Abstract:Proline with strong hydrophilic property is the only sub-amino acid being used for protein synthesis. The function and mechanism for proline has been extensively studied in plant. Proline is not only an osmolyte, but it also has important roles in scavenging reactive oxygen species, acting as a signal molecule to regulate growth, development, proliferation and cell death in plant. Recent studies have demonstrated that a proper amount of proline plays important roles in bacterial cells. The biosynthesis, degradation, intracellular and extracellular transport as well as the function of proline produced by bacteria were reviewed in this paper.