title: Segregating metabolic processes into different microbial cells accelerates the consumption of inhibitory substrates.
abstract: Different microbial cell types typically specialize at performing different metabolic processes. A canonical example is substrate cross-feeding, where one cell type consumes a primary substrate into an intermediate and another cell type consumes the intermediate. While substrate cross-feeding is widely observed, its consequences on ecosystem processes is often unclear. How does substrate cross-feeding affect the rate or extent of substrate consumption? We hypothesized that substrate cross-feeding eliminates competition between different enzymes and reduces the accumulation of growth-inhibiting intermediates, thus accelerating substrate consumption. We tested this hypothesis using isogenic mutants of the bacterium Pseudomonas stutzeri that either completely consume nitrate to dinitrogen gas or cross-feed the intermediate nitrite. We demonstrate that nitrite cross-feeding eliminates inter-enzyme competition and, in turn, reduces nitrite accumulation. We further demonstrate that nitrite cross-feeding accelerates substrate consumption, but only when nitrite has growth-inhibiting effects. Knowledge about inter-enzyme competition and the inhibitory effects of intermediates could therefore be important for deciding how to best segregate different metabolic processes into different microbial cell types to optimize a desired biotransformation.
authors.affiliation: Department of Environmental Microbiology, Eawag, Dübendorf, Switzerland.|Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
authors.forename: Elin E
authors.initials: EE
authors.lastname: Lilja
authors.affiliation: Department of Environmental Microbiology, Eawag, Dübendorf, Switzerland.
authors.forename: David R
authors.initials: DR
authors.lastname: Johnson
mesh_terms: D009154:Mutation; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D011549:Pseudomonas / Q000235:genetics / Q000378:metabolism*
chemical_list: D009566:Nitrates; D009573:Nitrites