Search Results (93)

Oilfield-produced water contains petroleum hydrocarbons, suspended solids, salts and other refractory constituents that challenge conventional biological treatment. Suspended activated sludge systems can suffer from microbial washout, poor retention of slow-growing functional microorganisms and unstable settling, whereas conventional ceramic biofilm packings often provide limited surface area and slow biofilm start-up. Here, a modified polyurethane biosponge was evaluated as a three-dimensional carrier for immobilized microbial growth during the treatment of real oilfield produced water. Three parallel systems were compared under identical start-up and operating conditions: suspended activated sludge without a carrier, Raschig ring-packed biofilm reactors, and the biosponge-based composite system. The biosponge system developed a visible and stable biofilm within 7 days, whereas the Raschig ring system showed only sparse and uneven biofilm coverage. During an 8-day treatment test with real produced water, the biosponge system decreased the COD concentration from 800 to 13 mg L⁻¹ in the aerobic zone and from 1500 to 16 mg L⁻¹ in the anoxic zone, corresponding to removal efficiencies of 98.4% and 98.9%, respectively. In contrast, the activated sludge and Raschig ring systems showed much lower COD removal under the same test period. 16S rRNA gene sequencing indicated that the biosponge selectively enriched petroleum hydrocarbon-associated genera, including Sphingopyxis, Achromobacter and Gordonia, in the aerobic zone, together with fermentative and anaerobic genera such as Dysgonomonas and Clostridium in the anoxic zone. PICRUSt2-based functional prediction further suggested the coexistence of aerobic hydrocarbon degradation, chemoheterotrophy, fermentation and nitrate respiration potentials. These results indicate that the modified polyurethane biosponge provides a favorable carrier for rapid biofilm establishment and short-term removal of organic pollutants from oilfield produced water. Further long-term operation, adsorption controls and direct functional gene validation are recommended to confirm the engineering robustness and degradation mechanisms of the system. The system also avoided sludge bulking and maintained short-term stability, providing a promising low-cost strategy for treating high-salinity refractory oilfield produced water. Full article

The dynamics of methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂) in groundwater have rarely been investigated. As dissolved gases they may be transported to distant sites and, hence, to the atmosphere. Crumps Cave (CC) is located on a perched aquifer in south-central Kentucky. Water was sampled at a waterfall within the cave located 15 m below the surface, at two adjacent surface wells 15 m and 50 m deep, providing samples from the epikarst and regional aquifer, respectively. Dissolved gases and geochemistry parameters were analyzed for seasonal changes across three years of weekly monitoring (2015–2017) using Kruskal–Wallis H tests and Bonferroni-corrected pairwise comparisons. Dissolved CO₂ concentrations are mainly controlled by percolation through the epikarst, influenced by soil respiration, and vary with rainfall and seasonal temperature fluctuations. CH₄ showed a site-dependent pattern: concentrations were significantly elevated in warm seasons at the shallow and deep wells, where anaerobic conditions and agriculturally derived organic matter promote methanogenesis; no seasonal variation was detected at the cave site, where oxic conditions limit CH₄ year-round. N₂O was significantly elevated in cold seasons at all three sites, driven by cold-season denitrification of agriculturally derived nitrates. N₂O did not differ between sites, indicating seasonal temperature-driven denitrification as the primary control rather than site hydrology, with cold-season denitrification of agriculturally derived nitrates from fertilizer application. Indirect gas emissions are characteristic of karst systems and may be transported or stored in aquifers through complex interactions of groundwater recharge, microbial activity, and seasonal land-use variability. Full article

