Final answer:
Bacterial cells have one primary genome composed of a single circular double-stranded DNA molecule and may also contain plasmids, which are not separate genomes but additional genetic elements. While a bacterium can harbor multiple plasmids, it has only one primary genome.
Step-by-step explanation:
The question of whether bacterial cells may contain multiple genomes can be somewhat tricky. Bacterial cells have a primary genome composed of a single circular double-stranded DNA molecule, which includes essential genes for the bacterium's survival. This main part of the genome is located in an area of the cell called the nucleoid. However, bacteria may also contain plasmids, which are smaller loops of non-essential DNA that can carry additional genes and can be transferred between bacteria.
In terms of multiple genomes, it is important to note that plasmids are not considered separate genomes, but rather extrachromosomal genetic elements that can coexist with the bacterial chromosome. Therefore, while a bacterium may have its chromosomal DNA and one or multiple plasmids, it only has one primary genome. Bacteria are capable of exchanging plasmids, which can result in the spread of traits like antibiotic resistance.