Cell-specific detection of phosphorus stress in Trichodesmium from the Western North Atlantic

The low phosphorus concentrations observed in the western North Atlantic and the western Central Atlantic suggest that phosphorus bioavailability may limit Trichodesmium productivity and N2 fixation. However, the degree to which the concentration and composition of the total phosphorus pool affects actual bioavailability is poorly understood. To better examine how phosphorus bioavailability may constrain primary production and marine N2 fixation, we have developed a molecular diagnostic tool for quickly detecting the phosphorus status of the diazotroph Trichodesmium. This diagnostic method uses a commercially available substrate to fluorescently tag cells expressing the phosphate-regulated enzyme, alkaline phosphatase. Using this diagnostic tool, we were able to distinguish phosphorus-replete from phosphorus-stressed Trichodesmium populations along a transect from Grand Bahama Island to Bermuda in November 2000.