Replacing peat in green roof substrates with sustainable alternatives while maintaining plant performance and ecosystem services remains a critical challenge. We studied biochar-substrate interactions across four commercial green roof formulations (based on the type of organic component) in a greenhouse experiment: pure vermicompost, vermicompost + fen peat, fen peat, and mixed fen/high-moor peat. Substrates were amended with straw biochar, pine bark biochar, or left unamended (5% v/v, n = 4 replicates) and planted with a grass seed mixture mimicking early green roof establishment. Plant growth, nutrient contents (nitrate and phosphate contents), and microbial indicators (microbial biomass carbon (MBC), qCO₂, and enzyme activities) were measured 30 days after the experiment began. Straw biochar in vermicompost boosted nitrate (90.8 mg kg⁻¹) and root N (3.1%) compared to the control, while pine bark biochar in mixed peat released phosphate (+375%) and maximized MBC (874 µg g⁻¹). Biochar intensified substrate effects, suppressing CO₂ in peat through liming effects (pH from 4.6 to 6.5–7.1) but priming respiration in vermicompost via labile C supply. PCA explained 63% of the variance, with nitrate, plant N, and microbial parameters driving substrate separation. These short-term greenhouse results demonstrate critical biochar-substrate specificity for green roof substrate development, emphasizing formulation-specific matching over universal biochar application. Full article

Salmonella enterica serovar Infantis, an important zoonotic pathogen with increasing prevalence in the poultry industry, often persists despite rigorous disinfection. This study characterized the transcriptomic response of the multidrug-resistant Salmonella Infantis strain SE016, isolated from a poultry plant, to osmotic stress, a condition frequently induced by the use of industrial disinfectants. Phenotypic assays demonstrated that stress induced by 15% sucrose simulated osmotic stress, producing a drastic reduction in flagellar motility and a significant increase in biofilm formation in SE016, compared with a susceptible control strain. RNA-seq analysis indicated that SE016 undergoes coordinated transcriptional changes consistent with altered metabolic activity under osmotic stress. Key mechanisms include metabolic braking through repression of tricarboxylic acid (TCA) cycle genes (icd, mdh) and induction of anaerobic nitrate respiration (narGHI, narZWV) as an energy contingency. Furthermore, SE016 showed increased expression of genes involved in osmoprotectant uptake, including the proU transport system and endogenous trehalose synthesis (ostAB) while repressing proline degradation (putA). Furthermore, robust biofilm formation was observed despite repression of the master regulator csgD. This was mediated by the CsgD-independent induction of the diguanylate cyclase adrA, activating cellulose synthesis (bcs). These results suggest that pathways associated with the OmpR/EnvZ two-component system may contribute to energy balance and persistence-related phenotypes under industrial-like stress conditions. Full article

Wildfires are increasing in frequency and severity across Mediterranean ecosystems. However, the immediate soil biogeochemical responses that determine shortly post-fire resilience remain poorly understood. This study assessed how contrasting fire severity levels influence soil physicochemical, nutrient, and biochemical properties in ecologically relevant vegetation microsites—beneath Quercus ilex L. canopy, Stipa tenacissima L. tussock, and open interspaces—in a Mediterranean holm oak woodland in central Spain. Soils were sampled early after a wildfire and analyzed for organic matter, nutrient pools, water repellency, microbial respiration, nitrogen mineralization, and enzyme activities. Fire severity was the dominant driver of immediate post-fire soil responses. High-severity fire reduced soil organic matter, cation exchange capacity, total C and N, nitrate, microbial respiration, and all measured enzyme activities, with the most pronounced losses occurring beneath Q. ilex canopy. In contrast, ammonium, labile phosphorus, pH and soil water repellency increased under high severity, mainly in this microsite. Low-severity fire generally preserved biological functioning, with values comparable to unburned soils. Microsite identity modulated the magnitude of fire effects, with soils beneath Q. ilex cover microsite showing the greatest sensitivity, and open interspaces the least. The microsite × severity interaction detected for key nutrients and biochemical variables suggests that high-severity fire might destroy the microsite-specific fertility islands that constitute the functional core of Mediterranean woodland soils. These findings should be considered in management strategies prioritizing their monitoring and protection. Full article

