Nano- and microplastics trigger secretion of protein-rich extracellular polymeric substances from phytoplankton.

The substantial increase in plastic pollution in marine ecosystems raises concerns about its adverse impacts on the microbial community. Microorganisms (bacteria, phytoplankton) are important producers of exopolymeric substances (EPS), which govern the processes of marine organic aggregate formation, microbial colonization, and pollutant mobility. Until now, the effects of nano- and micro-plastics on characteristics of EPS composition have received little attention. This study investigated EPS secretion by four phytoplankton species following exposure to various concentrations of polystyrene nano- and microplastics (55 nm nanoparticles; 1 and 6 µm microparticles). The 55 nm nanoparticles induced less growth/survival (determined on a DNA basis) and produced EPS with higher protein-to-carbohydrate (P/C) ratios than the exposure to microplastic particles. The amount of DNA from the four marine phytoplankton showed a higher negative linear correlation with increasing P/C ratios, especially in response to nanoplastic exposure. These results provide evidence that marine phytoplankton are quite sensitive to smaller-sized plastics and actively modify their EPS chemical composition to cope with the stress from pollution. Furthermore, the release of protein-rich EPS was found to facilitate aggregate formation and surface modification of plastic particles, thereby affecting their fate and colonization. Overall, this work offers new insights into the potential harm of different-sized plastic particles and a better understanding of the responding mechanism of marine phytoplankton for plastic pollution. The data also provide needed information about the fate of marine plastics and biogenic aggregation and scavenging processes.

Role of Polysaccharides in Diatom Thalassiosira pseudonana and its Associated Bacteria in Hydrocarbon Presence.

Diatoms secrete a significant amount of polysaccharides, which can serve as a critical organic carbon source for bacteria. The 2010 Deepwater Horizon oil spill exposed the Gulf of Mexico to substantial amounts of oil that also impacted the phytoplankton community. Increased production of exopolymeric substances was observed after this oil spill. Polysaccharides make up a major fraction of exopolymeric substances; however, their physiological role during an oil spill remains poorly understood. Here, we analyzed the role of polysaccharides in the growth and physiology of the oil-sensitive diatom Thalassiosira pseudonana and how they shape the surrounding bacterial community and its activity in the presence of oil. We found that inhibition of chrysolaminarin synthesis had a negative effect on the growth of T pseudonana and intracellular monosaccharide accumulation, which in turn suppressed photosynthesis by feedback inhibition. In addition, by acting as a carbon reserve, chrysolaminarin helped in the recovery of T pseudonana in the presence of oil. Inhibition of chrysolaminarin synthesis also influenced the bacterial community in the free-living fraction but not in the phycosphere. Exposure to oil alone led to increased abundance of oil-degrading bacterial genera and the activity of exoenzyme lipase. Our data show that chrysolaminarin synthesis plays an important role in the growth and survival of T pseudonana in the presence of oil, and its inhibition can influence the composition and activity of the surrounding bacterial community.

Impact of exposure of crude oil and dispersant (Corexit) on aggregation of extracellular polymeric substances.

Spilled oil treated with Corexit dispersant can cause unintended impacts on marine environment systems including altering marine organic matter dynamics; however, impacts on microgels and marine oil snow (MOS) formation are still debated and remain to be fully understood. Extracellular polymeric substances (EPS) are a major source of marine organic carbon for MOS and microgel formation. EPS initial aggregation plays key roles in the oil degrading process and various biogeochemical reactions. Here we used four types of EPS with water accommodated fraction (WAF), chemically-enhanced WAF (CEWAF) and Corexit, to represent potential situations during oil spills and post-application of Corexit. We found that Corexit alone can inhibit EPS aggregation and disperse pre-existing microgels. CEWAF can enhance EPS aggregation with efficiency by up to 80%-100% and more aggregates accumulated within the air-water interface. Additionally, more hydrophobic EPS aggregates showed high resistance to Corexit dispersion while hydrophilic EPS were more sensitive. Effects of oil spills on marine gel particle formation are primarily determined by chemical characteristics (hydrophobicity and protein content) of the constituent EPS. This study offers unique insights for organic particle dynamics and identifies controlling factors for MOS or gel particles associated with oil spills and Corexit dispersant used.

Perovskite Nanoparticles Toxicity Study on Airway Epithelial Cells.

