Hypoxic Zone Research Articles

STEM-07. UNVEILING THE ROLE OF HYPOXIA AND TAM-SECRETED TGF-Β1 IN PROMOTING GLIOMA STEM CELL MAINTENANCE VIA YAP/TAZ ACTIVATION IN GLIOBLASTOMA PERI-NECROTIC NICHE

Abstract Glioblastoma (GBM) is a highly malignant brain tumor with rapid growth and poor outcomes. In the tumor microenvironment (TME), necrosis triggers significant reshaping and rapid progression, marked by tumor-associated macrophages (TAMs) and glioma stem cells (GSCs) accumulation in peri-necrotic zones. Analysis of Ivy-GAP and single-cell RNA-Seq data revealed consistent Hippo pathway activation in the hypoxic peri-necrotic zone, despite canonical stem-cell transcription factors such as SOX2, OLIG2, and FOXM1 not being upregulated. We hypothesize that Hippo transcription activation may promote GSC stemness via direct effects of hypoxia and/or TAM-secreted cytokines. Exposing patient-derived GBM neurospheres to 1% hypoxia increased nuclear YAP1 and TAZ expression, along with CYR61, a Hippo pathway readout, compared to normoxia at 48 hours. Single-cell RNA-Seq identified potential hypoxia-regulated genes upstream of YAP/TAZ, including Zyxin, upregulated in 1% hypoxia-treated cultures, possibly facilitating nuclear YAP/TAZ transport. Culturing GBM cells with primary macrophage-conditioned media activated Hippo transcription, with TGF-β1 identified as a hypoxia-specific driver of malignant cell gene expression with single-cell RNA-Seq analysis using NichenetR. Treating GBM cells with TGF-β1 increased CYR61 expression, signifying Hippo transcription activation. Furthermore, we showed that hypoxia and TGF-β1 synergistically maintained GSCs with extreme limiting dilution assays. In the immunocompetent RCAS/tv-a mouse model, Verteporfin, a YAP/TAZ inhibitor, significantly reduced tumor size and prolonged mouse lifespan. TAZ knockdown similarly extended lifespan and reduced tumor growth, with flow cytometry showing a decrease in CD133/CD44 positive GSC populations in knockdown mice. These findings suggest the conclusion that hypoxia and TAM-secreted TGF-β1 directly stimulate YAP/TAZ activation and potentially promote GSC stemness in the GBM peri-necrotic niche.

A temperature tipping point in hypoxic zone size

AbstractTemperature increases will have ubiquitous effects on aquatic food webs, from microbes to consumers, and affect the quality and quantity of carbon flows within and between water layers. A decline in the biological pump moving carbon from surface to lower layers is anticipated. We reviewed 37 years of data on hypoxic zone size and water quality in the northern Gulf of Mexico to determine if air and bottom water temperature increases (0.5°C decade−1) are significantly related to variations in its areal size. There was no significant decline in important river water quality in the 24 years since the national Hypoxia Action Plan was developed to reduce its size. Changes in the ratio of km2 hypoxia per 1000 mt nitrate loading from the Mississippi River from 2000 to 2023 reveals a tipping point in the hypoxic zone size that is driven by ocean warming. Biological factors varying with temperature such as ectotherm growth rates, zooplankton grazing, cell sinking rates, and diatom sequestration of Si or N are apparently more important influences on recent hypoxic zone size than variations in physical factors. This tipping point may be common to similarly warmed and eutrophic coastal waters where warming will likely result in diminished oxygen deficiency (< 2 mgO2 L−1). Hypoxia and food web models assuming a stationary equipoise of nutrient loadings, ratios and food webs will be deficient as coastal waters warm further, coastal storm and hurricane frequency increase and land uses in the watershed are altered with climate change.