Salmonella in gut habitats have traditionally been thought to conserve energy for growth via fermentation. However, recent reports indicate that ingested Salmonella can stimulate host-derived nitrate accumulation in the mucosal microenvironment, thereby enabling growth through nitrate respiration. Sodium tungstate is an effective treatment that inhibits the growth of certain nitrate-respiring bacteria, including Escherichia coli, Paracoccus and Proteus, when cultured under gut simulating conditions or within the gut of experimentally treated mice. This inhibitory effect is hypothesized to occur by inactivation of molybdenum-containing enzymes required for nitrate metabolism. Information is lacking on whether tungstate can inhibit the growth of Salmonella, particularly in the presence of culturable gut microbiota. Therefore, the objectives of this study were to evaluate the effects of sodium tungstate on Salmonella during pure culture or when cultured with freshly collected bovine rumen microbiota and to assess its impact on fermentation as well as nitrate and nitrite metabolism within the rumen microbial cultures. Our results indicate that 50 mM sodium tungstate treatment, whether alone or in combination with 5 mM nitrate, markedly increased the growth of Salmonella serovars Newport, Dublin and Typhimurium during pure culture. Moreover, during in vitro incubation, increased growth of experimentally inoculated S. Newport as well as wildtype E. coli and lactic acid bacteria was observed with ruminal microbiota treated with 100 mM tungstate when compared to non-tungstate-treated controls. Effects of tungstate on nitrate and nitrite metabolism were as expected during pure and mixed culture. When cultured with reduced tungsten rather than tungstate, the latter being bound to four oxygen atoms, an inhibitory effect on the growth of S. Newport was observed and effects on nitrate and nitrite metabolism were consistent with those observed with tungstate. These results suggest that, under conditions used in the present experiments, tungstate may have served as a source of oxygen for respiration above that achieved with nitrate alone. While this hypothesis has yet to be proven, it is supported by an adverse effect of tungstate, whether alone or in combination with 5 mM nitrate, on methane and volatile fatty acid production by the ruminal microbiota when compared to untreated or nitrate-only-treated microbiota. Full article

Biogeochemical processes, including the oxygen cycle, were investigated in Lake Baikal during the spring thermal bar using a coupled numerical model that takes into account the intraday variability of atmospheric parameters and contains the following variables: nitrate, ammonium, phosphate, oxygen, chlorophyll a, phytoplankton, zooplankton, and small and large detritus. Nitrification, photosynthesis, remineralization, and respiration processes describe the biochemical dynamics of oxygen in the model. As a study area, the deep-water cross-section of Lake Baikal, Boldakov River–Maloye More Strait, was considered using meteorological data for June 2024 at the lake surface. Numerical results show that the thermal bar can contribute to the transport of dissolved oxygen and phyto- and zooplankton to the deeper layers of the lake. Full article

The Qinghai–Tibet Plateau is undergoing rapid warming and humidification, with altered precipitation regimes increasingly affecting soil nitrogen cycling and N₂O emissions. Denitrification—a key nitrogen transformation pathway—is particularly sensitive to these hydrological changes. Here, we investigated the response of nirK-type denitrifying microbial communities to altered precipitation in an alpine wetland on the northern shore of Qinghai Lake. Using a long-term precipitation manipulation platform with five gradients (ambient, ±25%, and ±50%), we integrated high-throughput sequencing with bioinformatics to systematically assess community shifts. Short-term precipitation treatments did not significantly alter alpha diversity, but markedly restructured community composition. Extreme wetting (+50%) increased within-group heterogeneity. At the phylum level, Proteobacteria remained dominant across all treatments, whereas extreme drought (−50%) suppressed Planctomycetes. At the genus level, Ochrobactrum was enriched under reduced precipitation, while Rhodopseudomonas increased under increased precipitation. Functional predictions indicated that reduced precipitation enhanced nitrogen fixation potential, whereas increased precipitation favored nitrate respiration. Soil pH and carbon fractions were the key environmental filters driving community variation. Ecological process analysis revealed that community assembly was entirely governed by deterministic processes, specifically variable selection. Together, these findings elucidate how precipitation shifts reconfigure the structure and functional potential of denitrifying microbial communities in alpine wetlands, primarily via changes in soil pH and moisture under variable selection. This work provides critical insights into microbial regulation of the nitrogen cycle on the Tibetan Plateau under ongoing climate change. Full article

