Effects of elevated carbon dioxide on environmental microbes and its mechanisms: A review

Adaptive mechanism of the marine bacterium Pseudomonas sihuiensis-BFB-6S towards pCO2 variation: Insights into synthesis of extracellular polymeric substances and physiochemical modulation

Marine bacteria can adapt to various extreme environments by the production of extracellular polymeric substances (EPS). Throughout this investigation, impact of variable pCO2 levels on the metabolic activity and physiochemical modulation in EPS matrix of marine bacterium Pseudomonas sihuiensis - BFB-6S was evaluated using a fluorescence microscope, excitation-emission matrix (EEM), 2D-Fourier transform infrared correlation spectroscopy (2D-ATR-FTIR-COS), FT-NMR and TGA-DSC. From the results at higher pCO2 levels, there was a substantial reduction in EPS production by 58-62.8 % (DW). In addition to the biochemical composition of EPS, reduction in carbohydrates (8.7-47.6 %), protein (7.1-91.5 %), and lipids (16.9-68.6 %) content were observed at higher pCO2 levels. Functional discrepancies of fluorophores (tyrosine and tryptophan-like) in EPS, speckled differently in response to variable pCO2. The 2D-ATR-FTIR-COS analysis revealed functional amides (CN, CC, CO bending, -NH bending in amines) of EPS were preferentially altered, which led to the domination of polysaccharides relevant functional groups at higher pCO2. 1H NMR analysis of EPS confirmed the absence of chemical signals from H-C-COOH of proteins, α, β anomeric protons, and acetyl group relevant region at higher pCO2 levels. These findings can contribute new insights into the influence of pCO2 on the adaptation of marine microbes in future ocean acidification scenarios.

Generalized Ulam-Hyers-Rassias stability and novel sustainable techniques for dynamical analysis of global warming impact on ecosystem

Marine structure changes as a result of climate change, with potential biological implications for human societies and marine ecosystems. These changes include changes in temperatures, flow, discrimination, nutritional inputs, oxygen availability, and acidification of the ocean. In this study, a fractional-order model is constructed using the Caputo fractional operator, which singular and nol-local kernel. A model examines the effects of accelerating global warming on aquatic ecosystems while taking into account variables that change over time, such as the environment and organisms. The positively invariant area also demonstrates positive, bounded solutions of the model treated. The equilibrium states for the occurrence and extinction of fish populations are derived for a feasible solution of the system. We also used fixed-point theorems to analyze the existence and uniqueness of the model. The generalized Ulam-Hyers-Rassias function is used to analyze the stability of the system. To study the impact of the fractional operator through computational simulations, results are generated employing a two-step Lagrange polynomial in the generalized version for the power law kernel and also compared the results with an exponential law and Mittag Leffler kernel. We also produce graphs of the model at various fractional derivative orders to illustrate the important influence that the fractional order has on the different classes of the model with the memory effects of the fractional operator. To help with the oversight of fisheries, this research builds mathematical connections between the natural world and aquatic ecosystems.

CO2 uptake in ethanol-driven chain elongation system: Microbial metabolic mechanisms

CO2 as a byproduct of organic waste/wastewater fermentation has an important impact on the carboxylate chain elongation. In this study, a semi-continuous flow reactor was used to investigate the effects of CO2 loading rates (Low = 0.5 LCO2·L-1·d-1, Medium = 1.0 LCO2·L-1·d-1, High = 2.0 LCO2·L-1·d-1) on chain elongation system Ethanol and acetate were utilized as the electron donor and electron acceptor, respectively. The results demonstrate that low loading rate of CO2 has a positive effect on chain elongation. The maximum production of caproate and CH4 were observed at a low CO2 loading rate. Caproate production reached 1.88 g COD·L-1·d-1 with a selectivity of 62.55 %, while CH4 production reached 129.7 ml/d, representing 47.4 % of the total. Metagenomic analysis showed that low loading rate of CO2 favored the enrichment of Clostridium kluyveri, with its abundance being 3.8 times higher than at of high CO2 loading rate. Metatranscriptomic analysis revealed that high CO2 loading rate induced oxidative stress in microorganisms, as evidenced by increased expression of heat shock proteins and superoxide dismutase genes. Further investigation suggested that genes associated with the reverse β-oxidation pathway, CO2 uptake pathway and hydrogenotrophic methanogenesis pathway were reduced at high CO2 loading rate. These findings provide insight into the underlying mechanisms of how CO2 affects chain elongation, and it could be a crucial reason for the poor performance of chain elongation systems with high endogenous CO2 production.

Elevated carbon dioxide concentrations increase the risk of Cd exposure in rice

Since the Industrial Revolution, crops have been exposed to various changes in the environment, including elevated atmospheric carbon dioxide (CO2) concentration and cadmium (Cd) pollution in soil. However, information about how combined changes affect crop is limited. Here, we have investigated the changes of japonica and indica rice subspecies seedlings under elevated CO2 level (1200 ppm) and Cd exposure (5 μM Cd) conditions compared with ambient CO2 level (400 ppm) and without Cd exposure in CO2 growth chambers with hydroponic experiment. The results showed that elevated CO2 levels significantly promoted seedling growth and rescued the growth inhibition under Cd stress. However, the elevated CO2 levels led to a significant increase in the shoot Cd accumulation of the two rice subspecies. Especially, the increase of shoot Cd accumulation in indica rice was more than 50% compared with control. Further investigation revealed that the decreases in the photosynthetic pigments and photosynthetic rates caused by Cd were attenuated by the elevated CO2 levels. In addition, elevated CO2 levels increased the non-enzymatic antioxidants and significantly enhanced the ascorbate peroxidase (APX) and glutathione reductase (GR) activities, alleviating the lipid peroxidation and reactive oxygen species (ROS) accumulation induced by Cd. Overall, the research revealed how rice responded to the elevated CO2 levels and Cd exposure, which can help modify agricultural practices to ensure food security and food safety in a future high-CO2 world.

Effect of vacuum and modified atmosphere packaging on moisture state, quality, and microbial communities of grouper (Epinephelus coioides) fillets during cold storage

The study aimed to assess the impact of different packaging methods on the moisture state, quality, and microbial composition of grouper fillets. The grouper fillets were packaged under the following four conditions: vacuum packaging (VP), 70% CO2/30% N2 (MAP1); 60% CO2/30% N2/10% O2 (MAP2); 40% CO2/30% N2/30% O2 (MAP3). Physicochemical and microbiological parameters were evaluated during 21 days of cold storage. The result demonstrated that MAP was effective in inhibiting microbial growth and accumulation of total volatile basic nitrogen (TVB-N), while also maintaining the water-holding capacity (WHC) of grouper fillets. Additionally, MAP1 effectively inhibited lipid and protein oxidation and protected the secondary structure of myofibrils compared to MAP2 and MAP3, with MAP1 samples having the lowest thiobarbituric acid reactive substances (TBARS) value (0.009-0.04 MDA/kg) and carbonyl content (0.20-0.26 μmol/g) and the highest sulfhydryl content (0.25-0.49 μmol/g) during cold storage. The results of high-throughput sequencing revealed that the presence of oxygen in the packaging system significantly influenced bacterial succession. Over time, Carnobacterium gradually became the dominant genera of fillets stored in MAP, and the presence of oxygen in MAP2 and MAP3 accelerated this transition by 9 days, compared to MAP1. In contrast, Enterobacteriaceae and Carnobacterium were the main dominant genera in VP. Remarkably, Enterobacteriaceae were virtually absent in MAP2 and MAP3 during storage, suggesting that the presence of oxygen exerted a significant inhibitory effect on Enterobacteriaceae. This study provides valuable insights into the application of MAP in the preservation of grouper fillets.

