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Applied and Environmental Microbiology, May 2001, p. 2202-2207, Vol. 67, No. 5
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.5.2202-2207.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

In Vivo Regulation of Glutamine Synthetase Activity in the Marine Chlorophyll b-Containing Cyanobacterium Prochlorococcus sp. Strain PCC 9511 (Oxyphotobacteria)

Sabah El Alaoui,¹ Jesús Diez,¹ Lourdes Humanes,¹ Fermín Toribio,¹ Frédéric Partensky,² and José Manuel García-Fernández^1,*

Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, E-14071 Córdoba, Spain,¹ and Station Biologique de Roscoff (CNRS UPR 9042 et Université Paris VI),² 29682 Roscoff Cedex, France

Received 9 June 2000/Accepted 8 February 2001

The physiological regulation of glutamine synthetase (GS; EC 6.3.1.2) in the axenic Prochlorococcus sp. strain PCC 9511 was studied. GS activity and antigen concentration were measured using the transferase and biosynthetic assays and the electroimmunoassay, respectively. GS activity decreased when cells were subjected to nitrogen starvation or cultured with oxidized nitrogen sources, which proved to be nonusable for Prochlorococcus growth. The GS activity in cultures subjected to long-term phosphorus starvation was lower than that in equivalent nitrogen-starved cultures. Azaserine, an inhibitor of glutamate synthase, provoked an increase in enzymatic activity, suggesting that glutamine is not involved in GS regulation. Darkness did not affect GS activity significantly, while the addition of diuron provoked GS inactivation. GS protein determination showed that azaserine induces an increase in the concentration of the enzyme. The unusual responses to darkness and nitrogen starvation could reflect adaptation mechanisms of Prochlorococcus for coping with a light- and nutrient-limited environment.

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^* Corresponding author. Mailing address: Departamento de Bioquímica y Biología Molecular, Edificio C-6, 1^a Planta, Campus de Rabanales, Universidad de Córdoba, E-14071 Córdoba, Spain. Phone: 34 957 211 075. Fax: 34 957 218 592. E-mail: bb1gafej{at}uco.es.

We dedicate this work to the memory of our friend and teacher, Antonio López-Ruiz, who shared with us many hours in the laboratory. We are in many ways indebted to his outstanding example of talented hard work and human qualities.

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Applied and Environmental Microbiology, May 2001, p. 2202-2207, Vol. 67, No. 5
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.5.2202-2207.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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