Isolation of 2,5-diketopiperazines from Lysobacter capsici AZ78 with activity against Rhodococcus fascians

Inhibitory activity of the biocontrol bacterial strain Lysobacter capsici AZ78 is related to the production of cyclo(l-Pro-l-Tyr), a 2,5-diketopiperazine with in vitro and in vivo toxic activity against Phytophthora infestans and Plasmopara viticola. Further investigation of culture filtrate organic extracts showed its ability to produce other 2,5-diketopiperazines. They were isolated and identified by spectroscopic (1H NMR and ESIMS) and physic (specific optical rotation) methods as cyclo(l-Pro-l-Val), cyclo(d-Pro-d-Phe), cyclo(l-Pro-l-Leu), and cyclo(d-Pro-l-Tyr). When tested against the phytopathogenic Gram-positive bacterium Rhodococcus fascians LMG 3605, cyclo(l-Pro-l-Val) showed a toxic activity similar to chloramphenicol at a comparable concentration. Overall, these data suggest that 2,5-diketopiperazines represent a class of metabolites characterizing the metabolome of L. capsici AZ78. Furthermore, the toxic activity showed by cyclo(l-Pro-l-Val) against R. fascians LMG 3605 broaden the spectrum activity of 2,5-diketopiperazines against phytopathogenic microorganisms enforcing their potential development as biopesticides.