Comparison of Machine Learning-Based Predictive Models of the Nutrient Loads Delivered from the Mississippi/Atchafalaya River Basin to the Gulf of Mexico

Predicting nutrient loads is essential to understanding and managing one of the environmental issues faced by the northern Gulf of Mexico hypoxic zone, which poses a severe threat to the Gulf’s healthy ecosystem and economy. The development of hypoxia in the Gulf of Mexico is strongly associated with the eutrophication process initiated by excessive nutrient loads. Due to the complexities in the excessive nutrient loads to the Gulf of Mexico, it is challenging to understand and predict the underlying temporal variation of nutrient loads. The study was aimed at identifying an optimal predictive machine learning model to capture and predict nonlinear behavior of the nutrient loads delivered from the Mississippi/Atchafalaya River Basin (MARB) to the Gulf of Mexico. For this purpose, monthly nutrient loads (N and P) in tons were collected from US Geological Survey (USGS) monitoring station 07373420 from 1980 to 2020. Machine learning models—including autoregressive integrated moving average (ARIMA), gaussian process regression (GPR), single-layer multilayer perceptron (MLP), and a long short-term memory (LSTM) with the single hidden layer—were developed to predict the monthly nutrient loads, and model performances were evaluated by standard assessment metrics—Root Mean Square Error (RMSE) and Correlation Coefficient (R). The residuals of predictive models were examined by the Durbin–Watson statistic. The results showed that MLP and LSTM persistently achieved better accuracy in predicting monthly TN and TP loads compared to GPR and ARIMA. In addition, GPR models achieved slightly better test RMSE score than ARIMA models while their correlation coefficients are much lower than ARIMA models. Moreover, MLP performed slightly better than LSTM in predicting monthly TP loads while LSTM slightly outperformed for TN loads. Furthermore, it was found that the optimizer and number of inputs didn’t show effects on the LSTM performance while they exhibited impacts on MLP outcomes. This study explores the capability of machine learning models to accurately predict nonlinearly fluctuating nutrient loads delivered to the Gulf of Mexico. Further efforts focus on improving the accuracy of forecasting using hybrid models which combine several machine learning models with superior predictive performance for nutrient fluxes throughout the MARB.

The Role of Benthic Fluxes in Acidifying the Bottom Waters in the Northern Gulf of Mexico Hypoxic Zone Based on an Updated Water Column Biogeochemical‐Seabed Diagenetic and Sediment Transport Model

AbstractThe seabed and the water column are tightly coupled in shallow coastal environments. Numerical models of seabed‐water interaction provide an alternative to observational studies that require concurrent measurements in both compartments, which are hard to obtain and rarely available. Here, we present a coupled model that includes water column biogeochemistry, seabed diagenesis, sediment transport and hydrodynamics. Our model includes realistic representations of biogeochemical reactions in both seabed and water column, and fluxes at their interface. The model was built on algorithms for seabed‐water exchange in the Regional Ocean Modeling System and expanded to include carbonate chemistry in seabed. The updated model was tested for two sites where benthic flux and porewater concentration measurements were available in the northern Gulf of Mexico hypoxic zone. The calibrated model reproduced the porewater concentration‐depth profiles and benthic fluxes of O2, dissolved inorganic carbon (DIC), TAlk, NO3 and NH4. We used the calibrated model to explore the role of benthic fluxes in acidifying bottom water during fair weather and resuspension periods. Under fair weather conditions, model results indicated that bio‐diffusion in sediment, labile material input and sediment porosity have a large control on the importance of benthic flux to bottom water acidification. During resuspension, the model indicated that bottom water acidification would be enhanced due to the sharp increase of the DIC/TAlk ratio of benthic fluxes. To conclude, our model reproduced the seabed‐water column exchange of biologically important solutes and can be used for quantifying the role of benthic fluxes in driving bottom water acidification over continental shelves.

Oxygen loss compromises growth and cognition of cuttlefish newborns.

Ocean deoxygenation and standing levels of hypoxia are shrinking fundamental niches, particularly in coastal areas, yet documented repercussions on species development and behaviour are limited. Here, we tackled the impacts of deoxygenation (7 mg O2 l-1), mild hypoxia (nocturnal 5 mg O2 l-1) and severe hypoxia (nocturnal 2 mg O2 l-1) on cuttlefish (Sepia officinalis) development (hatching success, development time, mantle length), cognition (ability to learn individually and socially) and behaviour (ability to camouflage and to explore its surroundings spatially). We found that hypoxia yielded lower survival rates, smaller body sizes and inhibited predatory (increased latency to attack the prey) and anti-predator (camouflage) behaviours. Acute and chronic exposure to low oxygen produced similar effects on cognition (inability to socially learn, increased open-field activity levels, no changes in thigmotaxis). It is thus expected that, although cuttlefish can withstand oxygen limitation to a certain degree, expanding hypoxic zones will diminish current habitat suitability.

