Nitrification by heterotrophic denitrifiers and its relationship to autotrophic nitrification

Applied Science

Evaluation of the influence of CO2 on hydrogen production by Caldicellulosiruptor saccharolyticus

Stripping gas is generally used to improve hydrogen yields in fermentations. Since CO2 is relatively easy to separate from hydrogen it could be an interesting stripping gas. However, a higher partial CO2 pressure is accompanied with an increased CO2 uptake in the liquid, where it hydrolyses and induces an increased requirement of NaOH to maintain the pH. This enhances the osmotic pressure in the culture by 30%, which inhibited the growth of Caldicellulosiruptor saccharolyticus. Indications for this conclusion are: i) Inhibition could almost completely be circumvented by reducing the bicarbonate through decreasing the pH (from 6.5 to 5.5), ii) Growth rates were reduced by 60 ± 10% at an osmotic pressure of 0.218 ± 0.005 osm/kg H2O independently of the stripping gas, iii) Increased extracellular DNA and protein concentrations were observed as a function of the osmotic pressure. In addition to growth inhibition, the increased sodium bicarbonate in the effluent will contribute to a negative environmental impact when applied at industrial scal

Substrate and product inhibition of hydrogen production by the extreme thermophile, Caldicellulosiruptor saccharolyticus

Substrate and product inhibition of hydrogen production during sucrose fermentation by the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus was studied. The inhibition kinetics were analyzed with a noncompetitive, nonlinear inhibition model. Hydrogen was the most severe inhibitor when allowed to accumulate in the culture. Concentrations of 5-10 mM H-2 in the gas phase (= partial hydrogen pressure (pH(2)) of (1-2) . 10(4) Pa) initiated a metabolic shift to lactate formation. The extent of inhibition by hydrogen was dependent on the density of the culture. The highest tolerance for hydrogen was found at low volumetric hydrogen production rates, as occurred in cultures with low cell densities. Under those conditions the critical hydrogen concentration in the gas phase was 27.7 mM H-2 (= pH(2) of 5.6 . 10(4) Pa); above this value hydrogen production ceased completely. With an efficient removal of hydrogen sucrose fermentation was mainly inhibited by sodium acetate. The critical concentrations of sucrose and acetate, at which growth and hydrogen production was completely inhibited (at neutral pH and 70degreesC), were 292 and 365 mM, respectively. Inorganic salts, such as sodium chloride, mimicked the effect of sodium acetate, implying that ionic strength was responsible for inhibition. Undissociated acetate did not contribute to inhibition of cultures at neutral or slightly acidic pH. Exposure of exponentially growing cultures to concentrations of sodium acetate or sodium chloride higher than ca. 175 mM caused cell lysis, probably due to activation of autolysins. (C) 2003 Wiley Periodicals, Inc

Heterotrophic nitrification and aerobic denitrification in Alcaligenes faecalis strain TUD.

Heterotrophic nitrification and aerobic and anaerobic denitrification byAlcaligenes faecalis strain TUD were studied in continuous cultures under various environmental conditions. Both nitrification and denitrification activities increased with the dilution rate. At dissolved oxygen concentrations above 46% air saturation, hydroxylamine, nitrite and nitrate accumulated, indicating that both the nitrification and denitrification were less efficient. The overall nitrification activity was, however, essentially unaffected by the oxygen concentration. The nitrification rate increased with increasing ammonia concentration, but was lower in the presence of nitrate or nitrite. When present, hydroxylamine, was nitrified preferentially. Relatively low concentrations of acetate caused substrate inhibition (KI=109 μM acetate). Denitrifying or assimilatory nitrate reductases were not detected, and the copper nitrite reductase, rather than cytochrome cd, was present. Thiosulphate (a potential inhibitor of heterotrophic nitrification) was oxidized byA. faecalis strain TUD, with a maximum oxygen uptake rate of 140–170nmol O2·min-1·mg prot-1. Comparison of the behaviour ofA. faecalis TUD with that of other bacteria capable of heterotrophic nitrification and aerobic denitrification established that the response of these organisms to environmental parameters is not uniform. Similarities were found in their responses to dissolved oxygen concentrations, growth rate and ammonia concentration. However, they differed in their responses to externally supplied nitrite and nitrate

Polyphosphate formation by Acinetobacter johnsonii 210A: effect of cellular energy status and phosphate-specific transport system

In acetate-limited chemostat cultures of Acinetobacter johnsonii 210A at a dilution rate of 0.1 h-1 the polyphosphate content of the cells increased from 13% to 24% of the biomass dry weight by glucose (100 mM), which was only oxidized to gluconic acid. At this dilution rate, only about 17% of the energy from glucose oxidation was calculated to be used for polyphosphate synthesis, the remaining 83% being used for biomass formation. Suspensions of non-growing, phosphate-deficient cells had a six- to tenfold increased uptake rate of phosphate and accumulated polyphosphate aerobically up to 53% of the biomass dry weight when supplied with only orthophosphate and Mg2+. The initial polyphosphate synthesis rate was 98 ± 17 nmol phosphate min-1 mg protein-1. Intracellular poly-β-hydroxybutyrate and lipids served as energy sources for the active uptake of phosphate and its subsequent sequestration to polyphosphate. The H+-ATPase inhibitor N,N'- dicyclohexylcarbodiimide caused low ATP levels and a severe inhibition of polyphosphate formation, suggesting the involvement of polyphosphate kinase in polyphosphate synthesis. It is concluded that, in A. johnsonii 210A, (i) polyphosphate is accumulated as the energy supply is in excess of that required for biosynthesis, (ii) not only intracellular poly-β- hydroxybutyrate but also neutral lipids can serve as an energy source for polyphosphate-kinase-mediated polyphosphate formation, (iii) phosphate- deficient cells may accumulate as much polyphosphate as activated sludges and recombinants of Escherichia coli designed for polyphosphate accumulation