MUTANTI pnc IN ESCHERICHIA COLI K-12

Mutans of E. coli K12 deficient in the recycling pathway of NAD were isolated. Nutritional properties of mutants provide elucidations regarding NAD turnover and utilization of exogenous NAD

Method and parameters for genetic transformation of Streptococcus sanguis Challis.

A simple procedure for genetic transformation of Streptococcus sanguis Challis was developed and standardized. During the exponential phase of growth, cells became competent while growing as diplococci in broth containing 10% foetal calf serum. High levels of competence were maintained by the cultures for 60 min. Competent cells could be stored frozen without loss of competence for at least three years. Using total chromosomal DNA as donor, the dose-response curve for transformation of a point mutation (streptomycin resistance) showed one-hit kinetics, as the DNA concentration varied from 0.000001 to 10 micrograms/ml. At 10 micrograms/ml, more than 2.2% of the colony-forming units were transformed to streptomycin resistance, while transforming activity remained detectable with 1 pg of DNA/ml. Optimal time of exposure of competent cells to transforming DNA was 30 min. The transformation reaction was inhibited at 0 and 4 degrees C, whereas it occurred efficiently both at 25 and 37 degrees C

Method and parameters for genetic transformation of Streptococcus sanguis Challis.

A simple procedure for genetic transformation of Streptococcus sanguis Challis was developed and standardized. During the exponential phase of growth, cells became competent while growing as diplococci in broth con- taining 10 % foetal calf serum. High levels of competence were maintained by the cultures for 60 min. Competent cells could be stored frozen without loss of competence for at least three years. Using total chromosomal DNA as donor, the dose-response curve for transformation of a point mutation (streptomycin resistance) showed one-hit kinetics, as the DNA concentration varied from 0.000001 to 10 ~tg/ml. At 10 ~tg/ml, more than 2.2 % of the colony-forming units were transformed to streptomycin resistance, while trans- forming activity remained detectable with 1 pg of DNA/ml. Optimal time of exposure of competent cells to transforming DNA was 30 min. The trans- formation reaction was inhibited at 0 and 4\ub0C, whereas it occurred efficient- ly both at 25 and 37\ub0C

Production of functional killer protein in batch cultures upon a shift from aerobic to anaerobic conditions

The aim of this work was to study the production of functional protein in yeast culture. The cells of Saccharomyces cerevisiae Embrapa 1B (K+R+) killed a strain of Saccharomyces cerevisiae Embrapa 26B (K-R-)in grape must and YEPD media. The lethal effect of toxin-containing supernatant and the effect of aeration upon functional killer production and the correlation between the products of anaerobic metabolism and the functional toxin formation were evaluated. The results showed that at low sugar concentration, the toxin of the killer strain of Sacch. cerevisiae was only produced under anaerobic conditions . The system of killer protein production showed to be regulated by Pasteur and Crabtree effects. As soon as the ethanol was formed, the functional killer toxin was produced. The synthesis of the active killer toxin seemed to be somewhat associated with the switch to fermentation process and with concomitant alcohol dehydrogenase (ADH) activity