Soil respiration (Rs) plays an important role in the carbon (C) dynamics of terrestrial ecosystems and is strongly regulated by nitrogen (N) inputs. While the impact of N fertilization on Rs has been widely documented in conventional farmland ecosystems, its patterns and influencing factors in perennial tea plantation systems are still poorly understood. In the study, we conducted a 15-year field experiment in a representative tea plantation to investigate the effects of different N rates (0, 112.5, 225, and 450 kg N ha⁻¹ yr⁻¹) on Rs. Compared to the control (N0), soil pH decreased significantly (p < 0.05) by 6.07%, 11.82%, and 16.12% under N112.5, N225, and N450, respectively. Concurrently, cation exchange capacity (CEC), ammonium (NH₄⁺-N), nitrate (NO₃⁻-N), and available phosphorus (AP) increased with increasing N rates, whereas available potassium (AK) decreased. Soil microbial biomass carbon (MBC) initially increased and then decreased with increasing N rates, while dissolved organic carbon (DOC) content increased consistently. The Rs rate exhibited a distinct seasonal pattern with a single peak in August. The annual mean Rs rates were 2.79, 3.15, 4.06, and 3.85 μmol·m⁻²·s⁻¹ for the N0, N112.5, N225, and N450 treatments, respectively. Soil temperature explained 55.41% to 61.08% of the variation in Rs rates across N treatments, and a composite model incorporating both soil temperature and moisture further improved the prediction of Rs dynamics. Cumulative soil CO₂ emissions (CCEs) over the study period ranged from 10,427 to 14,221 kg CO₂-C ha⁻¹ across treatments and were significantly negatively correlated with soil pH, and positively correlated with DOC, MBC, and NO₃⁻-N content. A non-linear relationship between N application rate and CCEs was observed, highlighting the complexity of optimizing N management for balancing productivity and climate mitigation in tea plantation systems. These findings provide a theoretical basis for developing rational N fertilization strategies and improving the predictive capacity of C cycle models in agroecosystems. Full article

As a sustainable biological approach for polluted water management, algal-bacterial systems are increasingly being explored because of their synergistic physiological and metabolic interactions. This study established an algal-bacterial consortium composed of Escherichia coli and Chlorella vulgaris to evaluate treatment performance of simulated livestock wastewater and elucidate the associated synergistic mechanisms. Compared with the pure algal system, the algal-bacterial consortium significantly enhanced algal growth, increasing chlorophyll concentration by 52.8% and achieving a maximum algal density of 16.46 × 10⁶ cells mL⁻¹. The biochemical composition of the biomass was improved, with total lipids, neutral lipids, and proteins increasing by 18.9%, 26.8%, and 16.4%, respectively. Pollutant removal efficiencies were markedly enhanced, as total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), and nitrite nitrogen (NO₂⁻-N) increased by 19.1%, 9.5%, 26.0%, 13.5%, 17.2%, and 13.8%, respectively, compared with the monoculture. Mechanistic analysis was supported by monitoring chlorophyll content, algal density, dissolved oxygen, bacterial density, total inorganic carbon, and pH, which collectively suggested the involvement of a synergistic carbon–oxygen exchange process: oxygen produced by microalgae supported bacterial respiration, while carbon dioxide generated by bacteria enhanced algal photosynthesis and growth. Furthermore, the presence of E. coli markedly stimulated nitrogen metabolism-associated enzymatic functions in C. vulgaris, which may have facilitated their mutual growth. Overall, this study provides a conceptual and experimental basis for algal-bacterial consortium design for treating livestock wastewater, thereby enhancing pollutant removal efficiency and algal biomass accumulation, highlighting its potential as a sustainable and resource-efficient wastewater treatment strategy. Full article

