title: Temperature dependence of inorganic nitrogen uptake: reduced affinity for nitrate at suboptimal temperatures in both algae and bacteria.
abstract: Nitrate utilization and ammonium utilization were studied by using three algal isolates, six bacterial isolates, and a range of temperatures in chemostat and batch cultures. We quantified affinities for both substrates by determining specific affinities (specific affinity = maximum growth rate/half-saturation constant) based on estimates of kinetic parameters obtained from chemostat experiments. At suboptimal temperatures, the residual concentrations of nitrate in batch cultures and the steady-state concentrations of nitrate in chemostat cultures both increased. The specific affinity for nitrate was strongly dependent on temperature (Q10 approximately 3, where Q10 is the proportional change with a 10 degrees C temperature increase) and consistently decreased at temperatures below the optimum temperature. In contrast, the steady-state concentrations of ammonium remained relatively constant over the same temperature range, and the specific affinity for ammonium exhibited no clear temperature dependence. This is the first time that a consistent effect of low temperature on affinity for nitrate has been identified for psychrophilic, mesophilic, and thermophilic bacteria and algae. The different responses of nitrate uptake and ammonium uptake to temperature imply that there is increasing dependence on ammonium as an inorganic nitrogen source at low temperatures.
authors.affiliation: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, United Kingdom. dsreay@essex.ac.uk
authors.forename: D S
authors.initials: DS
authors.lastname: Reay
authors.forename: D B
authors.initials: DB
authors.lastname: Nedwell
authors.forename: J
authors.initials: J
authors.lastname: Priddle
authors.forename: J C
authors.initials: JC
authors.lastname: Ellis-Evans
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D003470:Culture Media; D056890:Eukaryota / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D005618:Fresh Water; D006090:Gram-Negative Bacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012623:Seawater; D013696:Temperature; D014871:Water Microbiology
chemical_list: D003470:Culture Media; D009566:Nitrates; D000644:Quaternary Ammonium Compounds