Phenol biodegradation using a repeated batch culture of Candida tropicalis in a multistage bubble column.

As in many other microorganisms, the growth rate of C. tropicalis is affected by phenol. Besides, when the yeast is aerobically cultivated in a medium containing phenol, using a bubble column, the yeast cell flotation phenomenon occurs, which makes the continuous operation of this type of reactor difficult. Therefore, a system of phenol degradation, which recycles the biomass separated by flotation, was devised in this work. In order to reduce the substrate toxicity observed at high phenol concentrations, the bubble column used in the biodegradation studies was fed in a semibatch mode. So, a semicontinuous system was implemented to treat effluents with relatively high concentrations (> 9,000 ppm) of phenol, by replacing periodically about 22% of the bioreactor operational volume. The phenol removal efficiencies obtained with this system were higher than 98.7%.

Growth kinetic model that describes the inhibitory and lytic effects of phenol on Candida tropicalis yeast.

The object of this work was to carry out a kinetic study on the Candida tropicalis cell lysis and to obtain a kinetic model that would describe the inhibitory and lytic effects of phenol on the yeast growth. From the experiments, a model for the growth kinetic behavior of the yeast was evolved. The proposed model describes satisfactorily the inhibitory and lytic effects of phenol on yeast cultures. From the kinetic model constants, it was found that C. tropicalis showed high affinity and tolerance toward phenol. The overall growth yields decreased when the initial phenol concentration increased, and it may be due to an increased maintenance coefficient and to cell lysis.

Differences in the growth kinetic behaviour of Torulopsis cremoris in batch and continuous cultures.

Torulopsis cremoris growth in whey was described satisfactorily by Monod's model. The maximum specific growth rate of T. cremoris obtained in batch culture was approximately 26% higher than that estimated in continuous culture. This rate was higher than that reported for Kluyveromyces fragilis, which is the yeast used in large-scale processes for the biomass production from whey. In batch and continuous cultures, the yeast utilized some other carbon and energy source, different from lactose. In batch cultures, the overall growth yield coefficients exhibited a significant dependence on initial lactose concentration. The single-stage continuous culture is not a convenient system for T. cremoris. The results obtained in this work demonstrate that the kinetic parameters may vary significantly according to the culture type used, and this could have economic repercussions.

Producción de enzimas por streptomycoses sp cresciendo con caparazón de camarón como sustrato / Enzyme production of streptomyces up growing on shrimp shell as substrate

Se hizo un estudio comparativo en cuanto a la producción de enzimas por ima ceá de Streptomyces sp, utilizando como substrato caparazón de camarón desmineralizado ó quitina semipurificada. Se encontró que la producción de quitinasas está asociada al crecimiento microbiano cuando se usa como substrato caparazón de camarón, alcanzando una producción máxima de quitinasa, qutitosanasa, carboximetilcelulasa y de proteasa a las 96 h de incubación. Cuando el substrato fue la quitina, se obtuvo un máximo en la producción quitinolítica y quitosanolítica al alcanzar la fase de crecimiento estacionario. El crecimiento de Streptomyces sp fue mayor en caparazón de camarón que en quitina, siendo muy pequeñas las velocidades específicas de crecimiento tanto en caparazón de camarón como en quitina semipurificada