Stained Wolbachia pipensis inside wasp egg.
Wolbachia is a very common and very interesting group of bacteria. It infects insects and arthropods, living inside their cells, and is known for modifying the reproduction of host species in a variety of ways. It may play a role in rapid speciation, lateral gene transfer, and has potential as a vector in genetic engineering.
Some of the ways Wolbachia modifies reproduction:
- It spreads from mother to offspring. The mechanism is pretty clever: Wolbachia causes what is known as cytoplasmic incompatibility. Basically, infected eggs are compatible with infected and uninfected sperm, but uninfected eggs are only compatible with uninfected sperm. Thus infected eggs have more options, and the infection spreads through the population.
- Parthenogenesis. This is what you see above in the wasp eggs. Parthenogenesis means reproduction without fertilization. The bacteria cause an egg to develop into a female wasp without being fertilized by wasp sperm. The bacteria accumulate in the end of the egg that will develop into reproductive organs.
- Feminization of genetic males. Wolbachia can make genetically male offspring into sterile or fertile females. This is to Wolbachia’s advantage, since it spreads through the maternal line. For example, in the woodlouse, Wolbachia supresses an androgenic gland, and genetic males become fertile females.
- Selective killing of males. Wolbachia can also straight-up kill males, making sure that females survive to bring the parasite into the offspring.
Wolbachia can also cause bidirectional incompatibility. This may lead to rapid speciation. For example, Nasonia is a wasp genus consisting of three sibling species. They can’t reproduce with each other, and each species has its own strain of Wolbachia. It is, however, unclear which one preceded the other.
Vertical gene transfer is the usual, parent to offspring. Gene transfer outside parent-to-offspring is called lateral gene transfer. It’s uncommon to see lateral gene transfer between prokaryotes and multicellular eukaryotes, but scientists have found evidence of gene transfer between Wolbachia and insect as well as roundworm species. Some species had the entire Wolbachia genome embedded in their own.
Finally, there’s the potential for using these bacteria in biological control. Genetic engineers prefer to piggyback on nature: that way is a lot easier. Genetically modified Wolbachia can potentially be used to control insects that carry diseases like Malaria, either by transferring genes that make the carriers unable to carry the parasite, or by using Wolbachia’s manipulation of reproduction to reduce the fertility of the insect population.
dailymeh posted this on January 18, 2012
