Biodegradable dissolved organic matter in a temperate and a tropical stream determined from ultra-high resolution mass spectrometry

Abstract

We investigated dissolved organic matter (DOM) metabolism by employing plug-flow biofilm reactors and ultrahigh resolution mass spectrometry of DOM isolated by C 18 extraction in two forested stream ecosystems, a low DOM tropical stream sampled at baseflow and a higher DOM temperate stream sampled during a storm. On passage through the bioreactors, DOM concentrations in the tropical stream sample declined by 22%, whereas they declined by 42% in the temperate stream sample. The extracted DOM was subjected to electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry to obtain information on molecular weight distributions and elemental compositions for the thousands of compounds whose masses are calculated with sufficient accuracy to allow calculation of unique elemental formulas. In both streams, metabolism modifies DOM to lower molecular weight molecules, and oxygen-rich molecules are selectively biodegraded. Applying van Krevelen analyses for the unique elemental formulas of DOM constituents revealed that hydrogen-deficient molecules with low H : C ratios (assigned to black carbon-derived molecules) are present and generally not metabolized. Black carbon molecules are refractory to biodegradation compared with other components of DOM, supporting the suggestion that black carbon molecules in DOM flow to the ocean without experiencing significant microbial degradation.Dissolved organic matter (DOM) provides energy and carbon for microorganisms in aquatic ecosystems, especially heterotrophic bacteria. Understanding controls on the processes of DOM uptake and metabolism enhances our understanding of aquatic food webs. Similarly, describing the chemical composition of the biodegradable component of DOM (BDOM) helps clarify how heterotrophic bacteria obtain energy and nutrients. Consequently, there have been numerous studies on the utilization of DOM by microorganisms where bioassays, combined with bulk parameters and molecular-level parameters, have been used to study the biologically labile portion of DOM.Bulk parameters such as DOC concentration, elemental composition, oxidation state of DOM, and dissolved oxygen concentration, as well as molecular-level analyses such as

Electrospray and photoionization mass spectrometry for the characterization of organic matter in natural waters: a qualitative assessment

“…This comparison is facilitated by the NMR molecular mixing model and the van Krevelen analysis (Kim et al 2003a;Baldock et al 2004). Although classifying species identified by FT-ICR MS into only five biochemical categories is an obvious oversimplification, we do so here for the sake of comparing ionization techniques to one another and to NMR mixing model results.…”

“…These molecules are thought to consist primarily of water-stable byproducts of charcoal and soot decomposition in soils. Charcoal decomposition byproducts have been widely detected in dissolved NOM and can be distinguished by their condensed aromatic structures (Kim et al 2003a(Kim et al , 2004Hockaday et al 2006Hockaday et al , 2007. Therefore, we refer to charcoal carbon and condensed aromatic structures interchangeably.…”

“…Natural biomolecules have relatively uniform and discrete elemental compositions such that different types of molecules can be distinguished by some combination of their H/C, O/C, and N/C ratios. The van Krevelen diagram can be used to visualize the elemental composition-space occupied by molecules identified by FT-ICR MS, and this facilitates an approximation of the biomolecule distribution (e.g., lipid, lignin, carbohydrate, and peptide) (Kim et al 2003a). …”

“…Likewise, the coupling of electrospray ionization (ESI) to high-field Fourier-transform ion cyclotron resonance (FT-ICR) MS has provided unprecedented resolution of the molecular components of natural organic matter (NOM) as well as molecular details of biogeochemical processes (Kujawinski et al 2002;Kim et al 2003aKim et al , 2003bKim et al , 2004Kim et al , 2006Kramer et al 2004;Kujawinski et al 2004;Koch et al 2005;Dittmar and Koch 2006;Grannas et al 2006;Hertkorn et al 2006; Kujawinski and Behn 2006;Mopper et al 2007;Reemtsma et al 2008;Sleighter and Hatcher 2008).…”

Characterization of unknown iodinated disinfection byproducts during chlorination/chloramination using ultrahigh resolution mass spectrometry

“…Recently, ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been successfully used to characterize the previously unknown Cl-DBPs and Br-DBPs (Zhang et al, 2012a;Zhang et al, 2012b;Lavonen et al, 2013;Zhang et al, 2014). The ultrahigh resolution and mass accuracy of FT-ICR MS combined with electrospray ionization (ESI) allows the determination of unambiguous and exact molecular formulas (Stenson et al, 2003;Kim et al, 2006aKim et al, , 2006bHertkorn et al, 2008). It is thus anticipated that the ESI FT-ICR MS method could also be suitable for identifying the molecular formulas of unknown I-DBPs.…”