyde-3-phosphate dehydrogenase using genetically engineeredEscherichia coli

SummaryA high productivity process for glyceraldehyde-3-phosphate dehydrogenase using a strain ofEscherichia coli genetically modified for the high production of this enzyme is described. The fermentation is srongly dependent on the levels of essential nutrients, implying strict physiological control of the gene expression.

The use of date waste for lactic acid production by a fed-batch culture using Lactobacillus casei subsp. rhamnosus

The production of lactic acid from date juice by Lactobacillus caseisubsp. rhamnosus in batch and fed-batch cultures has been investigated. The fed-batch culture system gave better results for lactic acid production and volumetric productivity. The aim of this work is to determine the effects of the feeding rate and the concentration of the feeding medium containing date juice glucose on the cell growth, the consumption of glucose and the lactic acid production by Lactobacillus casei subsp. rhamnosus in fed-batch cultures. For this study, two concentrations of the feeding medium (62 and 100 g/L of date juice glucose) were tested at different feeding rates (18, 22, 33, 75 and 150 mL/h). The highest volumetric productivity (1.3 g/L.h) and lactic acid yield (1.7 g/g) were obtained at a feeding rate of 33 mL/h and a date juice glucose concentration of 62 g/L in the feeding medium. As a result, most of the date juice glucose was completely utilised (residual glucose 1 g/L), and a maximum lactic acid production level (89.2 g/L) was obtained.

Valorization of residual yoghurt whey by lactic acid production: An optimized process

Associate Prof. AÏCHA NANCIB1, Prof. NABIL NANCIB, Master ABDENOUR AZZOUG, Master AISSA ABED, Prof. HOCINE DABA 1nancibaicha@yahoo.fr Laboratory of Applied Microbiology, Ferhat Abbas University, Setif, Algeria Emeritus Prof. JOSEPH BOUDRANT Laboratory Reactions and Chemical Engineering (LRGP), UMR CNRS 7224, University of Lorraine, ENSAIA, Vandoeuvre Cedex, 54505, France DAOM ELLIE R. AMIROVA2 2eamirova@hotmail.com Pacific College of Oriental Medicine, 7445 Mission Valley Road, San Diego, CA, 92108, USA ITMO University, 191002, Lomonosov str., 9, Russia, St. Petersburg D. Sc. TATIANA V. MELEDINA3, Ph. D. OKSANA V. GOLOVINSKAYA 3Meledina07@mail.ru ITMO University, 191002, Lomonosov str., 9, Russia, St. Petersburg

Plasmid Loss Probability in Escherichia coli as a Function of the Growth Rate of Plasmid-Bearing Cells. I: Variation During Continuous Cultures

Modelling of plasmid containing cell cultures aids in developing a greater understanding of these complex systems. For such modelling, a number of investigators have introduced key kinetic parameters: the frequency of generation of plasmid-free daughter cells from plasmid-carrying mother cells, the specific growth rate difference between plasmid-carrying (µ+) and plasmid-free cells (µ-) and the probability of plasmid loss pr [1,2,3]. However, little experimental data have been reported [4,5]. In the previous paper the probability of plasmid loss pr varies with the growth rate of the plasmid-carrying cells µ+ [6]. We propose a modelling approach, allowing the simulation of this variation.