Bottom-up and top-down controls on Alteromonas macleodii lead to different dissolved organic matter compositions

The effects of both bottom-up (e.g. substrate) and top-down (e.g. viral lysis) controls on the molecular composition of dissolved organic matter (DOM) have not been investigated. In this study, we investigated the DOM composition of the model bacterium Alteromonas macleodii ATCC 27126 growing on different substrates (glucose, laminarin, extracts from a Synechococcus culture, oligotrophic seawater and eutrophic seawater), and infected with a lytic phage. The ultra-high resolution mass spectrometry analysis showed that when growing on different substrates A. macleodii preferred to use reduced, saturated nitrogen-containing molecules (i.e. O4 formular species) and released or preserved oxidized, unsaturated sulfur-containing molecules (i.e. O7 formular species). However, when infected with the lytic phage, A. macleodii produced organic molecules with higher hydrogen saturation, and more nitrogen- or sulfur-containing molecules. Our results demonstrate that bottom-up (i.e. varying substrates) and top-down (i.e. viral lysis) controls leave different molecular fingerprints in the produced DOM.