Mutations production

Analysis and Comparison of Strains. To get hints for more rational strain improvement approaches, (1) highly mutated production strains were genetically andphysiologically compared with their less-productive ances-tors, (2) concentrations of pathway intermediates were determined to identify potential pathway bottlenecks, and (3) regulatory mechanisms were investigated. 

The dominant-lethal test is the most relevant test for mutation production in mammals that is available at present. It has been used with hundreds of compounds, and has given very important information. The results of the dominant-lethal test must be carefully interpreted since there is a variation of responses in regard to sex and strain. In a case where the host-mediated test gives positive results and the dominant-lethal test is negative, it is most important that the dominant-lethal test be tried with other strains of mice (if the mouse is used as the indicator organism). 

I Next cycle I (Mutated product I acts as the template)... 

A large number of polycyclic aromatic hydrocarbons are known Many have been synthesized m the laboratory and several of the others are products of com bustion Benzo[a]pyrene for example is present m tobacco smoke contaminates food cooked on barbecue grills and collects m the soot of chimneys Benzo[a]pyrene is a carcinogen (a cancer causing substance) It is converted m the liver to an epoxy diol that can induce mutations leading to the uncontrolled growth of certain cells... 

Fig. 9. Mutagenesis by a synthetic oligonucleotide of a cloned sequence available in single-stranded form (a) single-stranded M13 template containing uracil (U) residues (b) double-stranded product, uracil residues are not mutagenic (c) strong selection for M13 phages containing mutation of interest (23).

To obtain reproducible antibiotic production by fermentation, it is necessary to obtain a pure culture of the producing organism. Pure cultures are isolated from mixed soil sample populations by various streaking and isolation techniques on nutrient media. Once a pure culture has been found that produces a new antibiotic typically on a mg/L scale, improvement in antibiotic yield is accompHshed by modification of the fermentation medium or strain selection and mutation of the producing organism. Production of g/L quantities may take years to accomplish. 

Literature reports iadicate that sodium sorbate causes weak genotoxic effects such as chromosomal aberrations and mutations ia mammalian cells (172,173). This effect is thought to be caused by oxidative products of sodium sorbate ia stored solutions (173—175). The main oxidation product of sodium sorbate, 4,5-oxohexenoate, is mutagenic ia a Salmonella mammahan-microsome test (176). Sorbic acid and potassium sorbate were not genotoxic under the same test procedures (167,172,174—177). 

Penicillins. Since the discovery of penicillin in 1928 as an antibacterial elaborated by a mold, Penicillium notatum the global search for better antibiotic-producing organism species, radiation-induced mutation, and culture-media modifications have been used to maximize production of the compound. These efforts have resulted in the discovery of a variety of natural penicillins differing in side chains from the basic molecule, 6-aminopenici11anic acid [551-16-6], These chemical variations have produced an assortment of dmgs having diverse pharmacokinetic and antibacterial characteristics (see Antibiotics, P-lactams). 

The process employed by RhcJ)ne-Poulenc for production of vitamin B 2 has not been revealed. However, from a variety of sources (83,86) it can be inferred that a Pseudomonas dentrificans producing over 200 mg/L is employed. The high production is the result of classical mutation as well as (possibly) genetic engineering. 

More frequently, however, mutation is used to block a particular pathway. Streptomyces fradiae produces neomycin. 2-Deoxystreptamine is an intermediate in the biosynthetic pathway leading to the production of neomycin (see Figure 6.20). 

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