Aquatic Sciences Meeting, Albuquerque 2001

CS39 Trace Metal Limitation of Biogeochemistry

Date: Tuesday, February 13, 2001, Time: 12:00:00 PM

Location: Dona Ana

Tuit, C, B, MIT/Woods Hole Oceanographic Joint Program, Woods Hole, USA, ctuit@whoi.edu

Waterbury, J, , Woods Hole Oceanographic Institution, Woods Hole, USA, jwaterbury@whoi.edu

Ravizza, G, E, Woods Hole Oceanographic Institution, Woods Hole, USA, gravizza@whoi.edu

DIEL CYCLING OF MOLYBDENUM (MO) CELL QUOTAS IN RESPONSE TO NOCTURNAL NITROGEN FIXATION IN CROCOSPHAERA SPP. STRAIN WHOI 8501

Molybdenum, which is required for the common form of the nitrogenase enzyme, is an important non-limiting micronutrient in situ for marine nitrogen-fixing cyanobacteria. We present preliminary studies examining Mo cycling in laboratory cultures of Crocosphaera spp., a single-celled nitrogen-fixing cyanobacterium found in the western equatorial Atlantic where it reaches a maximum abundance of approximately 10^3 cells/ml. Crocosphaera separates nitrogen fixation and photosynthesis over a diel cycle with peak nitrogen fixation occurring at midnight. Axenic Crocosphaera cultures, grown under Fe and Mo replete conditions and harvested at peak nitrogen fixation activity exhibit a 4 to 10-fold increase in Mo/cell compared to actively photosynthesizing cells during the light period. These cells also exhibited a 2-fold diel variation in Fe/cell with peak Fe cell quotas corresponding to peak nitrogen fixation. These results support evidence that cyanobacteria that separate dinitrogen fixation and photosynthesis, synthesize nitrogenase de novo just prior to the peak period of nitrogen fixation and surprisingly, excrete Mo during the day when nitrogenase is degraded.

This Session Listing

Aquatic Sciences Meeting, Albuquerque 2001

Quicklinks