Fig. 5

Euglena gracilis has flexible and fault-tolerant mitochondrial metabolism. Proteins involved in mitochondrial pathways and complexes are shown, including: tricarboxylic acid (TCA) cycle, pyruvate dehydrogenase, fatty acid metabolism, complexes I-V of respiratory chain, ubiquinone biosynthesis, sulfate assimilation pathway, Fe-S cluster assembly and export, TIM/TOM complex and mitochondrial import machinery. Colour codes: dark blue, nucleus encoded, present in predicted mitochondrial proteome; light blue, present in transcriptome without evidence for mitochondrial localization; light blue/white, mitochondrion-encoded proteins identified previously [39]; grey, expected in nuclear transcriptome and not found; grey/white, expected in mitochondrial genome and not found. The E. gracilis mitochondrion can produce energy under both aerobic and anaerobic conditions and has workarounds for the main mitochondrial pathways, such as TCA cycle and respiratory chain, which may in part explain the outstanding adaptability of this organism