Transparent Exopolymer Particles Research Articles

Bacteria enhance the production of extracellular polymeric substances by the green dinoflagellate Lepidodinium chlorophorum

High biomasses of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations along Southern Brittany (NE Atlantic, France). The viscosity associated to these phenomena has been related to problems in oyster cultivation. The harmful effect of L. chlorophorum might originate from the secretion of Extracellular Polymeric Substances (EPS). To understand whether the EPS are produced by L. chlorophorum or its associated bacteria, or if they are a product of their interaction, batch cultures were performed under non-axenic and pseudo-axenic conditions for three strains. Maximum dinoflagellate cell abundances were observed in pseudo-axenic cultures. The non-sinking fraction of polymers (Soluble Extracellular Polymers, SEP), mainly composed of proteins and the exopolysaccharide sulphated galactan, slightly increased in pseudo-axenic cultures. The amount of Transparent Exopolymer Particles (TEP) per cell increased under non-axenic conditions. Despite the high concentrations of Particulate Organic Carbon (POC) measured, viscosity did not vary. These results suggest that the L. chlorophorum-bacteria interaction could have a detrimental consequence on the dinoflagellate, translating in a negative effect on L. chlorophorum growth, as well as EPS overproduction by the dinoflagellate, at concentrations that should not affect seawater viscosity.

Transparent Exopolymer Particles in a Coastal Frontal Zone of the Northern South China Sea and the Associated Biogeochemical Implications

AbstractTransparent exopolymer particles (TEP) are essential for the ocean carbon cycle. However, their relationships with physical and biogeochemical processes remain inadequately understood in the coastal ocean. Here, we focus on TEP dynamics across a temperature front in the coastal waters of the Northern South China Sea (NSCS). Our results suggested that TEP concentration was relatively high across the frontal system with 35.0–160.5 μg Xeq L−1 (μg Gum Xanthan equivalent per liter) in the surface waters, 70.0–197.2 μg Xeq L−1 in the bottom waters, and 12.1–16.3 mg Xeq g−1 in the surficial sediment. In the surface layer of the front, TEP distributions appeared to be driven by cross‐front physical and biogeochemical variations, as it showed significant correlations with both temperature and nutrients, as well as chlorophyll‐a along with its size‐fractionated components. TEP dominated on the shore side of the front with high phytoplankton biomass and intense TEP production in the surface layer. In contrast, there were much lower TEP concentrations and higher TEP production efficiencies on the seaside driven by nutrient limitation. In the bottom layer of the frontal zone, sediment resuspension associated with the front's secondary circulation was found to play a crucial role in enhancing the levels of TEP‐rich aggregates with prominent distribution patterns characterized by the localized accumulation in the bottom waters at the frontal zone. Our results provide valuable insights about the controlling factors that modulate TEP dynamics in a coastal frontal system and highlighted their potential role in the carbon cycling of the NSCS shelf‐sea.

Ecological relevance of high and low nucleic acid content bacteria in a monsoon influenced tropical estuary: Implications on the β-Glucosidase activity

Heterotrophic bacteria that differ in their nucleic acid content are frequently observed in aquatic environments. However, their relevance and roles in organic matter utilization in monsoon-influenced tropical estuaries have not been addressed. Transparent exopolymer particles (TEP) are one of the carbohydrate rich organic matter forms in aquatic environments, and their breakdown is mostly mediated by a heterotrophic bacterial ectoenzyme, i.e., β – glucosidase (BGase). The present study evaluated the influence of shifts in high nucleic acid content– (HNA) and low nucleic acid content – (LNA) bacteria on the degradation of TEP with emphasis on BGase activity. For this, monthly observations were carried out along the Zuari estuary, India, on the abundance of HNA, LNA bacteria, bacterial production (BP), and BGase activity. The results showed that the contribution of HNA bacteria to total bacterial count was high and positively influenced the BP and BGase activity during the non-monsoon seasons, which represents a well-mixed water column. During this time, HNA also influenced the active utilization of TEP. Whereas, LNA bacteria dominated during the monsoon, wherein the water column is strongly stratified, and showed decoupling with BGase activity, irrespective of the depth. Redundancy and response curve analyses revealed that the interactive effect of monsoon (rainfall) and stratification significantly altered the bacterial activity in this estuary. Besides, the variability in side scatter (SSC), and fluorescence intensity (FL 1) of HNA and LNA bacteria suggest that these two groups play distinct ecological roles in the tropical estuarine systems. Unravelling the links between the different nucleic acid content bacteria and their phylogenetic composition can provide insights into their functional roles in monsoonal estuaries.

