Diversity of regulatory mechanisms in the C/N metabolism of the marine cyanobacteria Prochlorococcus and synechococcus

Abstract

Marine picocyanobacteria are the most abundant photosynthetic organisms on Earth, with only two genera, Prochlorococcus (Johnson et al., 2006, Olson et al., 1990, Partensky et al., 1999) and Synechococcus (Scanlan, 2003, Scanlan & West, 2002) numerically dominating most oceanic waters. During this research project our main goal was to study the diversity of the regulatory mechanisms in the C/N metabolism of these cyanobacteria. Recent advances in the knowledge of nitrogen metabolism of Prochlorococcus have shown that it has fine regulatory systems to optimize nitrogen assimilation (Rocap et al., 2003, García-Fernández et al., 2004, Lindell et al., 2002). Thus, we have studied the role of 2-oxoglutarate in the control of the C/N balance in order to check whether there exist differences with respect to other model cyanobacteria and among strains of Prochlorococcus. The comparative study performed show that 2-oxoglutarate is the molecule responsible in Prochlorococcus to control the balance between carbon and nitrogen metabolism and there are differences among strains in sensing this metabolite. These results could be an explanation for its adaptation to different ecological niches in the ocean. Besides, we wanted to know how Synechococcus is able to successfully coexist with Prochlorococcus. For that, the hypothesis was that Synechococcus could be more efficient at the utilization of low concentration of nitrate. The results showed that when concentrations of nitrate in the range of nanomolar are present, the genes related with the assimilation of that source are up-regulated in Synechococcus WH7803. Therefore, these facts suggest that the machinery is working at transcriptional level in order to uptake the nitrate. This could be an evolutionary advantage against Prochlorococcus in the real field.