Microbial Genomes Are Seqenced

Our understanding of microbes has grown tremendously through the study of their genomes. A genome is the total genetic information contained in an organism's chromosomal DNA (Fig. 1.6). By determining the sequence of genes in a microbe's genome, we learn a lot about how that microbe grows and associates with other species. For example, if a microbe's genome includes genes for nitrogenase, a nitrogen-fixing enzyme, that microbe probably can fix nitrogen from the atmosphere into compounds that plants can assimilate into protein. And by comparing DNA sequences, we can measure the degree of relatedness between different species based on the time since they diverged from a common ancestor. Historically, the first genomes to be sequenced were those of viruses. The first genome whose complete DNA sequence was determined was that of a bacteriologic (a virus that infects bacteria), bacteriologic +X174. The DNA sequence of 0174 was determined in 1977 by Fred Sanger (Fig. 1.7A), who shared the 1980 Nobel Prize in Chemistry with Walter Gilbert and Paul Berg for developing the method of DNA sequence analysis. The genome of bacteriophage 40074 includes over