ABSTRACT
Ecological studies on three bacterial lineages symbiotic in aphids have shown that they impose a variety of effects on their hosts, including resistance to parasitoids and tolerance to heat stress. Phylogenetic analyses of partial sequences of
gyrB
and
recA
are consistent with previous analyses limited to 16S rRNA gene sequences and yield improved confidence of the evolutionary relationships of these symbionts. All three symbionts are in the
Enterobacteriaceae
. One of the symbionts, here given the provisional designation “
Candidatus
Serratia symbiotica,” is a
Serratia
species that has acquired a symbiotic lifestyle. The other two symbionts, here designated “
Candidatus
Hamiltonella defensa” and “
Candidatus
Regiella insecticola,” are sister groups to one another and together show a relationship to species of
Photorhabdus
.