Genetics of Prokaryotes (2B) Practice Test

A bacterial strain becomes resistant after incubation with extracellular DNA, but only when CaCl$_2$ treatment and a brief heat shock are applied. No donor cells are present. Which statement is most consistent with the experimental requirement, given the focus on transformation?

Two bacterial strains are mixed: Strain 1 is F+ and carries a plasmid encoding gentamicin resistance $(Gen^R$). Strain 2 is F− and $Gen^S$. After co-incubation, $Gen^R$ appears in Strain 2 only when cells are allowed direct contact; separating strains with a 0.22 µm filter prevents transfer. Which statement is most consistent with the observed genetic change?