The transcriptome of Euglena gracilis reveals unexpected metabolic capabilities for carbohydrate and natural product biochemistry

Abstract

Euglena gracilis is a highly complex alga belonging to the green plant line that shows characteristics of both plants and animals, while in evolutionary terms it is most closely related to the protozoan parasites Trypanosoma and Leishmania. This well-studied organism has long been known as a rich source of vitamins A, C and E, as well as amino acids that are essential for the human diet. Here we present de novo transcriptome sequencing and preliminary analysis, providing a basis for the molecular and functional genomics studies that will be required to direct metabolic engineering efforts aimed at enhancing the quality and quantity of high value products from E. gracilis. The transcriptome contains over 30,000 protein-encoding genes, supporting metabolic pathways for lipids, amino acids, carbohydrates and vitamins, along with capabilities for polyketide and non-ribosomal peptide biosynthesis. The metabolic and environmental robustness of Euglena is supported by a substantial capacity for responding to biotic and abiotic stress: it has the capacity to deploy three separate pathways for vitamin C (ascorbate) production, as well as producing vitamin E (α-tocopherol) and, in addition to glutathione, the redox-active thiols nor-trypanothione and ovothiol.

Exploring the Glycans of <em>Euglena gracilis</em>

“…There are also many more CAZymes encoded than in the other sequenced Euglenozoa, such as the human pathogens Trypanosoma brucei and Leishmania braziliensis (orange circles in the lower left). One major change is the loss of enzymes involved in α-glucan biosynthesis and an increase in those involved in synthesis of β-glucans [4]. This reflects the use of paramylon, an insoluble β-1,3-glucan [15], as the storage polysaccharide, as opposed to the α-1,4/6-linked glucan used as the energy store in plants, animals and bacteria (starch or glycogen, respectively).…”

“…Protein glycosylation appears to be fairly typical in Euglena, synthesising the same N-glycan precursor oligosaccharide as animals and fungi (Glc3Man9GlcNAc2-Asn) [9], with sequences for all of the enzymes required for the synthesis present in the transcriptome [4]. There are three sequences for the oligosaccharyltransferases that couple this pre-formed oligosaccharide to proteins, in common with Trypanosomes where the enzymes have different substrate specificities [10].…”

Exploring the Glycans of Euglena Gracilis

“…[1] As 34 they are easy to grow and have a large metabolic capacity, Euglena have been proposed as a platform 2 of 13 (GPI) membrane anchors which may be involved in anchoring these glycans to internal membranes 49 or the cell surface. [4] N-Acetylglucosamine-1-phosphate transferase activity has been detected in 50 membrane preparations of Euglena cells [7] and a complex xylose-containing material has been found 51 associated with the flagella. [8] A wide range of glycosyltransferases are present in the Euglena 52 transcriptome, supporting the capacity for synthesis of complex glycans, although the exact structure 53 of such glycans remains to be elucidated.…”

“…Inspection of the transcriptome of Euglena showed that there are many more CAZymes encoded 161 [4] than in the other sequenced Euglenozoa, such as the human pathogens Trypanosoma brucei and…”

“…[4] There are three sequences for 57 the oligosaccharyltransferases that couple this pre-formed oligosaccharide to proteins, in common…”