Nitrogen deprivation results in photosynthetic hydrogen production in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> |
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Authors: | Gabriele?Philipps Thomas?Happe Email author" target="_blank">Anja?HemschemeierEmail author |
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Institution: | 1.AG Photobiotechnologie, Fakult?t für Biologie und Biotechnologie, Lehrstuhl für Biochemie der Pflanzen,Ruhr-Universit?t Bochum,Bochum,Germany;2.AG Photobiotechnologie, Fakult?t für Biologie und Biotechnologie, Lehrstuhl für Biochemie der Pflanzen,Ruhr-Universit?t Bochum,Bochum,Germany;3.AG Photobiotechnologie, Fakult?t für Biologie und Biotechnologie, Lehrstuhl für Biochemie der Pflanzen,Ruhr-Universit?t Bochum,Bochum,Germany |
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Abstract: | The unicellular green alga Chlamydomonas
reinhardtii is able to use photosynthetically provided electrons for the production of molecular hydrogen by an FeFe]-hydrogenase HYD1
accepting electrons from ferredoxin PetF. Despite the severe sensitivity of HYD1 towards oxygen, a sustained and relatively
high photosynthetic hydrogen evolution capacity is established in C. reinhardtii cultures when deprived of sulfur. One of the major electron sources for proton reduction under this condition is the oxidation
of starch and subsequent non-photochemical transfer of electrons to the plastoquinone pool. Here we report on the induction
of photosynthetic hydrogen production by Chlamydomonas upon nitrogen starvation, a nutritional condition known to trigger the accumulation of large deposits of starch and lipids
in the green alga. Photochemistry of photosystem II initially remained on a higher level in nitrogen-starved cells, resulting
in a 2-day delay of the onset of hydrogen production compared with sulfur-deprived cells. Furthermore, though nitrogen-depleted
cells accumulated large amounts of starch, both hydrogen yields and the extent of starch degradation were significantly lower
than upon sulfur deficiency. Starch breakdown rates in nitrogen or sulfur-starved cultures transferred to darkness were comparable
in both nutritional conditions. Methyl viologen treatment of illuminated cells significantly enhanced the efficiency of photosystem
II photochemistry in sulfur-depleted cells, but had a minor effect on nitrogen-starved algae. Both the degradation of the
cytochrome b
6
f complex which occurs in C. reinhardtii upon nitrogen starvation and lower ferredoxin amounts might create a bottleneck impeding the conversion of carbohydrate reserves
into hydrogen evolution. |
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Keywords: | |
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