156 Chapter 5 • The Genetics of Bacteria and Their Viruses Figure 5-6 Bacteria can transfer plasmids (circles of DNA) through conjugation. A donor cell extends one or more projections—pili—that attach to a recipient cell and pull the two bacteria together. [Oliver Meckes/MPI-Tübingen, Photo Researchers.] Figure 5-5 Physical contact between bacterial cells is required for genetic recombination. Auxotrophic bacterial strains A and B are grown on either side of a U-shaped tube. Liquid may be passed between the arms by applying pressure or suction, but the bacterial cells cannot pass through the ﬁlter. After incubation and plating, no recombinant colonies grow on minimal medium. Fine filter Porous cotton plug Pressure or suction Strain B Strain A having regained the ability to grow without added nutri-ents. Some of the dishes were plated only with strain A bacteria and some only with strain B bacteria to act as controls, but from these no prototrophs arose. Figure 5-4b illustrates the experiment in more detail. These
This is the end of the preview. Sign up
access the rest of the document.
This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.