Facultative H2-dependent anoxygenic photosynthesis in the unicellular cyanobacterium Gloeocapsa alpicola CALU 743

Larissa Serebryakova,Ivan Gogotov,Natalia Novichkova

doi:10.1155/s1110662x0200020x

Larissa Serebryakova, Ivan Gogotov + Show 1 more

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https://doi.org/10.1155/s1110662x0200020x

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Abstract

When cells of the unicellular cyanobacterium Gloeocapsa alpicola CALU 743 are deprived of nitrate, the phycobilisomes are actively degraded by a proteolytic process termed chlorosis, which accompanied by decrease of rates of oxygen evolution and carbon dioxide fixation, increase of amount of stored glycogen and increase of hydrogenase activity. Suspensions of such cells exhibited a capacity for light-dependent inorganic carbon photoassimilation under anaerobic conditions in the presence of hydrogen and DCMU. The rate of <mml:math alttext="${}^{{\text{14}}} {\text{C}}$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mrow><mml:mtext>14</mml:mtext></mml:mrow></mml:msup><mml:mtext>C</mml:mtext></mml:mrow></mml:math> incorporation was commensurable with that for nitrate-sufficient cells at oxygenic photosynthesis and reached 35–38 <mml:math alttext="$\mu $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>mol <mml:math alttext="${}^{{\text{14}}} {\text{C}}$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mrow><mml:mtext>14</mml:mtext></mml:mrow></mml:msup><mml:mtext>C</mml:mtext></mml:mrow></mml:math><mml:math alttext="${\text{h}}^{{\text{ - 1}}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext>h</mml:mtext><mml:mrow><mml:mtext>-1</mml:mtext></mml:mrow></mml:msup></mml:mrow></mml:math><mml:math alttext="${\text{mg}}^{ - 1} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext>mg</mml:mtext><mml:mrow><mml:mn>-1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> Chl a. Incubation of G. alpicola grown aerobically in the presence of limiting concentrations of nitrate under anaerobic conditions (Ar, <mml:math alttext="${\text{CO}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>CO</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>, DCMU) in the light with addition of nitrate and <mml:math alttext="${\text{H}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>H</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>, resulted in the increase of cellular protein, evidencing that G. alpicola cells with high level of hydrogenase activity are able to perform <mml:math alttext="${\text{H}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>H</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>-dependent anoxygenic photosynthesis at levels supporting the growth of this cyanobacterium.

Highlights

Cyanobacteria are plant-type phototrophs which carry out water-splitting oxygenic photosynthesis based on light-mediated electron flow through photosystem II (PSII) and photosystem I (PSI) thereby generating ATP and reducing power for photoassimilation of inorganic carbon
The low redox potential intracellular medium in nitrate-starved G. alpicola developed due to inactive PSII and unaltered respiration induced the increase of hydrogenase activity (Table 1) [12]
The process was insensitive to DCMU, an inhibitor of PSII, DBMIB, inhibitor of plastoquinone oxidation, prevented this reaction (Table 1)

Summary

Introduction

Cyanobacteria (blue-green algae) are plant-type phototrophs which carry out water-splitting oxygenic photosynthesis based on light-mediated electron flow through photosystem II (PSII) and photosystem I (PSI) thereby generating ATP and reducing power for photoassimilation of inorganic carbon. In addition to oxygenic photosynthesis a facultative CO2 photoassimilation using sulfide as electron donor has been demonstrated in many different cyanobacteria [1,2,3]. This type of photosynthesis is called anoxygenic photosynthesis, since it involves PSI only and no oxygen is evolved. Molecular hydrogen, being as sulfide highly reducing electron donor, can be utilized to photoreduction of CO2 by cyanobacteria but by eucaryotic algae as well [8, 9] This reaction requires hydrogenase participation and is driven by PSI, possible involvement of PSII has been indicated [10]

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