Introduction to Fungi, Third Edition

4
Straminipila: minor fungal phyla
4.1 Introduction
The kingdom Chromista was erected by Cavalier-
Smith (1981, 1986) to accommodate eukaryotic
organisms which are distinguishable from the
Protozoa by a combination of characters. Some
of these are concerned with details of photosynthesis,
such as the enclosure of chloroplasts
in sheets of endoplasmic reticulum, and the
absence of chlorophyll b, the latter feature
being used for the naming of the kingdom.
Other defining characters apply also to the nonphotosynthetic
members of the Chromista (Kirk
et al., 2001). These are as follows:
1. The structural cell wall polymer is cellulose,
in contrast to walls of Eumycota which
contain chitin.
2. The inner mitochondrial membrane is
folded into tubular cristae (Fig. 4.1a) which are
also found in plants. In contrast, mitochondrial
cristae are generally lamellate in the kingdoms
Eumycota (Fig. 4.1b) and Animalia.
3. Golgi stacks (dictyosomes) are present;
these are also found in the Protozoa (see p. 64).
In contrast, in the Eumycota the Golgi apparatus
is usually reduced to single cisternae (see
Figs. 1.3, 1.10).
4. Flagella are usually present during particular
stages of the life cycle; they always include
one straminipilous flagellum (Lat. stramen ¼
straw, pilus ¼ hair). Dick (2001a) considered
this feature to be of such high phylogenetic
significance that he has renamed the kingdom
Chromista as Straminipila. The straminipilous
flagellum is discussed in detail in the following
section.
5. The amino acid lysine is synthesized via
the a,e-diaminopimelic acid (DAP) pathway.
Diaminopimelic acid originates from aspartic
semialdehyde and pyruvic acid and is present
in terrestrial plants, green algae, Chromista
and prokaryotes. The alternative route, the
a-aminoadipic acid (AAA) pathway, draws on
a-ketoglutaric acid and acetyl-CoA and is found
almost exclusively in members of the Eumycota.
Yet other organisms, including animals and
Protozoa, are auxotrophic for lysine (Griffin,
1994). Lysine biosynthesis has been used as a
chemotaxonomic marker for some time (Vogel,
1964; LéJohn, 1972).
The kingdom Chromista/Straminipila currently
includes the diatoms, golden and
brown algae, chrysophytes and cryptomonads,
as well as three phyla of straminipilous organisms
traditionally studied by mycologists,
i.e. the Oomycota, Hyphochytriomycota and
Labyrinthulomycota. The first two groups are
also called straminipilous fungi because of the
similarity of their mode of life to the fungal
lifestyle (Dick, 2001a). The Oomycota are by far
the more important of these, and are considered
in detail in Chapter 5. The Hyphochytriomycota
and Labyrinthulomycota are treated briefly in
the present chapter. The Straminipila as circumscribed
above are a diverse but natural