Laboratory In-Situ Production of Autochthonous and Allochthonous Fluorescent Organic Matter by Freshwater Bacteria

Fox, Bethany; Thorn, Robin; Reynolds, Darren M.

doi:10.3390/microorganisms9081623

Cited by 3 publications

(3 citation statements)

References 86 publications

(160 reference statements)

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“…In addition, sediments often have a stronger potential to retain higher molecular weight DOM in mineral complexes (Jaffé et al 2008 ; Xu et al 2019 ; Xu et al 2021 ). However, microbial metabolism can result in the production of complex DOM traditionally associated with allochthonous-like characteristics (Fox et al, 2017 ; Fox et al, 2021 ) which can make it difficult to interpret the diverse DOM transformations that occur in natural systems.…”

Section: Discussionmentioning

confidence: 99%

Dissolved organic matter transformations in a freshwater rivermouth

et al. 2023

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River-to-lake transitional areas are biogeochemically active ecosystems that can alter the amount and composition of dissolved organic matter (DOM) as it moves through the aquatic continuum. However, few studies have directly measured carbon processing and assessed the carbon budget of freshwater rivermouths. We compiled measurements of dissolved organic carbon (DOC) and DOM in several water column (light and dark) and sediment incubation experiments conducted in the mouth of the Fox river (Fox rivermouth) upstream from Green Bay, Lake Michigan. Despite variation in the direction of DOC fluxes from sediments, we found that the Fox rivermouth was a net sink of DOC where water column DOC mineralization outweighed the release of DOC from sediments at the rivermouth scale. Although we found DOM composition also changed during our experiments, alterations in DOM optical properties were largely independent of the direction of sediment DOC fluxes. We found a consistent decrease in humic-like and fulvic-like terrestrial DOM and a consistent increase in the overall microbial composition of rivermouth DOM during our incubations. Moreover, greater ambient total dissolved phosphorus concentrations were positively associated with the consumption of terrestrial humic-like, microbial protein-like, and more recently derived DOM but had no effect on bulk DOC in the water column. Unexplained variation indicates that other environmental controls and water column processes affect the processing of DOM in this rivermouth. Nonetheless, the Fox rivermouth appears capable of substantial DOM transformation with implications for the composition of DOM entering Lake Michigan.

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Section: Discussionmentioning

confidence: 99%

Dissolved organic matter transformations in a freshwater rivermouth

et al. 2023

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“…A simulated freshwater (SFW) matrix, adapted from Smith et al (2002), was developed, standardized, and used throughout the study. In contrast to previous laboratory-based studies (Fox et al, 2017(Fox et al, , 2018(Fox et al, , 2021, the SFW matrices contains concentrations of ionic constituents found within oligotrophic fresh waters (Smith et al, 2002), i.e., contains a low baseline concentration of nitrate, phosphate, and dissolved organic carbon (DOC) in the form of glucose. Importantly, the developed SFW exhibited low background fluorescence, unlike many studies which utilize environmental freshwaters (Fox et al, 2018;Kominoski et al, 2018;Berggren et al, 2020).…”

Section: Introductionmentioning

confidence: 83%

“…Further work is required to determine the relative recalcitrance of the presumed higher molecular weight FOM that is produced, by monitoring the fluorescence in this region over longer periods of time and in the presence of a more diverse microbial community. Recent literature has suggested that the origin of Peak C+ is partly derived from extracellular microbial products ( Sorensen et al, 2020 ; Fox et al, 2021 ) However, to date, the overwhelming consensus is that Peaks C and C+ in freshwater environments are associated with material that is allochthonous in origin ( Coble et al, 2014 ).…”

Section: Discussionmentioning

confidence: 99%

The in situ Production of Aquatic Fluorescent Organic Matter in a Simulated Freshwater Laboratory Model

et al. 2022

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Dissolved organic matter (DOM) is ubiquitous throughout aquatic systems. Fluorescence techniques can be used to characterize the fluorescing proportion of DOM, aquatic fluorescent organic matter (AFOM). AFOM is conventionally named in association with specific fluorescence “peaks,” which fluoresce in similar optical regions as microbially-derived proteinaceous material (Peak T), and terrestrially-derived humic-like compounds (Peaks C/C+), with Peak T previously being investigated as a tool for bacterial enumeration within freshwaters. The impact of anthropogenic nutrient loading on the processing of DOM by microbial communities is largely unknown. Previous laboratory studies utilizing environmental freshwater have employed growth media with complex background fluorescence, or very high nutrient concentrations, preventing the investigation of AFOM production under a range of more representative nutrient concentrations within a matrix exhibiting very low background fluorescence. We describe a laboratory-based model with Pseudomonas aeruginosa that incorporates a low fluorescence growth matrix consisting of a simulated freshwater (SFW), representative of low-hardness freshwater systems allowing controlled nutrient conditions to be studied. The effects of microbial processing of DOM as a function of available nitrogen, phosphorous, and dissolved organic carbon (DOC) in the form of glucose were investigated over 48 h at highly resolved time increments. The model system demonstrates the production of a range of complex AFOM peaks in the presence and absence of DOC, revealing no linear relationship between cell numbers and any of the peaks for the bacterial species studied, with AFOM peaks increasing with microbial cell number, ranging from 55.2 quinine sulfate units (QSU) per 106 cells to 155 QSU per 106 cells (p < 0.05) for Peak T during the exponential growth phase of P. aeruginosa under high nutrient conditions with 5 mg L−1 DOC. Nutrient and DOC concentration was found to cause differential production of autochthonous- or allochthonous-like AFOM, with lower DOC concentrations resulting in higher Peak T production relative to Peaks C/C+ upon the addition of nutrients, and high DOC concentrations resulting in higher Peak C/C+ production relative to Peak T. Our results show the production of allochthonous-like AFOM from a simple and non-fluorescent carbon source, and provide uncertainty in the use of Peak T as a reliable surrogate for specific bacterial enumeration, particularly in dynamic or nutrient-impacted environments, pointing toward the use of fluorescence as an indicator for microbial metabolism.

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