Wolbachia

Wolbachia is a genus of gram-negative bacteria that infects arthropod species, including a high proportion of insects, and also some nematodes.It is one of the most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere.Its interactions with its hosts are often complex, and in some cases have evolved to be mutualistic rather than parasitic.Some host species cannot reproduce, or even survive, without Wolbachia colonisation. One study concluded that more than 16% of neotropical insect species carry bacteria of this genus,and as many as 25 to 70% of all insect species are estimated to be potential hosts. The genus was first identified in 1924 by Marshall Hertig and Simeon Burt Wolbach in the common house mosquito. Hertig formally described the species in 1936 as Wolbachia pipientis. Research on Wolbachia intensified after 1971, when Janice Yen and A. Ralph Barr of UCLA discovered that Culex mosquito eggs were killed by a cytoplasmic incompatibility when the sperm of Wolbachia-infected males fertilized infection-free eggs. The genus Wolbachia is of considerable interest today due to its ubiquitous distribution, its many different evolutionary interactions, and its potential use as a biocontrol agent. These bacteria can infect many different types of organs, but are most notable for the infections of the testes and ovaries of their hosts. Wolbachia species are ubiquitous in mature eggs, but not mature sperm. Only infected females, therefore, pass the infection on to their offspring. Wolbachia bacteria maximize their spread by significantly altering the reproductive capabilities of their hosts, with four different phenotypes: Several host species, such those within the genus Trichogramma, are so dependent on sexual differentiation of Wolbachia that they are unable to reproduce effectively without the bacteria in their bodies, and some might even be unable to survive uninfected. One study on infected woodlice showed the broods of infected organisms had a higher proportion of females than their uninfected counterparts. Wolbachia, especially Wolbachia-caused cytoplasmic incompatibility, may be important in promoting speciation. Wolbachia strains that distort the sex ratio may alter their host's pattern of sexual selection in nature, and also engender strong selection to prevent their action, leading to some of the fastest examples of natural selection in natural populations. The male killing and feminization effects of Wolbachia infections can also lead to speciation in their hosts. For example, populations of the pill woodlouse, Armadillidium vulgare which are exposed to the feminizing effects of Wolbachia, have been known to lose their female-determining chromosome. In these cases, only the presence of Wolbachia can cause an individual to develop into a female. Cryptic species of ground wētā (Hemiandrus maculifrons complex) are host to different lineages of Wolbachia which might explain their speciation without ecological or geographical separation. Wolbachia has been linked to viral resistance in Drosophila melanogaster, Drosophila simulans, and mosquito species. Flies infected with the bacteria are more resistant to RNA viruses such as Drosophila C virus, norovirus, flock house virus, cricket paralysis virus, chikungunya virus, and West Nile virus.