Carbidopa and Phenylalanine Are Involved in Algicidal Activity of Pseudoalteromonas sp. Strain 17-6 against Karenia mikimotoi

The marine bacterium strain 17-6 isolated from the East China Sea seabed showed strong algicidal activities against the dinoflagellate Karenia mikimotoi. Based on l6S rRNA gene sequence analysis, strain 17-р6 belonged to the genus Pseudoalteromonas. Using preparative high-performance liquid chromatography (prep-HPLC) and electrospray ionization/quadrupole-time of flight mass spectrometer coupled with a high-performance liquid chromatograph (LC/MS-Q-TOF) system, we isolated and characterized two algicidal substances produced by strain 17-6 and determined their molecular structures. Both algicidal compounds produced by strain 17-6 were found to be thermostable and were identified as carbidopa ((+)-2-(3,4-dihydroxybenzyl)-2-hydrazinopropionic acid) and phenylalanine. Our study is the first report of carbidopa’s activity against K. mikimotoi, as well as of carbidopa production by a Pseudoalteromonas species.