Organic matter is a dynamic entity turning over in aquatic systems at highly variable time scales. In the search for controls on organic matter degradation, a multitude of interacting environmental factors have been proposed, including biotic and abiotic conditions, the molecular composition of DOM itself and the low concentrations of the different DOM components. Recent advances in analytical chemistry and biotechnology have provided researchers with an unprecedented ability to characterize the specific organic compounds that participate in biotic and abiotic transformations as well as the enzymes involved in metabolic processes and the genes encoding them. Furthermore, abiotic factors including photolytic degradation and adsorption processes interact with biotic factors in complicated fashion. In this session, we encourage presentations based on studies examining controls and mechanisms of OM turnover, as well as comparative studies and modelling efforts describing a framework for predicting OM turnover. In this session, we will explore how measuring the activities of extracellular and cytoplasmic enzymes in aquatic ecosystems, the concentrations and fluxes of metabolites, the microbes, genes, transcripts, and proteins present in those ecosystems, and the compounds present in dissolved and particulate organic matter all influence each other and the broader ecosystem. Consistent with this year's meeting theme, we are particularly interested in how microbial metabolic processes and microbe-organic matter interactions influence the resilience and recovery of aquatic ecosystems.
Lead Organizer: Andrew Steen, University of Tennessee - Knoxville (asteen1@utk.edu)
Co-organizers:
Maria Montserrat Sala, Institut de Ciències del Mar (CSIC) (msala@icm.csic.es)
Jesus M. Arrieta, Spanish Institute of Oceanography (jesus.arrieta@ieo.csic.es)
Jutta Niggemann, ICBM, University of Oldenburg (jutta.niggemann@uol.de)
Presentations
05:00 PM
LONG-TERM STABILITY OF SYNECHOCCOCUS-DERIVED FLUORESCENT DISSOLVED ORGANIC MATTER (5206)
Primary Presenter: Michael Gonsior, UMCES (gonsior@umces.edu)
Lysed cell material of Synechococcus (open ocean strain WH7803) was prepared using French press (Glenn Mills, Clifton, NJ, USA), filtered through a glass fiber filter (GF/F Whatman), and then added to 20 L of Gulf Stream surface water. Triplicate samples and controls were incubated at room temperature and in the dark for over 500 days. Optical properties were determined at specific time intervals throughout the experiment and revealed fluorescent dissolved organic matter (FDOM) similar to deep ocean FDOM, confirming results from an earlier shorter incubation experiment. New insights in the behavior of statistically-derived Parallel Factor Analysis (PARAFAC)components revealed processing of the initially produced fluorophores and the accumulation of a molecularly modified degradation product that maintained the core fluorescence, with slight spectral shifts indicated by a change from one PARAFAC components to another over time. Microbially transformed FDOM derived from of <em>Synechococcus</em> can therefore accumulate in the dark ocean over long-time periods and hence is confirmed to be a viable source of marine FDOM. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry supports the notion that the core fluorescence could be derived from pyrrole substructures.
05:15 PM
MOLECULAR INSIGHTS INTO THE ROLE OF RIVERINE SUSPENDED PARTICULATE ORGANIC MATTER IN C AND N CYCLING (4672)
Primary Presenter: Leonardo Mena-Rivera, Universidad Nacional (lmena@una.ac.cr)
Suspended POM plays an important role in nutrient cycling in freshwater. However, information regarding its composition and dynamic interactions with the dissolved phase are still poorly defined. Here, we explore the chemical and microbial composition of suspended POM at contrasting sites in a lowland river (River Chew, UK). Composite samples were characterised using a selection of hyphenated mass spectrometry techniques to target different individual and compound classes, including building-block compounds (hydrolysable amino acids and neutral carbohydrates), semi- and non-polar compounds of natural and anthropogenic origin (e.g., n-alkanes, fatty acids, sterols, dicarboxylic acids and flame retardants), and macro-molecular material derived compounds (e.g., polysaccharides and lignin). Particle-attached microbial communities were characterised through next-generation amplicon sequencing. We also investigate the molecular-level mechanisms in which these particle-attached microorganisms assimilate low molecular weight DOM. Incubation experiments were carried out using isotopically labelled glutamate (C and N) over a 6-day period. Microbial assimilation was traced via compound-specific stable isotope analysis of proteinaceous amino acids using GC-C-IRMS. Our results demonstrate both spatial changes in the complex composition of suspended POM, and changes in the rates of assimilation of C and N from the organic substrate, suggesting a distinctive metabolism which is potentially related to the changes in composition as well as in the environmental conditions.
05:30 PM
MOLECULAR AND CELLULAR MECHANISMS OF GLYCAN DEGRADATION IN ALTEROMONAS (6951)
Primary Presenter: Laura Alonso-Sáez, AZTI (lalonso@azti.es)
Alteromonas are ecologically relevant microorganisms, which are widespread in marine environments and can proliferate in response to pulses of organic matter. Furthermore, they feature a wide ability to degrade polymers, such us polysaccharides produced during algal blooms. Here, we studied two Alteromonas isolates with different capabilities to degrade marine polysaccharides (i.e., laminarine and alginate) with focus on understanding the molecular and cellular mechanisms employed to degrade different carbon (C) sources. The consumption of the polysaccharides was faster than that of glucose for both strains, suggesting their specialization in the utilization of polymeric C. By combining different omics approaches, we identified potential Polysaccharide Utilization Loci and analysed their expression patterns during growth on different C sources. Additionally, by high resolution microscopy we visualized a dense exopolysaccharide (EPS) matrix in Alteromonas strains when growing on some carbohydrates. Up to four different gene clusters involved in EPS synthesis were identified in their genomes, which were differentially expressed under different growth conditions. By comparative genomics we found that the EPS synthesis clusters were generally present and highly conserved in a set of 24 Alteromonas genomes, suggesting a widespread distribution. Our results suggest that Alteromonas modulates the secretion of specialized extracellular matrices for degrading different carbohydrates, unveiling a potential role of this cellular mechanism for marine C remineralization.