The behaviour of Escherichia coli and Pseudomonas aeruginosa in bottled mineral water

Microbial contamination of bottled water during the filling and capping procedure is a problem which should be avoided. The examination of the influence of carbon dioxide (CO2) on bacterial growth of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in bottled mineral water was the aim of this study. Commercially available glass bottles with plastic screw caps filled with natural mineral water (without additional CO2 "still" (StMW) and with CO2 "sparkling" (SpMW) were obtained from a manufacturer in the province of Styria, Austria. The artificial contamination was performed in the lab by opening the bottle with subsequent addition of a bacterial solution with a defined number of bacteria. For each bacterial strain, 12 bottles were prepared. Samples (100 mL) were taken after a specific number of days, filtrated and placed on Endo Agar for cultivation. After incubation for 24 h bacterial colonies were counted. In this study CO2 addition to bottled water reduced colony forming units of the two investigated bacterial strains over time.

Fate of Planktonic and Biofilm-Derived Listeria monocytogenes on Unwaxed Apples during Air and Controlled Atmosphere Storage

Multiple recalls and outbreaks involving Listeria monocytogenes-contaminated apples have been linked to the post-harvest packing environment where this pathogen can persist in biofilms. Therefore, this study assessed L. monocytogenes survival on apples as affected by harvest year, apple cultivar, storage atmosphere, and growth conditions. Unwaxed Gala, Granny Smith, and Honeycrisp apples were dip-inoculated in an 8-strain L. monocytogenes cocktail of planktonic- or biofilm-grown cells (~6.5 log CFU/mL), dried, and then examined for numbers of L. monocytogenes during air or controlled atmosphere (CA) (1.5% O2, 1.5% CO2) storage at 2 °C. After 90 days, air or CA storage yielded similar L. monocytogenes survival (p > 0.05), regardless of harvest year. Populations gradually decreased with L. monocytogenes quantifiable in most samples after 7 months. Apple cultivar significantly impacted L. monocytogenes survival (p < 0.05) during both harvest years with greater reductions (p < 0.05) seen on Gala compared to Granny Smith and Honeycrisp. Biofilm-derived cells survived longer (p < 0.05) on L. monocytogenes-inoculated Gala and Honeycrisp apples compared to cells grown planktonically. These findings should aid in the development of improved L. monocytogenes intervention strategies for apple growers and packers.

Impact of carbon dioxide on the radial growth of fungi isolated from dairy environment

In dairy industry, filamentous fungi are used as adjunct cultures in fermented products for their technological properties but they could also be responsible for food spoilage and mycotoxin production. The consumer demands about free-preservative products has increased in recent years and lead to develop alternative methods for food preservation. Modified Atmosphere Packaging (MAP) can inhibit fungal growth and therefore increase the food product shelf-life. This study aimed to evaluate radial growth as a function of CO2 and more particularly carbonic acid for fourteen adjuncts and/or fungal spoiler isolated from dairy products or dairy environment by using predictive mycology tools. The impact of the different chemical species linked to CO2 (notably carbonic acid) were study because it was reported previously that undissociated carbonic acid impacted bacterial growth and bicarbonates ions were involved in modifications of physiological process of fungal cells. A significant diversity in the responses of selected strains was observed. Mucor circinelloides had the fastest growth rates (μ > 11 mm. day-1) while Bisifusarium domesticum, Cladosporium herbarum and Penicillium bialowiezense had the slowest growth rates (μ < 1 mm. day-1). Independently of the medium pH, the majority of strains were sensitive to total carbonic acid. In this case, it was not possible to conclude if CO2 active form was gaseous or aqueous so modeling were performed as a function of CO2 percentage. Only Geotrichum candidum and M. circinelloides strains were sensitive to undissociated carbonic acid. Among the fourteen strains, P. bialowiezense was the less sensitive strain to CO2, no growth was observed at 50% of CO2 only for this strain. M. lanceolatus was the less sensitive strain to CO2, the CO250 which reduce the growth rates by 50% was estimated at 138% of CO2. Low CO2 percentage improved the growth of Penicillium expansum, Penicillium roqueforti and Paecilomyces niveus. Mathematical models (without and with optimum) were suggested to describe the impact of CO2 percentage or undissociated carbonic acid concentration on fungal growth rate.

The regulation of carbon dioxide on food microorganisms: A review

This review presents a survey of two extremely important technologies about CO2 with the effectiveness of controlling microorganisms - atmospheric pressure CO2-based modified atmosphere packaging (MAP) and high pressure CO2 non-thermal pasteurization (HPCD). CO2-based MAP is effectively in delaying the lag and logarithmic phases of microorganisms by replacing the surrounding air, while HPCD achieved sterilization by subjecting food to either subcritical or supercritical CO2 for some time in a continuous, batch or semi-batch way. In addition to the advantages of healthy, eco-friendly, quality-preserving, effective characteristic, some challenges such as the high drip loss and packaging collapse associated with higher concentration of CO2, the fuzzy mechanisms of oxidative stress, the unproven specific metabolic pathways and biomarkers, etc., in CO2-based MAP, and the unavoidable extraction of bioactive compounds, the challenging application in solid foods with higher efficiency, the difficult balance between optimal sterilization and optimal food quality, etc., in HPCD still need more efforts to overcome. The action mechanism of CO2 on microorganisms, researches in recent years, problems and future perspectives are summarized. When dissolved in solution medium or cellular fluids, CO2 can form carbonic acid (H2CO3), and H2CO3 can further dissociate into bicarbonate ions (HCO3-), carbonate (CO32-) and hydrogen cations (H+) ionic species following series equilibria. The action mode of CO2 on microorganisms may be relevant to changes in intracellular pH, alteration of proteins, enzyme structure and function, alteration of cell membrane function and fluidity, and so on. Nevertheless, the effects of CO2 on microbial biofilms, energy metabolism, protein and gene expression also need to be explored more extensively and deeply to further understand the action mechanism of CO2 on microorganisms.

