Utilization of inorganic and organic nitrogen by bacteria in marine systems1

Abstract

The relative contribution of various inorganic and organic forms of nitrogen to the nitrogen requirements of picoplankton was examined with 15N tracers. Size fractionation was used to measure uptake by < l-pm size microorganisms, and inhibitors of protein synthesis were used to separate procaryotic from eucaryotic nitrogen uptake, Picoplankton utilized mainly ammonium and amino acids and only negligible amounts of nitrate and urea. Nearly all amino acid uptake was by procaryotes, while both procaryotes and eucaryotes utilized ammonium. About 78% of total ammonium uptake was by procaryotes, and a significant portion of this was due specifically to heterotrophic bacteria. Regeneration of ammonium was correlated with eucaryotic rather than procaryotic activity. Ammonium accounted for at least 20-60% of the summed ammonium plus amino acid utilization by bacteria. The results suggest that a significant portion of ammonium uptake in the euphotic zone was by heterotrophic bacteria rather than solely by phytoplankton. This may invalidate the use of the Rcdfield C : N ratio for estimating rates of nitrogen assimilation in the euphotic zone from carbon assimilation rates.

Size-fractionated measurements of nitrogen uptake in aged upwelled waters: Implications for pelagic food webs

“…The influence of bacterial activity at night cannot be ruled out. It has been demonstrated that a substantial portion of NH4+ uptake by the <2-pm fraction may be due to heterotrophic bacteria (Wheeler and Kirchman 1986) when C is not limiting (Keil and Kirchman 1987). In our study we found a good linear correlation between Chl and N productivity in the <2-pm fraction (r = 0.95, P < O.OOS), providing indirect evidence that phototrophs were dominant.…”

Nutrient limitation of bacterioplankton growth in Lake Dillon, Colorado

“…This work was supported by NSF grant BSR 90-20684. disproportionately large amount of P (Vadstein et al 1988;Glide 1989;Jiirgens and Giide 1990) and N (Wheeler and Kirchman 1986;Kirchman et al 1990) compared to other planktonic organisms. Although these studies support the presumption that bacteria compete favorably for inorganic nutrients, they do not show conclusively that planktonic bacteria grow under conditions of nutrient sufficiency.…”

Isotope fractionation associated with ammonium uptake by a marine bacterium

“…Bacteria also process on the order of 50% of primary production (Cole et al 1988). Much of this production can be supported by NH4+, and a large fraction of total NH,+ uptake by marine plankl Present address: Texas A&M Univ., % U.S. EPA-GBERL, Gulf Breeze, Florida 3256 1. ton can be attributed to bacteria (Wheeler and Kirchman 1986). NH,+ uptake by bacteria may influence phytoplankton population structure and new production (Kirchman et al 1990).…”