The genome of the protozoan parasite Toxoplasma gondii was found to contain two genes encoding tyrosine hydroxylase; that produces l-DOPA. The encoded enzymes metabolize phenylalanine as well as tyrosine with substrate preference for tyrosine. Thus the enzymes catabolize phenylalanine to tyrosine and tyrosine to l-DOPA. The catalytic domain descriptive of this class of enzymes is conserved with the parasite enzyme and exhibits similar kinetic properties to metazoan tyrosine hydroxylases, but contains a unique N-terminal extension with a signal sequence motif. One of the genes, TgAaaH1, is constitutively expressed while the other gene, TgAaaH2, is induced during formation of the bradyzoites of the cyst stages of the life cycle. This is the first description of an aromatic amino acid hydroxylase in an apicomplexan parasite. Extensive searching of apicomplexan genome sequences revealed an ortholog in Neospora caninum but not in Eimeria, Cryptosporidium, Theileria, or Plasmodium. Possible role(s) of these bi-functional enzymes during host infection are discussed.
Vertical transmission (VT) and associated manipulation of host reproduction are widely reported among prokaryotic endosymbionts. Here, we present evidence for widespread use of VT and associated sex-ratio distortion in a eukaryotic phylum. The Microspora are an unusual and diverse group of eukaryotic parasites that infect all animal phyla. Following our initial description of a microsporidian that feminizes its crustacean host, we survey the diversity and distribution of VT within the Microspora. We find that vertically transmitted microsporidia are ubiquitous in the amphipod hosts sampled and that they are also diverse, with 11 species of microsporidia detected within 16 host species. We found that infections were more common in females than males, suggesting that host sex-ratio distortion occurs in five out of eight parasite species tested. Phylogenetic reconstruction demonstrates that VT occurs in all major lineages of the phylum Microspora and that sex-ratio distorters are found on multiple branches of the phylogenetic tree. We propose that VT is either an ancestral trait or evolves with peculiar frequency in this phylum. If the association observed here between VT and host sex-ratio distortion holds true across other host taxa, these eukaryotic parasites may join the bacterial endosymbionts in their importance as sex-ratio distorters.
Many pollinator populations are declining, with large economic and ecological
implications. Parasites are known to be an important factor in the some of the
population declines of honey bees and bumblebees, but little is known about the
parasites afflicting most other pollinators, or the extent of interspecific
transmission or vectoring of parasites. Here we carry out a preliminary
screening of pollinators (honey bees, five species of bumblebee, three species
of wasp, four species of hoverfly and three genera of other bees) in the UK for
parasites. We used molecular methods to screen for six honey bee viruses,
Ascosphaera fungi, Microsporidia, and
Wolbachia intracellular bacteria. We aimed simply to detect
the presence of the parasites, encompassing vectoring as well as actual
infections. Many pollinators of all types were positive for
Ascosphaera fungi, while Microsporidia were rarer, being
most frequently found in bumblebees. We also detected that most pollinators were
positive for Wolbachia, most probably indicating infection with
this intracellular symbiont, and raising the possibility that it may be an
important factor in influencing host sex ratios or fitness in a diversity of
pollinators. Importantly, we found that about a third of bumblebees
(Bombus pascuorum and Bombus terrestris)
and a third of wasps (Vespula vulgaris), as well as all honey
bees, were positive for deformed wing virus, but that this virus was not present
in other pollinators. Deformed wing virus therefore does not appear to be a
general parasite of pollinators, but does interact significantly with at least
three species of bumblebee and wasp. Further work is needed to establish the
identity of some of the parasites, their spatiotemporal variation, and whether
they are infecting the various pollinator species or being vectored. However,
these results provide a first insight into the diversity, and potential
exchange, of parasites in pollinator communities.
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