Mulholland, M. R. Chesapeake Biological Lab, University of Maryland Center for Environmental Science, margie@cbl.umces.edu
Capone, D. R. Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, capone@cbl.umces.edu

 
NITROGEN AND CARBON UTILIZATION BY TRICHODESMIUM SPP.
 
It is generally held that the cyanobacterium, Trichodesmium, relies entirely upon N2 fixation for their N requirement. However, N-based growth rate estimates in natural populations are generally substantially lower than those based on C, suggesting utilization of other N sources. Moreover, Trichodesmium releases combined N (as DON) and in blooms this can result, after regeneration, in elevated ambient NH4+ levels. We examined the capacity of Trichodesmium to assimilate various forms of combined N (NH4+, NO3-, urea, and glutamate) at tracer levels. Our results indicate that in laboratory cultures of Trichodesmium IMS101 and NIBB1067 between 70 and 85% of the daily nitrogen uptake in cultures can be accounted for by combined N uptake (primarily NH4+). While the assimilated NH4+ ultimately derives from N2 fixation, NH4+ uptake can represent a substantial portion of N utilization. Rates of NH4+ uptake paralleled the concentration of NH4+ in the media. N2 fixation was restricted to the light period and accounted for the balance of total daily uptake. Both Trichodesmium NIBB1067 and field populations had a high affinity for NH4+. Carbon incorporation is also being examined over a diel cycle in cultures of Trichodesmium IMS101 to determine whether measured N utilization satisfied the N demand estimated from rates of C fixation. Our results suggest that in nature, Trichodesmium populations do utilize ambient pools of NH4+, possibly for net growth.
 
Day: Wednesday, Feb. 3
Time: 10:45 - 11:00am
Location: Hilton of Santa Fe
 
Code: SS38WE1045H