Cupriavidus necator is a well-studied microorganism with potential application in bioregenerative life support systems for single-cell protein and bioplastic production. Most studies have been carried out in autotrophy or heterotrophy, requiring O₂ as the final electron acceptor. In the context of inhabited missions, access to O₂ will primarily be limited to the crew. In this study, we investigated the capacity of C. necator to carry out nitrate respiration as a strategy to limit oxygen supply to the cultures by providing nitrate from another compartment of the Bioregenerative Life Support System (BLSS). Batch bioreactor experiments were carried out to determine the best conditions for nitrate utilization in terms of pH and aeration. Continuous cultures were then performed under two carbon sources (glucose vs. acetic acid) and two substrate limitations (nitrate vs. carbon). The optimal conditions were found to be pH 7.5 under anaerobiosis. They were applied in chemostats, where three steady-states were obtained at a low dilution rate. In all cases, the biomass consisted of a mixture of protein (from 29 ± 1% Cell Dry Weight (CDW) to 39 ± 2% CDW) and polyhydroxybutyrate (from 45 ± 2% CDW to 57 ± 3% CDW), which was found to be a key component for nitrate respiration metabolism. Microaerobic conditions were also tested in batch culture, reporting for the first time aerobic nitrate respiration in C. necator. Under these conditions, growth parameters improved during the nitrate phase; however, the specific growth rate during the nitrite phase was lower than that observed under strictly anaerobic conditions. Full article

The application of plasma-activated water and biostimulants offers a sustainable approach to supporting plant growth under reduced-nutrient conditions by supplying bioavailable nitrogen. This study investigated the growth and postharvest performance of hydroponically grown cos lettuce (Lactuca sativa L.) supplied with three Hoagland-based nutrient treatments: half-strength solution prepared with tap water (HS), half-strength solution with plasma-activated water (HS+PAW), and half-strength solution with plasma-activated water containing 1 mL L⁻¹ milk protein hydrolysate (HS+PAW+MPH). Plants treated with PAW, particularly those in the HS+PAW+MPH, exhibited increases in growth, biomass accumulation, and mineral composition, with reduced nitrate content compared to controls. At harvest, lettuce under HS+PAW+MPH exhibited nearly double fresh yield and enhanced dry matter, protein, lipid, phenolic, and flavonoid profiles as well as increased antioxidant capacity, indicating improved nitrogen utilization and nutritional quality under reduced nutrient input. Postharvest quality was evaluated by packing samples in polypropylene bags and storing them at 10 ± 1 °C and 95–98% relative humidity for 21 days. The HS+PAW+MPH treatment substantially suppressed respiration and production of ethylene, limited weight loss and color change, and better preserved pigments, bioactive compounds, and antioxidant stability compared to HS and HS+PAW, indicating HS+PAW+MPH as a sustainable nutrient management approach for hydroponic systems. Full article

