Microbial photoautotroph-heterotroph interactions underlie marine food webs and shape ecosystem diversity and structure in upper ocean environments. Here, bacterial community composition, lifestyle ...preference, and genomic- and proteomic-level metabolic characteristics were investigated for an open ocean
ecotype and its associated heterotrophs over 91 days of cocultivation. The associated heterotrophic bacterial assembly mostly constituted five classes, including
,
,
,
, and
The seven most abundant taxa/genera comprised >90% of the total heterotrophic bacterial community, and five of these displayed distinct lifestyle preferences (free-living or attached) and responses to
growth phases. Six high-quality genomes, including
and the five dominant heterotrophic bacteria, were reconstructed. The only primary producer of the coculture system,
, displayed metabolic processes primarily involved in inorganic nutrient uptake, photosynthesis, and organic matter biosynthesis and release. Two of the flavobacterial populations,
and
, and an SM1A02 population, displayed preferences for initial degradation of complex compounds and biopolymers, as evinced by high abundances of TonB-dependent transporters (TBDTs), glycoside hydrolase, and peptidase proteins. Polysaccharide utilization loci present in the flavobacterial genomes influence their lifestyle preferences and close associations with phytoplankton. In contrast, the alphaproteobacterium
sp. population mainly utilized low-molecular-weight dissolved organic carbon (DOC) through ATP-binding cassette (ABC), tripartite ATP-independent periplasmic (TRAP), and tripartite tricarboxylate transporter (TTT) transport systems. The heterotrophic bacterial populations exhibited complementary mechanisms for degrading
derived organic matter and driving nutrient cycling. In addition to nutrient exchange, removal of reactive oxygen species and vitamin trafficking might also contribute to the maintenance of the
-heterotroph coculture system and the interactions shaping the system.
The high complexity of
ecosystems renders it difficult to study marine microbial photoautotroph-heterotroph interactions. Two-member coculture systems of picocyanobacteria and single heterotrophic bacterial strains have been thoroughly investigated. However,
interactions comprise far more diverse heterotrophic bacterial associations with single photoautotrophic organisms. In the present study, combined metagenomic and metaproteomic data supplied the metabolic potentials and activities of uncultured dominant bacterial populations in the coculture system. The results of this study shed light on the nature of interactions between photoautotrophs and heterotrophs, improving our understanding of the complexity of
environments.
Dissolved organic matter (DOM) represents an essential component of the carbon cycle and controls biogeochemical and ecological processes in aquatic systems. The composition and reactivity of DOM are ...determined by the spatial distribution of its sources and its residence time in a watershed. While the effects of agricultural land cover on DOM quality have been reported across spatial and temporal scales, the influence of riparian land cover on stream DOM composition has received little attention. Furthermore, the combined effects of riparian land cover and streamflow rates on DOM composition require investigation. To this end, a multi-year (2016–2018) DOM characterization study was conducted using bi-weekly water samples collected from seven sub-watersheds nested within the Little River Experimental Watershed (LREW) near Tifton, Georgia, USA. DOM optical properties were determined to assess compositional variations using UV–Vis and excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis. PARAFAC analysis indicated that DOM in the LREW was dominated by three humic-like fluorescing components of terrestrial, microbial, and anthropogenic origin and a protein-like component. DOM composition was influenced by riparian land cover and hydrology, and shifted towards recently produced, low molecular weight DOM with low aromaticity as the percentage of agricultural land within riparian wetlands increased. During periods of high discharge and high baseflow, the DOM pool was dominated by recalcitrant and terrestrial-derived material but shifted towards protein-like and microbial-derived with increasing cropland in the riparian area. The results of this two-year study indicate that the replacement of forested riparian buffers with agricultural land can result in altered DOM composition which may affect carbon cycling and downstream water quality in agricultural watersheds.
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•The optical properties of DOM in agricultural streams were assessed.•DOM composition was influenced by riparian land cover and hydrology.•Agricultural land increases fresh DOM of low molecular weight and low aromaticity.•Microbial-derived DOM dominates during periods of low discharge and baseflow.
