Fig. 1.

The uptake and synthesis of AI-2 in E. coli. AI-2 was transported into the cell by LsrACDB. LsrK was involved in the following phosphorylation of AI-2 signal molecule. When AI-2-P was accumulated to a specific value, the repression of lsr operon caused by LsrR was relieved. And then, the AI-2-P was degraded by LsrFG. AI-2 is the byproducts of the activated methyl cycle (AMC) and the process of AI-2 synthesis were depicted. Moreover, there is another pathway directing the conversion from SAH to HCY to complete the AMC, i.e. one-step conversion by SAH hydrolase (SahH). However, there was no AI-2 produced through the second route