Strict Aerobic Lifestyle and Anaerobic Survival of Bacteria: Inseparable Twins?
For many decades the existence of strict aerobic bacteria was part of every textbook. However, considering habitats like soils or surfaces, many of these microorganisms are exposed to drastic changes in oxygen tension. A simple rain shower can change oxygen diffusion rates by a factor of 10.000. Thus, for many of the so-called strict aerobic bacteria, anaerobic growth and survival strategies were discovered, mainly relying on the use of alternative electron acceptors to oxygen, redox-active metabolites, or fermentation processes generating ATP at the substrate level. Survival without growth was recognized as an important lifestyle of bacteria. With the increasing availability of genome data, many highly diverse growth and survival strategies have become apparent in bacteria. But the overall picture is far from complete. Only recently, a novel puzzle piece of the anaerobic survival strategy of the opportunistic pathogen and model bacterium Pseudomonas aeruginosa in the absence of alternative electron acceptors was elucidated. It relies on the re-wiring of carbon flux away from the Entner-Doudoroff pathway towards the pentose-phosphate pathway and use of a phosphoketolase to allow for metabolic flux while preventing nonproductive NADH formation under these fermentation conditions and for ATP generation via acetate kinase.