Biology Reference
In-Depth Information
von Dohlen et al. (2001)
found that there can be “bugs within bugs within
mealybugs.” Mealybugs (Pseudococcidae) have endosymbionts that live within
the cytoplasm of large, polyploid host cells within a specialized structure (bacteri-
ome). These symbionts provide nutrients to their hosts. The relationship between
the mealybugs and these primary endosymbionts is ancient, perhaps dating to the
origins of the families or superfamilies 100-250 million years ago (
von Dohlen et al.
2001
). The mealybug host
Planococcus citri
packages its intracellular endosymbi-
onts into mucus-filled spheres that surround the mealybug-cell nucleus and occupy
most of the cytoplasm. These spheres are structurally unlike eukaryotic cell vesicles
and actually harbor two types of Proteobacteria. The two bacteria are not coinhab-
itants of the spheres. Rather, the spheres themselves involve the internalization of
the one bacterium by the second bacterium, which may facilitate the exchange of
genes and gene products that could slow or reverse the genetic degradation that is
common to organelles or long-term intracellular symbionts over evolutionary time.
Broderick et al. (2006)
found that midgut bacteria are required for
Bacillus
thuringiensis
to be effective as an entomopathogen.
Kikuchi et al. (2012)
found that the bean bug
Riptortus pedestris
, a pest of legumes in Japan (as
well as related bugs in the family Alydidae), has a gut symbiont in the genus
Burkholderia
in a posterior region of the midgut. The adult bug has up to 10
8
Burkholderia
cells. The symbiont enhances growth and size of the bug and is
transmitted when the bug acquires the symbiont as a second instar from the
soil. If the bug acquires a strain of
Burkholderia
from the soil that is resistant
to the pesticide fenitrothion, the bugs become resistant. Experimental applica-
tions of the pesticide increased the resistant bacterial strain to
>
80%. More than
90% of the bean bugs reared in the enriched soil established symbiosis with the
pesticide-resistant
Burkholderia
, conferring a useful level of pesticide resistance
to the bug. The bugs amplify the bacteria in their symbiotic organ and could
spread the bacteria when they fly to new sites.
An unusual symbiosis involves the presence of the bacterium
Candidatus
Midichloria mitochondrii in the mitochondria of ticks (
Pistone et al. 2012
).
(When a new bacterial species name is proposed, but the international com-
mittee on bacterial nomenclature has not yet accepted it, the proposed spe-
cies is called
Candidatus
, which is italicized, but the proposed genus and species
names are not italicized.) This bacterium is a member of the Rickettsiaceae and
is found inside mitochondria in hard ticks. It has been best studied in
Ixodes
ricinus
(Ixodidae), where it seems to inhabit 100% of the wild-caught females,
although it is present in lower frequencies in laboratory populations. The bac-
teria replicate in the mitochondria, reducing the numbers of mitochondria. It
