Department of Biology, Indiana University, Bloomington, Indiana, USA; email:
Annu Rev Microbiol. 2023 Sep 15;77:277-297. doi: 10.1146/annurev-micro-032521-023815. Epub 2023 Jun 7.
The metabolism of a bacterial cell stretches beyond its boundaries, often connecting with the metabolism of other cells to form extended metabolic networks that stretch across communities, and even the globe. Among the least intuitive metabolic connections are those involving cross-feeding of canonically intracellular metabolites. How and why are these intracellular metabolites externalized? Are bacteria simply leaky? Here I consider what it means for a bacterium to be leaky, and I review mechanisms of metabolite externalization from the context of cross-feeding. Despite common claims, diffusion of most intracellular metabolites across a membrane is unlikely. Instead, passive and active transporters are likely involved, possibly purging excess metabolites as part of homeostasis. Re-acquisition of metabolites by a producer limits the opportunities for cross-feeding. However, a competitive recipient can stimulate metabolite externalization and initiate a positive-feedback loop of reciprocal cross-feeding.
细菌细胞的代谢活动超出了其自身的边界范围，通常与其他细胞的代谢活动相连接，形成延伸的代谢网络，这些网络跨越群落，甚至延伸到全球范围。在最不容易被察觉的代谢连接中，有一种涉及到经典的细胞内代谢物的交叉喂养。这些细胞内代谢物是如何以及为何被外化的？细菌是否只是易渗透的？在这里，我考虑了对于一个细菌来说易渗透意味着什么，并且我从交叉喂养的角度回顾了代谢物外化的机制。尽管存在普遍的说法，但大多数细胞内代谢物通过细胞膜扩散的可能性不大。相反，可能涉及被动和主动转运蛋白，可能将多余的代谢物作为体内平衡的一部分清除。生产者重新获取代谢物会限制交叉喂养的机会。然而，具有竞争力的接受者可以刺激代谢物的外化，并启动互惠交叉喂养的正反馈循环。
