The multifaceted inhibitory effects of an alkylquinolone on the diatom Phaeodactylum tricornutum

Abstract

The mechanisms underlying interactions between diatoms and bacteria are crucial to understand diatom behaviour and proliferation, and can result in far-reaching ecological consequences. Recently, 2-alkyl-4-quinolones have been isolated from marine bacteria, both of which (the bacterium and isolated chemical) inhibited growth of microalgae, suggesting these compounds could mediate diatom - bacteria interactions. We investigated the effects of several quinolones on three diatom species. The growth of all three was inhibited, with half-maximal inhibitory concentrations reaching the sub-micromolar range. Using multiple techniques, dual inhibition mechanisms were uncovered for 2-heptyl-4-quinolone (HHQ) in Phaeodactylum tricornutum. Firstly, photosynthetic electron transport was obstructed, primarily via inhibition of the cytochrome b6f complex. Secondly, respiration was inhibited, leading to repression of ATP supply to plastids from mitochondria via organelle energy coupling. These data clearly show how HHQ could modulate diatom proliferation in marine environments.