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. 2025 Sep 19;15:1655335. doi: 10.3389/fcimb.2025.1655335

Figure 2.

Diagram illustrating anaerobic metabolism divided into four sections: anaerobic respiration, fermentation, nitrate and nitrite, and phenazines. Anaerobic respiration includes nitrate reduction steps with enzymes NAR, NIR, NOR, and N2OR. The arginine section shows arginine converting to citrulline, ornithine, and carbamoyl phosphate, with enzymes ADI, CK, and OTC. The pyruvate section displays pyruvate conversion to lactate, ethanol, and acetate by enzymes Ldh, Adh, and Pta/AckA. Phenazines are shown with electron transfer involving Fe3+. Center image of bacteria represents anaerobic metabolism.

Anaerobic metabolism of P. aeruginosa biofilms under oxygen-limited conditions. Two primary anaerobic metabolic pathways are shown: anaerobic respiration and fermentation. Anaerobic respiration mainly involves denitrification pathways utilizing nitrate and phenazine to maintain cellular redox balance. Fermentation includes the arginine and pyruvate fermentation pathways, which generate ATP to sustain bacterial survival. (A) Reduction of nitrate, nitrite, nitric oxide, and nitrous oxide by nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase, respectively. (B) Electron transfer cycle of phenazine within biofilm. Cells are represented as rods, phenazine as blue hexagons, electrons as white circles, and oxygen concentration is depicted by the blue background. (C) Arginine deiminase (ADI) pathway. Key enzymes include arginine deiminase (ADI), ornithine carbamoyltransferase (OTC), and carbamate kinase (CK). (D) Pyruvate fermentation pathway. Key enzymes include lactate dehydrogenase (Ldh), alcohol dehydrogenase (Adh), phosphate acetyltransferase (Pta), and acetate kinase (AckA). Created with BioRender.com.