The Genomes of Free-Living Spirochetes Are Larger Than Those Living

Multiple Choice

The genomes of free-living spirochetes are larger than those living in animal hosts. Why might this be so?

A) Free-living spirochetes will need genes for additional proteins to synthesize or obtain their own food from the environment. Parasitic spirochetes obtain nutrients from the animal host.
B) The spirochetes in animal hosts are different species entirely. As different species, they would naturally have smaller genomes.
C) A smaller genome implies simplicity-the spirochetes living in animal hosts have fewer needs, so they need fewer genes.
D) It isn't so-all spirochetes would have the same size genomes, since they're all the same species of microbe.
E) Parasitic spirochetes are smaller than free-living spirochetes. Because of this, their genomes are also smaller; they need less genes.