Introduction to Fungi, Third Edition

74 STRAMINIPILA: MINOR FUNGAL PHYLA
Fig 4.8 Thraustochytriales. (a) Thallus of Thraustochytrium sp. growing on a pollen grain sprinkled onto seawater. (b) Thalli of
Schizochytrium sp. growing on a pollen grain. (c) Thalli of Schizochytrium sp. growing on agar medium. Note the slime net extending
away from the thalli.
and these can settle onto a suitable substratum,
giving rise to new thalli (Porter, 1990).
Thus, these zoospores of Thraustochytriales
are mitospores formed following mitosis, in
contrast with those of Labyrinthulales which
are meiospores, i.e. formed by meiosis. Although
thraustochytrid zoospores lack a recognizable
eye-spot, they are phototropic, reacting to light
of blue wavelengths such as that produced by
bioluminescent bacteria (Amon & French, 2004).
Chemotropism has also been described for
thraustochytrid zoospores (Fan et al., 2002), and
both sensual responses may enable zoospores
to locate potential food sources.
Thraustochytrids, and especially the genera
Thraustochytrium and Schizochytrium, have recently
attracted attention as producers of polyunsaturated
fatty acids (PUFAs). These are important
as nutrient supplements, and thraustochytrid
oils might eventually be able to compete with
fish oils on the market (Yokochi et al., 1998;
Lewis et al., 1999).