D-canavanine and Racemization: How it All Leads to The Severe Alteration of The Rhizobial Cell Wall

 By: Umberto Fasci

Figure 3. High D-canavanine incorporation changes the structure and amount of peptidoglycan in A. tumefaciens.

Aliashkevich and colleagues investigated the effects of the D-amino acid (D-AA), D-canavanine (D-CAN), on soil rhizobia bacteria. By testing the capacity of alfalfa seed extract on the peptidoglycan chemical structure of Psuedomonas putida, they discovered a new potential muropeptide which is promptly identified as L-canavanine (L-CAN). As a matter of investigation, the researchers further explored how L-CAN interacts with the P. putida encoded BSAR (broad-spectrum amino acid racemace), which induces the conversion of L-AAs to D-AAs. They found that BSAR converted L-CAN into a mixture of D-CAN and L-CAN (DL-CAN). To test for the functionality of D-CAN, the researchers investigated its effects on root development in comparison with sole L-CAN. Knowing the inhibitory effects of L-CAN on root development, they found that only L-CAN held these effects and there were no significant effects by D-CAN. This interesting result shows that D-CAN has a different function over L-CAN. To determine D-CAN effect on bacteria species, the researchers employed tests on a series of bacteria species that could potentially be exposed to this D-AA. Interestingly, it was found that Rhizobiales were the most affected species suggesting that BSAR producing species have developed a tolerance. Furthermore, it was determined that D-CAN severely alters cell wall composition in these Rhizobiales.

 

Reference

Aliashkevich, A. Howell, M. Brown, P. J. B. and Cava, F. (2021) D-canavanine affects peptidoglycan structure, morphogenesis and fitness in Rhizobiales. Environ Microbiol 23, 1462-2912.