A nanotheranostics with hypoxia-switchable fluorescence and photothermal effect for hypoxia imaging-guided immunosuppressive tumor microenvironment modulation

Modulating the immunosuppressive tumor immune microenvironment (TIME) is considered a promising strategy for cancer treatment. However, effectively modulating the immunosuppressive TIME within hypoxic zones remains a significant challenge. In this work, we developed a hypoxia-responsive amphiphilic drug carrier using boron-dipyrromethene (BODIPY) dye-modified chitosan (CsB), and then fabricated a hypoxia-targeted nanotheranostic system, named CsBPNs, through self-assembly of CsB and pexidartinib (5-((5-Chloro-1H-pyrrolo[2,3-b]pyridin-3-yl)methyl)-N-((6-(trifluoromethyl)pyridin-3-yl)methyl), PLX3397), an immunotherapeutic drug targeting tumor-associated macrophages (TAMs), for synergistic photothermal/immunotherapy and hypoxia imaging. CsBPNs demonstrated uniform size, good stability, and hypoxia-switchable fluorescence and photothermal effects, enabling deep penetration and hypoxia imaging capacities in three-dimensional tumor cell spheres and tumor tissues. In vitro and in vivo experiments showed that CsBPNs under laser irradiation promoted TAMs repolarization, reversed the immunosuppressive TIME, and enhanced the therapeutic outcome of PLX3397 in solid tumors by facilitating deep delivery into hypoxic regions and synergistic photothermal therapy. This work provides a new strategy for detecting and modulating the immunosuppressive TIME in hypoxic zones, potentially enabling more precise and effective photo-immunotherapy in the future.

Long-term trends in dissolved oxygen and environmental parameters in Jinhae Bay, Korea: A 25-year analysis (1997–2021)

In recent decades, global oceanic dissolved oxygen (DO) levels have been consistently declining, leading to a notable increase in hypoxic zones. However, comprehensive information on the current trends of DO in Jinhae Bay remains scarce. This study investigated the long-term variations in bottom dissolved oxygen (DO) in Jinhae Bay, specifically focusing on recurring occurrences of oxygen-deficient water (ODW) in August, coinciding with the lowest average DO levels with the most stratified water. ODW events predominantly manifested in the inner bay, while the outer bay exhibited fewer instances due to robust water exchange processes. Analysis of the Low DO group revealed higher surface temperature and salinity, indicating diminished oxygen solubility compared to the High DO group. Lower Chemical oxygen demand (COD) and chlorophyll-a (Chl-a) values in the Low DO group suggested enhanced bacterial decomposition and subdued photosynthesis, in contrast to the High DO group. Over the last 25 years, Jinhae Bay has experienced a discernible decline in bottom DO concentrations. Contrastingly, surface temperature has exhibited a consistent upward trend, notably accelerating in the last 12 years, indicating reduced oxygen solubility. Notably, a substantial reduction in bottom DO levels was observed in the outer bay, previously considered less susceptible to hypoxic conditions. Furthermore, a concurrent decrease in pH highlights the urgency for a comprehensive investigation encompassing both summer hypoxia and seawater acidification, crucial for protecting Jinhae Bay's ecosystem from further deterioration.

Why Is Reducing the Dead Zone in the Gulf of Mexico Such a Complex Goal? Understanding the Structure That Drives Hypoxic Zone Formation via System Dynamics

The Northern Gulf of Mexico hosts a severe dead zone, an oxygen-depleted area spanning 1,618,000 hectares, threatening over 40% of the U.S. fishing industry and causing annual losses of USD 82 million. Using a System Dynamics (SD) approach, this study examined the Mississippi–Atchafalaya River Basin (MARB), a major contributor to hypoxia in the Gulf. A dynamic model, developed with Vensim software version 10.2.1 andexisting data, represented the physical, biological, and chemical processes leading to eutrophication and simulated dead zone formation over time. Various policies were assessed, considering natural system variability. The findings showed that focusing solely on nitrogen control reduced the dead zone but required greater intensity or managing other inputs to meet environmental goals. Runoff control policies delayed nutrient discharge but did not significantly alter long-term outcomes. Extreme condition tests highlighted the critical role of runoff dynamics, dependent on nitrogen load relative to flow volume from upstream. The model suggests interventions should not just reduce eutrophication inputs but enhance factors slowing down the process, allowing natural denitrification to override anthropogenic nitrification.

