Mutant strain

In addition, Ee protein-1 has at least two noncatalytic roles related to nitrogen fixation, and presumably Ee protein-2 and Ee protein-3 do also. The first function is somehow involved in the early stages of EeMo-cofactor biosynthesis because mutant strains having a deletion in nifil produce neither Ee protein nor EeMo-cofactor, rather only a EeMo-cofactor-deficient apo-MoEe protein (104,105). The second role involves insertion of preformed EeMo-cofactor into these apo-MoEe proteins (106). 

Many kinds of amino acids (eg, L-lysine, L-omithine, t-phenylalanine, L-threonine, L-tyrosine, L-valine) are accumulated by auxotrophic mutant strains (which are altered to require some growth factors such as vitamins and amino acids) (Table 6, Primary mutation) (22). In these mutants, the formation of regulatory effector(s) on the amino acid biosynthesis is genetically blocked and the concentration of the effector(s) is kept low enough to release the regulation and iaduce the overproduction of the corresponding amino acid and its accumulation outside the cells (22). 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Work on mutant cultures provided the first practical, although partial, solution to the dehydration phenomenon. A mutant strain whose parent produced chlortetracycline (2) was... 

A 100 ml aliquot of this medium is placed In a 500 ml Erlenmeyer flask and sterilized by autoclaving for 20 minutes under 15 psi pressure. Spores of mutant strain S. aureofaciens S1308 (ATCC No. 12,748) are washed from an agar slant Into the flask with sterile distilled water to form a suspension containing approximately 10 spores per milliliter. A 1.0 ml portion of this suspension is used to inoculate the fermentation media in the example which follows. A fermentation medium consisting of the following ingredients was prepared. 

It is necessary to introduce the GDH recombinant plasmid into a GOGAT-defident mutant strain of AS1 because ... 

Cell lysates from mutant strains of X. campestris were incubated with radiolabelled UDP[14C] glucose or GDP[,4C] mannose, the other sugar nudeotide substrates being unlabelled. The reaction mixture was then divided into lipid and soluble fractions. Where would you expect the radiolabel to be found and what produd, if any, would you expert from strains with defidendes in the following genes ... 

Two types of mutants have been used for amino add overproduction auxotrophic and regulatory mutants. In some cases, mutant strains have been further improved through DNA-recombination. 

Several potential and mutant strains of T. viride have been identified in SCP production. Their capacity for amyloletic enzyme production was enhanced severalfold in SCP from lingnocellulosic resources. The process of bioconversion of agricultural wastes to SCP appeared to be too complex to find an economic application for agricultural waste. 

Of increasing concern is the development of mutant strains of tuberculosis that are resistant to many of the aiititubercular drug s currently in use. Bacterial resistance develops, sometimes rapidly, with the use of anti-tubercular drag s. Treatment is individualized and... 

Sulfoxidations are not restricted to MOs but can also be carried out by dioxygenases. For example. Pseudomonas mutant strain UV4 producing a toluene dioxygenase (TOO) and Pseudomonas NCIMB 8859 expressing a naphthalene dioxygenase (NDO) were used to oxidize aryl sulfides to antipodal chiral sulfoxides [203]. 

Metabolic pathways containing dioxygenases in wild-type strains are usually related to detoxification processes upon conversion of aromatic xenobiotics to phenols and catechols, which are more readily excreted. Within such pathways, the intermediate chiral cis-diol is rearomatized by a dihydrodiol-dehydrogenase. While this mild route to catechols is also exploited synthetically [221], the chirality is lost. In the context of asymmetric synthesis, such further biotransformations have to be prevented, which was initially realized by using mutant strains deficient in enzymes responsible for the rearomatization. Today, several dioxygenases with complementary substrate profiles are available, as outlined in Table 9.6. Considering the delicate architecture of these enzyme complexes, recombinant whole-cell-mediated biotransformations are the only option for such conversions. E. coli is preferably used as host and fermentation protocols have been optimized [222,223]. 

In contrast to 2,3-dioxygenases, the related ipso/ortho oxygenation of aryl carbox-ylates has received considerable less attention and has hardly been utilized by the synthetic community, so far. Biooxidation of benzoic acid and P-naphthalene carboxylate provide access to corresponding 1,2-dihydroxylated dihydroaryl compounds in excellent stereoselectivity (Scheme 9.35), analogous to TDO- and NDO-mediated ortho/meta oxygenations. Whole-cell-mediated biotransformations were performed with mutant strains of Rahtonia and Pseudomonas and enable access to preparative quantities in >5 gl titers [261,262]. 

A shift in temperature from 38 to 22 °C leads to desaturation of fatty acids in Anabaena variabilis [110], resulting in control of the fluidity of the plasma membrane. Mutants have been isolated in Synechocystis PCC 6803 that were defective in desaturation of fatty acids, and the growth rate of one of these mutants was much lower than that of the wild-type at 22 °C [112]. It turned out that the mutant strain had a mutation in the gene desA, and when the wild-type allele was introduced into the chilling-sensitive cyanobacterium Anacystis nidulans, it resulted in increasing the tolerance of that strain to low temperature [113]. These experiments nicely demonstrate the existence of a mechanism of adaptation to low temperature in a chilling-tolerant cyanobacterium. 

The microorganism is again P. chrysogenum. A manufacturer may use the same mutant strain to make both products or may have different mutants for the two penicillins. Parallel situations of a single organism producing more than one natural product occur with other types of antibiotics, for example strains of Streptomyces aureofaciens are used for both chlortetracycline and demethylchlortetracycline fermentations. 

Forward mutation refers to mutation of the natural ( wild-type ) organism to a more stringent organism. By contrast, reverse (backward) mutation is the return of a mutant strain to the wild-type form, i.e. it is a heritable change in a previously mutated gene that restores the original function of that gene. 

Goldie, A.H. and Subden, R.E., The neutral carotenoids of wild-type and mutant strains of Neurospora crassa, Biochem. Genet. 10, 275, 1973. 

Powls, R. and Britton, G., The roles of isomers of phytoene, phytofluene and zeta-carotene in carotenoid biosynthesis by a mutant strain of Scenedesmus obliquus. Arch. Microbiol. 115, 175, 1977. 

Purification and characterisation of galactose-induced pectinases from the exo-1 mutant strain of Neurospora crassa... 

Figure 4. Isoenzyme profiles of wild type and mutant strains. Detection of PG activity was by ruthenium red staining on pectate-agarose overlay gels after lEF. WT indicates wild type and the numbers refer to specific mutant isolates.

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