Effect of Temperature on the Release of Transparent Exopolymer Particles (TEP) and Aggregation by Marine Diatoms (Thalassiosira weissflogii and Skeletonema marinoi)

The presence of diatoms is accompanied by the production of a large amount of extracellular polymeric substances, which are mainly composed of carbohydrates. Transparent exopolymer particles (TEP) are a large class of extracellular polymeric substances with high stickiness that promotes the formation of aggregates and marine snow, which affects marine bio-carbon pump efficiency. The purpose of this research was to determine how temperature increases affect the allocation of cellular carbohydrates and the formation and aggregation of TEP. The results showed that the responses of two different diatom species (Thalassiosira weissflogii and Skeletonema marinoi) differed according to temperature. The cell density and chlorophyll a concentration of the former were not significantly correlated with temperature, while those of the latter were significantly decreased with increasing temperature. This indicates that the two species of diatom may have different heat tolerance ranges. A temperature increase will promote significant formation of TEP by both types of diatoms, including aggregation of S. marinoi as the temperature rises, meaning that the high temperature will produce an aggregate with a larger particle size and thus may increase the sedimentation rate of organic carbon. Moreover, the TEP aggregation of T. weissflogii did not increase; therefore, its particle size was smaller, and so it may remain on the sea surface at high temperatures for longer periods. These influences have a profound impact on the biogeochemical cycling of carbon.

Fundamental Thermodynamic Mechanisms of Membrane Fouling Caused by Transparent Exopolymer Particles (Tep) in Water Treatment

Fundamental Thermodynamic Mechanisms of Membrane Fouling Caused by Transparent Exopolymer Particles (Tep) in Water Treatment

Legacy Phosphorus in Lake Okeechobee (Florida, USA) Sediments: A Review and New Perspective

Lake Okeechobee is one of the largest freshwater lakes in the United States. As a eutrophic lake, it has frequent algal blooms composed predominantly of the cyanobacterium genus Microcystis. Many of the algal blooms are associated with the resuspension of a thixotropic benthic mud containing legacy nutrients. Since Lake Okeechobee has an area of 1732 km2 (40–50 km radius) and a mean depth of only 2.7 m, there is sufficient fetch and shallow water depth to allow frequent wind, wave, and current generated events, which cause sediment resuspension. Three types of mud exist in the lake including an immobile dark-colored, consolidated mud, a brownish-colored mud, which is poorly consolidated and mobile, and a dark-colored thixotropic, highly mobile mud that is a mixture of organic matter and clay-sized minerals. Altogether, these muds contain an estimated 4.6 × 106 kg of total phosphorus and commensurate high amounts of labile nitrogen. The thixotropic mud covers most of the lakebed and contains the suitable nutrient ratios to trigger algal blooms. A bioassay analysis of the thixotropic mud compared to the consolidated mud showed that it produced up to 50% more nutrient mass compared to the consolidated mud. The thixotropic mud does not consolidate, thus remains mobile. The mobility is maintained by the dynamics of the algal blooms and bacterial decay of extracellular secretions (transparent exopolymer particles) that bind sediment, transfer it to the bottom, and undergo bacterial digestion causing gas emissions, thus maintaining the organic/sediment matrix in suspension. Despite major efforts to control external nutrient loading into the lake, the high frequency of algal blooms will continue until the muds bearing legacy nutrients are removed from the lake.

