Biology Reference
In-Depth Information
Beckage (1998)
speculated that polydnaviruses have potential value in agricul-
tural pest-management programs if genetically engineered pathogens (viruses,
bacteria, fungi) containing polydnavirus genes could produce products that sup-
pressed the target pest's immune system. Alternatively, genetically engineered
parasitoids could be developed that exhibit a modified host range, making
them more effective in controlling pests.
4.12.4 Gut Symbionts in Arthropods
Some gut symbionts are obligatory, whereas others are facultative. Gut sym-
bionts often provide key nutritional benefits to their hosts and, in return,
receive shelter and nutrition. Insects may contain complex and diverse societ-
ies of microbes in their guts; yet, much remains to be learned about how these
microbes shape the physiology of their hosts (
Cazemier et al. 1997, Kaufman
et al. 2000, Konig and Varma 2006
). The primary habitat for microorganisms
associated with insect digestive tracts is the hindgut.
4.12.4.1 Termite and Cockroach Symbionts
In termites, the symbionts in the hindgut provide nitrogen (N) and vitamins and
degrade cellulose and hemicellulose. The microbial components of the termite gut
are extremely complex, but molecular tools are improving our ability to resolve
the taxonomy and the complex relationships among termite gut symbionts.
The hindguts of termites can be compared to small bioreactors where wood
and litter is degraded, with the help of symbiotic microorganisms, to provide
nutrients. The hindgut of termites is a structured environment with distinct
microhabitats (
Brune and Friedrich 2000
). The dense gut microbiota includes
organisms from the Bacteria, Archaea, Eukaryotes, Protozoa, and yeasts. These
diverse organisms do not occur randomly within the gut but have specific loca-
tions: they may be suspended in the gut contents, located within or on the
surface of flagellates, or attached to the gut wall. The identity, exact number,
and location of most are inadequately known because they cannot be cultured.
Molecular tools are providing significant new information. For example, the
microbiota of termites includes spirochaetes, which account for as many as 50%
of the organisms present in some termite species. Spirochaetes are a distinct
phylum within the bacterial domain. One molecular analysis of spirochaetes in
the termite
Reticulitermes flavipes
suggested there are at least 21 previously
unknown species of
Treponema
(
Lilburn et al. 1999
). The authors concluded that
the long-recognized and striking morphological diversity of termite gut spiro-
chaetes is paralleled by their genetic diversity and could reflect substantial phys-
iological diversity (
Lilburn et al. 1999
).
