Phosphate and ATP uptake and growth kinetics in axenic cultures of the cyanobacteriumSynechococcusCCMP 1334

Abstract

Phosphorus potentially limits the growth and productivity of the unicellular cyanobacterium Synechococcus in many oligotrophic oceans. Both dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) could be important P sources in these regimes. We compared DIP and adenosine tri-phosphate (ATP) uptake and growth kinetics using axenic semi-continuous cultures of Synechococcus CCMP 1334 grown on both P substrates, under both P-limited and P-replete conditions. Molar C:total P ratios and N:total P ratios were 417-431 and 65-68, respectively, under severely P-limited growth conditions for both P sources, but were near Redfield values at >1.0 mM P as either DIP or ATP, and were inversely proportional to growth rates. Synechococcus grown on ATP as the sole P-source have the same maximum growth rates, lower half-saturation constants for growth, and similar cellular P quotas compared with cultures grown on DIP. DI 33 P and 33 P-ATP uptake experiments confirmed that both can be used by Synechococcus, with relative uptake rates depending on prior growth history. DIP-limited cultures assimilated ATP faster than DIP, while DIP-replete cultures took up DIP more rapidly. In contrast, for Synechococcus grown under ATP-limited conditions, there is no priority for the utilization of ATP or DIP, but ATP-replete cultures have a greater ability to use DIP. Like other phytoplankton, kinetic constants for Synechococcus DIP uptake and cellular P quotas, C:P and N:P ratios of DIP-grown cells differ when total cellular and intracellular P pools are compared, suggesting a need to re-evaluate these parameters to account for abiotic phosphate scavenging onto cell surfaces. DIP half-saturation constants for growth of this Synechococcus strain would not support observed natural growth rates at the nanomolar DIP concentrations found in most oligotrophic regimes, and hence populations in these areas probably rely primarily on DOP.

Functional Characterization of Synechocystis sp. Strain PCC 6803 pst1 and pst2 Gene Clusters Reveals a Novel Strategy for Phosphate Uptake in a Freshwater Cyanobacterium

“…The kinetic values reported here for the Pst1 and Pst2 transporters are within the range reported for other cyanobacteria (20,21) and natural phytoplankton populations (12). However, much of the culture data relates to strains for which genome information is lacking, and hence, for which it is not known whether there is more than one P i ABC transporter.…”

Improved methodology to measure taxon‐specific phosphate uptake in live and unfiltered samples

“…One of the most problematic steps used in previously published methods to measure taxon-specific P i uptake lies in the use of a fixative before samples are sorted (Fu et al 2006;Zubkov et al 2007;Larsen et al 2008;Casey et al 2009). This study shows that signal loss due to a 0.5% PFA fixation ranged between 17% and 50%, for both bulk and sorted samples.…”

Ecological Genomics of Marine Picocyanobacteria

“…It is not surprising, then, that marine picocyanobacteria have adopted several approaches for acquiring phosphorus (P) from this nutrient-poor environment, e.g., affinity, scavenging, storage, or growth strategies, the latter reallocating P-containing constituents within the cell. Low P quotas for both genera, and particularly Prochlorococcus (16,110), and high phosphate uptake rates (81,123) underlie an intense competition for this macronutrient in situ (196,338). Indeed, Prochlorococcus and heterotrophic bacteria of the SAR11 clade (96) are the major competing groups for bioavailable P in the oligotrophic North Atlantic gyre (338), where each can be responsible for around 45% of total P uptake.…”