The 10 µm polystyrene and polyethylene-terephthalate microplastics (MPs), prevalent in finished drink water, were employed to investigate the effect of normal dosage ...UVC-based advanced-oxidation-processes (UVC-AOPs) on the interaction between MPs and their derived disinfection-byproducts (DBPs) during subsequent chlorination-disinfection, in the presence of Br-, for the first time. The results indicated that UVC/H2O2 caused higher leaching of microplastic-derived dissolved-organic-matter (MP-DOM), with smaller and narrower molecular-weight-distribution than UVC and UVC/peroxymonosulfate (UVC/PMS). The trihalomethanes (as dominant DBPs) molar-formation-potentials (THMs-MFPs) for MP-DOM leached in different UVC-AOPs followed the order of UVC/H2O2>UVC/PMS>UVC. The adsorption of formed THMs, especially Br-THMs, back on MPs was observed in all MPs suspensions with or without UVC-AOPs pre-treatment. The Cl-THMs adsorption by MPs is more sensitive to UVC-AOPs than Br-THMs. The adsorption experiments showed that UVC-AOPs reduce the capacity but increase the rate of THMs adsorption by MPs, suggesting the halogen and hydrogen bonding forces governed the THMs adsorption rate while hydrophobic interaction determines their adsorption capacity. The UVC-AOPs pre-treatment sharply increased the total yield of THMs via both indirectly inducing MP-DOM leaching and directly increasing the THMs-MFPs of MPs by oxidation. 21.36–41.96% of formed THMs adsorbed back on the UVC-AOPs-pretreated MPs, which might increase the toxicity of MPs.
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•THMs-MFP for MP-DOM leached in UVC-AOPs followed the order of UVC/H2O2>UVC/PMS>UVC•UVC-AOPs reduce the capacity but increase the rate of THMs adsorption by MPs•Cl-THMs adsorption is more sensitive to UVC-AOPs than Br-THMs•21.36-41.96% of formed THMs adsorb back on UVC-AOPs pre-treated MPs
Anthropogenic activities and natural erosion caused abundant influx of heavy metals (HMs) and organic matter (OM) into estuaries characterized by the dynamic environments governed by tidal action and ...river flow. Similarities and differences in the fate of HM and OM as well as the influences of OM on HMs remain incomplete in estuaries with seasonal human activity and hydrodynamic force. To address this gap, dissolved HMs (dHMs) and fluorescence dissolved OM (FDOM) were investigated in the Pearl River Estuary, a highly seasonally anthropogenic and dynamic estuary. It aimed to elucidate the effects of hydrodynamic conditions and DOM on the seasonal fate of dHMs via the multivariate statistical methods. Our findings indicated dHMs and FDOM exhibited consistently higher levels in the upper estuarine and coastal waters in both seasons, predominantly controlled by the terrestrial/anthropogenic discharge. In the wet season, dHMs and humic-like substances (HULIS) were positively correlated, showing that dHMs readily combined with HULIS. This association led to a synchronous decrease offshore along the axis of the estuary and the transport following the river plume in the surface affected by the salt wedge. Contrarily, dHMs were prone to complex with protein-like components impacted by the hydrodynamics during the dry season. Principal component analysis (PCA) results revealed the terrestrial/anthropogenic inputs and the fresh-seawater mixing process were the most crucial factors responsible for the fate of dHM in wet and dry seasons, respectively, with DOM identified as a secondary but significant influencing factor in both seasons. This study holds significance in providing valuable insights into the migration, transformation, the ultimate fate of dHMs in anthropogenically influenced estuaries, as well as the intricate dynamics governing coastal ecosystems.
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•Elucidated the relationship between dHMs & DOM and impacts of estuarine dynamics.•Salt wedge synchronously affected dHMs and humic-like substances in wet season.•dHMs bound with humic-like component in wet season but protein-like in dry season.•Hydrodynamics primarily influenced the fate of dHM, DOM played a secondary role.
