Evolution and Genetic Engineering - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 703

original
FBR5

hydrolysate
challenge

transfer

t ransfer transfer

fermentation
medium

overnight culture

in liquid medium

compare
with parent

dilutions

plating

selective medium

FIGURE 14.1 Schematic diagram of strain adaptation (Liu et al. 2010).

A well-known example of natural selection is the development of antibiotic resistance
in microorganisms and development of insecticide resistance in insects overtime.
The individual organisms in the natural populations of bacteria contain considerable
genetic variations, including genes that confer resistance against antibiotics. In the
presence of antibiotics, the bacterial cells that do not have genetic (and thereby pheno-
typic) capability of inactivating antibiotics die out quickly, leaving behind a population
of cells that can survive in the presence of antibiotics. These surviving bacteria will repro-
duce to generate a next generation of bacterial cells that are resistant to the antibiotic
agent.

14.2.2. Artificial Selection (Selection of Mutants with Useful Mutations)
Scientists have exploited the natural process of genetic variations and selection to
better understand the cell physiology, workings of the cellular processes, and to control
the regulation of biological processes for industrial benefits. Methods to induce
mutations and then select for mutants are important tools for catalyst development in
bioprocessing.
The selection of a mutant with desirable properties is no easy task. Mutations are classified
as selectable or unselectable.
Selectable mutations provide an organism with characteristics that increase its survival
under certain specific sets of environmental conditions, such that the mutants can survive
but the wild type cannot. An example is the survival of antibiotic-resistant bacteria in the
presence of antibiotics. Wild-type bacteria will be killed by the antibiotic. A selectable
mutation confers upon the mutant an advantage for growth or survival under a specific set
of environmental conditions; thus, only mutants with the desired characteristics will
remain (e.g. green pigment).