Thesis-PDF - IAP/TU Wien

Chapter 4
Euglena gracilis
4.1 Overview
4.1.1 Introduction
The algal flagellate Euglena has for long been an outstanding subject of study for
biologists. It has been maintained in culture in many laboratories as an experimental
organism and almost every biology student has observed it during microscopy
courses. As of today this species is one of the most completely studied. ([82])
These small yet complex organisms dispose over a plethora of bionanotechnological
machinery in order to live, survive and procreate. Their long feature list
includes amongst others a flexible outer shell (the pellicle) that protects them, a
mobile thread (the emergent flagellum) that propels them with high speed through
the liquid, a protein crystal that enables them to sense light and chloroplasts
that convert sunlight photons into storable energy. This energy is in turn stored
through means of lipid vesicles and semicrystalline starch deposits (paramylum 1
grains). If the cell cannot use its flagellum for locomotion it can move by metabolic
movements (this so-called "euglenoid movement" is similar to that of a worm contracting
the back and extending the front part) - sliding along solid material and
being lubricated by its own muciferous lubricant excreted from pellicle pores.
The ability to feed on sunlight only (although it must take up the vitamin
B-12, which it cannot synthesize itself, from the surrounding) and to survive even
with no light present at all by forcing itself to heterotrophic 2 metabolism has raised
some discussion whether this organism is more ’plant-like’ or ’animal-like’. Photosynthesis
(and its prerequisites, the chloroplast plastids within the cell) is a strong
argument to classify it amongst plants, yet an Euglena cell has no cellulose cell wall
1 "paramylum" is equivalent to "paramylon"
2 Heterotrophic means that the cell requires organic substrates as source for carbon in order
to grow and develop.
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