Controls on Oxygen Variability and Depletion in the Patuxent River Estuary

Oxygen depletion in coastal waters is increasing globally due primarily to eutrophication and warming. Hypoxia responses to nutrient loading and climate change have been extensively studied in large systems like the Chesapeake Bay and the Baltic Sea, while fewer studies have investigated smaller, shallower hypoxic zones. Thus, an improved understanding of the interactions of eutrophication and warming on hypoxia expansion (or reduction) in the wide variety of different estuarine environments is needed. We examined interannual controls on oxygen depletion in the Patuxent River estuary, a eutrophic sub-estuary of Chesapeake Bay where seasonal hypoxia develops annually. We conducted a spatial and temporal analysis of dissolved oxygen (DO) trends, timing, and several metrics of depletion over a long-term record (1985–2021). We found an internally generated hypoxic zone that initiates in the middle estuary, spreading upstream and downstream as the summer progresses, and that hypoxic volume days (HVD) have been increasing (0.11 per year, p = 0.03) over the record despite reduced watershed nitrogen loads and stable phosphorus loads. River flow and temperature have been increasing and are major drivers of increased HVD, with river flow explaining 40% of the interannual variation in HVD (temperature has increased 0.03 and 0.06 °C per year in summer and fall, respectively). Apparent oxygen utilization (AOU) is increasing in bottom waters in the fall, consistent with increasing trends of both water temperature and stratification strength. HVD was negatively related (r2 = 0.34, slope = −0.59*HVD) to the biomass of benthic invertebrates in the middle region of the estuary, suggesting that benthic forage for higher trophic levels will be limited by sustained hypoxia. These results indicate that current and future climate variability plays an important role in regulating oxygen depletion in the Patuxent River estuary, which reinforces the need to factor climate change into strategies for the restoration and management of estuaries.

When an explosion of life leads to death – hypoxic zones in the Menilite Shales from the Silesian Unit (Polish Outer Carpathians)

Oligocene siliciclastics belonging to the Silesian Unit in the Outer Carpathians were sampled from five locations (Iwonicz Zdrój, Krosno, Równe, Rymanów Zdrój, Zmysłówka) with the first four locations connected to Menilite Shales. The sample from Zmysłówka is an example of the lowermost part of the Krosno Beds. Preliminary geochemical results obtained from the Rock-Eval analysis suggested the presence of immature mixed II/III Type kerogen. Detailed geochemical (GC-MS) and petrological analyses show evidence of extensive phytoplankton blooms, causing the occurrence of episodic ferruginous hypoxic zones. Hypoxic zones were present in the photic zone, where molecular evidence of green and/or brown pigmented sulfur reducing bacteria were marked. The size and character of the blooms were controlled by the palaeoenvironmental conditions. In cases of intense nutrient-rich freshwater loading by a palaeoestuary and/or rainfall, extensive algal blooms were reported. With the increasing aridity and/or decrease of the palaeoestuary impact, the phytoplankton blooms gradually acquired a mostly bacterial character and were reduced in size. The most hypoxic conditions were noted in causes linked with the most intense algal blooms. In most of the cases, algal blooms were dominated by diatoms, suggested by the extensive presence of C25 Highly Branched Isoprenoid, a specific biomarker linked with these organisms. The dinoflagellates only recorded a dominant role in blooms in the Krosno location. A comparison of diterpenoids and triterpenoids revealed that terrestrial organic matter was mostly dominated by gymnosperms like conifers from the Cupressaceae, Pinaceae and Podocarpaceae families. Beside these, the molecular evidence of the angiosperms, bryophytes, and fungi was marked. Both geochemical and petrological analyses confirm the minor role of palaeo-wildfires in the land areas near the deposition place of the analysed samples.

