Some
organisms that influence our everyday life are so small that we do
not even notice
them. Also we are used to what they do without being conscious and we
hardly know how they master difficult situations. In the euphotic
zone some organisms are non-motile so they are transported by
vertically mixing waters and have to deal with different intensities
of light exposure. One of these organisms is Prochlorococcus
which is a small phototroph that plays an important role in the
carbon cycle (Munn, 2011).
It is found in the euphotic zone and is the most abundant oxygenic
phototroph (Coe et al.,
2016). The strains are classified as high light (HL) and low light
(LL) adapted (Coe et al.,
2016). The main questions of this study where if Prochlorococcus
has developed the ability to recover after light-deprivation and if
the presence of the heterotroph Alteromonas
macleodii and the
presence of organic compounds (glucose and
sodium pyruvate) affect the recovery of Prochlorococcus
after light-deprivation.
Coe
et al.
found that the majority of strains of Prochlorococcus
can survive after 35 h
light-depriviation but none can after 59 h or more. Furthermore
the capability to recover was not related to HL or LL. The
heterotroph A. macleodii
reduces the oxidative stress of Prochlorococcus,
partly because of its reducing effect
on hydrogen peroxide due to its production of extracellular
catalase-peroxidase. As a result the
ability of Prochlorococcus
to recover extended (from 3 - 11
days). The same effect was detected when adding sodium pyruvate
(reduces hydrogen peroxide). Adding glucose and sodium pyruvate
enable Prochlorococcus
to recover after periods of darkness up to 83 h.
To
investigate the affect of the lack of light different strains of
Prochlorococcus
were exposed to a light : dark cycle before
light-deprivation. Coe et al.
used flow cytometry and bulk chlorophyll fluorescence to test the
abundance and the viability of the cells after the periods of
darkness. In their conclusion Coe et al.
outline that their questions are not completely resolved but the
study shows interesting facts about which role oxidative stress plays
in the dark.
As
mentioned before we do not notice
many of the processes around us. To understand how the world would be
without these processes we need to understand how the organisms are
involved and how they are all related. This study takes a step
forward to investigate this.
I
think it is really interesting to see that the recovery of
Prochlorococcus
after a certain time in the dark
is not strain related. So even a strain that grows the best in high
light conditions is able to survive the long mixing periods in the
euphotic zone as well as a low light adapted strain. Additionally
I would suggest more studies with other
heterotrophs to see whether they have the same effect as A.macleodii.
Reviewed
paper:
Coe,
A., Ghizzoni, J., LeGault, K., Biller, S., Roggensack, S. E. and
Chisholm, S. W. (2016). Survival of Prochlorococcus
in extended darkness. Limnology and
Oceanography, 61, 1375-1388.
onlinelibrary.wiley.com/doi/10.1002/lno.10302/full
References:
Munn,
C. (2011). Marine microbiology: Ecology and applications (2nd
ed.). Garland Science.
ISBN: 978-0-8153-6517-4
Hi Eleni,
ReplyDeleteGreat post – its amazing that a photoautotroph can survive such extreme light deprivation! I’m quite intrigued however that light deprivation is associated with increased oxidative stress as this is typically associated with extreme UV irradiation in the cyanobacteria (shown in a fresh water species by He and Haeder, 2002). Do you think the physiological response for high vs low light stresses are comparable and if so would co-culture and metabolic exchange of the cyanobacterium with the heterotrophic Alteromonas produce a similar result in your opinion?
Thanks,
Davis
He, Y. Y., & Häder, D. P. (2002). Involvement of reactive oxygen species in the UV-B damage to the cyanobacterium Anabaena sp. Journal of Photochemistry and Photobiology B: Biology, 66(1), 73-80.
Hi Davis,
ReplyDeleteI was really confused when I first read the reviewed paper because I also associated the increased oxidative stress with UV irradiation. So I read a paper about the dark production of hydrogen peroxide and apparently there is not only the photosynthetic way of producing hydrogen peroxide but also a biological way of producing extracellular hydrogen peroxide (Vermilyea et al. 2010). I have not found any paper about the exact mechanism of biological production of hydrogen peroxide.
So I don't know if we can compare HL vs LL because I think that the mechanism is hardly known. But I would suggest to conduct a study about this with especially Prochlorococcus as hydrogen peroxide producer.
I am sorry that I could not really answer the question because there seem to be a lack of results.
Eleni
Vermilyea, A. W., Paul Hansard, S., & Voelker, B. M. (2010). Dark production of hydrogen peroxide in the Gulf of Alaska. Limnology and Oceanography, 55(2), 580.