Biosciences and Living Systems Institute, University of Exeter, Exeter, UK.
Nat Commun. 2024 Sep 6;15(1):7810. doi: 10.1038/s41467-024-52043-9.
Microbial secretions, such as metabolic enzymes, are often considered to be cooperative public goods as they are costly to produce but can be exploited by others. They create incentives for the evolution of non-producers, which can drive producer and population productivity declines. In response, producers can adjust production levels. Past studies suggest that while producers lower production to reduce costs and exploitation opportunities when under strong selection pressure from non-producers, they overproduce secretions when these pressures are weak. We challenge the universality of this trend with the production of a metabolic enzyme, invertase, by Saccharomyces cerevisiae, which catalyses sucrose hydrolysis into two hexose molecules. Contrary to past studies, overproducers evolve during evolutionary experiments even when under strong selection pressure from non-producers. Phenotypic and competition assays with a collection of synthetic strains - engineered to have modified metabolic attributes - identify two mechanisms for suppressing the benefits of invertase to those who exploit it. Invertase overproduction increases extracellular hexose concentrations that suppresses the metabolic efficiency of competitors, due to the rate-efficiency trade-off, and also enhances overproducers' hexose capture rate by inducing transporter expression. Thus, overproducers are maintained in the environment originally thought to not support public goods production.
微生物分泌物，如代谢酶，通常被认为是合作的公共物品，因为它们的生产成本很高，但可以被他人利用。它们为非生产者的进化创造了激励，这可能导致生产者和种群生产力下降。作为回应，生产者可以调整生产水平。过去的研究表明，虽然当受到非生产者的强烈选择压力时，生产者会降低产量以降低成本和减少被利用的机会，但当这些压力较弱时，它们会过度分泌分泌物。我们通过酿酒酵母（Saccharomyces cerevisiae）生产代谢酶 - 蔗糖酶来挑战这一趋势，蔗糖酶将蔗糖水解成两个六碳糖分子。与过去的研究相反，即使在受到非生产者的强烈选择压力下，过度生产者也会在进化实验中进化。利用一组经过工程改造的具有修饰代谢特性的合成菌株进行表型和竞争测定，确定了两种抑制利用蔗糖酶的个体从中受益的机制。由于速率-效率权衡，蔗糖酶的过度产生会增加细胞外六碳糖浓度，从而降低竞争者的代谢效率，并且通过诱导转运蛋白的表达来提高过度生产者对六碳糖的捕获率。因此，过度生产者在原本被认为不支持公共物品生产的环境中得以维持。
