Structure and evolution of the magnetochrome domains: no longer alone

Magnetotactic bacteria (MTB) can swim along Earth's magnetic field lines, thanks to the alignment of dedicated cytoplasmic organelles. These organelles, termed magnetosomes, are proteolipidic vesicles filled by a 35–120 nm crystal of either magnetite or greigite. The formation and alignment of magnetosomes are mediated by a group of specific genes, the mam genes, encoding the magnetosome-associated proteins. The whole process of magnetosome biogenesis can be divided into four sequential steps; (i) cytoplasmic membrane invagination, (ii) magnetosomes alignment, (iii) iron crystal nucleation and (iv) species-dependent mineral size and shape control. Since both magnetite and greigite are a mix of iron (III) and iron (II), iron redox state management within the magnetosome vesicle is a key issue. Recently, studies have started pointing out the importance of a MTB-specific c-type cytochrome domain found in several magnetosome-associated proteins (MamE, P, T, and X). This magnetochrome (MCR) domain is almost always found in tandem, and this tandem is either found alone (MamT), in combination with a PDZ domain (MamP), a domain of unknown function (MamX) or with a trypsin combined to one or two PDZ domains (MamE). By taking advantage of new genomic data available on MTB and a recent structural study of MamP, which helped define the MCR domain boundaries, we attempt to retrace the evolutionary history within and between the different MCR-containing proteins. We propose that the observed tandem repeat of MCR is the result of a convergent evolution and attempt to explain why this domain is rarely found alone

Microscopic eukaryotes living in a dying lake (Lake Koronia, Greece)

The morphological and phylogenetic diversity of the microscopic eukaryotes of the Lake Koronia water column was investigated during a mass kill of birds and fish in August-September 2004. The dominant morphospecies corresponded to the known toxin-producing species Prymnesium parvum, followed by Amoebidium sp., a taxon belonging to the group of parasitic Mesomycetozoea, and the common chlorophyte Pediastrum boryanum. Prymnesium exhibited heteromorphic life-cycle stages (flagellate and nonmotile coccoid cells). Phylogenetic analysis with 18S rRNA gene suggested that these heteromorphic stages belonged to the Platychrysis-Prymnesium monophyletic group. The most abundant phylotype was almost identical to P. boryanum. The fungal phylotypes were related to the Chytridiomycota, and the ciliate-like ones were closely related to Enchelys polynucleata and Pattersoniella vitiphila. Two phylotypes representing novel members belonging to the Jakobida and the Apicomplexa were also found. The microscopic eukaryotes of Lake Koronia include several organisms that are related to parasitic life modes