ABSTRACT
The effects of various nitrogen sources and of the cultivation time on the biosynthesis of N-labelled azoverdin were studied in batch cultures of Azomonas macrocytogenes ATCC 12334. Growth for 48 h in the presence of ammonium sulfate (0.2 g/liter) resulted in 95% labelling of azoverdin with N. A growth-related synthesis of azoverdin, under both nitrogen-fixing and ammonium-assimilating conditions, was observed.
ABSTRACT
The effect of plasmid-mediated metabolic burden of on the expression of the host genes and its consequences on the plasmid maintenance were studied in carbon-limited chemostat culture of Escherichia coli 1EA(pBR322) subject to selection for strains overproducing chromosomally coded ribitol dehydrogenase. The chemostat population became rapidly heterogeneous and the competition among evolved strains was found to be crucial for the kinetics of the plasmid loss from the culture. The selective disadvantages in growth rate associated with plasmid carriage in the parent-like and ribitol dehydrogenase-overproducing strains was estimated.
ABSTRACT
An efficient modification of ethyl methanesulfonate mutagenic action is based on mutagenization of small volumes of cell suspensions in micro-sample tubes. This provides for a rapid and safe handling of solutions of cancerogenic mutagens. A 3-4-h exposition to 30-40 mmol/L of mutagen appeared optimal, inducing more than 20% auxotrophs or, after a simultaneous application of the penicillin method, 60% of auxotrophs. Moreover, the modification proved its value in repeated applications of ethyl methanesulfonate, resulting in an accumulation of various mutation types. Consecutive mutations were accompanied by an increase in sensitivity. Based on the distribution of nucleoids in the mutagenized population, the penicillin method was modified to allow detection of mutants segregated from cells with several nucleoids.