Effect of size fractioned alginate-based transparent exopolymer particles on initial bacterial adhesion of forward osmosis membrane support layer

In the forward osmosis (FO) process, biofouling is well pronounced on the active side where wastewater and seawater are used as feed and draw solution, respectively. However, the biofouling tendencies within the support layer are not clear. Therefore, the objective of this study was to investigate the effect of TEP pre-conditioning on hydophobicity and initial bacterial attachment of FO membrane support layer. Two structurally distinct FO membranes from different manufacturers were pre­conditioned by soaking in artificial sea water filtrates containing size fractioned TEP. The conditioning solution pre-treated with a 0.4μm pore size filter, contributed to the highest bacterial adhesion rates during bacterial attachment testing in both steady state and cross-flow mode in a lab-scale FO system for both membrane types. CTA-ES support exhibited higher numbers of adhered bacteria when compared to PA-TFC support in a steady state. Conversely, in cross-flow lab-scale testing, a negative impact of fouling on PA-TFC was more apparent than the CTA-ES membrane. This was attributed to the higher porosity and surface roughness of the PA-TFC membrane. Overall, our findings reinforce the potential impact of hydrodynamics conditions and membrane properties on the fouling behavior of FO membrane support layer.

Heavy metal resistance in Marinobacter adhaerens HP15 supports colonization of transparent exopolymer particles during its interaction with diatoms

Marine diatoms and heterotrophic bacteria play a crucial role in the oceanic carbon cycle as they form aggregates that sink and transport biomass down in the water column. Polysaccharides are a major component of these aggregates and can bind heavy metal cations. Therefore, both organism groups might also be important for the vertical or micro-scale distribution of heavy metals in the ocean. Our model organism for diatom-bacteria interactions, Marinobacter adhaerens HP15, possesses 2 operons coding for heavy metal efflux pumps of the czcCBA type that are responsible for zinc resistance in this bacterium. The goal of this study was to elucidate the role of zinc resistance in M. adhaerens HP15 during its interaction with the diatom Thalassiosira weissflogii. For this, an HP15 mutant deficient in both czcCBA gene clusters was used in diatom co-cultivation experiments with or without zinc stress. When zinc was added to the co-cultures, the release of Alcian Blue-stainable particles increased 10-fold compared to assays without zinc. Both M. adhaerens HP15 wild-type and ΔczcCBA.1/2 mutant colonized the aggregates, and the percentage of bacteria attaching to transparent exopolymer particles (TEP) increased significantly under zinc stress. In the assays with zinc, HP15 wild-type had a higher cell density inside the aggregates than the mutant, although the zinc concentrations inside TEP were comparable. As TEP can bind and thus enrich heavy metals, resistance against them may help M. adhaerens HP15 to colonize aggregates. These results suggest that heavy metal resistance can be beneficial for bacteria during TEP- and aggregate-associated lifestyles.

Transparent exopolymer particles (TEPs)-associated protobiofilm: A neglected contributor to biofouling during membrane filtration

Transparent exopolymer particles (TEPs) are a class of transparent gel-like polysaccharides, which have been widely detected in almost every kind of feed water to membrane systems, including freshwater, seawater and wastewater. Although TEP have been thought to be related to the membrane fouling, little information is currently available for their influential mechanisms and the pertinence to biofouling development. The present study, thus, aims to explore the impact of TEPs on biofouling development during ultrafiltration. TEP samples were inoculated with bacteria for several hours before filtration and the formation of “protobiofilm” (pre-colonized TEP by bacteria) was examined and its influence on biofouling was determined. It was observed that the bacteria can easily and quickly attach onto TEPs and form protobiofilms. Ultrafiltration experiments further revealed that TEP-protobiofilms served as carriers which facilitated and accelerated transport of bacteria to membrane surface, leading to rapid development of biofouling on the ultrafiltration membrane surfaces. Moreover, compared to the feed water containing independent bacteria and TEPs, more flux decline was observed with TEP-protobiofilms. Consequently, it appeared from this study that TEP-protobiofilms play a vital role in the development of membrane biofouling, but unfortunately, this phenomenon has been often overlooked in the literature. Obviously, these findings in turn may also challenge the current understanding of organic fouling and biofouling as membrane fouling caused by TEP-protobiofilm is a combination of both. It is expected that this study might promote further research in general membrane fouling mechanisms and the development of an effective mitigation strategy.