The characteristics of lake dissolved organic matter (DOM) pool and lake ecosystem interact, and studying the responses between sediment DOM characteristics and lake ecosystem changes may shed light ...on the inherent connection between ecosystem evolution and carbon biogeochemical cycles. Lakes in cold and arid regions are sensitive to changes and accumulate large amounts of carbon as DOM, which may provide a window into more explicit relationships between ecosystem evolution and changes in sediment DOM characteristics in time dimension. However, considerable blind spots exist in the responses between the sediment DOM and ecosystem evolution on time scale and the underlying mechanisms. In this study, multiple approaches were combined to investigate the relationship between the variation trend of sediment DOM characteristics and the evolution of fragile lake ecosystems across three different lake ecosystems in cold and arid regions of China. A strong positive relationship between sediment DOM stabilities, especially humification, and ecosystem degradation was found, consistent for the three lakes. Ultra-high-resolution mass spectrometry and structural equation modeling revealed that the changes of ecosystems affected sediment DOM stability through direct pathways (0.24), such as the contents of terrestrial DOM in lake DOM pool, and indirect pathways, including algae-mediated (0.43) and salinity-mediated pathways (0.22), which all increased the contents of refractory DOM in the lake DOM pool and sediments. Based on the fact that DOM stability changes could act on the ecosystem in turn, a possible positive feedback mechanism between ecosystem degradation and increased DOM stability was further inferred. These results suggested that the continuous increased stability of sediment DOM in may implies ecosystem degradation of lakes in the cold and arid regions. This study provides a new perspective for recognizing ecosystem evolution through sediment DOM and improves the understanding of the interaction of lake ecosystem evolution and the biogeochemical cycle of DOM.
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•Sediment DOM stability showed negative correlations with lake ecosystem health.•Terrestrial DOM, increased salinity and algae blooms increase lake stable DOM.•Positive feedback exists between ecosystem degradation and increased DOM stability.•The stability of sediment DOM is potentially indicative of ecosystem degradation.
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Microplastics, as a type of anthropogenic pollution in aquatic ecosystems, affect the carbon cycle of organic matter. Although some studies have investigated the effects of ...microplastics on dissolved organic matter (DOM), the impact of alterations in the chemical properties of microplastics on refractory DOM and carbon release remains unclear. Here, we observed that microplastic treatments (e.g., polystyrene, PS) altered the composition and function of microbial community, notably increasing the abundance of microbial families involved in consuming easily degradable organic matter. During the process in which microbial community decomposed organic matter into DOM, PS underwent surface oxidation. The oxidized PS aggregated with DOM and microorganisms through electrostatic interactions and chemical bonds. Moreover, these interactions between oxidized PS and microbial community affect the utilization of organic matter, resulting in a significant decrease in CO2 emissions. Specifically, total CO2 emissions decreased by approximately 23.76 % with 0.1 mg/L PS treatment and by 44.97 % with 10 mg/L PS treatment compared to those in PS-free treatments over the entire reaction. These findings underscored the significance of the chemical properties of PS in the interactions among DOM and microorganisms, emphasizing the potential impact of PS microplastics on the carbon cycle in ecosystems.
