Heterotroph response to phytoplankton dissolved organic matter

Phytoplankton release massive amounts of dissolved organic matter (DOM) into the later column during recurring blooms in coastal waters and inland seas. The released DOM encompasses a complex mixture of both known and unknown compounds, and is a rich nutrient source for heterotrophic bacteria. The metabolic activity of bacteria during and after phytoplankton blooms can hence be expected to reflect the characteristics of the released DOM. We therefore investigated if bacterioplankton could be used as living sensors of phytoplankton DOM quantity or quality, by applying gene expression analyses to identify bacterial metabolisms induced by DOM. We used transcriptional analysis of two Baltic Sea bacterial isolates (Polaribacter sp. BAL334 and Brevundimonas sp. BAL450) growing with DOM from axenic cultures of the dinoflagellate Prorocentrum minimum. We observed pronounced differences between the two bacteria both in bacterial growth and the expressed metabolic pathways in cultures exposed to dinoflagellate DOM compared with controls.