Plant Growth Promoters Isolated from a Marine Bacterium Associated with<i>Palythoa</i>sp

Abstract

Abstract The fermentation broth of bacterial strain A108, isolated from tissues aseptically excised from Palythoa sp., was found to exhibit plant growth promotion activity in an agrochemical screen employed in our laboratory. Bioassay-guided fractionation and purification yielded three compounds, cyclo[L-(4-hydroxyprolinyl)-L-leucine], cyclo[L-(4-hydroxyprolinyl)-D-leucine], and cyclo[L-(4-hydroxyprolinyl)-L-phenylalanine]. All three compounds stimulated plant growth. Two of the three diketopiperazines are previously known compounds associated with drought resistance and growth promotion in rice seedlings; a similar function for Palythoa spp. is hypothesized. Cyclo[L-(4-hydroxyprolinyl)-L-phenylalanine] is the only one of the three previously isolated from a marine source.