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Enhanced nutrient uptake is sufficient to drive emergent cross-feeding between bacteria in a synthetic community.
The ISME Journal ( IF 11.0 ) Pub Date : 2020-08-12 , DOI: 10.1038/s41396-020-00737-5
Ryan K Fritts 1 , Jordan T Bird 2 , Megan G Behringer 3 , Anna Lipzen 4 , Joel Martin 4 , Michael Lynch 3 , James B McKinlay 1
Affiliation  

Interactive microbial communities are ubiquitous, influencing biogeochemical cycles and host health. One widespread interaction is nutrient exchange, or cross-feeding, wherein metabolites are transferred between microbes. Some cross-fed metabolites, such as vitamins, amino acids, and ammonium (NH4+), are communally valuable and impose a cost on the producer. The mechanisms that enforce cross-feeding of communally valuable metabolites are not fully understood. Previously we engineered a cross-feeding coculture between N2-fixing Rhodopseudomonas palustris and fermentative Escherichia coli. Engineered R. palustris excretes essential nitrogen as NH4+ to E. coli, while E. coli excretes essential carbon as fermentation products to R. palustris. Here, we sought to determine whether a reciprocal cross-feeding relationship would evolve spontaneously in cocultures with wild-type R. palustris, which is not known to excrete NH4+. Indeed, we observed the emergence of NH4+ cross-feeding, but driven by adaptation of E. coli alone. A missense mutation in E. coli NtrC, a regulator of nitrogen scavenging, resulted in constitutive activation of an NH4+ transporter. This activity likely allowed E. coli to subsist on the small amount of leaked NH4+ and better reciprocate through elevated excretion of fermentation products from a larger E. coli population. Our results indicate that enhanced nutrient uptake by recipients, rather than increased excretion by producers, is an underappreciated yet possibly prevalent mechanism by which cross-feeding can emerge.



中文翻译:

增强的营养吸收足以推动合成群落中细菌之间的紧急交叉喂养。

互动微生物群落无处不在,影响生物地球化学循环和宿主健康。一种广泛的相互作用是营养交换或交叉喂养,其中代谢物在微生物之间转移。一些交叉饲喂的代谢物,例如维生素、氨基酸和铵 (NH 4 + ),具有公共价值,并且会增加生产者的成本。强制交叉喂养具有公共价值的代谢物的机制尚不完全清楚。先前我们工程改造N之间的横进给共培养2 -定影沼泽红假单胞菌和发酵大肠杆菌。工程R. palustris 将必需的氮以 NH 4 + 的形式排泄到E.coli,而E.coli 将必需的碳作为发酵产物分泌到R. palustris。在这里,我们试图确定一种互惠的交叉喂养关系是否会在与野生型R. palustris 共培养中自发进化,后者不知道排泄 NH 4 +。事实上,我们观察到 NH 4 +交叉喂养的出现,但仅由大肠杆菌的适应驱动。大肠杆菌NtrC(氮清除调节剂)中的错义突变导致 NH 4 +转运蛋白的组成型激活。该活动可能允许大肠杆菌以少量泄漏的 NH 4 +为生,并通过从更大的大肠杆菌群中增加发酵产物的排泄来更好地进行回报。我们的研究结果表明,接受者增加营养吸收,而不是生产者排泄增加,是一种被低估但可能普遍存在的机制,通过这种机制可以出现交叉喂养。

更新日期:2020-08-12
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