Asma Ait Kaki

Optimization of Baker’s Yeast Production on Date Extract Using Response Surface Methodology (RSM)

This work aims to study the production of the biomass of S. cerevisiae on an optimized medium using date extract as the only carbon source in order to obtain a good yield of the biomass. The biomass production was carried out according to the central composite experimental design (CCD) as a response surface methodology using Minitab 16 software. Indeed, under optimal biomass production conditions, temperature (32.9 °C), pH (5.35) and the total reducing sugar extracted from dates (70.93 g/L), S. cerevisiae produced 40 g/L of their biomass in an Erlenmeyer after only 16 h of fermentation. The kinetic performance of the S. cerevisiae strain was investigated with three unstructured models i.e., Monod, Verhulst, and Tessier. The conformity of the experimental data fitted showed a good consistency with Monod and Tessier models with R2 = 0.945 and 0.979, respectively. An excellent adequacy was noted in the case of the Verhulst model (R2 = 0.981). The values of kinetic parameters (Ks, Xm, μm, p and q) calculated by the Excel software, confirmed that Monod and Verhulst were suitable models, in contrast, the Tessier model was inappropriately fitted with the experimental data due to the illogical value of Ks (−9.434). The profiles prediction of the biomass production with the Verhulst model, and that of the substrate consumption using Leudeking Piret model over time, demonstrated a good agreement between the simulation models and the experimental data.

Flow cytometry approach for studying the interaction between Bacillus mojavensis and Alternaria alternata

Tomato, Solanum lycopersicum is one of the most important vegetable crops consumed in Algeria. Tomato crops are often infected by Alternaria alternata, which causes early blight disease. Chemical pesticides are intensively used to protect this plant, which lead to environmental pollution that might endanger animal and human health. The main objective of this study is to select potential biocontrol agents from arid soil as an alternative to chemical products. The phytopathogenic fungus which was isolated from infested tomato leaves, stems and fruits cultured in Constantine-Algeria, was identified as Alternaria cf. alternata. Thirty five bacteria isolates were obtained from arid soil in the south of Algeria. Three of the isolates inhibited the growth of A. alternata. However, the most potent isolate, E1B3 reached a 75% inhibition rate. The molecular identification of this isolate showed that it was closely related to Bacillus mojavensis (KC977492). This strain does not produce chitinase, but does produce lipase, protease and lipopeptides. The interaction between A. alternata and B. mojavensis was investigated for the first time in this work by flow cytometric analysis. In conclusion, B. mojavensis strain was antagonistic to A. alternata which could possibly be exploited as a biopesticide in tomato crops management. Key words: Tomato, Bacillus mojavensis, early blight, Alternaria alternata, flow cytometry.

Ponte et qualité d'oeufs de cailles élevées en conditions semi intensives dans l'Est algérien

This work investigates laying performances and egg quality of 200 quails during 266 laying days. The first collected 240 eggs, for the periods: 12, 16, 20, 24, 28, 32, 36, 40, 44 weeks were used in this study. The average laying rate calculated over a period of 37 weeks is 74.44 %. All studied eggs quality parameters were significantly (p<0.001) influenced by the age of the quail. The average weight of the whole egg (13.66 g), yolk (3.99 g) and shell (2.28 g) reach their maximum value at the 40th week. The maximum albumen average weight (7.45 g) was observed at 32nd week. Albumen (12.02) and yolk (48.72) indices recorded their highest values at the 12th and the 16th weeks, respectively. The eggs freshness, expressed here by Haugh units decreased with age. They range from 89.56 at the 12th week to 83.71 at the 44th week of age. Yolk color registered values with irregular fluctuations (7.12 to 9.33) in a colorimetric scale of 15 ladders. Highly significant and positive correlations (p<0.001) and were recorded between the whole egg weight and the weight of albumen, yolk and shell. To conclude, the quail age affects significantly the various egg quality parameters.