05:45 PM
Temperature Effects on Benthic Microbial Carbon Remineralization Across Seasons in a Shallow Estuary (5425)
Primary Presenter: Silje Pedersen, University of Southern Denmark (silpe17@student.sdu.dk)
Benthic microbes in shallow temperate systems experience substantial daily and seasonal temperature fluctuations, but whether changing temperatures couple or decouple microbial processes involved in carbon remineralization is not well understood. Here, we measured temperature effects (along a 40°C range) on rates of enzymatic activities (cell-free vs. cell-present) and aerobic respiration in surface sediments of a shallow estuary. Temperature effects under cell-free vs. cell-present conditions differed and suggests a decoupling at certain temperatures. Varying temperature effects on enzyme activities and aerobic respiration were evident across seasons, but show complex relationships with in-situ temperature and microbial counts. Temperature effects on these processes were also consistently decoupled across seasons, with enzymatic activities relatively more stimulated than aerobic respiration with increasing temperatures. Thus, periods when temperature fluctuates substantially in shallow oxic sediments likely exhibit dynamic elemental cycles, altering the pools of organic and inorganic carbon in these systems. The highly complex nature of temperature effects on microbial function may be difficult to capture with simple equations and warrant empirical measurements across time and diverse conditions and microorganisms. Nevertheless, disentangling temperature effects on different diagenetic processes is necessary to understand impacts of weather, climate, and anthropogenic stressors for the biogeochemical function of coastal systems.
06:00 PM
Increased DOM lability and depletion of the POM inventory during winter in an Arctic fjord (Ramfjord, Tromsø) (6493)
Primary Presenter: Yasemin Bodur, UiT - the Arctic University of Norway (yasemin.bodur@uit.no)
Particulate (POM) and dissolved (DOM) organic matter in the ocean are important players in the earth’s biogeochemical cycle and in constant dynamic change. However, they are often treated as distinct entities, separated operationally by size (0.7µm). We studied the dynamics of DOM and POM in an Arctic fjord between September 2020 and August 2021. Surface water was filtered through a GF/F filter (0.7 µm), while another part was unfiltered, and then rotated for 36h. Samples for dissolved and particulate organic carbon concentrations (DOC, POC), DOM composition, extracellular polymeric substances (EPS) and flow cytometry were taken before and after the incubation. From April to September, POC concentrations increased in both, filtered and unfiltered treatments by a factor of 0.04 - 1.5, while the lability of DOM decreased. Contrary to the measurements in the field, POC concentrations in the filtered water before the incubation were highest in the winter months and decreased in both treatments by 0.1 - 0.6, while the DOM composition indicated a transformation of recalcitrant to labile DOM. In both scenarios, EPS and bacterial activity increased. We confirm that during productive phases, POM can be replenished by the DOM pool through aggregation. However, POM dissolution, DOM transformation and increased bacterial activity during winter suggest that organic matter could be altered by bacteria into more labile material when new production is limited. This challenges common understandings of microbial degradation of DOM and presents a so far unexplored aspect of the carbon cycle.
06:15 PM
BACTERIA IN ARCTIC FJORDS RESPOND FASTER AND MORE EFFICIENT TO INCREASED ORGANIC MATTER INPUT COMPARED TO THEIR MARINE COUNTERPARTS (6858)
Primary Presenter: Oliver Müller, University of Bergen (oliver.muller@uib.no)
The warming of the Arctic causes increased input of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems and increased production of phytoplankton derived organic matter (pDOM). Studies have shown that increased DOM input results in both increased bacterial activity and community change. However, it is less clear whether this will affect fjord and marine systems with similar bacterial communities to the same extent and hence influence predictions for the entire Arctic Ocean. In this study, we aim to highlight the effects of the addition of different DOM sources on the activity and structure of marine and fjord bacterial communities in the Arctic. tDOM isolated from Svalbard permafrost soil and pDOM from Diatom exudates was added to water sampled from an Arctic fjord (Isfjorden, Svalbard) and from the Northern Barents Sea (79.8 N and 33.7 E) in August 2019. The samples were incubated for six days and bacterial abundance, activity and community composition measured in regular intervals. While starting communities where similar, responses were very distinct in fjord and marine waters. Bacterial abundance and production increased in both environments over the incubation period, but were 10-fold higher in fjord incubations. This higher productivity was accompanied with a large shift in community composition, mainly driven by the increase of Glaciecola (Gammaproteobacteria). In the marine community, Polaribacter (Flavobacteriia) increased most in abundance. In both environments, the combined addition of pDOM and tDOM gave the strongest response in terms of bacterial abundance and productivity. We show that responses in terms of community composition change and productivity are highly different between fjord and open ocean environments and this highlights the need for further studies to determine the fate of increased DOM input in different Arctic marine ecosystems.
SS052B Microbial and Abiotic Factors Influencing the Turnover and Fate of Organic Matter in Aquatic Systems
Description
Time: 5:00 PM
Date: 6/6/2023
Room: Sala Ibiza A