Physiology and evolution of nitrate acquisition in Prochlorococcus.
Paul M Berube1, Steven J Biller1, Alyssa G Kent2
1Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
The ISME Journal
|October 29, 2014
Summary
Marine cyanobacteria Prochlorococcus can now be cultured using nitrate, a key nutrient. This study reveals complex evolutionary gains of nitrate assimilation genes within this dominant ocean phototroph.
Area of Science:
- Marine microbiology
- Oceanography
- Genomics
Background:
- Prochlorococcus is the most abundant phototroph in oligotrophic oceans, crucial for primary productivity.
- Previous research suggested nitrate uptake but lacked supporting cultures and genomic evidence.
- Existing Prochlorococcus genomes lacked genes for nitrate assimilation.
Purpose of the Study:
- To introduce and characterize Prochlorococcus strains capable of growth on nitrate.
- To investigate the physiology and genome architecture related to nitrate assimilation.
- To explore the evolutionary history of nitrate assimilation genes in Prochlorococcus.
Main Methods:
- Culturing of three Prochlorococcus strains on nitrate.
- Physiological analysis of growth rates on nitrate versus ammonium.
- Genomic analysis of 41 Prochlorococcus genomes and environmental metagenomic sequences.
Main Results:
- Successfully cultured Prochlorococcus strains utilizing nitrate.
- Nitrate-based growth was approximately 17% slower than ammonium-based growth in high-light adapted strains.
- Nitrate assimilation genes have been acquired multiple times across at least three Prochlorococcus lineages.
- Genomic location and context of these genes vary between low-light and high-light adapted strains.
- Evidence suggests both stable genetic acquisition and independent, duplicated acquisitions of nitrate utilization genes.
Conclusions:
- Provides direct evidence for nitrate utilization in Prochlorococcus.
- Highlights the complex and dynamic evolutionary pathways of nitrate assimilation in this globally significant marine cyanobacterium.
- Suggests potential for Prochlorococcus to utilize nitrate in diverse oceanic environments.
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