Sources and quality of dissolved organic matter (DOM) in streams may be largely controlled by the landscape and season. In this study, we attempted to answer three critical questions: 1) Do land ...use/land cover (LULC) types affect DOM characteristics? 2) Is there a seasonal fluctuation in DOM components? 3) How do DOM quality and LULC types influence aqueous carbon dioxide partial pressure (pCO2). To achieve this, we investigated the fluorescence characteristics of DOM and its implication for pCO2 in three streams draining land with different urban intensities under distinctive dry and wet seasons. Four fluorescence components were identified, including two terrestrial humic-like components, one protein-like component and one microbial humic-like component. We found a significant positive relationship of the maximum fluorescence intensity (Fmax) of the four components and fluorescence index (FI370) with urbanization intensity in both the dry and wet seasons. The mean Fmax, biological index (BIX) and FI370 all exhibited an increasing trend from upstream to downstream in the stream with highest proportions of urban and cropland. The fluorescence characteristics were negatively related to proportion of forested land in the both seasons. The terrestrial humic-like DOM was dominating in the studied streams. Moreover, the seasonality altered the DOM composition, with protein-like component emerging only in stream waters during the dry season, while microbial humic-like component exclusively occurred during the wet season. pCO2 values were positively related to terrestrial humic-like and biological protein-like components, and urban land. The dry season had much higher pCO2 than the wet season. Results from the Partial Least Squares Path (PLS-PM) models further indicated that LULC types were important in mediating fluorescence DOM whilst pCO2 was more sensitive to the direct effect from FDOM dynamics. We conclude that DOM source and quality in streams are reflective to LULC and climate seasonality, and are good indicators of pCO2 via source tracer and quality of fluorescence components.
•Urban land significantly increases levels of endogenous and exogenous DOM, and pCO2.•Elevated forest land decreases the terrestrial and autochthonous DOM, and pCO2.•Protein-like DOM occurs in the dry season while microbial DOM emerges in wet season.•Higher protein-like DOM and FI370 in dry season indicates increasing stream DOM process.•DOM is a good indicator of pCO2 via source tracer and fluorescence component quality.
To assess the influence of dissolved organic matter (DOM) on the acid–base system of the Baltic Sea, 19 stations along the salinity gradient from Mecklenburg Bight to the Bothnian Bay were sampled in ...November 2011 for total alkalinity (AT), total inorganic carbon concentration (CT), partial pressure of CO2 (pCO2), and pH. Based on these data, an organic alkalinity contribution (Aorg) was determined, defined as the difference between measured AT and the inorganic alkalinity calculated from CT and pH and/or CT and pCO2. Aorg was in the range of 22–58μmolkg−1, corresponding to 1.5–3.5% of AT. The method to determine Aorg was validated in an experiment performed on DOM-enriched river water samples collected from the mouths of the Vistula and Oder Rivers in May 2012. The Aorg increase determined in that experiment correlated directly with the increased DOC concentration caused by enrichment of the >1kDa DOM fraction. To examine the effect of Aorg on calculations of the marine CO2 system, the pCO2 and pH values measured in Baltic Sea water were compared with calculated values that were based on the measured alkalinity and another variable of the CO2 system, but ignored the existence of Aorg. Large differences between measured and calculated pCO2 and pH were obtained when the computations were based on AT and CT. The calculated pCO2 was 27–56% lower than the measured value whereas the calculated pH was overestimated by more than 0.4 pH units. Since biogeochemical models are based on the transport and transformations of AT and CT, the acid–base properties of DOM should be included in calculations of the CO2 system in DOM-rich basins like the Baltic Sea. In view of our limited knowledge about the composition and acid/base properties of DOM, this is best achieved using a bulk dissociation constant, KDOM, that represents all weakly acidic functional groups present in DOM. Our preliminary results indicated that the bulk KDOM in the Baltic Sea is 2.94·10−8molkg−1. Although this KDOM has no thermodynamic meaning, it can be a useful tool in numerical studies as it allows an approximation of Aorg in seawater.
•Organic alkalinity (Aorg) constitutes 1.5–3.5% of AT in the Baltic Sea.•Ignoring Aorg causes significant uncertainty in the calculations of pH and pCO2.•The highest uncertainty occurs when pH and pCO2 are calculated from CT and AT.•Bulk dissociation constant of DOM (KDOM) in the Baltic Sea amounts to 2.94·10−8molkg−1.
•Peptides-like and protein-like compounds in mass spectrum increased after 28 days.•AOM degraded after 28 days still inhibited the MeHg uptake by phytoplankton.•Inhibition after 28 days on MeHg ...uptake resulted from bacterial metabolites.
