The uptake of inorganic nutrients by heterotrophic bacteria

Abstract

It is now well known that heterotrophic bacteria account for a large portion of total uptake of both phosphate (60% median) and ammonium (30% median) in freshwaters and marine environments. Less clear are the factors controlling relative uptake by bacteria, and the consequences of this uptake on the plankton community and biogeochemical processes, e.g., new production. Some of the variation in reported inorganic nutrient uptake by bacteria is undoubtedly due to methodological problems, but even so, uptake would be expected to vary because of variation in several parameters, perhaps the most interesting being dissolved organic matter. Uptake of ammonium by bacteria is very low whereas uptake of dissolved free amino acids (DFAA) is high in eutrophic estuaries (the Delaware Bay and Chesapeake Bay). The concentrations and turnover of DFAA are insufficient, however, in oligotrophic oceans where bacteria turn to ammonium and nitrate, although the latter only as a last resort. I argue here that high uptake of dissolved organic carbon, which has been questioned, is necessary to balance the measured uptake of dissolved inorganic nitrogen (DIN) in seawater culture experiments. What is problematic is that this DIN uptake exceeds bacterial biomass production. One possibility is that bacteria excrete dissolved organic nitrogen (DON). A recent study offers some support for this hypothesis. Lysis by viruses would also release DON.While ammonium uptake by heterotrophic bacteria has been hypothesized to affect phytoplankton community structure, other impacts on the phytoplankton and biomass production (both total and new) are less clear and need further work. Also, even though bacteria account for a very large fraction of phosphate uptake, how this helps to structure the plankton community has not been examined. What is clear is that the interactions between bacterial and phytoplankton uptake of inorganic nutrients are more complicated than simple competition.

Carbon‐nitrogen coupling and algal‐bacterial interactions during an experimental bloom: Modeling a 13C tracer experiment

“…Higher trophic levels derive their energy from algal tissue either directly (grazers) or indirectly (predators). The direct link from algae to bacteria is via DOM, the main source of bacterial carbon and the preferred source of bacterial nitrogen (Wheeler and Kirchman 1986;Kirchman 1994). Algae produce DOM through lysis, passive leakage, or exudation of carbon-rich material (Anderson and Williams 1998), but there are other sources of DOM as well that are either indirectly linked to or independent of algal dynamics.…”

Diverse, uncultivated bacteria and archaea underlying the cycling of dissolved protein in the ocean

“…LMW-DON such as DFAA released by protein hydrolysis (Billen and Fontigny, 1987) are readily assimilated by bacteria in aquatic systems (Hobbie et al, 1968) and can support up to~50% of bacterial production in the oceans (Kirchman, 2000).…”

Bacterial and Phytoplankton Production in Two Coastal Systems Influenced by Distinct Eutrophication Processes

“…The optimal DOM C:N for bacterial uptake is around 5.0, which equals their elemental composition (Goldman et al 1987). Therefore, under high DOM C:N conditions, bacterioplankton will adjust the C:N balance by using inorganic N (Kirchman 1994), what compromises their growth effi ciency (Guenther et al 2008b). The higher BP rates of Guanabara Bay are thus result of local organic matter quality (i.e., lower DOM C:N) and higher water temperatures.…”