Selection by temperature of nitrate-reducing bacteria from estuarine sediments: species composition and competition for nitrate

Abstract

Nitrate‐metabolising bacteria were isolated from estuarine sediment in carbon‐limited anaerobic chemostats with nitrate as the only electron acceptor, at constant low temperature (5°C), constant high temperature (20°C), or square wave temperature cycle (5–20°C over 24 h). The steady‐state communities isolated were sampled randomly, and isolates identified. At constant 20°C and under cycling temperature the communities were dominated by bacteria with obligately fermentative metabolism; Klebsiella spp. at 20°C and Enterobacter spp. in cycling temperature, which were nitrate‐ammonifiers. The dominant isolates at 5°C were bacteria with the capacity for oxidative, respiratory metabolism, which were able to denitrify. The physiologies of representative isolates of these two distinct high and low temperature communities were examined further. An Arrhenius plot for growth of the 20°C isolate A1 (Klebsiella oxytoca) increased linearly from 10°C up to the optimum at 28°C, but decreased above the optimum and at temperatures <10°C. A1 was unable to grow at 5°C. The unidentifiable 5°C isolate (E3) was capable of both fermentative and oxidative metabolism, but when respiring nitrate the Arrhenius plot for growth was linear between 3–18°C with an optimum at 19°C. A cross‐over in μmax of these two isolates occurred at about 23°C. The ability of each bacterium to scavenge nitrate was examined in anaerobic nitrate‐limited chemostats, measuring the specific affinity (aA) of each bacterium for nitrate at different temperatures. Specific affinity for nitrate increased with temperature in both bacteria, indicating an improved ability to sequester nitrate at higher temperatures. Isolate A1 had a higher aA for nitrate than E3 at 20°C, but E3 had a higher aA at low temperature. A crossover in the specific affinities of these two bacteria occurred between 5 and 20°C, so that A1 was better able to sequester nitrate at high temperature while E3 was more effective in sequestering nitrate at lower temperature. We propose that at low temperature denitrifying bacteria predominate in estuarine sediments as they are selected by their improved ability to scavenge limited concentrations of nitrate at low temperature, whereas fermentative nitrate‐ammonifiers are better competitors for nitrate at the higher summer temperatures. Seasonal changes in environmental temperature therefore result in seasonal selection of different nitrate‐utilising communities.

Organic carbon, and not copper, controls denitrification in oxygen minimum zones of the ocean

“…Nevertheless, a reasonable exponential fit for 3 -4 points could be obtained for the cell numbers, suggesting that most of the assemblage underwent exponential growth in the bags. The generation times computed for the incubations are longer than usually observed under culture conditions (on the order of 5 -45 hr; Otte et al 1996;Ogilvie et al 1997), but the curve fits implied that growth commenced almost immediately in some incubations (e.g., ETSP and AS Station 17).…”

Dissimilatory reduction of nitrate to ammonium, not denitrification or anammox, dominates benthic nitrate reduction in tropical estuaries

“…Although there is no data specifically on tropical isolates, previous work in temperate European estuarine sediments (King and Nedwell 1984;Jørgensen 1989) have shown that nitrate ammonifiers predominate over denitrifiers during higher temperature summer periods, but denitrifiers predominate during autumn and winter. Furthermore, in anaerobic chemostat isolations from temperate sediments Ogilvie et al (1997) showed that only nitrate ammonifiers (Klebsiella and Enterobacter) were isolated from estuarine sediment in anaerobic chemostats at 20uC, but only denitrifiers at low temperature, and the reason seemed to be the greater affinity for nitrate (as measured by a A ) of nitrate ammonifiers than denitrifiers for nitrate at higher temperatures. If these bacteria are representative of a general metabolic trend, it would suggest that at tropical temperatures permanently .…”

Sources of nitrogen used for denitrification and nitrous oxide formation in sediments of the hypernutrified Colne, the nutrified Humber, and the oligotrophic Conwy estuaries, United Kingdom

“…The estuary catchment is 500 km 2 , of which the River Colne drains 300 km 2 , much of which is rich, arable land. The estuary exhibits strong gradients of both NO and Ϫ 3 NH concentrations decreasing with distance downstream ϩ 4 (King and Nedwell 1987;Ogilvie et al 1997a;Robinson et al 1998) as a result of inputs from the River Colne and a major sewage treatment work at Colchester . Three benthic sampling sites were selected ( Fig.…”

“…et al 2000b). This is subject to influences of various factors that affect rates of denitrification and the bacterial community of denitrifiers in sediments (King and Nedwell 1987;Ogilvie et al 1997b;Dong et al 2000b), of which nitrate concentration in the water column and freshwater flushing time of an estuary seem to be dominating factors. Although the main end product of denitrification is in the form of N 2 , nitrous oxide is also produced in the process of denitrification either as intermediate or as an end product or as both (Lloyd 2000;.…”

“…Rates of denitrification vary considerably in different estuaries, at different sites within an estuary, and at different times of the year. As a result, the extent of nitrate removal by estuarine denitrification is variable from less than 1% to 100% of total nitrate input into an estuary (Nielsen et al 1995;Ogilvie et al 1997a; Barnes and Owens 1998;Trimmer et al 1998;Dong 1 Corresponding author (nedwd@essex.ac.uk).…”