$(0\mathrm{.}5$ pt$)$ You also found that some of these isolates encode the lytH gene, which is a gene important for making cell walls in Gram$-$positive organisms $($but not Gram$-$negative organisms$).$ You found that lytH is encoded in the genomes of isolates $4$ and $5,$ but not in $1,3,$ or $2.$ How do you think this gene was acquired $($horizontal transfer, vertical transmission, or novel mutation$)$ and why?