Electrophoretic variants, strains

Contamination. Unlike the short-term experiments where contamination by other E. coli strains during the course of the experiment is obvious, E. coli contamination is of serious concern for these long-term experiments. Replacement of the culture by the contaminant will appear the same as an adaptive replacement. Strains should be tagged with various genetic markers so they can be distinguished from contaminants. These can be subtle changes such as electrophoretic variants and DNA sequence changes or more obvious ones such as resistance to certain antibiotics. Alternate chemostats should have strains that are marked differently so that cross-contamination can be detected. 

It is important to distinguish between electrophoretic variants, posttranslational modification, physiological variants, and genetic variants. The electrophoretic variants described here could be true genetic variants produced either by mutations of existing genes in Newton, or by the introduction into the strain of new genes allelic... 

A recently developed version of the specific-locus test detects electrophoretic protein variants at at least 21 loci.101 198 It is based on early test-system development by Mailing and Valcovic270 and Soares.1+24 A significant increase in the mutation frequency for ENU has been demonstrated with this test. 95 Two inbred strains of mice are used that differ at 10 loci whose protein products are electrophoretically demonstrable. In addition, mutations resulting in the loss of any of 11 other proteins common to the two strains can be detected. Males of either strain are exposed to the test substance, and, at the desired time after exposure, they are mated with females of the other strain. Later, all parental and Fi animals are examined for the biochemical characters of interest. 

Some time in 1968, Carter saw his first enzyme variants —beautiful little bands of sky blue on a China white gel (a flat slab of starch gel on a glass plate that had been laid between electrodes), each band at a precise and different position on the gel according to the strain of malaria parasite whose content had been extracted for electrophoretic separation (Carter, 1970). They were the biochemical genetic markers of two strains of Plasmodium berghei yoelii (as then defined), 17X and 33X that Walliker needed in order to be able to analyze a genetic cross between these two parasites. 

Especially outstanding separation of 10 MC variants has been reported in MEKC mode of capillary electrophoresis with UV detection.This is preferable method for electrophoretic determination of MC as their separation can be impeded by adsorption of analytes onto the capillary wall, hence separation conditions in basic media with micelles should prevent such interaction. As BGE for such separation 40 mM (3-(cyclohexylamino)-l-propanesulfonate buffer of pH 10.6, containing acetate and 15 mM sodium dodecyl sulfate (SDS), was used and UV detection was carried out at 238 nm. The electropherogram obtained for a mixture of MC isolated with a preparative HPLC from cyanobacterial Anahaena 90 strains is shown in Eig. 5. 

As described by Williams et al. (1990), random amplified polymorphic DNA-PCR (RAPD-PCR) is a variant of PGR that utilizes oligonucleotide probes (9 to 12 base pairs or bp) to amplify several regions of the genome. The amplification products are then separated electrophoretically. Resolution depends upon the primer sequence and reaction conditions. RAPD-PCR can be made more specific by use of highly specific oligonucleotide probes. Holt and Cote (1998) applied this technique toward the identification of dextran-producing Oenococcus strains, and Esteve-Zarzoso et al. (1998) were able to identify Saccharomyces and Zygosaccharomyces species. Quesada and Cenis (1995) used the method to characterize wine yeasts. 

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