The hydrogenosomes of Psalteriomonas lanterna

Area of Science:

• Cell Biology
• Evolutionary Biology
• Microbiology

Background:

• Hydrogenosomes are organelles producing hydrogen and ATP, with independent evolutionary origins suggested by their hosts' distribution.
• The microaerophilic amoeboflagellate Psalteriomonas lanterna, possessing hydrogenosomes and "modified mitochondria", belongs to the Heterolobosea, a group primarily of aerobic organisms.
• This organism's phylogenetic placement is distant from taxa with previously studied hydrogenosomes.

Purpose of the Study:

• To investigate the nature of hydrogenosomes and "modified mitochondria" in Psalteriomonas lanterna.
• To determine the phylogenetic relationship of P. lanterna within the Heterolobosea.
• To explore the evolutionary origins of hydrogenosomes in this organism.

Main Methods:

• Electron microscopy was used to examine the ultrastructure of P. lanterna's organelles.
• Phylogenetic analysis of expressed sequence tag (EST) sequences, including Hsp60 and Propionyl-CoA carboxylase, was performed.
• Key mitochondrial and hydrogenosomal genes were identified and analyzed.

Main Results:

• Electron microscopy revealed that "modified mitochondria" and hydrogenosomes share similar ultrastructure and size, suggesting they are different morphs of the same organelle.
• Phylogenetic analysis placed P. lanterna close to aerobic Heterolobosea, such as Naegleria gruberi.
• EST analysis confirmed the presence of key genes for mitochondrial/hydrogenosomal function, including a [FeFe] hydrogenase.

Conclusions:

• The ultrastructural and molecular data strongly suggest that "modified mitochondria" and hydrogenosomes in P. lanterna are interconvertible forms of the same organelle.
• Physiological similarities were noted between P. lanterna hydrogenosomes and those of Trichomonas vaginalis and Trimastix pyriformis.
• The findings corroborate the hypothesis that hydrogenosomes in P. lanterna evolved from a common, mitochondriate ancestor within the Heterolobosea.