Volatilome Analysis and Evolution in the Headspace of Packed Refrigerated Fish

Fresh fish is a perishable food in which chemical (namely oxidation) and microbiological degradation result in undesirable odor. Non-processed fish (i.e., raw fish) is increasingly commercialized in packaging systems which are convenient for its retailing and/or which can promote an extension of its shelf-life. Compared to fish sent to its retail unpackaged, fish packaging results in a modification of the gaseous composition of the atmosphere surrounding it. These modifications of atmosphere composition may affect both chemical and microbiological degradation pathways of fish constituents and thereby the volatile organic compounds produced. In addition to monitoring Total Volatile Basic Nitrogen (TVB-N), which is a common indicator to estimate non-processed fish freshness, analytical techniques such as gas chromatography coupled to mass spectrometry or techniques referred to as "electronic nose" allow either the identification of the entire set of these volatile compounds (the volatilome) and/or to selectively monitor some of them, respectively. Interestingly, monitoring these volatile organic compounds along fish storage might allow the identification of early-stage markers of fish alteration. In this context, to provide relevant information for the identification of volatile markers of non-processed packaged fish quality evolution during its storage, the following items have been successively reviewed: (1) inner atmosphere gaseous composition and evolution as a function of fish packaging systems; (2) fish constituents degradation pathways and analytical methods to monitor fish degradation with a focus on volatilome analysis; and (3) the effect of different factors affecting fish preservation (temperature, inner atmosphere composition, application of hurdle technology) on volatilome composition.

Elevated CO2 alleviated the dissemination of antibiotic resistance genes in sulfadiazine-contaminated soil: A free-air CO2 enrichment study

Climate change affects soil microbial communities and their genetic exchange, and subsequently modifies the transfer of antibiotic resistance genes (ARGs) among bacteria. However, how elevated CO₂ impacts soil antibiotic resistome remains poorly characterized. Here, a free-air CO₂ enrichment system was used in the field to investigate the responses of ARGs profiles and bacterial communities to elevated CO₂ (+200 ppm) in soils amended with sulfadiazine (SDZ) at 0, 0.5 and 5 mg kg^-1. Results showed that SDZ exposure induced the co-occurrence of beta-lactamase and tetracycline resistance genes, and SDZ at 5 mg kg^-1 enhanced the abundance of aminoglycoside, sulfonamide and multidrug resistance genes. However, elevated CO₂ weakened the effects of SDZ at 0.5 mg kg^-1 following an observed reduction in the total abundance of ARGs and mobile genetic elements. Additionally, elevated CO₂ significantly decreased the abundance of vancomycin resistance genes and alleviated the stimulation of SDZ on the dissemination of aminoglycoside resistance genes. Correlation analysis and structural equation models revealed that elevated CO₂ could directly influence the spread of ARGs or impose indirect effects on ARGs by affecting soil properties and bacterial communities. Overall, our results furthered the knowledge of the dissemination risks of ARGs under future climate scenarios.

Dissolved Carbon Dioxide: The Lifespan of Staphylococcus aureus and Enterococcus faecalis in Bottled Carbonated Mineral Water

During the process of mineral water production, many possible contamination settings can influence the quality of bottled water. Microbial contamination can originate from different sources, for example, the ambient air, the bottles, the caps, and from the bottling machine itself. The aim of this study was to investigate the influence of three different carbon dioxide (CO2) concentrations (3.0 g/L, 5.5 g/L, and 7.0 g/L; 20 bottles each) in bottled mineral water on the bacterial growth of Staphylococcus aureus (S. aureus) and Enterococcus faecalis (Ent. faecalis). The examined mineral water was artificially contaminated before capping the bottles inside the factory. After a specific number of days, water samples were taken from freshly opened bottles and after filtration (100 mL), filters were placed on Columbia Agar with 5% Sheep blood to cultivate S. aureus and Slanetz and Bartley Agar to cultivate Ent. faecalis. The respective colony-forming units (CFU) were counted after incubation times ranging from 24 to 120 h. Colony-forming units of S. aureus were not detectable after the 16th and 27th day, whereas Ent. faecalis was not cultivable after the 5th and 13th day when stored inside the bottles. The investigation of the bottles that were stored open for a certain amount of time with CO2 bubbling out showed only single colonies for S. aureus after the 5th day and no CFUs for Ent. faecalis after the 17th day. A reduction in the two investigated bacterial strains during storage in carbonated mineral water bottles means that a proper standardized disinfection and cleaning procedure, according to valid hygiene standards of industrial bottling machines, cannot be replaced by carbonation.

Facile synthesis of lead-tin nanoparticles for electrocatalyzing carbon dioxide reduction to formate

A series of Pb-Sn catalysts were synthesized via facile chemical reduction for electrocatalytic CO₂ reduction (ECR). The optimized sample (Pb₇Sn₁) achieved 90.53% formate faradaic efficiency (FE) at a potential of -1.9 V vs. Ag/AgCl. Electrochemical and material evaluation reveals that its high performance can be attributed to the rich active sites exposed by the high specific surface area of the electrode. In addition, the synergy between Pb and Sn is also a strong contributor to the high selectivity of formate. This work provides some insights into the preparation of simple and efficient ECR catalysts.

Recovery of Pure Methanol from Humid Gas Using Mn-Co Prussian Blue Analogue

Conventional methanol recovery and purification processes are highly energy-intensive; processes using selective adsorbents that consume low energy are preferable. However, conventional adsorbents have low methanol selectivity under humid conditions. In this study, we develop a selective methanol adsorbent, manganese hexacyanocobaltate (MnHCC), which enables the efficient removal of methanol from waste gas and its subsequent reuse. MnHCC adsorbs 4.8 mmol-methanol/g-adsorbent at 25 °C in a humid gas containing 5000 ppmv of methanol, which is five times higher than the adsorption capacity of activated carbon (0.86 mmol/g). Although MnHCC exhibits the simultaneous adsorption of methanol and water, it has a higher adsorption enthalpy for methanol. Thus, pure methanol (95%) was recovered via thermal desorption at 150 °C after dehydration. The estimated energy of this recovery was 18.9 MJ/kg-methanol, approximately half that of existing mass production methods. MnHCC is reusable and stable even after 10 cyclic experiments. Consequently, MnHCC has the potential to contribute to both the recycling of methanol from waste gas and its low-cost purification.

Effects of natural non-volcanic CO2 leakage on soil microbial community composition and diversity

Geological carbon capture and storage (CCS) can reduce anthropogenic CO₂ emissions, but questions exist about impacts at the surface if CO₂ leaks from deep storage reservoirs. To examine potential impacts on soils, previous studies have investigated the geochemistry and microbiology of volcanic soils hosting high fluxes of CO₂ rich gas. This study builds on those previous investigations by considering impacts of CO₂ leakage at a non-volcanic site, where deep geogenic CO₂ leaks from a cracked well casing. At the site, we collected 26 soil cores adjacent to soil gas monitoring wells. Based on measured CO₂ fluxes, the soil samples fall into two groups 1) high CO₂ (flux = 304.6 ± 272.1 g m^-2 d^-1, conc. = 29.1 ± 34 %) and 2) low CO₂ (flux = 15.8 ± 6.1 g m^-2 d^-1, conc. = 0.8 ± 0.9 %). Soil pH was significantly lower (p < 0.05) in high flux group samples (4.6 ± 0.3) than the low flux ones (5.3 ± 0.7). Beta diversity calculations using 16S rRNA gene sequences and redundancy analysis (RDA) revealed clear clustering of microbial communities relative to CO₂ flux and significant correlations of community composition with pH and organic carbon content. In the high flux soils, abundant microbial groups included Acidobacteriota, Ktedonobacteria, and SC-I-84 in the phylum Proteobacteria, as well as Nitrososphaeria, a genus of ammonia oxidizing archaea. Compared to volcanic sites described previously, our non-volcanic site had slight differences in soil geochemical properties and gradual shifts in community compositions between CO₂ hotspots and background locations. Moreover, the elevated abundance of SC-I-84 has not been reported in studies of volcanic sites. This study improves our ability to predict potential environmental impacts of geological CCS by expanding the range of conditions over which existing CO₂ leakage has been observed.