Research on the toxicity of nanoparticles has developed over recent years due to their increasing prevalence in common everyday materials. Various nanoparticles have been reported to promote and induce mucus secretion, which could potentially lead to airway damages and respiratory complications. Lanthanum strontium manganite (LSM) is a nanoparticle widely used in solar oxidized fuel cells (SOFCs) due to its high electrical conductivity, high electrochemical activity for O2 reduction reaction, high thermal stability and compatibility of SOFC electrolytes, and most importantly, its microstructural stability and long-term performance. Very few studies have been conducted on LMS's toxicity, thus its effect on airway cells was investigated in this study. After treating trachea cells with increasing concentrations of LSM ranging up to 500 µg/ml, we found that it has a moderate effect on cell viability, ROS production, cytochrome C, and caspase 3 expression. Despite its minimal impact on stated apoptosis-inducing characteristics, LSM illustrated an inhibiting effect on mucus secretion. We obtained a decreasing trend in mucus secretion with an increased concentration of the LSM treatment. Overall, LSM's advancement in SOFCs necessitated a toxicity study, and although it does not show a significant toxicity to trachea cells, LSM reduces mucus secretion, and can potentially interfere with airway clearance.

Sunlight induced aggregation of dissolved organic matter: Role of proteins in linking organic carbon and nitrogen cycling in seawater.

Organic matter export from the euphotic zone is a key component of oceanic carbon (C) and nitrogen (N) cycles. Although interactions between these two cycles are important, studies on geochemical processes to directly connect them are limited. Here we show that sunlight can induce chemical aggregation of dissolved organic matter (DOM) into high N containing photo-aggregates. The size of microgels in natural coastal seawaters increased by18~25% compared to corresponding dark controls. Within a relatively short time (1 h), the C and N sequestered into the photo-aggregates accounted for 10% and 13% of the bulk particulate C and N, respectively. The N/C ratio of the photo-aggregates was two times higher after sunlight irradiation. Furthermore, we show that the aggregation process was dependent on reactive oxygen species (ROS). To accommodate for the different organic material in the marine environment, we monitored the particle size in various extracellular polymeric substances (EPS) and model biopolymers using flow cytometry, dynamic laser scattering, and scanning electron microscopy. We found that proteins play important roles in light-induced aggregation, which is in contrast to previous views that sunlight can break down DOM and interrupt aggregation. The photo-flocculation process involving organic N provides new insights into DOM assembly, bioavailability, and sedimentation, and thus potentially link the C and N cycles.

Extracellular polymeric substances (EPS) producing and oil degrading bacteria isolated from the northern Gulf of Mexico.

Sinking marine oil snow was found to be a major mechanism in the transport of spilled oil from the surface to the deep sea following the Deepwater Horizon (DwH) oil spill. Marine snow formation is primarily facilitated by extracellular polymeric substances (EPS), which are mainly composed of proteins and carbohydrates secreted by microorganisms. While numerous bacteria have been identified to degrade oil, there is a paucity of knowledge on bacteria that produce EPS in response to oil and Corexit exposure in the northern Gulf of Mexico (nGoM). In this study, we isolated bacteria from surface water of the nGoM that grow on oil or Corexit dispersant. Among the 100 strains isolated, nine were identified to produce remarkable amounts of EPS. 16S rRNA gene analysis revealed that six isolates (strains C1, C5, W10, W11, W14, W20) belong to the genus Alteromonas; the others were related to Thalassospira (C8), Aestuariibacter (C12), and Escherichia (W13a). The isolates preferably degraded alkanes (17-77%), over polycyclic aromatic hydrocarbons (0.90-23%). The EPS production was determined in the presence of a water accommodated fraction (WAF) of oil, a chemical enhanced WAF (CEWAF), Corexit, and control. The highest production of visible aggregates was found in Corexit followed by CEWAF, WAF, and control; indicating that Corexit generally enhanced EPS production. The addition of WAF and Corexit did not affect the carbohydrate content, but significantly increased the protein content of the EPS. On the average, WAF and CEWAF treatments had nine to ten times more proteins, and Corexit had five times higher than the control. Our results reveal that Alteromonas and Thalassospira, among the commonly reported bacteria following the DwH spill, produce protein rich EPS that could have crucial roles in oil degradation and marine snow formation. This study highlights the link between EPS production and bacterial oil-degrading capacity that should not be overlooked during spilled oil clearance.

High-throughput label-free microcontact printing graphene-based biosensor for valley fever.

The highly prevalent and virulent disease in the Western Hemisphere Coccidioidomycosis, also known as Valley Fever, can cause serious illness such as severe pneumonia with respiratory failure. It can also take on a disseminated form where the infection spreads throughout the body. Thus, a serious impetus exists to develop effective detection of the disease that can also operate in a rapid and high-throughput fashion. Here, we report the assembly of a highly sensitive biosensor using reduced graphene oxide (rGO) with Coccidioides(cocci) antibodies as the target analytes. The facile design made possible by the scalable microcontact printing (µCP) surface patterning technique which enables rapid, ultrasensitive detection. It provides a wide linear range and sub picomolar (2.5 pg/ml) detection, while also delivering high selectivity and reproducibility. This work demonstrates an important advancement in the development of a sensitive label-free rGO biosensor for Coccidioidomycosis detection. This result also provides the potential application of direct pathogen diagnosis for the future biosensor development.