Spatio-temporal variation of transparent exopolymer particles (TEP) and their sinking flux in a temperate bay: Jiaozhou Bay, China

This study investigates transparent exopolymer particles (TEP) distribution, seasonal variability and its sinking flux in a shallow coastal sea, Jiaozhou Bay, China. The TEP concentrations in the bay ranged from 75 to 553 μg xanthum gum equivalents per liter (Xeq. L−1), which was within the range of values reported in other coastal seas. Spatially, high levels of TEP were always observed in the northern bay during all four seasons. In the southern and outer bay, TEP levels were relatively low. Significant positive correlations were observed between TEP and chlorophyll a during spring, summer and fall, suggesting that phytoplankton was the primary source of TEP during these three seasons. Seasonally, TEP concentrations were highest in summer (mean = 275 ± 142 μg Xeq. L−1), followed by winter (mean = 209 ± 53 μg Xeq. L−1), and lowest in spring (mean = 142 ± 43 μg Xeq. L−1) and fall (mean = 180 ± 49 μg Xeq. L−1). High phytoplankton biomass and temperature contributed to the high TEP levels in summer, while the relatively high amount of TEP in winter was most probably derived from re-suspension of sedimentary particles. For the whole year, TEP carbon (TEP-C) contributed to a mean of ~26% of POC in the bay, representing the second most important contributor to POC pool after phytoplankton (mean: 38%). Sinking flux of TEP was measured with sediment trap, and the results revealed that sinking TEP contributed to a mean of 20% of total POC flux for the four seasons in the bay. This study highlights the fact that TEP-C could represent a significant fraction of the POC pool in the coastal sea, and their sedimentation could play an important role in the carbon sedimentation in these areas.

Assessing the Temporal Variability and Drivers of Transparent Exopolymer Particle Concentrations and Production Rates in a Subtropical Estuary

Transparent exopolymer particles (TEP) are the central mechanism by which carbon is shuttled from the surface to the deep ocean. Despite the importance of these particles, the magnitude and drivers of temporal variability in the concentration and production rate of TEP in the ocean are not well resolved, especially in highly dynamic and productive regions like estuaries. Here, TEP dynamics were evaluated across weekly, tidal, and diel time scales within the Skidaway River Estuary (GA, USA) and adjacent coastal waters in the South Atlantic Bight. No significant trends in TEP concentration or production rates were observed over weekly time scales, though over tidal cycles, TEP concentration varied between tide stage and TEP:chlorophyll ratios were always lower at low relative to high tides. Over sequential diel cycles, TEP concentrations were two times higher at night relative to midday. Different biological and environmental variables were correlated with TEP dynamics (Spearman ρ) depending on the time scale considered, reinforcing the importance of time-specific drivers of TEP. These results emphasize the importance in considering the temporal variability of field-based TEP measurements, with implications for accurate assessments of carbon cycling in coastal ecosystems and the incorporation of TEP into carbon export models.

Concentrations and sinking rates of transparent exopolymer particles (TEPs) in a coastal sea: the Changjiang River (Yangtze River) Estuary

Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. To investigate the role of coastal TEPs in sinking carbon from the upper layer, samples were collected in the spring and summer of 2011 in the Changjiang River (Yangtze River) Estuary, a typical coastal water. The concentrations and sinking rates of TEPs were measured, and potential sedimentation flux of TEPs was estimated. TEPs concentrations ranged from 40.00 µg/L to 1 040.00 µg/L (mean=(209.70±240.93) µg/L) in spring and 56.67 µg/L to 1 423.33 µg/L (mean=(433.33±393.02) µg/L) in summer, and they were higher at bloom stations than at non-bloom stations during both cruises. A significant positive correlation between TEPs concentration and chlorophyll a (Chl a) concentration was detected, suggesting that phytoplankton was the primary source of TEPs in this area. TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of (0.28±0.14) m/d in spring and 0.10 m/d to 1.08 m/d with a mean of (0.34±0.31) m/d in summer. The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d) to 29.40 mg/(m2·d) with a mean of (14.66±8.83) mg/(m2·d) in spring and 6.80 mg/(m2·d) to 30.45 mg/(m2·d) with a mean of (15.71±8.73) mg/(m2·d) in summer, which was ∼17.81% to 138.27% (mean=65.15%±31.75%) of sedimentation flux of phytoplankton cells in the study area. Due to the increase of TEPs concentrations and their sinking rates, sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises. This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary, especially during bloom events, and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.

