Biology

More advances have been made in the field of the biology of zygomycosis. In particular, very interesting data have been obtained concerning the production of toxins by zygomycetes (Partida-Martinez et al., 2006; Partida-Martinez & Hertweck, 2005). R. microsporus is a human pathogen but is also known to cause rice seedling blight, an economically important agricultural disease. This disease is mediated by rhizoxin, a macrocyclic polyketide metabolite. This toxin binds to beta-tubulin of the plant cells resulting in cell cycle arrest. Interestingly, rhizoxin is also known as a strong antimitotic agent against various human cancer cell lines. A very elegant study has recently shown that rhizoxin was not synthesized by the fungus itself, but by endosymbiont bacteria (Partida-Martinez & Hertweck, 2005). Several lines of evidence demonstrated that endosymbiotic bacteria belonging to the genus Burkholderia were living in the cytoplasm of rhizoxin producing strains of R. microsporus and were responsible for the synthesis of the toxin. Curing the fungus by antibiotic treatment resulted in symbiont-free strains that were unable to produce rhizoxin and toxin production was recovered after reintroduction of the bacterium in the symbiont-free fungus host. Moreover, pure culture of the Burkholderia sp. strain was able to produce rhizoxin as well as some other rhizoxin derivatives (Partida-Martinez & Hertweck, 2005). Fungus-bacteria associations are very rare (Lumini et al., 2006) and R. microsporus is the first human pathogenic fungus known to harbor endosymbiotic bacteria. This discovery may have medical implications. First, rhizoxin derivatives produced by the endosymbiont have been shown to be potent antimitotic agents (Scherlach et al., 2006). Second, as recently highlighted (Chamilos et al., 2006), it could be possible that the pathogenicity of some zygomycetes species may be enhanced by the presence of endosymbiotic toxin-producing bacteria. It has also been hypothesized that the recent emergence of zygomycosis in cancer patients could be related to the higher frequency of multi-drug-resistant Pseudomonas spp. induced by the extensive use of broad-spectrum antibiotics in these patients (Chamilos et al., 2006). These hypotheses need to be tested by experimental studies in animals and to be supported by clinical and microbiological data obtained in patients.

Some R. microsporus strains are also known to produce mycotoxins such as rhizonin A and B, two cyclic heptapeptides that are highly hepatotoxic. Since closely related Rhizopus species are used in many part of the world for the production of fermented foods, detection of toxinogenic strains is of prime importance. Once again, it has been demonstrated that rhizonin was not synthesized by the fungus itself but by endosymbiont Burkholderia sp. living in the fungal cytosol (Partida-Martinez et al., 2006).

Advances have also been made in the knowledge of zygomycetes genome and in the technical field of genetic manipulation of these fungi. Firstly, a genome-sequencing project of R. oryzae is currently under way (http://www.broad.mit.edu/ annotation/genome/rhizopus_oryzae/Info.html). The available data have already been used, for example for identification and study of the 14-alpha-demethylase of R. oryzae (Chau et al., 2006). Secondly, new tools for genetic manipulation of zygomycetes are now available (Ibrahim & Skory, 2006).

Cure Your Yeast Infection For Good

Cure Your Yeast Infection For Good

The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.

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