As a fast-growing timber tree species with a wide cultivation area, poplar is facing the problem of declining economic benefits under long-term monoculture. Intercropping provides an effective solution. Using Illumina Miseq sequencing, we analyzed soil microbiomes under four patterns: poplar monoculture, and intercropping with amorpha fruticosa, black locust, or cassia seed. The results showed that the Alpha diversity index of intercropping area was significantly higher than that of single planting poplar area under intercropping and monoculture conditions. In the intercropping area, the highest species richness was the intercropping of poplar and black locust, and the lowest was the intercropping of poplar and amorpha fruticosa. The dominant microorganisms in the intercropping mode were Vicinamibacterales, and the fungi were Alternaia and Enterocarpus. In the single planting poplar area, a large number of bacteria gathered in the soil were Dongia and Alphaproteobacteria, and fungi were Fusarium and Mortierella. Functional prediction results showed that the biosynthetic function of ansamycin was the highest in the bacterial community. In the intercropping area, the functional abundance of methanol oxidation, sulfate respiration, sulfate compound respiration, nitrate denitrification, nitrite denitrification, and nitrous oxide denitrification was higher than that in the single planting poplar area. On the contrary, the abundance of methanotrophy function is lower than that of single planting poplar area. In the fungal community, the functional abundance of animal pathogens and the animal pathogen–dung saprotroph–endophyte–plant saprotroph–soil saprotroph–wood saprotroph group in the monoculture poplar area was higher than that in the three intercropping areas. In summary, the intercropping mode of poplar is better than the monoculture mode, and the species richness is the highest when poplar and black locust are intercropped. Therefore, the intercropping pattern of poplar and other tree species improved microbial community. This provides some theoretical guidance for the subsequent solution of continuous cropping obstacles in poplar. Full article

Glycyrrhiza uralensis is a highly valued medicinal species worldwide. However, a paradox arises in its cultivation in that high nitrogen fertilization boosts yield at the expense of root quality, a problem linked to nitrogen’s regulation of tricarboxylic acid (TCA) cycle-driven respiration. It remains unclear how different nitrogen forms coordinate respiratory and primary metabolism. We examined the regulatory mechanisms of nitrate (NO₃⁻) versus ammonium (NH₄⁺) on these processes in cultivated G. uralensis by supplying seedlings with varying concentrations of K¹⁵NO₃ or (¹⁵NH₄)₂SO₄ in a modified Hoagland solution (HNS). Using non-invasive micro-test technology (NMT) and ¹⁵N tracing, we found that G. uralensis employs distinct nitrogen acquisition strategies: sustaining uptake at optimal NH₄⁺ and low-to-moderate NO₃⁻, while declining uptake under high NO₃⁻. These strategies drove form-specific differences in the activity of key nitrogen assimilation enzymes, nitrate reductase and nitrite reductase (NR/NiR), as well as glutamine synthetase and glutamate synthase (GS/GOGAT), and subsequent glutamate and glutamine accumulation. Ammonium nutrition enhanced primary ammonia assimilation and gamma-aminobutyric acid (GABA) metabolism, leading to greater glutamate and endogenous GABA levels. In contrast, nitrate nutrition preferentially stimulated the TCA cycle, resulting in higher accumulation of α-ketoglutarate (KGA) and succinate. The concomitant increase in GABA catabolism supported this nitrogen-responsive respiratory metabolism, acting as a compensatory mechanism to maintain KGA homeostasis. Our findings inform nitrogen form strategies for G. uralensis cultivation. Full article

Brucella are intracellular pathogens that use flexible respiratory strategies to adapt to oxygen-limited conditions. The nor operon encodes components of nitric oxide reductase (Nor), which are involved in denitrification and nitric oxide (NO) detoxification. In this study, the role of the norD gene in nitrate-dependent respiration, resistance to nitrosative stress, and intracellular persistence in B. abortus was evaluated. A non-polar ΔnorD mutant was generated in strain 2308W and its survival and growth under aerobic and anaerobic conditions, with and without nitrate, as well as its tolerance to NO donors, were analyzed. In addition, its behavior was evaluated in activated and non-activated murine RAW264.7 and human THP-1 macrophages and in a murine infection model. The deletion of norD did not affect viability or growth under any of the conditions tested, nor did it alter resistance to NO in vitro or within activated macrophages. Furthermore, the mutant showed virulence comparable to the wild-type strain in BALB/c mice. These results contrast with those described for other Brucella species, suggesting that norD is dispensable in B. abortus 2308W virulence and that in the Brucella genus, there are species-specific differences in the role of the nor operon during infection. Full article