Variable pH and subsequent change in pCO2 modulates the biofilm formation, synthesis of extracellular polymeric substances, and survivability of a marine bacterium Bacillus stercoris GST-03

Biofilm-forming bacteria adhere to the substrates and engage in the nutrient cycling process. However, environmental conditions may interrupt the biofilm formation ability, which ultimately may affect various biogeochemical cycles. The present study reports the effect of varying pH and subsequent change in pCO₂ on the survivability, biofilm formation, and synthesis of extracellular polymeric substances (EPS) of a biofilm-forming marine bacterium Bacillus stercoris GST-03 isolated from the Bhitarkanika mangrove ecosystem, Odisha, India. Understanding the pH-dependent alteration in EPS constituents, and associated functional groups of a marine bacterium will provide better insight into the adaptability of the bacteria in future ocean acidification scenarios. The strain was found to tolerate and form biofilm up to pH 4, with the maximum biofilm formation at pH 6. EPS yield and the synthesis of the key components of the EPS, including carbohydrate, protein, and lipid, were found maximum at pH 6. Changes in biofilm formation patterns and various topological parameters at varying pH/pCO₂ conditions were observed. A cellular chaining pattern was observed at pH 4, and maximum biofilm formation was obtained at pH 6 with biomass of 5.28582 ± 0.5372 μm³/μm² and thickness of 9.982 ± 1.5288 μm. Structural characterization of EPS showed changes in various functional groups of constituent macromolecules with varying pH. The amorphous nature of the EPS and the changes in linkages and associated functional groups (-R₂CHOR, -CH₃, and -CH₂) with pH variation was confirmed. EPS showed a two-step degradation with a maximum weight loss of 59.147% and thermal stability up to 480 °C at pH 6. The present work efficiently demonstrates the role of EPS in providing structural and functional stability to the biofilm in varying pH conditions. The findings will provide a better understanding of the adaptability of marine bacteria in the future effect of ocean acidification.

New opportunities in plant microbiome engineering for increasing agricultural sustainability under stressful conditions

Plant microbiome (or phytomicrobiome) engineering (PME) is an anticipated untapped alternative strategy that could be exploited for plant growth, health and productivity under different environmental conditions. It has been proven that the phytomicrobiome has crucial contributions to plant health, pathogen control and tolerance under drastic environmental (a)biotic constraints. Consistent with plant health and safety, in this article we address the fundamental role of plant microbiome and its insights in plant health and productivity. We also explore the potential of plant microbiome under environmental restrictions and the proposition of improving microbial functions that can be supportive for better plant growth and production. Understanding the crucial role of plant associated microbial communities, we propose how the associated microbial actions could be enhanced to improve plant growth-promoting mechanisms, with a particular emphasis on plant beneficial fungi. Additionally, we suggest the possible plant strategies to adapt to a harsh environment by manipulating plant microbiomes. However, our current understanding of the microbiome is still in its infancy, and the major perturbations, such as anthropocentric actions, are not fully understood. Therefore, this work highlights the importance of manipulating the beneficial plant microbiome to create more sustainable agriculture, particularly under different environmental stressors.

Metagenomic shifts in mucus, tissue and skeleton of the coral Balanophyllia europaea living along a natural CO2 gradient

Using the Mediterranean coral Balanophyllia europaea naturally growing along a pH gradient close to Panarea island (Italy) as a model, we explored the role of host-associated microbiomes in coral acclimatization to ocean acidification (OA). Coral samples were collected at three sites along the gradient, mimicking seawater conditions projected for 2100 under different IPCC (The Intergovernmental Panel on Climate Change) scenarios, and mucus, soft tissue and skeleton associated microbiomes were characterized by shotgun metagenomics. According to our findings, OA induced functional changes in the microbiomes genetic potential that could mitigate the sub-optimal environmental conditions at three levels: i. selection of bacteria genetically equipped with functions related to stress resistance; ii. shifts in microbial carbohydrate metabolism from energy production to maintenance of cell membranes and walls integrity; iii. gain of functions able to respond to variations in nitrogen needs at the holobiont level, such as genes devoted to organic nitrogen mobilization. We hence provided hypotheses about the functional role of the coral associated microbiome in favoring host acclimatation to OA, remarking on the importance of considering the crosstalk among all the components of the holobiont to unveil how and to what extent corals will maintain their functionality under forthcoming ocean conditions.

Effects of anthropogenic nitrogen additions and elevated CO2 on microbial community, carbon and nitrogen content in a replicated wetland

Anthropogenic deposition of nitrogen (N) and elevated CO₂ (_eaCO₂) are expected to increase continuously and rapidly in the near future and influence global carbon cycling. These parameters affect the ecosystem by regulating the microbial community and contribute to soil organic matter decomposition. The study was performed to understand the effects of N additions (4 and 6mgl^-1) and _eaCO₂ (700 ppm) on carbon (C)/nitrogen (N) content in the soil, microbial community, and plant biomass (Alternanthera philoxeroides species). The results showed that when the atmospheric CO₂ concentration was raised, the total organic carbon (TOC) in the soil statistically increased (P < 0.05) by 4% and 3% under low and high N additions respectively, while the inorganic carbon content also increased by 1% and 3% (P > 0.05) under the same conditions. The increase in the soil TOC content was a result of the movement of carbon from water to the soil due to the presence of vascular tissues of plants in the water. The redundancy analysis (RDA) results revealed that the presence of plant species was responsible for the carbon content increment in the soil. The plant biomass content increased by 30.96% (P = 0.081) and 31.36%, (P = 0.002) under low and high N addition respectively due to the increment in atmospheric CO₂. The nitrogen content in the plant species decreased (p > 0.05) by 8.62% and 6.25% at low and high N addition respectively when atmospheric CO₂ was raised. This suggests that soil microbes competed with the plants for inorganic nitrogen in the soil and the microbes used up the inorganic nitrogen before it got to the plants. The gram-positive bacteria and fungi population decreased under high N addition and _eaCO₂ while gram-negative bacteria increased, suggesting that N additions and _eaCO₂ affected the microbial function and correlated with the nitrogen reduction in the soil. The results from this study serve as a guide to researchers and stakeholders in making policies with regard to the constant increasing CO₂ concentration in the atmosphere.

