GENUS
Genus (plural, genera), the next taxon, contains different
species that have several important features in common.
Each species within a genus differs sufficiently to maintain
its status as an individual species. Placement of a
species within a particular genus is based on various
genetic and phenotypic characteristics shared among the
species. Microorganisms do not possess the multitude of
physical features exhibited by higher organisms such as
plants and animals. For instance, they rarely leave any
fossil record, and they exhibit a tremendous capacity to
intermix genetic material among supposedly unrelated
species and genera. For these reasons, confidently establishing
a microorganism’s relatedness in higher taxa
beyond the genus level is difficult. Although grouping
similar genera into common families and similar families
into common orders is used for classification of plants
and animals, these higher taxa designations (i.e., division,
class, order) are not useful for classifying bacteria.