ABSTRACT
The yeast Candida tsukubaensis is of industrial importance for the production of microbial milk-clotting enzyme. Milk-clotting enzyme is an enzymatic complex capable of coagulating milk for cheese manufacturing. High clotting activity (CA) and low proteolytic activity (PA) are desirable qualities. To study the genetic nature of the CA and PA traits, we analyzed 179 colonies obtained after mutagenic treatment. Analysis of the data obtained for this populations showed that CA and PA are traits controlled by polygenes and that they are correlated (r = 0.3). The existence of a positive correlation indicates that selection for one trait without considering the other may alter one of the traits in an undesirable direction, since the objective of selection would be an increase in clotting activity and a decrease in proteolytic activity. Three cycles of recurrent mutation-selection were carried out to obtain improved strains. The ultraviolet light dose permitting a 5 per cent rate of cell survival was sufficient to generate genetic variability in the three selection cycles. At the end of the third cycle there was an increase of about 98 per cent in clotting activity and a decrease of about 20 per cent in proteolytic activity. Analysis of variance of the selective cycles showed that the linear effects were significant (P < 0.01) for both traits. Estimates of genetic variances and heritabilities of the three selection cycles are presented.
Subject(s)
Candida/genetics , Genetic Variation/radiation effects , Mutation/radiation effects , Selection, Genetic , Ultraviolet Rays/adverse effects , Analysis of Variance , Candida/metabolism , Cheese , Food Technology , Milk/enzymologyABSTRACT
O objetivo deste trabalho foi descrever o ciclo parassexual em Candida sp uma levedura que näo apresenta ciclo sexual. As condiçöes para isolamento e regeneraçäo de protoplastos foram estabelecidas para a linhagem selvagem de Candida sp. O polietileno glicol foi utilizado para induzir a fusäo dos protoplastos isolados a partir das linhagens auxotroficas (pab bio e ura arg). As colonias prototróficas originais após fusäo foram selecionadas por complementaçäo em meio mínimo. A partir de um produto de fusäo nuclear selecionado, foram obtidos vários recombinantes monoauxotróficos, os quais tiveram diametro nuclear similar às linhagens parenterais. este fato sugere que os recombinantes auxotróficos se originaram de perdas cromossomicas do produto de fusäo nuclear
Subject(s)
Candida , Nuclear Fusion , Polyethylene Glycols , Protoplasts , Recombination, Genetic , Yeasts , ReproductionABSTRACT
Um total de 88 amostras de Staphylococcus aureus, das quais 44 isoladas da narina e pele de estudantes e outras 44 isoladas do ambiente hospitalar, foi testado frente a 11 antibióticos. Os resultados obtidos mostraram níveis de resistência relativamente altos, principalmente com relaçäo à penicilina, nas amostras de estudantes