Biomarkers
a proportion of less than 9% in other photosynthetic dinoflagellates
or prymnesiophytes and usually traces in other orders (Joseph, 1993;
Viso tk Marty, 1993; Okuyama et al., 1993; Bodennec et al., 1993).
All-cis-18:5 (n-3) is an unusual PUFA which has been implicated in fish
kills caused by Gyrodinium aureolum blooms (Yasumoto et al., 1990)
and proposed to be characteristic of toxic algae (Joseph, 1993). In
G. mikimotoi cells, it was associated with a relatively high proportion
of 16:4 (n-3) and with less than 1% of 20:5 (n-3). When taken in ratio
to 16:4 (n-3), this compound may used as a signature index of G. mikimotoi blooms, considering the values noted in G. mikimotoi (ratio = 3.2)
in comparison with H. akashiwo (ratio = 20) and G. corii (ratio = 48).
The 18:5 (n-3)/l6:4 (n-3) ratio appeared relatively constant in G. mikimotoi cells grown in various culture conditions with an average value of
3.0 ± 0.7 (n = 53). In our local H. akashiwo strain, 18:5 (n-3) represented
only 5-8% of the fatty acid pool, a proportion similar to that found in
a previous study (Nichols et al., 1987) and more recently by Bell et al.
(1997). The 18:5 (n-3)/18:4 (n-3) ratio may also be a possible biomarker of G. mikimotoi blooms with a mean ratio value of 32.6 ± 16.9
(n = 68) according to culture conditions and growth phase in G. corii,
0.4 in H. akashiwo and an average value of 4.1 ± 2.4 in 12 dinoflagellate species in which both 18:5 (n-3) and 18:4 (n-3) are detected (Joseph, 1993; Volkman et al., 1989; Viso & Marty, 1993; Okuyama et al.,
1993; Arzul et al., 2000).
The acid 18:5 (n-3) was concentrated in the MGDG and DGDG fractions
which have been shown to be haemolytic in the Gymnodinium species
(Parrish et al, 1998). The fatty acid composition of these haemolytic
galactolipids again indicated differences between the two species as
previously shown on the TLC-FID chromatograms. However, PUFA
profiles in MGDG and DGDG from G. mikimotoi cells looked similar as
it was also noted for the two galactolipids of G. corii. This indicates that
the galactosyl transferase enzyme has no selectivity for molecular species
of MGDG for galactosylation to DGDG.
Conclusion
The chemical analyses of lipid compounds extracted from closely related
Gymnodinium and Heterosigma strains pointed up the presence of unusual
C16 and C18 PUFAs mainly in glycolipid structures. When taken in
ratio to other PUFAs, these fatty acids could be used as a signature index
of these harmful red tide flagellates. They may also be useful to assist
the assignment of these species in their algal taxonomic position as a
method between the usual microscopic observations and the more
sophisticated genetic techniques of species identification. The relative
proportion of MGDG to DGDG in association with 18:5 (n-3)/l6:4 (n-3)
or 18:5 (n-3)/18:4 (n-3) ratios appeared characteristic of G. mikimotoi
cells and could be proposed in a monitoring program to follow the contamination of water or seafood samples. Moreover, the Iatroscan TLC/FID
71
a proportion of less than 9% in other photosynthetic dinoflagellates
or prymnesiophytes and usually traces in other orders (Joseph, 1993;
Viso tk Marty, 1993; Okuyama et al., 1993; Bodennec et al., 1993).
All-cis-18:5 (n-3) is an unusual PUFA which has been implicated in fish
kills caused by Gyrodinium aureolum blooms (Yasumoto et al., 1990)
and proposed to be characteristic of toxic algae (Joseph, 1993). In
G. mikimotoi cells, it was associated with a relatively high proportion
of 16:4 (n-3) and with less than 1% of 20:5 (n-3). When taken in ratio
to 16:4 (n-3), this compound may used as a signature index of G. mikimotoi blooms, considering the values noted in G. mikimotoi (ratio = 3.2)
in comparison with H. akashiwo (ratio = 20) and G. corii (ratio = 48).
The 18:5 (n-3)/l6:4 (n-3) ratio appeared relatively constant in G. mikimotoi cells grown in various culture conditions with an average value of
3.0 ± 0.7 (n = 53). In our local H. akashiwo strain, 18:5 (n-3) represented
only 5-8% of the fatty acid pool, a proportion similar to that found in
a previous study (Nichols et al., 1987) and more recently by Bell et al.
(1997). The 18:5 (n-3)/18:4 (n-3) ratio may also be a possible biomarker of G. mikimotoi blooms with a mean ratio value of 32.6 ± 16.9
(n = 68) according to culture conditions and growth phase in G. corii,
0.4 in H. akashiwo and an average value of 4.1 ± 2.4 in 12 dinoflagellate species in which both 18:5 (n-3) and 18:4 (n-3) are detected (Joseph, 1993; Volkman et al., 1989; Viso & Marty, 1993; Okuyama et al.,
1993; Arzul et al., 2000).
The acid 18:5 (n-3) was concentrated in the MGDG and DGDG fractions
which have been shown to be haemolytic in the Gymnodinium species
(Parrish et al, 1998). The fatty acid composition of these haemolytic
galactolipids again indicated differences between the two species as
previously shown on the TLC-FID chromatograms. However, PUFA
profiles in MGDG and DGDG from G. mikimotoi cells looked similar as
it was also noted for the two galactolipids of G. corii. This indicates that
the galactosyl transferase enzyme has no selectivity for molecular species
of MGDG for galactosylation to DGDG.
Conclusion
The chemical analyses of lipid compounds extracted from closely related
Gymnodinium and Heterosigma strains pointed up the presence of unusual
C16 and C18 PUFAs mainly in glycolipid structures. When taken in
ratio to other PUFAs, these fatty acids could be used as a signature index
of these harmful red tide flagellates. They may also be useful to assist
the assignment of these species in their algal taxonomic position as a
method between the usual microscopic observations and the more
sophisticated genetic techniques of species identification. The relative
proportion of MGDG to DGDG in association with 18:5 (n-3)/l6:4 (n-3)
or 18:5 (n-3)/18:4 (n-3) ratios appeared characteristic of G. mikimotoi
cells and could be proposed in a monitoring program to follow the contamination of water or seafood samples. Moreover, the Iatroscan TLC/FID
71