Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties

Abstract

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean.

Molecular characteristics of microbially mediated transformations of Synechococcus‐derived dissolved organic matter as revealed by incubation experiments

“…). Comparison to previous studies indicated that S1 and S3 exhibited fluorescence peaks typical of humic‐like components, and the S2 peak represents protein‐like (tyrosine‐like) fluorophores (Jorgensen et al ., ; Tanaka et al ., ; Zhao et al ., ).…”

“…G). The byproducts arising from degradation of the fluorescent phycobilin pigments of Synechococcus may contribute to the abundance of component S1 (Zhao et al ., ) at the first time point. Increasing FI corresponded with increased TOC consumption over time (Fig.…”

“…An additional fraction of DOM that emits fluorescence after absorbing light is termed fluorescent DOM (FDOM) and can be used to trace the sources, reactivity, and partial chemical structures of DOM (Yamashita and Tanoue, ; Nieto‐Cid et al ., ; Jorgensen et al ., ; Martinez‐Perez et al ., ). The combination of FT‐ICR MS and optical measurements has increasingly been applied to evaluate the molecular properties of DOM pools in aquatic environments (Gonsior et al ., ; Martinez‐Perez et al ., ; Zhao et al ., ).…”

Microbial Processing of Sediment‐Derived Dissolved Organic Matter: Implications for Its Subsequent Biogeochemical Cycling in Overlying Seawater

“…The component C1 has been often associated with more labile organic matter, while C2 and C3 seem to be indicative of relatively recalcitrant DOM in natural environments (Catalá et al, ; Tanaka et al, ). The C2 and C3 have also been observed to be associated with sulfate reduction (Luek et al, ) and degradation of picocyanobacteria‐derived DOM (Zhao et al, ). These results from FDOM supports the process that the microbes in the overlying seawater utilized the labile materials and produced rather recalcitrant DOM, which then accumulates during the incubation experiments.…”

Sources, fluxes, and behaviors of fluorescent dissolved organic matter (FDOM) in the Nakdong River Estuary, Korea

“…The slopes of FDOM P concentrations against DOC concentrations varied significantly over different seasons, with steeper gradients in the spring (March and April) and fall (October). In general, FDOM P is known to be produced efficiently by biological production in water (Coble, 1996;Belzile et al, 2002;Steinberg et al, 2004;Zhao et al, 2017). Thus, higher FDOM P concentrations relative to DOC concentrations in the spring and fall seem to be associated with the spring and fall phytoplankton blooms in river waters (Mayer et al, 1999;Zhang et al, 2009).…”