The impact of nanoplastics on marine dissolved organic matter assembly.

The environmental impact of nanoplastics (NPs) released into natural aquatic surroundings is an increasing concern. NPs are widely generated from our daily waste disposal and eventually reach the ocean, wherein consequent influences on aquatic environments remain unclear. In this regard, there are few studies investigating NP-related ecological impacts. Comprising one of Earth's major carbon pools, marine dissolved organic matter (DOM) serves an essential role in global carbon dynamics. The spontaneous assembly of DOM into particulate organic matter (POM) plays important roles in the marine carbon cycle, and is involved in hemostasis of various ecological communities. Here, we report that 10 ppb NPs (polystyrene/polymethyl methacrylate, 25 nm) appeared in a water column accelerate the kinetic assembly rate of DOM-POM transition. NPs with various characteristics show similar influences on DOM assembly, and seawater samples collected from disparate sites were used to further confirm this unanticipated phenomenon. In this study, we demonstrated that hydrophobic interactions contribute to the facilitation of NP-DOM aggregations. Our results illustrate that NPs alter DOM-POM assembly, which may potentiate unanticipated perturbation to the largest marine carbon pool. Such effects would warrant increased vigilance on current practices of plastic usage and disposal.

CeO2 nanoparticles attenuate airway mucus secretion induced by TiO2 nanoparticles.

Nanotoxicity studies associated with various nanoparticles (NPs) have attracted intense research interest due to the broader applications of nanoparticles in our daily lives. The exposure of nanoparticles can lead to hypersecretion and accumulation of airway mucus which are closely associated with many respiratory diseases. Titanium dioxide (TiO2), one of the PM10 components, is a major NP that is widely utilized in many commercial products. Our previous study established the connection between induced airway mucus secretion and TiO2 NPs. However, the countermeasure to reduce the harmful effects of TiO2 NPs, especially airway mucus secretion, remains unexplored. One of the potential candidates to reduce airway mucus secretion is cerium oxide (CeO2) NPs. It has been reported that CeO2 NPs can protect cells by diminishing ROS and inflammatory responses. Herein, our study shows that CeO2 NPs are able to reduce cytosolic Ca2+ changes and mitochondrial damage caused by TiO2 NPs. Our results provide the evidence that hypersecretion of mucus and apoptosis progression induced by TiO2 NPs can be attenuated by CeO2 NPs. This study highlights the potential capacity of CeO2 NPs as a supplementary material for TiO2 NPs applications in the future.

Effect of Engineered Nanoparticles on Exopolymeric Substances Release from Marine Phytoplankton.

Engineered nanoparticles (ENPs), products from modern nanotechnologies, can potentially impact the marine environment to pose serious threats to marine ecosystems. However, the cellular responses of marine phytoplankton to ENPs are still not well established. Here, we investigate four different diatom species (Odontella mobiliensis, Skeletonema grethae, Phaeodactylum tricornutum, Thalassiosira pseudonana) and one green algae (Dunaliella tertiolecta) for their extracellular polymeric substances (EPS) release under model ENP treatments: 25 nm titanium dioxide (TiO2), 10-20 nm silicon dioxide (SiO2), and 15-30 nm cerium dioxide (CeO2). We found SiO2 ENPs can significantly stimulate EPS release from these algae (200-800%), while TiO2 ENP exposure induced the lowest release. Furthermore, the increase of intracellular Ca2+ concentration can be triggered by ENPs, suggesting that the EPS release process is mediated through Ca2+ signal pathways. With better understanding of the cellular mechanism mediated ENP-induced EPS release, potential preventative and safety measures can be developed to mitigate negative impact on the marine ecosystem.

Corexit, oil and marine microgels.

Corexit, an EPA-approved chemical dispersant, was intensively used during the 2010 Deepwater Horizon Oil Spill in the Gulf of Mexico. Current studies surrounding Corexit have mainly focused on its toxicity and oil removal capacity. The potential impact of Corexit on the surface ocean carbon dynamics has remained largely unknown. The spontaneous assembly of DOM (dissolved organic matter) polymers into microgels (POM, particulate organic matter) was demonstrated previously that it can influence various critical processes, such as colloidal pump, microbial loops, and nutrition availability in the surface ocean. Here, we report that Corexit alone can significantly inhibit DOM microgel formation and reduce the stability of pre-existing microgels. However, Corexit and oil, Chemically Enhanced Water Accommodated Fraction (CEWAF), could effectively facilitate DOM microgel formation. The unanticipated disturbance of Corexit and oil spills on the critical DOM-POM continuum warrant particular caution and thus should be considered for future application of Corexit during oil spills.

Light-induced aggregation of microbial exopolymeric substances.

