Divergent functional roles of D-amino acids secreted by Vibrio cholerae.

The L-forms of amino acids are used in all kingdoms of life to synthesize proteins. However, the bacterium Vibriocholerae, the causative agent of cholera, produces D-amino acids which are released to the environment at millimolar concentrations. We baptized these D-amino acids as non-canonical D-amino acids (NCDAAs) since they are different from those (i.e. D-alanine and D-glutamate) normally present in the bacterial cell wall. In V. cholerae, production of NCDAAs relies on the BsrV enzyme, a periplasmic broad spectrum racemase. BsrV multispecific activity, produces of a wide range of distinct D-amino acids. Using a combination of genetics and molecular physiology approaches we have demonstrated that NCDAAs target different cellular processes which may function as part of a cooperative strategy in vibrio communities to protect non-producing members from competing bacteria. Because NCDAA production is widespread in bacteria, we anticipate that NCDAAs are relevant modulators of microbial subpopulations in diverse ecosystems.