Quorum sensing regulates 'swim-or-stick' lifestyle in the phycosphere.

SummaryInteractions between phytoplankton and bacteria play major roles in global biogeochemical cycles and oceanic nutrient fluxes. These interactions occur in the microenvironment surrounding phytoplankton cells, known as the phycosphere. Bacteria in the phycosphere use either chemotaxis or attachment to benefit from algal excretions. Both processes are regulated by quorum sensing (QS), a cell–cell signalling mechanism that uses small infochemicals to coordinate bacterial gene expression. However, the role of QS in regulating bacterial attachment in the phycosphere is not clear. Here, we isolated a Sulfitobacter pseudonitzschiae F5 and a Phaeobacter sp. F10 belonging to the marine Roseobacter group and an Alteromonas macleodii F12 belonging to Alteromonadaceae, from the microbial community of the ubiquitous diatom Asterionellopsis glacialis. We show that only the Roseobacter group isolates (diatom symbionts) can attach to diatom transparent exopolymeric particles. Despite all three bacteria possessing genes involved in motility, chemotaxis, and attachment, only S. pseudonitzschiae F5 and Phaeobacter sp. F10 possessed complete QS systems and could synthesize QS signals. Using UHPLC–MS/MS, we identified three QS molecules produced by both bacteria of which only 3‐oxo‐C16:1‐HSL strongly inhibited bacterial motility and stimulated attachment in the phycosphere. These findings suggest that QS signals enable colonization of the phycosphere by algal symbionts.

Organic compounds and microbial assessment of a seawater reverse osmosis facility at Tampa Bay Water, USA

The Tampa Bay Water seawater reverse osmosis (SWRO) facility is the first large-capacity seawater desalination plant in the United States. The feedwater source for the facility is an estuarine system that is biologically very productive and contains naturally-occurring high concentrations of algae, marine bacteria, total organic carbon (mostly dissolved), transparent exopolymer particles (TEP), the biopolymer fraction of natural organic matter, and phosphate. The high-organic composition of the feedwater places stress on the conventional sand pretreatment system utilized at the facility resulting in high organic passage into the membrane process and flow through into the permeate. In particular, the direct passage of particulate TEP (p-TEP) into the membranes has a major impact on the biofouling rate. Based on the data collected, the pretreatment is ineffective at removing key organic components that impact the rate of membrane biofouling, particularly bacteria and p-TEP. Perhaps the pretreatment could be re-designed to use a dissolved air floatation system (DAF) followed by ultrafiltration as a remedy that would likely move the biofouling problem to the ultrafiltration process, which has an easier cleaning process. Consideration could be given to using a groundwater source of feedwater as a permanent remedy to the operational issues.

Phaeocystis globosa Bloom Monitoring: Based on P. globosa Induced Seawater Viscosity Modification Adjacent to a Nuclear Power Plant in Qinzhou Bay, China

The mucus produced by the outbreak of Phaeocystis globosa in the adjacent waters of the Fangchenggang Nuclear Power Plant (FCGNPP) in China has blocked the entrance of the cooling water filtration system of the FCGNPP, and posed a threat to the safe operation of the FCGNPP. At present, there is no related research on whether the changes in seawater viscosity could be used as a new method for monitoring and providing early warning of P. globosa tide. During a complete red tide cycle, the temporal and spatial changes in the hydrological conditions (temperature, salinity, dissolved oxygen), chlorophyll-a (Chl-a), composition and abundance of phytoplankton, number and size of P. globose colonies, concentration of transparent exopolymer particles (TEP) and the seawater viscosity were measured in this study. The results indicate that there was an extremely significant negative correlation between the physical seawater viscosity ηT,S and temperature, and the correlation coefficient reached −0.998. The biological seawater viscosity ηBio was positively correlated with the number of P. globosa colonies, and the correlation coefficients is 0.747. Because the increase in phytoplankton abundance, especially during the outbreak of P. globosa and a large amount of mucus produced by the colonies could significantly increase seawater viscosity, we suggest that biological factors were the main reasons for the increase in seawater viscosity. The ηBio was completely consistent with the occurrence process of P. globosa bloom and could be used as a valuable index for P. globosa bloom monitoring.