Aggravation Of the Climate Change Crisis in The Gulf Coast of The United States: A Review of Anthropogenic Factors

The Gulf Coast of the United States is increasingly at risk from the impacts of climate change, exacerbated by various human-induced factors. This review paper examined how human activities have worsened the effects of climate change in this region from 2005 to 2024, which is already vulnerable to hurricanes, sea-level rise, and coastal erosion. Influential factors include intensive industrial operations, such as oil and gas production, which release significant amounts of greenhouse gases and disrupt the natural landscape, leading to land subsidence and weakening coastal defenses. Urbanization and population growth have resulted in the loss of valuable wetlands and other natural buffers that mitigate flooding and storm surges. Alterations to river systems for flood control and navigation have reduced sediment deposition, affecting the preservation of coastal landforms. Agricultural practices in the region also play a role; fertilizer and pesticide runoff contaminate waterways and create hypoxic zones, impacting fisheries and marine habitats. The paper then emphasizes the need for impactful policy interventions and sustainable behaviors to address these human-induced pressures. In addition, the paper advocates for a comprehensive mitigation strategy that includes stricter emission controls, financial support for renewable energy sources, habitat restoration, and improved urban planning to enhance climate change resilience. After conducting a thorough review, we have discovered that the Gulf Coast region has experienced over fifteen deadly hurricanes over the past twenty years, poised to confront increasingly complex environmental and socioeconomic challenges if viable solutions are not implemented. These issues can potentially jeopardize the livelihoods of the region's inhabitants and the health of its diverse ecosystems.

Effect of Climate and Socio-Economic Changes on the State of the Baltic Sea Ecosystems

In this study, calculations are performed to reproduce the main components of the Baltic Sea ecosystems based on the stationary, boxed SANBALTS model under various scenarios of climate change in combination with two scenarios of the development of socio-economic conditions. Under various warming scenarios, a decrease in the nutrient load will lead to a reduction in the area of hypoxic zones in the Baltic Sea, while the most significant decrease in the area is due to the scenario of a reduction in the agricultural sector and population. The phosphorus in the benthic layer will decrease, the concentration of inorganic nitrogen will increase, and nitrogen fixation will decrease. The most noticeable decrease in primary production and an increase in water transparency is associated with a moderate climate change scenario and with a significant decrease in the nutrient load. The results showed that under certain combinations of scenarios, an improvement in the ecological state of the sea can be expected even under the most unfavorable climatic scenario.

Bottom water quality plasticity in the northern gulf of Mexico hypoxic zone

The growth of the now ubiquitous hypoxic zones found throughout the global coastal ocean are primarily a consequence of nutrient enrichment in surface waters increasing organic production that sinks into bottom waters where oxygen is depleted faster than it is replenished. Hypoxic zones may increase or decline in number because of future climate changes. Here we summarize the summertime variations of dissolved inorganic silicate (DSi), phosphate (DIP), nitrogen (DIN; nitrate + nitrite and ammonium) and ammonium concentrations in the bottom waters of the northern Gulf of Mexico continental shelf from 1985 to 2022. The concentrations of all three are strongly correlated to oxygen concentrations, but not in the same way. At zero oxygen concentration, the annual concentrations of DSi, DIP, and ammonium changed over 38 years at a rate of 1.6 % y−1, 2.0 % y−1 and -1.7 % y−1, respectively. However, the nitrate + nitrite concentrations at zero oxygen concentrations did not change over the same interval. The silicate efflux from anoxic sediments is directly related to warming temperatures and is co-related to phosphate concentrations. The bottom water DSi:DIN molar ratios increased over three decades as DIN:DIP molar ratios decreased, suggesting strong nitrogen limitation compared to silicate and phosphate, and reveal significant plasticity in regeneration rates in the bottom waters that may be dependent on changes in the surface waters. Hypoxia and food web models based on a stationary equipoise of these amounts and ratios in surface and bottom waters will likely be deficient as coastal waters warm, acidification increases, and river water quality changes. Data refreshment and improved understanding of food web changes and warming futures are recommended.

Characteristics of demersal fish community structure during summer hypoxia in the Pearl River Estuary, China.

