Tellurium as a valuable tool for studying the prokaryotic origins of mitochondria

• We analyzed the ability of respiration-proficient (ρ+) and -deficient (ρ− or ρ0) S. cerevisiae strains to grow with K2TeO3
• By TEM analyses we demonstrated their capacity to precipitate K2TeO3 into Te0 on the inner mitochondrial membrane or other cell structures
• We extended this analysis to three representative α-, β-, γ-proteobacterial and to archean strains in order to gain an additional evidence of the proteobacterial origin of mitochondria.

Mitochondria are eukaryotic organelles which contain the own genetic material and evolved from free-living Eubacteria, namely hydrogen-producing Alphaproteobacteria. Since 1965, biologists provided, by research at molecular level, evidence for the prokaryotic origins of mitochondria. However, determining the precise origins of mitochondria is challenging due to inherent difficulties in phylogenetically reconstructing ancient evolutionary events. The use of new tools to evidence the prokaryotic origin of mitochondria could be useful to gain an insight into the bacterial endosymbiotic event that resulted in the permanent acquisition of bacteria, from the ancestral cell, that through time were transformed into mitochondria. Electron microscopy has shown that both proteobacterial and yeast cells during their growth in the presence of increasing amount of tellurite resulted in dose-dependent blackening of the culture due to elemental tellurium (Te0) that formed large deposits either along the proteobacterial membrane or along the yeast cell wall and mitochondria. Since the mitochondrial inner membrane composition is similar to that of proteobacterial membrane, in the present work we evidenced the black tellurium deposits on both, cell wall and mitochondria of ρ+ and respiratory deficient ρ− mutants of yeast. A possible role of tellurite in studying the evolutionary origins of mitochondria will be discussed.