Energy conservation in chemotrophic organisms is generally coupled to redox reactions in catabolic pathways. In the oxidative part or branch, "energy-rich" compounds are formed, from which ATP is generated via substrate-level phosphorylation (SLP). In the reductive branch the electron carriers are reoxidized by a terminal acceptor; in this way an electrochemical ion gradient (⌬H ϩ or ⌬Na ϩ ) at the cytoplasmic membrane is established, which is used for ATP synthesis, transport across membranes, and motility. This second type of energy conservation is called respiration or electron transport phosphorylation (ETP). Bacterial fermentations are considered apparent exceptions to this generalization because they are thought to lack ETP (41). In these fermentations the substrate serves not only as an electron donor but also as a terminal acceptor, since oxygen, nitrate, fumarate, etc. are absent (44). An example is the fermentation of glutamate via 3-methylasparate by the closely related anaerobic bacteria Clostridium tetani, Clostridium tetanomorphum, and Clostridium pascui to ammonia, acetate, butyrate, and molecular hydrogen according to equation 1 (Fig. 1) (8,16,51):In the first part of this pathway, glutamate is converted to ammonia, acetate, and pyruvate, which is oxidized by ferredoxin and coenzyme A (CoA) to acetyl-CoA and CO 2 . In order to regenerate the oxidant, acetyl-CoA and protons are reduced to butyryl-CoA and hydrogen, respectively. From 2 butyrylCoA and 1 acetyl-CoA, 3 ATP are obtained via SLP. But the free enthalpy required to synthesize 1 ATP (Ϫ317/3 ϭ Ϫ106 kJ mol Ϫ1 ) is still much higher than that needed in other systems; i.e., the efficiency is low ( ϭ 42%). Usually, Ϫ75 Ϯ 5 kJ mol Ϫ1 ( ϭ 60%) is considered the minimum free enthalpy for ATP synthesis (44). It should be noted that without hydrogen formation the ATP yield would drop to 2.5 mol ATP (5 mol glutamate)Ϫ1 , because in order to maintain the redox balance, acetyl-CoA has to be completely reduced to butyrate. Thus, hydrogen formation increases SLP. If all the reducing equivalents dissipated as hydrogen and no butyrate was formed, the yield would rise to 5 mol ATP (5 mol glutamate)Ϫ1 . This, however, is thermodynamically not possible (Ϫ46 kJ mol glutamate Ϫ1 ). The oxidation of pyruvate derived from glutamate yields reduced ferredoxin (E 0 Ј Յ Ϫ420 mV), whereas NADH (E 0 Ј ϭ Ϫ320 mV) is the reductant in butyrate synthesis. The difference (Ն100 mV) could be used for additional energy conservation. Recently, we discovered the enzyme that catalyzes the reduction of NAD ϩ with reduced ferredoxin (Fig. 1) and characterized it as an Rnf-type NADH ferredoxin oxidoreductase localized in the membrane of C. tetanomorphum. Although it has not been demonstrated yet that this clostridial Rnf protein pumps protons or sodium ions, its cellular localization and the homology of four of its six subunits with four of the subunits of NADH-quinone reductase (Nqr) from Vibrio alginolyticus and Vibrio cholerae strongly suggest that this enzyme is involved in ener...

Colistin-tobramycin combinations are more efficient than respective single antibiotics for killing P. aeruginosa in biofilms in vitro, and they significantly reduced P. aeruginosa cell counts in a rat lung infection model and in patients with cystic fibrosis.

NO treatment may improve the therapy of chronic microbial lung infections in CF patients, particularly concerning pathogens with intrinsic or acquired resistance to antibiotics.

Anaerobic bacteria ferment glutamate via two different pathways to ammonia, carbon dioxide, acetate, butyrate and molecular hydrogen. The coenzyme B₁₂-dependent pathway in Clostridium tetanomorphum via 3-methylaspartate involves pyruvate:ferredoxin oxidoreductase and a novel enzyme, a membrane-bound NADH:ferredoxin oxidoreductase. The flavin- and iron-sulfur-containing enzyme probably uses the energy difference between reduced ferredoxin and NADH to generate an electrochemical Na⁺ gradient, which drives transport processes. The other pathway via 2-hydroxyglutarate in Acidaminococcus fermentans and Fusobacterium nucleatum involves glutaconyl-CoA decarboxylase, which uses the free energy of decarboxylation to generate also an electrochemical Na⁺ gradient. In the latter two organisms, similar membrane-bound NADH:ferredoxin oxidoreductases have been characterized. We propose that in the hydroxyglutarate pathway these oxidoreductases work in the reverse direction, whereby the reduction of ferredoxin by NADH is driven by the Na⁺ gradient. The reduced ferredoxin is required for hydrogen production and the activation of radical enzymes. Further examples show that reduced ferredoxin is an agent, whose reducing energy is about 1 ATP ‘richer’ than that of NADH.

Background/Aims: Several recent studies revealed an accumulation of ceramide in bronchial, tracheal and intestinal epithelial cells of mice and patients with cystic fibrosis (CF). Normalization of ceramide concentrations in lungs of CF mice employing the functional acid sphingomyelinase inhibitor amitriptyline also normalized mucociliary clearance, chronic inflammation and infection susceptibility to pulmonary P. aeruginosa in these mice. Methods: To test for a beneficial effect of amitriptyline in vivo, we performed a phase IIb randomised, double-blind, placebo-controlled study. Twenty-one CF patients were treated with 25 mg/d amitriptyline twice daily for 28 days. The placebo consisted of 19 patients and was also treated twice per day. The primary endpoint was the change in lung function in the intention-to-treat (ITT) population. Secondary endpoints were ceramide levels in epithelial cells and safety. Results: After treatment, forced expiratory volume in 1 sec predicted (FEV₁) increased 6.3±11.5% (p=0.08) in the ITT population (36 of 40 CF patients) and 8.5±10% (p=0.013) in the per protocol (PP) population (29 of 40 patients). Ceramide levels decreased in nasal epithelial cells after amitriptyline treatment. Amitriptyline had no severe and only mild and mostly transient adverse effects, i.e. xerostomia and tiredness. Conclusion: Amitriptyline is safe in CF-patients, increases FEV₁ and reduces ceramide in lung cells of CF patients.