In recent decades, hypoxic areas have rapidly expanded worldwide in estuaries and coastal zones. The Pearl River Estuary (PRE), one of China's largest estuaries, experiences frequent seasonal hypoxia due to intense human activities and eutrophication. However, the ecological effects of hypoxia in the PRE, particularly on fish communities, remain unclear. To explore these effects, we collected fish community and environmental data in July 2021 during the summer hypoxia development period. The results revealed that bottom-layer dissolved oxygen (DO) in the PRE ranged from 0.08 to 5.71 mg/L, with extensive hypoxic zones (DO ≤ 2 mg/L) observed. Hypoxia has varied effects on fish community composition, distribution, species, and functional diversity in the PRE. A total of 104 fish species were collected in this study, with approximately 30 species (28.6%) exclusively found in hypoxic areas. Species responses to hypoxia varied: species such as Sardinella zunasi, Coilia mystus, and Nuchequula nuchalis were sensitive, while Decapterus maruadsi, Siganus fuscescens, and Lagocephalus spadiceus showed higher tolerance. Within the hypoxia area, dissolved oxygen was the main limiting factor for fish community diversity. Functional diversity (FDiv) decreased with higher dissolved oxygen levels, indicating a potential shift in the functional traits and ecological roles of fish species in response to changing oxygen conditions. Further analysis demonstrated that dissolved oxygen had a significantly stronger effect on fish community structure at hypoxic sites than in the whole PRE. Moreover, other environmental variables also had significant effects on the fish community structure and interacted with dissolved oxygen in the hypoxia area. These findings suggest that maintaining sufficient dissolved oxygen levels is essential for sustaining fish communities and ecosystem health in the PRE. This study provides novel insights into the effects of hypoxia on fish communities in estuarine ecosystems and has significant implications for the ecological health and management of the PRE.

Distribution and sea-to-air fluxes of nitrous oxide and methane from a seasonally hypoxic coastal zone in the southeastern Arabian Sea

The seasonal variability, pathways, and sea-to-air fluxes of nitrous oxide (N2O) and methane (CH4) in the coastal environment, where coastal upwelling and mudbanks co-exist are presented based on the monthly time-series measurements from November 2021 to December 2022. Upwelling-driven hypoxic water's shoreward propagation and persistence were the major factors controlling the N2O concentrations, while the freshwater influx and sedimentary fluxes modulate CH4 concentrations. The N2O concentrations were high during the southwest monsoon (up to 35 nM; 19 ± 8 nM)), followed by spring inter-monsoon (up to 19 nM; 10 ± 5 nM), and lowest during the northeast monsoon (up to 13 nM; 8 ± 2 nM), whereas the CH4 levels were high during the spring inter-monsoon (8.4 to 65 nM), followed by southwest monsoon (6.8 to 53.1 nM) and relatively lower concentrations during the northeast monsoon (3.3 to 32.6 nM). The positive correlations of excess N2O with Apparent Oxygen Utilisation (AOU) and the sum of nitrate and nitrite (NOx) indicate that nitrification is the primary source of N2O in the mudbank regime. The negative correlation of CH4 concentrations with salinity indicates considerable input of CH4 through freshwater influx. CH4 exhibited a highly significant positive correlation with Chlorophyll-a throughout the study period. Furthermore, it displayed a statistically significant positive correlation with phosphate (PO43−) during the northeast monsoon while a strong negative correlation with PO43− during the spring inter-monsoon, pointing towards the role of aerobic CH4 production pathways in the mudbank regime. N2O and CH4 exhibited a contrasting seasonal pattern of sea-to-air fluxes, characterised by the highest N2O fluxes during the southwest monsoon (hypoxia) (13 ± 10 μM m−2 d−1), followed by spring inter-monsoon (12 ± 16 μM m−2 d−1), and the lowest during the northeast monsoon (0.6 ± 3 μM m−2 d−1). Conversely, the highest sea-to-air fluxes of CH4 were noticed during the spring inter-monsoon (74 ± 56 μM m−2 d−1), followed by the southwest monsoon (45 ± 35 μM m−2 d−1), and the lowest values during the northeast monsoon (19 ± 16 μM m−2d−1). Long-term time-series measurements will be invaluable in understanding the longer-term impacts of climate-driven variability on marine biogeochemical cycles in dynamic nearshore systems.

