Strain-specific Humic-like Fluorescent Organic Matter Production by Diverse Marine Bacterioplankton

Humic-like organic matter is of interest to marine scientists as it is material thought to compose a fraction of the ‘recalcitrant’ organic matter pool, while also having a role in metal availability (e.g. chelators) and protection of plankton from UV-damage. The chemical composition of autochthonous humic-like material in the ocean is challenging to fully resolve, as well as the processes that regulate its production. Humic-like fluorescent dissolved organic matter (FDOM) is readily detected based on optical properties (absorbance and fluorescence) and prior work suggests that fluorescent dissolved organic matter (FDOM) production varies between marine bacterioplankton strains. Inspired by this past work we examined production of humic-like fluorescent organic matter, particulate and dissolved, across estuarine and marine bacterioplankton isolates testing a hypothesis that optical signatures were consistent across phenotypes. Humic-like material present in base-extracted bacterioplankton biomass, as well as cell-free culture, was identified based on fluorescence excitation-emission matrices (EEM) as well as absorption spectra. Results point to a simplistic, understudied biochemical avenue for production of humic-like FDOM by bacterioplankton. Ecological implications of this production avenue will also be discussed – particularly in the context of deep ocean formation of humic-like FDOM and photolytic turnover of FDOM.