Metabolic cross-feeding via intercellular nanotubes among bacteria

Bacteria frequently exchange metabolites by diffusion through the extracellular environment, yet it remains generally unclear whether bacteria can also use cell–cell connections to directly exchange nutrients. Here we address this question by engineering cross-feeding interactions within and between Acinetobacter baylyi and Escherichia coli, in which two distant bacterial species reciprocally exchange essential amino acids. We establish that in a well-mixed environment E. coli, but likely not A. baylyi, can connect to other bacterial cells via membrane-derived nanotubes and use these to exchange cytoplasmic constituents. Intercellular connections are induced by auxotrophy-causing mutations and cease to establish when amino acids are externally supplied. Electron and fluorescence microscopy reveal a network of nanotubular structures that connects bacterial cells and enables an intercellular transfer of cytoplasmic materials. Together, our results demonstrate that bacteria can use nanotubes to exchange nutrients among connected cells and thus help to distribute metabolic functions within microbial communities.细菌通常通过扩散作用在细胞外环境中交换代谢物，但目前尚不清楚细菌是否也可借助细胞间连接直接交换营养物质。本研究通过构建鲍氏不动杆菌(Acinetobacter baylyi)与大肠杆菌(Escherichia coli)种内及种间的交叉喂养相互作用体系，解答了这一科学问题——该体系中两种亲缘关系较远的细菌可双向交换必需氨基酸。我们证实，在充分混合的环境中，大肠杆菌可通过膜衍生纳米管与其他细菌细胞建立连接，并借助此类结构交换细胞质组分，而鲍氏不动杆菌大概率无法实现这一过程。细胞间连接可由营养缺陷型突变诱导产生，当外源供给氨基酸时则不再形成。电子显微镜与荧光显微镜观察显示，细菌细胞间存在由纳米管结构组成的网络，可介导细胞质物质的细胞间转移。综上，本研究结果证实，细菌可通过纳米管在相连细胞间交换营养物质，从而助力微生物群落内代谢功能的协同分布。