Unraveling the interaction of co-encapsulated Saccharomyces cerevisiae and Metarhizium brunneum in calcium alginate-based attract-and-kill beads.

Attract-and-kill (AK) beads are biological, microbial insecticides developed as an alternative to synthetic soil insecticides. For wireworm control, beads are based on calcium alginate/starch co-encapsulating the carbon dioxide (CO2) producing yeast Saccharomyces cerevisiae H205 as the attract component, and the entomopathogenic fungus Metarhizium brunneum CB15-III as the kill component. However, the physicochemical processes inside beads during co-cultivation are still unclear. Here we reveal for the first time the spatiotemporal conditions of oxygen and pH inside AK beads measured with microelectrodes and describe the impact of S. cerevisiae on CO2 and conidia formation. Measurements revealed a steep oxygen gradient already 2 days after co-encapsulation, with an internal hypoxic zone. Encapsulating either S. cerevisiae or M. brunneum already decreased the average pH from 5.5 to 4.7 and 4.6, respectively. However, on day 3, co-cultivation lead to temporal strong acidification of beads down to pH 3.6 which followed the maximum CO2 productivity and coincided with the maximum conidiation rate. Decreasing the yeast load decreased the total CO2 productivity to half, and the conidial production by 93%, while specific productivities normalized to 1% yeast load increased eight-fold and three-fold, respectively, with day 3 being an exception. Our findings indicate a general beneficial interaction between M. brunneum and S. cerevisiae, but also suggest competition for resources. These findings will contribute to develop innovative co-formulations with maximum efficiency to save application rates and costs. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Prokaryotic community structure and key taxa in the Arabian Sea’s oxygen minimum zone

Microbial communities within oxygen minimum zones (OMZs) play crucial roles in the marine biogeochemical cycling. Arabian Sea (AS) has one of the largest OMZs among the global oceans, however, knowledge about the microbial ecology of the AS OMZ remained limited. In the present study, 44 water samples collected from six stations across the AS, spanning from the deep chlorophyll maximum (DCM) layer to 4000m depth were analyzed. High-throughput sequencing of 16S rRNA genes revealed the structural diversity of bacterial and archaeal communities, influenced primarily by depth and dissolved oxygen (DO) levels. Distinct community compositions were observed across different oxygen gradients, with shifts in the relative abundance of key taxa. Notably, Desulfosarcinaceae, UBA10353, Nitrospina, SUP05, Sva0996_marine_group, Microtrichaceae, and Nitrosopumilus emerged as bioindicator taxa in the AS hypoxic zones. Co-occurrence network analysis identified SAR324, Alteromonadaceae, and Sphingomonadaceae as keystone taxa. The spatial and depth-wise distribution patterns revealed that Desulfosarcinaceae was predominantly found in the hypoxic zones of the Arabian Sea, whereas UBA10353, Nitrospina, SUP05, Microtrichaceae and SAR324 were ubiquitous across AS, Bay of Bengal (BOB), and Eastern Tropical North Pacific (ETNP) OMZs, with OTU-level niche differentiation observed for the latter two. Functional profiling using FAPROTAX predicted higher metabolic potential for nitrogen and sulfur in the OMZ compared to other layers of the AS. Our findings provide valuable insights into the distribution, structure, and diversity of microbial communities in the AS OMZ, highlighting the ecological roles of key taxa in hypoxic environments. The established sequence database offers a foundation for further research into the complex interactions within these microbial ecosystems.

Ocean deoxygenation dampens resistance of diatoms to ocean acidification in darkness

