5.5. Genetic stability of microorganisms

Microorganisms are genetically much less stable than tightly organized chromosomes in higher eukaryotes. They possess faster growth rate and being unicellular can adapt quickly to the changing environment. Thus, they are able to change genetically easier than higher eukaryotes. As it has been already mentioned above, several mechanisms for horizontal gene transfer have been already identified. Movable DNA particles are responsible for changes of bacterial genetic material, which often leads to appearance of new phenotypic characteristics, inactivation of genes, gene losses and entire destabilization of genome. These movable particles of DNA involve insertion sequence (IS), plasmids, prophages, transposons. A lot of bacterial strains posses a great number of different IS elements and part of them often actively cause transposition.

The genome of eukaryotic microorganisms is also subjected to DNA changes. They could undergo series of rearrangements during the process of growth depending on the physical, chemical conditions and cultivation system. In some cases continuous cultures are efficient selective tools for stabilization of adopted new DNA sequences. Generally these changes arise by spontaneous transposition of movable elements (e.g. Ty retrotransposons) and segments of chromosomes. The last event is well manifested in chromosomal length polymorphism.

The phenomenon of genetic variability of microorganisms could affect also the stability of the recombinant DNA in GMMs. This possibility should be taken into account in case of evaluation of genetic stability of GMMs.

The localization of cloned gene(s) (chromosomal or plasmid) strongly influences the genetic stability of the recombinant DNA molecule. It makes the selection of convenient vector system very important for the fate of the recombinant DNA. When high copy number vector or integrated into chromosome recombinant DNA are used, the stability of the new genetic information will depend on basic biological mechanisms. The genetic stability of the transferred genetic material will be like those of the host microorganism. The high stability of the transferred genetic material requires profound knowledge on the location of transposons and IS element insertion, as well as the site for attachment of temperate phages.

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