Cysteine reduced the inhibition of CO2 on heterotrophic denitrification: Restoring redox balance, facilitating iron acquisition and carbon metabolism

The direct effect of CO₂ on denitrification has attracted great attention currently. Our previous studies have confirmed that CO₂ inhibited heterotrophic denitrification and caused high nitrite accumulation and nitrous oxide emission. Cysteine is a widely reported bio-accelerator; however, its effect on denitrification under CO₂ exposure remains unknown. In this paper, the effect of cysteine on heterotrophic denitrification and its mechanisms under CO₂ exposure were explored with the model denitrifier, Paracoccus denitrificans. We observed that total nitrogen removal increased from 17.9% to 90.4% as cysteine concentration increased from 0 to 50 μM, probably due to restoration of cell growth and viability. Further study showed that cysteine reduced the inhibition of CO₂ on denitrification due to multiple positive influences: (1) regulating glutathione metabolism to eliminate intracellular reactive nitrogen species (RNS), while reducing extracellular polymeric substances (EPS) levels and altering its composition, ultimately restoring cell membrane integrity (2) facilitating the transport and metabolism of carbon sources to increase NADH production, and (3) increasing intracellular iron and up-regulating the expression of key iron transporters genes (AfuA, AfuB, ExbB and TonB) to restore the transport and consumption of electron. This study suggests that cysteine can be added to recover heterotrophic denitrification performance after inhibition by elevated CO₂.

Effects of bioelectricity generation processes on methane emission and bacterial community in wetland and carbon fate analysis

Wetlands are an important carbon sink for greenhouse gases (GHGs), and embedding microbial fuel cell (MFC) into constructed wetland (CW) has become a new technology to control methane (CH4) emission. Rhizosphere anode CW-MFC was constructed by selecting rhizome-type wetland plants with strong hypoxia tolerance, which could provide photosynthetic organics as alternative fuel. Compared with non-planted system, CH4 emission flux and power output from the planted CW-MFC increased by approximately 0.48 ± 0.02 mg/(m2·h) and 1.07 W/m3, respectively. The CH4 emission flux of the CW-MFC operated under open-circuit condition was approximately 0.46 ± 0.02 mg/(m2·h) higher than that under closed-circuit condition. The results indicated that plants contributed to the CH4 emission from the CW-MFC, especially under open-circuit mode conditions. The CH4 emission from the CW-MFC was proportional to external resistance, and it increased by 0.67 ± 0.01 mg/(m2·h) when the external resistance was adjusted from 100 to 1000 Ω. High throughput sequencing further showed that there was a competitive relationship between electrogenic bacteria and methanogens. The flora abundance of electrogenic bacteria was high, while methanogens mainly consisted of Methanothrix, Methanobacterium and Methanolinea. The form and content of element C were analysed from solid phase, liquid phase and gas phase. It was found that a large amount of carbon source (TC = 254.70 mg/L) was consumed mostly through microbial migration and conversion, and carbon storage and GHGs emission accounted for 60.38% and 35.80%, respectively. In conclusion, carbon transformation in the CW-MFC can be properly regulated via competition of microorganisms driven by environmental factors, which provides a new direction and idea for the control of CH4 emission from wetlands.

Environmental Factors Affecting Feather Taphonomy

The exceptional preservation of feathers in the fossil record has led to a better understanding of both phylogeny and evolution. Here we address factors that may have contributed to the preservation of feathers in ancient organisms using experimental taphonomy. We show that the atmospheres of the Mesozoic, known to be elevated in both CO2 and with temperatures above present levels, may have contributed to the preservation of these soft tissues by facilitating rapid precipitation of hydroxy- or carbonate hydroxyapatite, thus outpacing natural degradative processes. Data also support that that microbial degradation was enhanced in elevated CO2, but mineral deposition was also enhanced, contributing to preservation by stabilizing the organic components of feathers.

Disentangling host-microbiota complexity through hologenomics

Research on animal-microbiota interactions has become a central topic in biological sciences because of its relevance to basic eco-evolutionary processes and applied questions in agriculture and health. However, animal hosts and their associated microbial communities are still seldom studied in a systemic fashion. Hologenomics, the integrated study of the genetic features of a eukaryotic host alongside that of its associated microbes, is becoming a feasible - yet still underexploited - approach that overcomes this limitation. Acknowledging the biological and genetic properties of both hosts and microbes, along with the advantages and disadvantages of implemented techniques, is essential for designing optimal studies that enable some of the major questions in biology to be addressed.

Effect of CO2 on biogeochemical reactions and microbial community composition in bioreactors with deep groundwater and basalt

Changes in subsurface microbiology following CO₂ injection have the potential to impact carbon trapping in CO₂ storage reservoirs. However, much remains to be learned about responses of natural microbial consortia to elevated CO₂ in basaltic systems. This study asks: how will microbes from deep (700 m) groundwater change along a gradient in CO₂ (0-20 psi) in batch reactor systems containing basalt chips and groundwater amended with lactate? Reactors incubated for 87 days at 23 °C. Results for reactors with low CO₂ (0 and 3 psi) differed considerably from those with high CO₂ (10 and 20 psi). In reactors with low CO₂, pH was >6.5 and lactate started to be used within 24 days. By 40 days, lactate was completely consumed and acetate increased to ~4 mM. As lactate was consumed, sulfate decreased from 0.16 to 0 mM after 40 days. In contrast, in reactors with high CO₂, pH was <6.5, lactate and sulfate concentrations varied little and acetate was not produced. Biogeochemical modeling and community analyses indicate that differences between reactors with low and high CO₂ reflect tolerances of reactor microbes to CO₂ exposure. Communities in the low CO₂ reactors carried out syntrophic lactate oxidation coupled with methanogenesis and sulfate reduction. Bacteroidota and Firmicutes became dominant phyla after 24 days and groups capable of sulfate reduction and methanogenesis were detected. In reactors with high CO₂, however, biogeochemical activity was insignificant, no groups capable of sulfate reducion or methanogenesis were observed, and the community became less diverse during the incubation. These findings show that the response of microbial consortia can vary sharply along a CO₂ gradient, creating significant differences in community composition and biogeochemistry, and that the timescale of basalt weathering is likely not rapid enough to prevent significant stress following a rapid increase in CO₂ abundance.

Directional Selection of Microbial Community Reduces Propionate Accumulation in Glycerol and Glucose Anaerobic Bioconversion Under Elevated pCO2

Volatile fatty acid accumulation is a sign of digester perturbation. Previous work showed the thermodynamic limitations of hydrogen and CO₂ in syntrophic propionate oxidation under elevated partial pressure of CO₂ (pCO₂). Here we study the effect of directional selection under increasing substrate load as a strategy to restructure the microbial community and induce cross-protection mechanisms to improve glucose and glycerol conversion performance under elevated pCO₂. After an adaptive laboratory evolution (ALE) process, viable cell density increased and predominant microbial groups were modified: an increase in Methanosaeta and syntrophic propionate oxidizing bacteria (SPOB) associated with the Smithella genus was found with glycerol as the substrate. A modest increase in SPOB along with a shift in the predominance of Methanobacterium toward Methanosaeta was observed with glucose as the substrate. The evolved inoculum showed affected diversity within archaeal spp. under 5 bar initial pCO₂; however, higher CH₄ yield resulted from enhanced propionate conversion linked to the community shifts and biomass adaptation during the ALE process. Moreover, the evolved inoculum attained increased cell viability with glucose and a marginal decrease with glycerol as the substrate. Results showed differences in terms of carbon flux distribution using the evolved inoculum under elevated pCO₂: glucose conversion resulted in a higher cell density and viability, whereas glycerol conversion led to higher propionate production whose enabled conversion reflected in increased CH₄ yield. Our results highlight that limited propionate conversion at elevated pCO₂ resulted from decreased cell viability and low abundance of syntrophic partners. This limitation can be mitigated by promoting alternative and more resilient SPOB and building up biomass adaptation to environmental conditions via directional selection of microbial community.

