THE RELATION BETWEEN N2 FIXATION AND H2 METABOLISM IN THE MARINE FILAMENTOUS NONHETEROCYSTOUS CYANOBACTERIUM LYNGBYA AESTUARII CCY 9616

Authors

  • Daniela Ferreira,

    1. IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal Faculdade de Ciências, Universidade do Porto, Departamento de Botânica, Edifício FC4, Rua do Campo Alegre, s/nº 4169-007 Porto, Portugal
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  • Lucas J. Stal,

    1. Department of Marine Microbiology, NIOO-KNAW, PO Box 140, 4400 AC Yerseke, the Netherlands
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  • Pedro Moradas-Ferreira,

    1. IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal Instituto de Ciências Biomédicas Abel Salazar (ICBAS), University of Porto, Largo Abel Salazar 2, 4099-003 Porto, Portugal
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  • Marta V. Mendes,

    1. IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
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  • Paula Tamagnini

    1. IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal Faculdade de Ciências, Universidade do Porto, Departamento de Botânica, Edifício FC4, Rua do Campo Alegre, s/nº 4169-007 Porto, Portugal
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  • Received 31 October 2008. Accepted 16 March 2009.

Abstract

The marine filamentous nonheterocystous nitrogen-fixing cyanobacterium Lyngbya aestuarii (F. K. Mert.) Liebman ex Gomont CCY 9616 was grown under diazotrophic and nondiazotrophic conditions and under an alternating 16:8 light:dark (L:D) regime. Nitrogenase activity appeared just before the onset of the dark period, reaching its maximum 1–2 h in the dark, subsequently decreasing to zero at the beginning of the following light period. Nitrogenase activity was only detected at low levels of O2 (5%) and when the culture was grown in the absence of combined nitrogen. Quantitative reverse transcriptase–PCR (RT-PCR) analysis of one of the structural genes encoding nitrogenase, nifK, showed that the highest levels of transcription preceded the maximum activity of nitrogenase by 2–4 h. nifK transcription was not completely abolished during the remaining time of the 24 h cycle. Even in the presence of nitrate, when nitrogenase activity was undetectable, nifK was still transcribed. The H2-uptake activity seemed to follow the nitrogenase, but the transcription of hupL (gene encoding the large subunit of uptake hydrogenase) preceded the nifK transcription. However, H2-uptake and hupL transcription occurred throughout the 24 h cycle as well as under nondiazotrophic conditions, albeit at much lower levels. The hoxH transcript levels (a structural gene coding for the bidirectional hydrogenase) were similar under diazotrophic or nondiazotrophic conditions but slightly higher during the dark period. All three enzymes investigated are involved in H2 metabolism. It is concluded that the uptake hydrogenase is mainly responsible for H2 uptake. Nevertheless, uptake hydrogenase and nitrogenase do not seem to be coregulated.

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