Biology Reference
In-Depth Information
Oxytricha trifallax
, has three TrHbs, one of them a three-domain chimera
(
Table 9.3
). The dinoflagellates (whirling flagella), represent a major alveolate
group and are among the largest microbial eukaryote groups (
Guiry, 2012
).
They are also part of the phytoplankton responsible for algal blooms, such
as the 'red tides' that occur off the coastal waters worldwide. The nefarious
effects of algal blooms are due to depletion of free oxygen and to the secretion
of toxins harmful to fish and shellfish. Furthermore, many dinoflagellates are
bioluminescent due to the presence of luciferase in individual cytoplasmic bod-
ies (
Haddock, Moline, & Case, 2010
). The three dinoflagellates have globins,
mostly SDgbs. The genus
Symbiodinium
occurs as an intracellular symbiont of
cnidarians, corals, jellyfish and sea anemones, as well as molluscs, flatworms
and sponges. Its transcriptome (
Bayer et al., 2012
) reveals half a dozen SDgbs.
The Rhizaria, first introduced by
Cavalier-Smith (2002)
, comprise three main
groups, the Cercozoa, Foraminifera and Radiolaria, and are represented
by 11 genomes and transcriptomes. The two acanthereans and the two
polycystineans lack globins. Of the five foraminifera only one,
Globobulimina
turgida
, has only TrHb1s. The two cercozoans each have a TrHb2.
4.3. Excavata
The Excavata, a major supergroup also proposed by
Cavalier-Smith (2002)
encompasses six phyla, the Euglenozoa, represented by 13 genomes
(
Table 9.3
), the Heterolobosea, Fornicata and Parabasalia, each with one
genome, and the Oxymonadida and Jakobida with none. The Euglenozoa,
include the Trypanosomatids, that are responsible for three major human dis-
eases, sleeping sickness (African trypanosomiasis), Chagas disease (South
American trypanosomiasis) and leishmaniasis. Although all trypanosomatids
are exclusively parasitic, and the
Trypanosoma brucei
,
T. congolense
,
T. cruzi
and
T. vivax
genomes lack globins, as does
Crithidia fasciculate
that parasitizes
insects, four of the five
Leishmania
genomes have an interesting chimeric,
600-700 residue globin, consisting of two N-terminal SDgb domains in tan-
dem, linked to a C-terminal nucleotidyl cyclase catalytic domain (
Table 9.3
).
The single heterolobosean genome, that of
Naegleria gruberi
, harbours an
SSDgb (
Fritz-Laylin, Ginger, Walsh, Dawson, & Fulton, 2011
). The genome
of
Giardia lamblia
representing the Fornicata contains two FHbs while the
genome of the human pathogen
Trichomonas vaginalis
, the only Parabasalia
genome, lacks globins (
Table 9.3
). Functions of these and other protozoal glo-
bins, insofar as they have been studied, are described in
Section 6
.