AMF Inoculation Can Enhance Yield of Transgenic Bt Maize and Its Control Efficiency Against Mythimna separata Especially Under Elevated CO2

The promotion and application of transgenic Bt crops provides an approach for the prevention and control of target lepidopteran pests and effectively relieves the environmental pressure caused by the massive usage of chemical pesticides in fields. However, studies have shown that Bt crops will face a new risk due to a decrease in exogenous toxin content under elevated carbon dioxide (CO2) concentration, thus negatively affecting the ecological sustainability of Bt crops. Arbuscular mycorrhizal fungi (AMF) are important beneficial microorganisms that can effectively improve the nutrient status of host plants and are expected to relieve the ecological risk of Bt crops under increasing CO2 due to global climate change. In this study, the Bt maize and its parental line of non-transgenic Bt maize were selected and inoculated with a species of AMF (Funneliformis caledonium, synonyms: Glomus caledonium), in order to study the secondary defensive chemicals and yield of maize, and to explore the effects of F. caledonium inoculation on the growth, development, and reproduction of the pest Mythimna separata fed on Bt maize and non-Bt maize under ambient carbon dioxide concentration (aCO2) and elevated carbon dioxide concentration (eCO2). The results showed that eCO2 increased the AM fungal colonization, maize yield, and foliar contents of jasmonic acid (JA) and salicylic acid (SA), but decreased foliar Bt toxin content and Bt gene expression in Bt maize leaves. F. caledonium inoculation increased maize yield, foliar JA, SA contents, Bt toxin contents, and Bt gene expression in Bt maize leaves, and positively improved the growth, development, reproduction, and food utilization of the M. separata fed on non-Bt maize. However, F. caledonium inoculation was unfavorable for the fitness of M. separata fed on Bt maize, and the effect was intensified when combined with eCO2. It is indicated that F. caledonium inoculation had adverse effects on the production of non-Bt maize due to the high potential risk of population occurrence of M. separata, while it was just the opposite for Bt maize. Therefore, this study confirms that the AMF can increase the yield and promote the expression levels of its endogenous (JA, SA) and exogenous (Bt toxin) secondary defense substances of Bt maize under eCO2, and finally can enhance the insect resistance capacity of Bt crops, which will help ensure the sustainable utilization and safety of Bt crops under climate change.

Altitudinal Zonation of Green Algae Biodiversity in the French Alps

Mountain environments are marked by an altitudinal zonation of habitat types. They are home to a multitude of terrestrial green algae, who have to cope with abiotic conditions specific to high elevation, e.g., high UV irradiance, alternating desiccation, rain and snow precipitations, extreme diurnal variations in temperature and chronic scarceness of nutrients. Even though photosynthetic green algae are primary producers colonizing open areas and potential markers of climate change, their overall biodiversity in the Alps has been poorly studied so far, in particular in soil, where algae have been shown to be key components of microbial communities. Here, we investigated whether the spatial distribution of green algae followed the altitudinal zonation of the Alps, based on the assumption that algae settle in their preferred habitats under the pressure of parameters correlated with elevation. We did so by focusing on selected representative elevational gradients at distant locations in the French Alps, where soil samples were collected at different depths. Soil was considered as either a potential natural habitat or temporary reservoir of algae. We showed that algal DNA represented a relatively low proportion of the overall eukaryotic diversity as measured by a universal Eukaryote marker. We designed two novel green algae metabarcoding markers to amplify the Chlorophyta phylum and its Chlorophyceae class, respectively. Using our newly developed markers, we showed that elevation was a strong correlate of species and genus level distribution. Altitudinal zonation was thus determined for about fifty species, with proposed accessions in reference databases. In particular, Planophila laetevirens and Bracteococcus ruber related species as well as the snow alga Sanguina genus were only found in soil starting at 2,000 m above sea level. Analysis of environmental and bioclimatic factors highlighted the importance of pH and nitrogen/carbon ratios in the vertical distribution in soil. Capacity to grow heterotrophically may determine the Trebouxiophyceae over Chlorophyceae ratio. The intensity of freezing events (freezing degree days), proved also determinant in Chlorophyceae distribution. Guidelines are discussed for future, more robust and precise analyses of environmental algal DNA in mountain ecosystems and address green algae species distribution and dynamics in response to environmental changes.

Effect of Ocean Acidification on Bacterial Metabolic Activity and Community Composition in Oligotrophic Oceans, Inferred From Short-Term Bioassays

Increasing anthropogenic CO₂ emissions in recent decades cause ocean acidification (OA), affecting carbon cycling in oceans by regulating eco-physiological processes of plankton. Heterotrophic bacteria play an important role in carbon cycling in oceans. However, the effect of OA on bacteria in oceans, especially in oligotrophic regions, was not well understood. In our study, the response of bacterial metabolic activity and community composition to OA was assessed by determining bacterial production, respiration, and community composition at the low-pCO₂ (400 ppm) and high-pCO₂ (800 ppm) treatments over the short term at two oligotrophic stations in the northern South China Sea. Bacterial production decreased significantly by 17.1–37.1 % in response to OA, since bacteria with high nucleic acid content preferentially were repressed by OA, which was less abundant under high-pCO₂ treatment. Correspondingly, shifts in bacterial community composition occurred in response to OA, with a high fraction of the small-sized bacteria and high bacterial species diversity in a high-pCO₂ scenario at K11. Bacterial respiration responded to OA differently at both stations, most likely attributed to different physiological responses of the bacterial community to OA. OA mitigated bacterial growth efficiency, and consequently, a larger fraction of DOC entering microbial loops was transferred to CO₂.

Elevated CO2 concentration modifies the effects of organic fertilizer substitution on rice yield and soil ARGs

Antibiotic resistance and rising CO2 levels are considered among the most significant challenges we will face in terms of global development over the following decades. However, the impact of elevated CO2 on soil antibiotic resistance has rarely been investigated. We used a free-air CO2 enrichment system to investigate the potential risks posed by applying mineral and organic fertilizers to paddy soil at current CO2 concentration (370 ppm) and future elevated CO2 (eCO2, 570 ppm predicted for 2100). Organic fertilizer substitution (substituting the mineral fertilizer by 50% N) alone increased the plant uptake and soil residue of sulfamethazine, and enriched sulfonamide resistance genes (sul1, sul2), tetracycline resistance genes (tetG, tetM) and class 1 integron (intl1). But it decreased the rice grain yield (by 7.6%). Comparatively, eCO2 decreased the sul2, tetG and intl1 gene abundances by organic fertilizer substitution, and meanwhile increased grain yield (by 8.4%). Proteobacteria and Nitrospirae were potential hosts of antibiotic resistance genes (ARGs). Horizontal gene transfer via intl1 may play an important role in ARGs spread under eCO2. Results indicated that future elevated CO2 concentration could modify the effects of organic fertilizer substitution on rice yield and soil ARGs, with unknown implications for future medicine and human health.