Sunlight can inhibit or disrupt the aggregation process of marine colloids via cleavage of high molecular weight compounds into smaller, less stable fragments. In contrast, some biomolecules, such as proteins excreted from bacteria can form aggregates via cross-linking due to photo-oxidation. To examine whether light-induced aggregation can occur in the marine environment, we conducted irradiation experiments on a well-characterized protein-containing exopolymeric substance (EPS) from the marine bacterium Sagitulla stellata. Our results show that after 1 h sunlight irradiation, the turbidity level of soluble EPS was 60% higher than in the dark control. Flow cytometry also confirmed that more particles of larger sized were formed by sunlight. In addition, we determined a higher mass of aggregates collected on filter in the irradiated samples. This suggests light can induce aggregation of this bacterial EPS. Reactive oxygen species hydroxyl radical and peroxide played critical roles in the photo-oxidation process, and salts assisted the aggregation process. The observation that Sagitulla stellata EPS with relatively high protein content promoted aggregation, was in contrast to the case where no significant differences were found in the aggregation of a non-protein containing phytoplankton EPS between the dark and light conditions. This, together with the evidence that protein-to-carbohydrate ratio of aggregates formed under light condition is significantly higher than that formed under dark condition suggest that proteins are likely the important component for aggregate formation. Light-induced aggregation provides new insights into polymer assembly, marine snow formation, and the fate/transport of organic carbon and nitrogen in the ocean.

The glutathione transferase of Nicotiana benthamiana NbGSTU4 plays a role in regulating the early replication of Bamboo mosaic virus.

Bamboo mosaic virus (BaMV) is a single-stranded positive-sense RNA virus. One of the plant glutathione S-transferase (GST) genes, NbGSTU4, responds as an upregulated gene in Nicotiana benthamiana post BaMV infection. In order to identify the role of NbGSTU4 in BaMV infection, the expression of NbGSTU4 was knocked down using a virus-induced gene silencing technique or was transiently expressed in N. benthamiana in BaMV inoculation. The results show a significant decrease in BaMV RNA accumulation when the expression level of NbGSTU4 is reduced; whereas the viral RNA accumulation increases when NbGSTU4 is transiently expressed. Furthermore, this study identified that the involvement of NbGSTU4 in viral RNA accumulation occurs by its participation in the viral early replication step. The findings show that the NbGSTU4 protein expressed from Escherichia coli can interact with the 3' untranslated region (UTR) of the BaMV RNA in vitro in the presence of glutathione (GSH). The addition of GSH in the in vitro replication assay shows an enhancement of minus-strand but not plus-strand RNA synthesis. The results suggest that the plant GST protein plays a role in binding viral RNA and delivering GSH to the replication complex to create a reduced condition for BaMV minus-strand RNA synthesis.

The silencing suppressor P25 of Potato virus X interacts with Argonaute1 and mediates its degradation through the proteasome pathway.

Previous evidence has indicated that the P25 protein encoded by Potato virus X (PVX) inhibits either the assembly or function of the effector complexes in the RNA silencing-based antiviral defence system (Bayne et al., Cell-to-cell movement of Potato Potexvirus X is dependent on suppression of RNA silencing. Plant J.44, 471-482). This finding prompted us to investigate the possibility that P25 targets the Argonaute (AGO) effector nuclease of RNA silencing. Co-immunoprecipitation and Western blot analysis indicated that there is a strong interaction between P25 and AGO1 of Arabidopsis when these proteins are transiently co-expressed in Nicotiana benthamiana. P25 also interacts with AGO1, AGO2, AGO3 and AGO4, but not with AGO5 and AGO9. As an effective suppressor, the amount of AGO1 accumulated in the presence of P25 was dramatically lower than that infiltrated with HcPro, but was restored when treated with a proteasome inhibitor MG132. These findings are consistent with the idea that RNA silencing is an antiviral defence mechanism and that the counter-defence role of P25 is through the degradation of AGO proteins via the proteasome pathway. Further support for this idea is provided by the observation that plants treated with MG132 are less susceptible to PVX and its relative Bamboo mosaic virus.

Expressing a bacterial mercuric ion binding protein in plant for phytoremediation of heavy metals.

A specific mercuric ion binding protein (MerP) originating from transposon TnMERI1 of Bacillus megaterium strain MB1 isolated from Minamata Bay displayed good adsorption capability for a variety of heavy metals. In this study, the Gram-positive MerP protein was expressed in transgenic Arabidopsis to create a model system for phytoremediation of heavy metals. Under control of an actin promoter, the transgenic Arabidpsis showed higher tolerance and accumulation capacity for mercury, cadium and lead when compared with the control plant. Results from confocal microscopy analysis also indicate that MerP was localized at the cell membrane and vesicles of plant cells. The developed transgenic plants possessing excellent metal-accumulative ability could have potential applications in decontamination of heavy metals.