Updated project metadata. Lactate produced in glycolysis has recently been discovered to modify lysine residues on eukaryotic proteins, a post-translational modification (PTM) called lysine lactylation (Kla). This modification not only participates in regulating gene expression through lactylation of histones, but also impacts the function of non-histone proteins. However, lactylation in prokaryotes has not been reported. Here, we report the identification of 1869 lysine lactylation sites in 465 proteins in the cariogenic organism Streptococcus mutans using a newly developed 4-dimensional label-free quantitative proteomic approach, representing the first Kla dataset in prokaryotes. Combining quantitative analysis, we report that the modification levels of 282 sites from 124 proteins increased by over 1.5-fold, and 80 sites from 52 proteins decreased by over 0.67-fold in the biofilm growth state. These results provide a systematic perspective of the distribution and function of Kla and improve our understanding of the role of lactate in the metabolic regulation of prokaryotes.