Final answer:
Most bacterial genomes have fewer than 4.6 million base pairs, with size depending on the bacterium's host-dependency. Smaller genomes are found in highly host-dependent bacteria, while others like Pseudomonas aeruginosa have larger genomes of 6.3 million base pairs due to their diverse metabolic functions.
Step-by-step explanation:
Most of the bacterial genomes described in the text have fewer than 4.6 million base pairs. Typically, the size of a bacterial genome is directly related to the bacterium's dependency on its host for survival. Bacteria that are highly dependent on a host tend to have smaller genomes because they lose genes for functions that the host can perform. For example, organisms such as Mycoplasma genitalium and Chlamydia trachomatis have genomes around 580,000 to 1.0 million base pairs, whereas Pseudomonas aeruginosa, which has a wide variety of metabolic capabilities, boasts a larger genome of 6.3 million base pairs. Supercoiling is a mechanism that allows the genomic DNA of even these larger genomes to fit inside the small confines of a bacterial cell, which is crucial for the proper packaging and function of the genome.