Figure 2.

The role of genetic engineering in strain improvement. Modifying a specific DNA sequence (even a single nucleotide) can cause a complete change in the bacteria's phenotype, leading to the overproduction of a certain type of antibiotic. The figure illustrates this with an example of soil bacteria Streptomyces. The cells are shown just as they emerge from the solid substrate. The figure also depicts the overproduction of a pigmented antibiotic, actinorhodin, by a colony of the species Streptomyces coelicolor. Streptomycetes are responsible for producing most of the naturally occurring antibiotics in use today.