2012 SURF: Growth Response of Prochlorococcus

Growth Response of Prochlorococcus to Different Nitrogen Sources

Mentor: Dr. Lisa Moore, Biology Department

Prochlorococcus is an important microbe in the marine microbial community because it serves as the base of the marine food chain, providing a food source for small grazers such as ciliates. Prochlorococcus produces 20 percent of global oxygen via photosynthesis and for this reason it plays a big role in carbon dioxide (CO₂) fixation and the global carbon cycle. Prochlorococcus also participates in the recycling of organic matter and may provide extracellular organic products that support growth of some marine bacteria.

In a comparison of different strains of Prochlorococcus and their closely related marine cyanobacteria, Synechococcus, it was found that both can use ammonia (NH₃) and urea but only some strains of Prochlorococcus can grow on nitrite (NO₂^-) while no Prochlorococcus strains can grow on nitrate (NO₃). However in the last decade several new strains have been isolated that can use nitrate.

Being the most abundant photosynthetic microbe in the oceans, understanding Prochlorococcus is vital to our existence. This study of nitrate-utilizing Prochlorococcus strains involved obtaining axenic strains (without heterotrophic bacterial contaminants), collecting biomass for sending to MIT to check for multiple strains in axenic cultures, and studying nitrogen utilization.

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Prochlorococcus 1: Cultivation Media for culturing the microbe was made with nitrate and ammonium. View Full-Size	Prochlorococcus 2: Flow Cytometry Cultures were screened to determine cell counts and characteristics. View Full-Size
Prochlorococcus 3: Results Cytometry yielded ratio of heterotrophic bacterial contaminants to Pro. cells. View Full-Size	Prochlorococcus 4: Making axenic cultures Dilution to extinction was used to eliminate heterotrophic bacteria. View Full-Size
Prochlorococcus 5: Collecting biomass When cultures were green, some cells were concentrated for analysis at MIT. View Full-Size	Prochlorococcus 6: Maintenance Molecular analysis at MIT showed identical axenic strains are being maintained. View Full-Size