Dynamics of organic matter and bacterial activity in the Fram Strait during summer and autumn.

The Arctic Ocean is considerably affected by the consequences of global warming, including more extreme seasonal fluctuations in the physical environment. So far, little is known about seasonality in Arctic marine ecosystems in particular microbial dynamics and cycling of organic matter. The limited characterization can be partially attributed to logistic difficulties of sampling in the Arctic Ocean beyond the summer season. Here, we investigated the distribution and composition of dissolved organic matter (DOM), gel particles and heterotrophic bacterial activity in the Fram Strait during summer and autumn. Our results revealed that phytoplankton biomass influenced the concentration and composition of semi-labile dissolved organic carbon (DOC), which strongly decreased from summer to autumn. The seasonal decrease in bioavailability of DOM appeared to be the dominant control on bacterial abundance and activity, while no temperature effect was determined. Additionally, there were clear differences in transparent exopolymer particles (TEP) and Coomassie Blue stainable particles (CSP) dynamics. The amount of TEP and CSP decreased from summer to autumn, but CSP was relatively enriched in both seasons. Our study therewith indicates clear seasonal differences in the microbial cycling of organic matter in the Fram Strait. Our data may help to establish baseline knowledge about seasonal changes in microbial ecosystem dynamics to better assess the impact of environmental change in the warming Arctic Ocean.This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.

Diatom aggregation when exposed to crude oil and chemical dispersant: Potential impacts of ocean acidification.

Diatoms play a key role in the marine carbon cycle with their high primary productivity and release of exudates such as extracellular polymeric substances (EPS) and transparent exopolymeric particles (TEP). These exudates contribute to aggregates (marine snow) that rapidly transport organic material to the seafloor, potentially capturing contaminants like petroleum components. Ocean acidification (OA) impacts marine organisms, especially those that utilize inorganic carbon for photosynthesis and EPS production. Here we investigated the response of the diatom Thalassiosira pseudonana grown to present day and future ocean conditions in the presence of a water accommodated fraction (WAF and OAWAF) of oil and a diluted chemically enhanced WAF (DCEWAF and OADCEWAF). T. pseudonana responded to WAF/DCEWAF but not OA and no multiplicative effect of the two factors (i.e., OA and oil/dispersant) was observed. T. pseudonana released more colloidal EPS (< 0.7 μm to > 3 kDa) in the presence of WAF/DCEWAF/OAWAF/OADCEWAF than in the corresponding Controls. Colloidal EPS and particulate EPS in the oil/dispersant treatments have higher protein-to-carbohydrate ratios than those in the control treatments, and thus are likely stickier and have a greater potential to form aggregates of marine oil snow. More TEP was produced in response to WAF than in Controls; OA did not influence its production. Polyaromatic hydrocarbon (PAH) concentrations and distributions were significantly impacted by the presence of dispersants but not OA. PAHs especially Phenanthrenes, Anthracenes, Chrysenes, Fluorenes, Fluoranthenes, Pyrenes, Dibenzothiophenes and 1-Methylphenanthrene show major variations in the aggregate and surrounding seawater fraction of oil and oil plus dispersant treatments. Studies like this add to the current knowledge of the combined effects of aggregation, marine snow formation, and the potential impacts of oil spills under ocean acidification scenarios.

