Microbially-Mediated Transformations of Estuarine Dissolved Organic Matter

Abstract

Microbially-mediated transformations of dissolved organic matter (DOM) in a marsh-dominated estuarine system were investigated at the molecular level using ultrahigh resolution mass spectrometry. In addition to observing spatial and temporal variability in DOM sources in the estuary, multiple incubations with endogenous microorganisms identified the influence of DOM composition on biodegradation. A clear microbial preference for degradation of compounds associated with marine DOM relative to those of terrestrial origin was observed, resulting in an overall shift of the remaining DOM toward a stronger terrigenous signature. During short, 1-day long incubations of samples rich in marine DOM, the molecular formulae that were enriched had slightly smaller mass (20-30 Da) and number of carbon atoms compared to the molecular formulae that were depleted. Over longer time scales (70 days), the mean differences in molecular mass between formulae that were depleted and enriched were substantially larger (∼270 Da). The differences in elemental composition over daily time scales were consistent with transformations in functional groups; over longer time scales, the differences in elemental composition may be related to progressive transformations of functional groups of intermediate products and/or other reactions. Our results infused new data toward the understanding of DOM processing by bacterioplankton in estuarine systems.

Dissolved Organic Matter Composition in a Marsh‐Dominated Estuary: Response to Seasonal Forcing and to the Passage of a Hurricane

“…The time series was not correlated with river discharge or with precipitation. The pattern revealed by the loading of PC 1, shown color coded in a van Krevelen diagram (Figure b), was different from the pattern typically observed in river to ocean transects (Medeiros, Babcock‐Adams, et al, ; Medeiros, Seidel, Dittmar, et al, ; Medeiros, Seidel, Gifford, et al, ; Medeiros, Seidel, Ward, et al, ; see also Figure d). This suggests that the mode was not related to the varying contribution of terrigenous vs marine sources to the estuarine DOM pool.…”

Identifying labile DOM components in a coastal ocean through depleted bacterial transcripts and chemical signals

“…DOM sources include inputs from river flow, salt marshes, phytoplankton and heterotrophic microbes, with the relative importance of these sources strongly modulated by river discharge (Medeiros et al ., ). The terrigenous character of the DOM is greater during spring compared with late summer/fall, and greater at low tide compared with high tide (Medeiros et al ., , ).…”

“…Additional details are presented in Medeiros et al . (). FT‐ICR data are available at BCO‐DMO (https://www.bco-dmo.org/dataset/735751).…”

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

“…The development of high throughput DNA sequencing approaches has led to the recognition of diverse marine bacterial communities and metabolic functions via a large number of studies (Zhang et al ., ; Bergauer et al ., ; Vorobev et al ., ). Concomitantly, ultrahigh‐resolution mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS), has been widely used to analyse complex marine DOM reservoirs (Koch et al ., ; Osterholz et al ., ; Rossel et al ., ; Medeiros et al ., ; Vorobev et al ., ). Importantly, these methods provide high enough resolution to identify the molecular composition of DOM pools.…”