[Effect of technical threonine sources on homoserine biosynthesis by mutant Brevibacteruim flavum 2T]

The effect of threonine technical sources on the homoserine biosynthesis by the threonine auxotroph Brevibacterium flavum 2T when cultivated on sucrose and acetic acid containing media was investigated. Various threonine sources (corn extract and fodder yeast, microbial biomass and soybean meal hydrolyzates) prepared by means of different hydrolyzing agents (acids, enzymes, autolysis) were used. The most effective substrate was protein--vitamin concentrate hydrolyzate, particularly combined with corn extract in the ratio 1: 0,25-0.5 (with respect to the dry weight of the initial material). The homoserine yield was 16.2 g/l on the sucrose containing medium and 18.4 g/l on the acetic acid containing medium which was in agreement with controls. The medium containing pure threonine was used as a control. With other threonine sources (corn extract, protein-vitamin concentrate autolyzate and enzymolyzate, fodder yeast and soybean meal hydrolyzates), the homoserine production was significantly lower, i.e. 40-70% of the control. The content of amino acids (threonine, isoleucine, methionine) in the initial material and their suitability for the homoserine biosynthesis were found to be correlated. The substrates with a high content of threonine (over 3.5%) and a low content of methionine (below 0.5%) proved most effective. The use of the material in which the ratio threonine: methionine was less than 6.0 caused the homoserine biosynthesis to be partially replaced with that of lysine.