In this experiment single cells or colonies were isolated
from samples of Pseudo-nitzschia seriata collected off the coast of
Greenland. This paper investigates the effects of temperature on the production
of DA in P.seriata, comparing the
production of DA at 4oC to that at 15oC. The effects of
temperature on the morphology of the frustule in the diatom were also tested.
The density, morphology and layout of the poroids within the frustule were tested,
comparing poroids at 4oC to those at 10oC and 15oC.
Before this study no diatoms had been found to produce DA in
polar waters, although P.seriata had
been found to produce the toxin this was found in samples taken from temperate
waters. The findings of this study have however shown that P.seriata is able to produce DA at temperatures of 4oC
and that the diatom didn’t produce any DA at 15oC, likely due to a
decrease in cell number due to the temperature stress.
It was also found in this study that the number of rows of
poroids, as well as their density, decreased in P.seriata with increasing temperatures. The morphology of P.seriata grown at 15oC was compared
with species of diatoms that grow in temperate regions and the morphology was
very similar, showing that using the morphology of the frustule in diatoms may
not be a good way of differentiating species. Although there were a lot of
similarities in morphology there was usually a distinguishing feature, such as
a higher density of poroids in P.seriata compared
with the temperate diatom P.australis.
This study highlights that the production of DA has been
shown to increase with longer photoperiods in diatoms, which is why it is
particularly important to investigate the production of DA in P.seriata from Polar Regions as during the
summer these areas may be exposed to sunlight for long periods of time. A
further study on the increase in DA production of P.seriata with increasing periods of light exposure would give a better
idea of how big a problem arctic diatoms may be in the accumulation of DA in
the arctic food web. The results of this study should be taken into
consideration by authorities in arctic regions when they are monitoring the levels
of toxic diatoms in the area as the current limit in many countries (before the
levels are tested in plankton and mussels) of 200,000 toxic diatom cells L-1
is thought to be too high, which may be putting many people’s healths at risk.
Reference: Hansen, L et al. (2011), Toxin production and
temperature-induced morphological variation of the diatom Pseudo-nitzschia
seriata from the Arctic, Harmful Algae, Vol 10, pg 689-696
3 comments:
Hi Matt,
This is interesting because in my last post the authors have found high levels of domoic acid in Monterey bay after a massive P.australis summer bloom (august-september). I guess that california waters are definitely warmer than 15°C during the summer, but in the article you've just reviewed, they say that diatom didn't produce any DA at 15°C...Perhaps there are differences between the two species of diatoms?
Ye, I'm assuming the results are only relevant to P.seriata and possibly other species of cold water toxic diatoms. The P.seriata cannot survive in higher temperatures as it hasn't evolved to live in these conditions and I'd assume that P.australis would likely die or not function to the best of its ability if it were in colder waters.
This paper talks a little about P.australis as the morphology of P.seriata begins to look like that of P.australis, and other temperate diatoms, when exposed to higher temperatures, which could indicate that it's trying to adapt to the new environment but the diatom begins to die so it obviously isn't enough.
Hey this study is quite interesting especially as it seems that the diatoms ability to produce the toxin seems to not have evolved in the separate population due to selection pressure, but it seems as if the ability to produce the toxin has been around for a very long time possibly before geographic separation and resultant branches in different locations of the diatoms, as it would be unusual for the diatoms to individually evolve this property.
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