Respiratory activity in the oceans is declining due to the expansion of hypoxic zones and progressive deoxygenation, posing threats to marine organisms along with impacts of concurrent ocean acidification. Therefore, understanding the combined impacts of reduced pO2 and elevated pCO2 on marine primary producers is of considerable significance. Here, to simulate diatoms’ sinking into the aphotic zone of turbid coastal water, we exposed the diatoms Thalassiosira pseudonana and Thalassiosira weissflogii in darkness at 20°C to different levels of pO2 and pCO2 conditions for ~3 weeks, and monitored their biomass density, photosynthetic activity and dark respiration, and examined their recovery upon subsequent exposure to light at 20°C, simulating surface water conditions. Along with decreased cell abundance and size, measured photosynthetic capacity and dark respiration rates in these two diatoms both gradually decreased during the prolonged darkness. Reduced pO2 alone did not negatively affect the photosynthetic machinery in both the dark-survived diatom, and enhanced their subsequent recovery upon light exposure. Nevertheless, the combination of the elevated pCO2 and reduced pO2 (equivalent to hypoxia) led to the biomass loss by about 90% in T. pseudonana, and delayed the recovery of both species upon subsequent exposure to light, though it did not reduce the cell concentration of T. weissflogii during the elongated darkness. Our results suggest that reduced O2 availability diminishes the abilities of the diatoms to cope with the acidic stress associated with ocean acidification, and the expansion of hypoxic waters could delay the photosynthetic recovery of coastal diatoms when they are transported upwards through mixing from dark layers to sunlit waters.

On the Oxygenation Efficacy of Geoengineered Artificial Downwelling in the Estuarine Ecosystem

AbstractThis study examines the oxygenation efficacy of geoengineered artificial downwelling (AD) in the hypoxia zone of the Pearl River Estuary (PRE) using a fine‐resolution coupled physical‐biogeochemical model. Like many estuaries worldwide, the PRE experiences summer hypoxia because of intense stratification and eutrophication. AD provides a potential solution for short‐term hypoxia relief via the mixture of surface and bottom water, but its oxygenation efficacy relying on both local hydrodynamics and biogeochemistry is largely uncertain. Our simulations suggest that AD has extremely low oxygenation efficacy in the PRE during the hypoxia period. The estimated oxygen transfer efficiency (OTE), defined as the rate of oxygen transfer per unit of power needed for pumping, varies between −0.81 and +0.92 kg O2 kWh−1. This is an order of magnitude less than the previous estimate of 10–100 kg kWh−1 in closed lakes and fjords. Moreover, a negative OTE means that AD sometimes backfires and exacerbates hypoxia in the bottom water. The above results remain unchanged when different values of engineering parameters including downwelling rate and discharging depth are used. Extremely low oxygenation efficacy is attributed to strong subtidal advection in the estuary as well as the engineering side effects including reduced vertical diffusion.

PH-responsive targeted nanoparticles release ERK-inhibitor in the hypoxic zone and sensitize free gemcitabine in mutant K-Ras-addicted pancreatic cancer cells and mouse model.

Therapeutic options for managing Pancreatic ductal adenocarcinoma (PDAC), one of the deadliest types of aggressive malignancies, are limited and disappointing. Therefore, despite suboptimal clinical effects, gemcitabine (GEM) remains the first-line chemotherapeutic drug in the clinic for PDAC treatment. The therapeutic limitations of GEM are primarily due to poor bioavailability and the development of chemoresistance resulting from the addiction of mutant-K-RAS/AKT/ERK signaling-mediated desmoplastic barriers with a hypoxic microenvironment. Several new therapeutic approaches, including nanoparticle-assisted drug delivery, are being investigated by us and others. This study used pH-responsive nanoparticles encapsulated ERK inhibitor (SCH772984) and surface functionalized with tumor-penetrating peptide, iRGD, to target PDAC tumors. We used a small molecule, SCH772984, to target ERK1 and ERK2 in PDAC and other cancer cells. This nanocarrier efficiently released ERKi in hypoxic and low-pH environments. We also found that the free-GEM, which is functionally weak when combined with nanoencapsulated ERKi, led to significant synergistic treatment outcomes in vitro and in vivo. In particular, the combination approaches significantly enhanced the GEM effect in PDAC growth inhibition and prolonged survival of the animals in a genetically engineered KPC (LSL-KrasG12D/+/LSL-Trp53R172H/+/Pdx-1-Cre) pancreatic cancer mouse model, which is not observed in a single therapy. Mechanistically, we anticipate that the GEM efficacy was increased as ERKi blocks desmoplasia by impairing the production of desmoplastic regulatory factors in PDAC cells and KPC mouse tumors. Therefore, 2nd generation ERKi (SCH 772984)-iRGD-pHNPs are vital for the cellular response to GEM and denote a promising therapeutic target in PDAC with mutant K-RAS.