Growth kinetics of Acetobacterium sp. on methanol-formate in continuous culture.

The fermentative metabolism of Acetobacterium sp. grown on methanol-formate in continuous culture is described. The reaction stoichiometry of methanol-formate, including cells, were as follows: CH3OH + 1.13HCOOH --> 0.87CH3COOH + 0.47 cell C. Formate enhanced growth yields by approximately 60% compared with methanol-CO2-grown cultures. Comparison of yields on methanol-formate allowed calculation of an energy yield of 1.3 mol ATP per mol acetate formed during homoacetate fermentation. The magnitudes of YEG,the theoretical maximum yield of YE, and m, the maintenance coefficient, were determined by growing the organism in methanol-formate and resulted in 16.5 g cell (mol methanol catabolized)-1 and 0.674 mmol methanol catabolized (g cell)-1 h-1, respectively. It is concluded that formate might replace CO2 as a source of carboxyl donor.

[Optimizing conditions for the discontinuous production of unicellular protein using whey]. / Optimización de condiciones para la producción discontínua de proteína unicelular utilizando suero de leche.

The cheese whey is one of the most important effluents which is being disposed off in our area. That is why the study for optimizing conditions in the process of recovering whey to produce protein biomass in a batch fermenter was undertaken. A yeast strain (Kluyveromyces marxianus var. lactis) was propagated on a medium based on whey from cheese making plants, the following conditions for cell development being optimized: temperature, pH and initial concentration of lactose. A methodology based on performing several tests ordered according to a "Latin Squares" structure was proposed; this enables the simultaneous study of three variables with a small number of experiences. Such experiences were performed in a cylindrical (air lift type) glass fermenter, obtaining a maximum yield (4.78 g/l by dry weight) when working with an initial lactose concentration equal to 4.8%. For all temperatures (27, 30 and 35 degrees C) and pH (3, 4 and 5) employed, an increase in the cell number occurred with the initial lactose concentration increasing from 2% to 4.8% (Table 2). It is preferable to work at 27 degrees C and pH 4 (since these conditions minimize the bacterial contamination) and with a lactose concentration equal to 4.8%, i.e. the concentration in the residual cheese whey. Thus, an optimum yield in protein biomass is obtained, enabling a good utilization of this effluent, and also diminishing its initial BOD from 60,000 to 15,000 ppm.

Optimización de condiciones para la producción discontínua de proteína unicelular utilizando suero de leche. / [Optimizing conditions for the discontinuous production of unicellular protein using whey]

The cheese whey is one of the most important effluents which is being disposed off in our area. That is why the study for optimizing conditions in the process of recovering whey to produce protein biomass in a batch fermenter was undertaken. A yeast strain (Kluyveromyces marxianus var. lactis) was propagated on a medium based on whey from cheese making plants, the following conditions for cell development being optimized: temperature, pH and initial concentration of lactose. A methodology based on performing several tests ordered according to a [quot ]Latin Squares[quot ] structure was proposed; this enables the simultaneous study of three variables with a small number of experiences. Such experiences were performed in a cylindrical (air lift type) glass fermenter, obtaining a maximum yield (4.78 g/l by dry weight) when working with an initial lactose concentration equal to 4.8

. For all temperatures (27, 30 and 35 degrees C) and pH (3, 4 and 5) employed, an increase in the cell number occurred with the initial lactose concentration increasing from 2

to 4.8

(Table 2). It is preferable to work at 27 degrees C and pH 4 (since these conditions minimize the bacterial contamination) and with a lactose concentration equal to 4.8

, i.e. the concentration in the residual cheese whey. Thus, an optimum yield in protein biomass is obtained, enabling a good utilization of this effluent, and also diminishing its initial BOD from 60,000 to 15,000 ppm.