Methylmercury (MeHg) uptake by phytoplankton represents a key step in determining the exposure risks of aquatic organisms and human beings to this potent neurotoxin. Phytoplankton uptake is believed to be negatively related to dissolved organic matter (DOM) concentration in water. However, microorganisms can rapidly change DOM concentration and composition and subsequent impact on MeHg uptake by phytoplankton has rarely been tested. Here, we explored the influences of microbial degradation on the concentrations and molecular compositions of DOM derived from three common algal sources and tested their subsequent impacts on MeHg uptake by the widespread phytoplankton species Microcystis elabens. Our results indicated that dissolved organic carbon was degraded by 64.3‒74.1% within 28 days of incubating water with microbial consortia from a natural meso‑eutrophic river. Protein-like components in DOM were more readily degraded, while the numbers of molecular formula for peptides-like compounds had increased after 28 days’ incubation, probably due to the production and release of bacterial metabolites. Microbial degradation made DOM more humic-like which was consistent with the positive correlations between changes in proportions of Peaks A and C and bacterial abundance in bacterial community structures as illustrated by 16S rRNA gene sequencing. Despite rapid losses of the bulk DOM during the incubation, we found that DOM degraded after 28 days still reduced the MeHg uptake by Microcystis elabens by 32.7‒52.7% relative to a control without microbial decomposers. Our findings emphasize that microbial degradation of DOM would not necessarily enhance the MeHg uptakes by phytoplankton and may become more powerful in inhibiting MeHg uptakes by phytoplankton. The potential roles of microbes in degrading DOM and changing the uptakes of MeHg at the base of food webs should now be incorporated into future risk assessments of aquatic Hg cycling.
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The temporal evolution of molecular compositions and changes in structural features of Hillsboro Canal (Florida, USA) dissolved organic matter (DOM) was studied with an emphasis on nitrogen and ...sulfur containing molecules, after a 13 day time-series exposure to simulated sunlight. The Hillsboro Canal drains from the ridge and slough wetland environment underlain by peat soils from the northern extent of the Greater Everglades Ecosystem. The Hillsboro Canal-DOM was characterized by combining ultrahigh-resolution mass spectrometry (FT-ICR-MS), high-field nuclear magnetic resonance spectroscopy (1H NMR), size exclusion chromatography (SEC) with UV detection, and ultraviolet/visible (UV/vis) absorbance and excitation emission matrix (EEM) fluorescence spectroscopy. Size exclusion chromatography (SEC) demonstrated progressive depletion of higher mass molecules and a concomitant decrease of absorbance during photo-irradiation. NMR and FT-ICR-MS revealed nonlinear temporal evolution of DOM. In fact, FT-ICR-MS showed an initial depletion of supposedly chromophoric molecules often carrying major unsaturation accompanied by an uneven evolution of numbers of CHO, CHOS and CHNO compounds. While CHNO compounds continually increased throughout the entire photo-exposure time, CHO and CHOS compounds temporarily increased but declined after further light exposure. Progressive loss of highly unsaturated compounds was accompanied by production of low mass CHO and CHNO compounds with high O/C ratios. Area-normalized 1H NMR spectra of DOM in water and of the water insoluble fraction (~5%) in methanol revealed clear distinctions between irradiated and non-irradiated samples and congruent evolution of DOM structural features during irradiation, with more uniform trends in methanolic-DOM. Photoirradiation caused initial photoproduction of oxygenated aliphatic compounds, continued depletion of phenols and oxygenated aromatics, substantial change from initial natural product derived olefins to photoproduced olefins, and uneven evolution of carboxylated and alkylated benzene derivatives. This study demonstrates longer-term heteroatom-dependent photochemistry of DOM, which will affect the speciation of N and S heteroatoms, their connections to inorganic nutrients, and potentially their bioavailability.
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•Photo-irradiation affects molecular and spectroscopic features of peat-derived DOM.•Longer-term heteroatom-dependent photochemistry affects DON and DOS speciation.•The temporal evolution of heteroatom photoproducts was non-linear.•Ultimate fate of DON and DOS compounds is strongly driven by photochemistry.
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