Abstract
Prochlorococcus contributes 25-60% of the chlorophyll a biomass to the tropical and subtropical oceans. Its importance to community structure in these areas has been demonstrated, but its nutrient requirements and nitrogen kinetics are not known. Nitrogen uptake of Prochlorococcus under a range of light conditions was investigated. Strains of Prochlorococcus isolated from three locations were used: Mediterranean Sea (CCMP 1378), Sargasso Sea (CCMP 1375), and Pacific Ocean (H36-16). Cultures grown on ammonia, urea or nitrate and acclimated to either high (75 []Ein m⁻²s⁻¹) or low light (5 []Ein m⁻²s⁻¹), were starved overnight, spiked with a single nitrogen source, and disappearance of the addition was measured after a two-hour incubation period. The Sargasso strain, acclimated to a high light environment and urea nitrogen source, had a high initial uptake, α[] [(amol N cell⁻¹h⁻¹)([]Ein m⁻²s⁻¹)⁻¹], of 1.29 whereas the ammonia culture of the same strain had a smaller α[] at 0.53. The high light acclimated Mediterranean strain had an α[] of 0.92 for ammonia, and 0.25 for urea. The high light acclimated Pacific strain showed the highest average α[] values with initial ammonia uptake at 3.80, urea at 4.08, and nitrate at 5.77. Photoinhibition was minimal for the high light acclimated cultures, with the exception of the ammonia uptake in the Pacific strain. The low light acclimated cultures showed similar photoinhibition, and lower am values for all but the ammonia uptake of the Sargasso strain. Differences between the strains point to the possibility that Prochlorococcus strains have evolved unique nitrogen preferences. When placed under identical conditions, each strain exhibited very different uptake characteristics. Prochlorococcus appeared not to grow well in a nitrate media. The Pacific strain had a large α[], but a growth rate comparable with cultures grown under low light conditions. Low growth rates prevented nitrate uptake curves from being performed on the other two strains.
Williams, Eli (1999). The nitrogen specific uptake of three strains of Prochlorococcus. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1999 -THESIS -W55.