Effects of rising atmospheric CO2 levels on physiological response of cyanobacteria and cyanobacterial bloom development: A review

Increasing atmospheric CO₂ concentration negatively impacts aquatic ecosystems and may exacerbate the problem of undesirable cyanobacterial bloom development in freshwater ecosystems. Elevated levels of atmospheric CO₂ may increase the levels of dissolved CO₂ in freshwater systems, via air-water exchanges, enhancing primary production in the water and catchments. Although high CO₂ levels improve cyanobacterial growth and increase cyanobacterial biomass, the impacts on their internal physiological processes can be more complex. Here, we have reviewed previous studies to evaluate the physiological responses of cyanobacteria to high concentrations of CO₂. In response to high CO₂ concentrations, the pressures of inorganic carbon absorption are reduced, and carbon concentration mechanisms are downregulated, affecting the intracellular metabolic processes and competitiveness of the cyanobacteria. Nitrogen and phosphorus metabolism and light utilization are closely related to CO₂ assimilation, and these processes are likely to be affected by resource and energy reallocation when CO₂ levels are high. Additionally, the responses of diazotrophic and toxic cyanobacteria to elevated CO₂ levels were specifically reviewed. The responses of diazotrophic cyanobacteria to elevated CO₂ concentrations were found to be inconsistent, probably because of differences in other factors in experimental designs. Toxic cyanobacteria tended to be superior to non-toxic strains at low levels of CO₂; however, the specific effects of microcystin on the regulation require further investigation. Furthermore, the effects of increasing CO₂ levels on cyanobacterial competitiveness in phytoplankton communities and nutrient cycling in aquatic ecosystems were reviewed. High CO₂ concentrations may make cyanobacteria less competitive relative to other algal taxa; however, due to the complexity of natural systems and the specificity of algal species, the dominant positions of the cyanobacteria do not seems to be changed. To better understand cyanobacterial responses to elevated CO₂ levels and help control cyanobacterial bloom developments, this review has identified key areas for future research.

Dynamics of the Apple Fruit Microbiome after Harvest and Implications for Fruit Quality

The contribution of the apple microbiome to the production chain of apple was so far largely unknown. Here, we describe the apple fruit microbiome and influences on its composition by parameters such as storage season, storage duration, storage technology, apple variety, and plant protection schemes. A combined culturing and metabarcoding approach revealed significant differences in the abundance, composition, and diversity of the apple fruit microbiome. We showed that relatively few genera contribute a large portion of the microbiome on fruit and that the fruit microbiome changes during the storage season depending on the storage conditions. In addition, we show that the plant protection regime has an influence on the diversity of the fruit microbiome and on the dynamics of pathogenic fungal genera during the storage season. For the genus Neofabraea, the quantitative results from the metabarcoding approach were validated with real-time PCR. In conclusion, we identified key parameters determining the composition and temporal changes of the apple fruit microbiome, and the main abiotic driving factors of microbiome diversity on apple fruit were characterized.

Direct and Indirect Effects of Increased CO2 Partial Pressure on the Bioenergetics of Syntrophic Propionate and Butyrate Conversion

Simultaneous digestion and in situ biogas upgrading in high-pressure bioreactors will result in elevated CO₂ partial pressure (pCO₂). With the concomitant increase in dissolved CO₂, microbial conversion processes may be affected beyond the impact of increased acidity. Elevated pCO₂ was reported to affect the kinetics and thermodynamics of biochemical conversions because CO₂ is an intermediate and end-product of the digestion process and modifies the carbonate equilibrium. Our results showed that increasing pCO₂ from 0.3 to 8 bar in lab-scale batch reactors decreased the maximum substrate utilization rate (r_smax) for both syntrophic propionate and butyrate oxidation. These kinetic limitations are linked to an increased overall Gibbs free energy change (ΔG_Overall) and a potential biochemical energy redistribution among syntrophic partners, which showed interdependence with hydrogen partial pressure (pH₂). The bioenergetics analysis identified a moderate, direct impact of elevated pCO₂ on propionate oxidation and a pH-mediated effect on butyrate oxidation. These constraints, combined with physiological limitations on growth exerted by increased acidity and inhibition due to higher concentrations of undissociated volatile fatty acids, help to explain the observed phenomena. Overall, this investigation sheds light on the role of elevated pCO₂ in delicate biochemical syntrophic conversions by connecting kinetic, bioenergetic, and physiological effects.

Patterns in microbiome composition differ with ocean acidification in anatomic compartments of the Mediterranean coral Astroides calycularis living at CO2 vents

Coral microbiomes, the complex microbial communities associated with the different anatomic compartments of the coral, provide important functions for the host's survival, such as nutrient cycling at the host's surface, prevention of pathogens colonization, and promotion of nutrient uptake. Microbiomes are generally referred to as plastic entities, able to adapt their composition and functionality in response to environmental change, with a possible impact on coral acclimatization to phenomena related to climate change, such as ocean acidification. Ocean sites characterized by natural gradients of pCO₂ provide models for investigating the ability of marine organisms to acclimatize to decreasing seawater pH. Here we compared the microbiome of the temperate, shallow water, non-symbiotic solitary coral Astroides calycularis that naturally lives at a volcanic CO₂ vent in Ischia Island (Naples, Italy), with that of corals living in non-acidified sites at the same island. Bacterial DNA associated with the different anatomic compartments (mucus, tissue and skeleton) of A. calycularis was differentially extracted and a total of 68 samples were analyzed by 16S rRNA gene sequencing. In terms of phylogenetic composition, the microbiomes associated with the different coral anatomic compartments were different from each other and from the microbial communities of the surrounding seawater. Of all the anatomic compartments, the mucus-associated microbiome differed the most between the control and acidified sites. The differences detected in the microbial communities associated to the three anatomic compartments included a general increase in subdominant bacterial groups, some of which are known to be involved in different stages of the nitrogen cycle, such as potential nitrogen fixing bacteria and bacteria able to degrade organic nitrogen. Our data therefore suggests a potential increase of nitrogen fixation and recycling in A. calycularis living close to the CO₂ vent system.

CO2/HCO3 - Accelerates Iron Reduction through Phenolic Compounds

In an oxygenic environment, poorly soluble Fe³⁺ must be reduced to meet the cellular Fe²⁺ demand. This study demonstrates that elevated CO₂/HCO₃⁻ levels accelerate chemical Fe³⁺ reduction through phenolic compounds, thus increasing intracellular Fe²⁺ availability. A number of biological environments are characterized by the presence of phenolic compounds and elevated HCO₃⁻ levels and include soil habitats and the human body. Fe²⁺ availability is of particular interest in the latter, as it controls the infectiousness of pathogens. Since the effect postulated here is abiotic, it generally affects the Fe²⁺ distribution in nature.

