Horizontal gene transfer (HGT) is defined as the transfer
of genetic material between bacterial cells uncoupled with
cell division [1-3]. In contrast, vertical inheritance is the
transmission of genetic material from mother cell to
daughter cell during cell division. Most often, HGT refers to
gene transfer across large phylogenetic distances (that is,
between otherwise unrelated organisms), whereby gene are
integrated into a replicon by illegitimate means. On
occasion, HGT is used to denote allelic exchange among
closely related bacterial strains where integration occurs via
homologous recombination; herein that process will be
referred to as “recombination.”