Effective membrane backwash with carbon dioxide under severe fouling and operation conditions

Membrane fouling is an intrinsic deficiency common for all membrane processes. Fouling mitigation is therefore required to achieve sustainable membrane performance. Our study suggests a novel backwash concept which utilizes network of ultrafiltration interconnected membrane pores as a substrate for CO2 bubbles nucleation from a saturated CO2 solution which enters membrane pores from the support side. As a result, enhanced fouling removal was achieved due to additional hydrodynamic forces caused by expanded and lifted CO2 bubbles. An investigation of CO2 nucleation kinetics using a high speed camera revealed that initial CO2 nucleation rate is strongly determined by the module height and feed water type. A saturated CO2 solution backwash effectively removed bovine serum albumin (BSA) which caused both internal and external membrane fouling. A fouling reduction was also observed in BSA/seawater matrix opposite to cake layer buildup observed experiments with Milli-Q backwash. CO2 nucleation allowed to remove hydraulically irreversible fouling which was caused by transparent exopolymer particles (TEP) at pH 4 and 8. This is a promising result as TEP is biofouling precursor which tends to adsorb to a membrane surface making conventional cleaning practices inefficient. Complete transmembrane pressure recovery was achieved with a feed water containing sodium alginate and SiO2 nanoparticles with sizes compatible with membrane pores. The observed results emphasized the importance of the specific interactions in membrane/foulant/CO2 bubble triangle for a successful membrane recovery.

Marvelous Marine Microgels: On the Distribution and Impact of Gel-Like Particles in the Oceanic Water-Column

Three-dimensional hydrogels of organic polymers have been suggested to affect a variety of processes in the ocean, including element cycling, microbial ecology, food-web dynamics, and air-sea exchange. However, their abundance and distribution in the ocean are hardly known, strongly limiting an assessment of their global significance. As a consequence, marine gels are often disregarded in biogeochemical or ecosystem models. Here, we demonstrate the widespread abundance of microgels in the ocean, from the surface to the deep sea. We exhibit size spectra of two major classes of marine gels, transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) for three different ocean regimes: a) polar seas, b) eastern upwelling systems and c) the oligotrophic open ocean. We show the variations of TEP and CSP over the water-column, and compare them to dissolved organic carbon (DOC). We also discuss how the observed distributional patterns give potential insight to the productivity and particle dynamics of these distinct oceanic regimes. Finally, we exploit current research topics, where consideration of microgels may give new insight into the role of organic matter for marine biogeochemical processes.

Transparent Exopolymer Particle (TEPs) Dynamics and Contribution to Particulate Organic Carbon (POC) in Jaran Bay, Korea

Transparent exopolymer particles (TEPs) are defined as acidic polysaccharide particles and they are influenced by various biotic and abiotic processes that play significant roles in marine biogeochemical cycles. However, little information on their monthly variation, relationship and contribution to particulate organic carbon (POC) is currently available particularly in coastal regions. In this study, the water samples were collected monthly to determine TEP concentrations and POC concentrations in a southern coastal region of Korea, Jaran Bay from April 2016 to March 2017. The TEP concentrations varied from 26.5 to 1695.4 μg Xeq L−1 (mean ± standard deviation (S.D.) = 215.9 ± 172.2 μg Xeq L−1) and POC concentrations ranged from 109.9 to 1201.9 μg L−1 (mean ± S.D. = 399.1 ± 186.5 μg L−1) during our observation period. Based on the 13C stable isotope tracer technique, monthly carbon uptake rates of phytoplankton ranged from 3.0 to 274.1 mg C m−2 h−1 (mean ± S.D. = 34.5 ± 45.2 mg C m−2 h−1). The cross-correlation analysis showed a lag-time of 2 months between chlorophyll a and TEP concentrations (r = 0.86, p &lt; 0.01; Pearson’s correlation coefficient). In addition, we observed a 2 month lag-phased correlation between TEP concentrations and primary production (r = 0.73, p &lt; 0.05; Pearson’s correlation coefficient). In Jaran Bay, the TEP contribution was as high as 78.0% of the POC when the TEP-C content was high and declined to 2.4% of the POC when it was low. These results showed that TEP-C could be a significant contributor to the POC pool in Jaran Bay.