Global gene expression of Prochlorococcus ecotypes in response to changes in nitrogen availability

Area of Science:

• Marine microbiology
• Oceanic biogeochemistry
• Molecular ecology

Background:

• Nitrogen (N) is a critical limiting nutrient for primary productivity in oceanic gyres.
• Prochlorococcus, the most abundant photosynthetic organism, comprises diverse strains with varied nitrogen utilization capabilities and depth distributions.

Purpose of the Study:

• To compare the responses of Prochlorococcus strains MED4 and MIT9313 to changing nitrogen availability.
• To understand the ecological implications of interstrain differences in nitrogen metabolism and gene regulation.

Main Methods:

• Quantified global mRNA expression, chlorophyll fluorescence, and photosystem II photochemical efficiency (Fv/Fm) under nitrogen starvation.
• Compared gene expression between strains grown in ammonium-replete medium and on alternative nitrogen sources.

Main Results:

• Identified conserved nitrogen (N) regulation mechanisms, including the activation of a putative NtcA regulon under N stress, across both strains.
• Observed significant interstrain differences in the expression patterns of carbon metabolism genes.
• Demonstrated fundamentally different strategies for integrating nitrogen and carbon metabolism between MED4 and MIT9313.

Conclusions:

• Prochlorococcus strains exhibit both conserved and distinct responses to nitrogen limitation.
• Differences in carbon metabolism gene expression highlight varied metabolic flexibility and ecological niches among Prochlorococcus ecotypes.
• Understanding these interstrain differences is crucial for predicting oceanic productivity and biogeochemical cycling.