Nitrous oxide production in sputum from cystic fibrosis patients with chronic Pseudomonas aeruginosa lung infection.

Chronic lung infection by Pseudomonas aeruginosa is the major severe complication in cystic fibrosis (CF) patients, where P. aeruginosa persists and grows in biofilms in the endobronchial mucus under hypoxic conditions. Numerous polymorphonuclear leukocytes (PMNs) surround the biofilms and create local anoxia by consuming the majority of O2 for production of reactive oxygen species (ROS). We hypothesized that P. aeruginosa acquires energy for growth in anaerobic endobronchial mucus by denitrification, which can be demonstrated by production of nitrous oxide (N2O), an intermediate in the denitrification pathway. We measured N2O and O2 with electrochemical microsensors in 8 freshly expectorated sputum samples from 7 CF patients with chronic P. aeruginosa infection. The concentrations of NO3(-) and NO2(-) in sputum were estimated by the Griess reagent. We found a maximum median concentration of 41.8 µM N2O (range 1.4-157.9 µM N2O). The concentration of N2O in the sputum was higher below the oxygenated layers. In 4 samples the N2O concentration increased during the initial 6 h of measurements before decreasing for approximately 6 h. Concomitantly, the concentration of NO3(-) decreased in sputum during 24 hours of incubation. We demonstrate for the first time production of N2O in clinical material from infected human airways indicating pathogenic metabolism based on denitrification. Therefore, P. aeruginosa may acquire energy for growth by denitrification in anoxic endobronchial mucus in CF patients. Such ability for anaerobic growth may be a hitherto ignored key aspect of chronic P. aeruginosa infections that can inform new strategies for treatment and prevention.

Extreme emission of n(2)o from tropical wetland soil (pantanal, South america).

Nitrous oxide (N(2)O) is an important greenhouse gas and ozone depleter, but the global budget of N(2)O remains unbalanced. Currently, ∼25% of the global N(2)O emission is ascribed to uncultivated tropical soils, but the exact locations and controlling mechanisms are not clear. Here we present the first study of soil N(2)O emission from the Pantanal indicating that this South American wetland may be a significant natural source of N(2)O. At three sites, we repeatedly measured in situ fluxes of N(2)O and sampled porewater nitrate [Formula: see text] during the low water season in 2008 and 2009. In 2010, 10 sites were screened for in situ fluxes of N(2)O and soil [Formula: see text] content. The in situ fluxes of N(2)O were comparable to fluxes from heavily fertilized forests or agricultural soils. An important parameter affecting N(2)O emission rate was precipitation, inducing peak emissions of >3 mmol N(2)O m(-2) day(-1), while the mean daily flux was 0.43 ± 0.03 mmol N(2)O m(-2) day(-1). Over 170 days of the drained period, we estimated non-wetted drained soil to contribute 70.0 mmol N(2)O m(-2), while rain-induced peak events contributed 9.2 mmol N(2)O m(-2), resulting in a total N(2)O emission of 79.2 mmol N(2)O m(-2). At the sites of repeated sampling, the pool of porewater nitrate varied [Formula: see text] with higher concentrations of [Formula: see text] (p < 0.05) found in drained soil than in water-logged soil, indicating dynamic shifts between nitrification and denitrification. In the field, O(2) penetrated the upper 60 cm of drained soil, but was depleted in response to precipitation. Upon experimental wetting the soil showed rapid O(2) depletion followed by N(2)O accumulation and a peak emission of N(2)O [Formula: see text] Assuming that the observed emission of N(2)O from these wetland soils is generally representative to the Pantanal, we suggest that this undisturbed tropical wetland potentially contributes ∼1.7% to the global N(2)O emission budget, a significant single source of N(2)O.