Iron is a vital mineral for almost all living organisms and has a pivotal role in central metabolism. Despite its great abundance on earth, the accessibility for microorganisms is often limited, because poorly soluble ferric iron (Fe³⁺) is the predominant oxidation state in an aerobic environment. Hence, the reduction of Fe³⁺ is of essential importance to meet the cellular demand of ferrous iron (Fe²⁺) but might become detrimental as excessive amounts of intracellular Fe²⁺ tend to undergo the cytotoxic Fenton reaction in the presence of hydrogen peroxide. We demonstrate that the complex formation rate of Fe³⁺ and phenolic compounds like protocatechuic acid was increased by 46% in the presence of HCO₃⁻ and thus accelerated the subsequent redox reaction, yielding reduced Fe²⁺. Consequently, elevated CO₂/HCO₃⁻ levels increased the intracellular Fe²⁺ availability, which resulted in at least 50% higher biomass-specific fluorescence of a DtxR-based Corynebacterium glutamicum reporter strain, and stimulated growth. Since the increased Fe²⁺ availability was attributed to the interaction of HCO₃⁻ and chemical iron reduction, the abiotic effect postulated in this study is of general relevance in geochemical and biological environments.

High Nitrate or Ammonium Applications Alleviated Photosynthetic Decline of Phoebe bournei Seedlings under Elevated Carbon Dioxide

Phoebe bournei is a precioustimber species and is listed as a national secondary protection plant in China. However, seedlings show obvious photosynthetic declinewhen grown long-term under an elevated CO2 concentration (eCO2). The global CO2 concentration is predicted to reach 700 μmol·mol−1 by the end of this century; however, little is known about what causes the photosynthetic decline of P. bournei seedlings under eCO2 or whether this photosynthetic decline could be controlled by fertilization measures. To explore this problem, one-year-old P. bournei seedlings were grown in an open-top air chamber under either an ambient CO2 (aCO2) concentration (350 ± 70 μmol·mol−1) or an eCO2 concentration (700 ± 10 μmol·mol−1) from June 12th to September 8th and cultivated in soil treated with either moderate (0.8 g per seedling) or high applications (1.2 g per seedling) of nitrate or ammonium. Under eCO2, the net photosynthetic rate (Pn) of P. bournei seedlings treated with a moderate nitrate application was 27.0% lower than that of seedlings grown under an aCO2 concentration (p < 0.05), and photosynthetic declineappeared to be accompanied by a reduction of the electron transport rate (ETR), actual photochemical efficiency, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), rubisco activase (RCA) content, leaf thickness, and stomatal density. The Pn of seedlings treated with a high application of nitrate under eCO2 was 5.0% lower than that of seedlings grown under aCO2 (p > 0.05), and photosynthetic declineoccurred more slowly, accompanied by a significant increase in rubisco content, RCA content, and stomatal density. The Pn of P. bournei seedlings treated with either a moderate or a high application of ammonium and grown under eCO2 was not significantly differentto that of seedlings grown under aCO2—there was no photosynthetic decline—and the ETR, chlorophyll content, rubisco content, RCA content, and leaf thickness values were all increased. Increasing the application of nitrate or the supply of ammonium could slow down or prevent the photosynthetic declineof P. bournei seedlings under eCO2 by changing the leaf structure and photosynthetic physiological characteristics.

Fine Root Length of Maize Decreases in Response to Elevated CO2 Levels in Soil

To assess the environmental risks of carbon capture and storage (CCS) due to underground CO2 leakage, many studies have examined the impact on plant growth; however, the effect of leaked CO2 on root morphology remains poorly understood. This study simulated the effects of CO2 leakage from CCS on maize (Zea mays L.) root systems through pot experiments—one control treatment (no added CO2) and two elevated soil CO2 treatments (1000 g m−2 d−1 and 2000 g m−2 d−1). Compared with the control, root length, root surface area, and root volume were reduced by 44.73%, 34.14%, and 19.16%, respectively, in response to CO2 treatments with a flux of 2000 g m−2 d−1. Meanwhile, the fine root length in CO2 treatments with a flux of 1000 g m−2 d−1 and 2000 g m−2 d−1 were reduced by 29.44% and 45.88%, respectively, whereas no obvious difference in regard to coarse roots was found. Understanding changes in plant root morphology in this experiment, especially the decrease in the fine root length, are essential for explaining plant responses to CO2 leakage from CCS.

Effects of CO2 on the transformation of antibiotic resistance genes via increasing cell membrane channels

The increase of CO₂ concentration in the atmosphere, water and soil environment can lead to the changes in microbial activities. However, the transformation of antibiotic resistance genes has not been investigated in the presence of higher levels of CO₂. This study demonstrated that CO₂ facilitated the transformation of pUC19 plasmid, carrying ampicillin resistance genes, into Escherichia coli. Mechanism studies revealed that the type Ⅱ secretion system, type Ⅳ pilus and some other secretion systems were enhanced by CO₂, leading to DNA capture by pilus, larger cell pore sizes and more cell membrane channels. CO₂ also increased reactive oxygen species production, leading to SOS response and cell membrane damage. Besides, changes in intracellular Fe²⁺ and Mg²⁺ concentrations induced by CO₂ caused greater damage to the cell membrane and enhanced secretion systems, respectively. Overall, increased CO₂ provided more cell membrane channels for plasmid uptake and led to higher transformation efficiencies. The potential risk of a natural factor on the transformation of ARGs was first studied in this study, which helps us understand the fate of ARGs in ecosystems. As the carbon emission will continue to grow and enhance the enrichment of CO₂ in water and soil, the findings revealed a more severe public health issue under the background of carbon emission and CO₂ leakage.

CO2 promotes the conjugative transfer of multiresistance genes by facilitating cellular contact and plasmid transfer

The dissemination of antibiotic resistance genes (ARGs), especially via the plasmid-mediated conjugation, is becoming a pervasive global health threat. This study reported that this issue can be worse by CO₂, as increased CO₂ was found to facilitate the conjugative transfer of ARGs carried on plasmid RP4 by 2.4-9.0 and 1.3-3.8 fold within and across genera, respectively. Mechanistic studies revealed that CO₂ benefitted the cell-to-cell contact by increasing cell surface hydrophobicity and decreasing cell surface charge, both of which resulted in the reduced intercellular repulsion. Besides, the transcriptional expression of genes responsible for global regulator (korA, korB and trbA), plasmid transfer and replication system (trfAp), and mating pair formation system (traF and traG) were all influenced by CO₂, facilitating the mobilization and channel transfer of plasmid. Furthermore, the presence of CO₂ induced the release of intracellular Ca²⁺ and increased the transmembrane potential of recipients, which contributed to the increased proton motive force (PMF), providing more power for DNA uptake. This is the first study addressing the potential risks of increased CO₂ on the propagation of ARGs, which provides a new insight into the concerns of anthropogenic CO₂ emissions and CO₂ storage.