Fluorescein Diacetate Hydrolysis Activity Research Articles

Asynchronous application of modified biochar and exogenous fungus Scedosporium sp. ZYY for enhanced degradation of oil-contaminated intertidal mudflat sediment.

Intertidal mudflats are susceptible to oil pollution due to their proximity to discharges from industries, accidental spills from marine shipping activities, oil drilling, pipeline seepages, and river outflows. The experimental study was divided into two periods. In the first period, microcosm trials were carried out to examine the effect of chemically modified biochar on biological hydrocarbon removal from sediments. The modified biochar's surface area increased from 2.544 to 25.378 m2/g, followed by a corresponding increase in the hydrogen-carbon and oxygen-carbon ratio, indicating improved stability and polarity. In the second period, the effect of exogenous fungus - Scedoporium sp. ZYY on the bacterial community structure was examined in relation to total petroleum hydrocarbon (TPH) removal. The maximum TPH removal efficiency of 82.4% was achieved in treatments with the modified biochar, followed by a corresponding increase in Fluorescein diacetate hydrolysis activity. Furthermore, high-throughput 16S RNA gene sequencing employed to identify changes in the bacterial community of the original sediment and treatments before and after fungal inoculation revealed Proteobacteria as the dominant phylum. In addition, it was observed that Scedoporium sp. ZYY promoted the proliferation of specific TPH-degraders, particularly, Hyphomonas adhaerens which accounted for 77% of the total degrading populations in treatments where TPH removal was highest. Findings in this study provide valuable insights into the effect of modified biochar and the fundamental role of exogenous fungus towards the effective degradation of oil-contaminated intertidal mudflat sediments.

Formaldehyde Removal by Expanded Clay Pellets and Biofilm in Hydroponics of a Green Wall System

Air pollution with formaldehyde (FA) has been an emerging concern over recent years. This study was aimed at evaluating the contribution of green wall system-derived expanded clay pellets (ECP) and biofilms to FA removal in liquid phase. The effects of four plant species on this process were compared. An inhibition of the fluorescein diacetate hydrolysis activity of biofilm-derived microorganisms was detected during the exposure to FA in both air and liquid phases, and this effect was plant-species-specific. Liquid chromatography with a UV detector was applied for the quantification of FA. The FA removal activity of ECP in the liquid phase was 76.5 mg ECP−1 after a 24 h incubation in the presence of 100 mg/L FA, while the removal activity of the biofilm differed depending on the plant species used, with the highest values detected in the set with Mentha aquatica, i.e., 59.2 mg ECP−1. The overall FA removal from the liquid phase during 24 h varied in the range from 63% to 82% with the initial FA concentration of 100 mg/L. Differences in biofilm formation upon ECP enrichment were detected by using confocal laser scanning microscopy. These results contribute to the understanding of air biofiltration mechanisms in hydroponic systems.

Characterization of Biofilm Formation and Bacterial Resistance to Benzalkonium Chloride under Contrasting Cultivation Conditions

Benzalkonium chloride (BAC) is one of the most commonly used quaternary ammonium compounds in the pharmaceutical, cosmetic, and food industries. The aim of our study was to compare the physiological responses of Escherichia coli MSCL 332, Pseudomonas putida MCCL 650, and Staphylococcus epidermidis MSCL 333 on 50 mg/L BAC in rich and poor medium (100% and 5% tryptone soya broth (TSB)) in the temperature range from 8 °C to 37 °C, under static and shaking conditions. A high-throughput, 96-well microplate method was used to compare a broad range of cultivation conditions. The effect of BAC on growth, biofilm formation activity, and dehydrogenase and fluorescein diacetate hydrolysis activity was evaluated. Addition of BAC to 100% TSB inhibited biofilm formation at 37 °C by 2.4, 1.8, and 1.6 times for E. coli, P. putida, and S. epidermidis, respectively. In turn, BAC stimulated biofilm formation in E. coli in 5% TSB at 37 °C and 100% TSB at 8 °C, i.e., 1.4 and 1.3 times, respectively. Statistical optimization of broth composition with emphasis on biofilm formation and further testing under experimental conditions was performed with P. putida.

Biochar application significantly increases soil organic carbon under conservation tillage: an 11-year field experiment

Biochar application and conservation tillage are significant for long-term organic carbon (OC) sequestration in soil and enhancing crop yields, however, their effects on native soil organic carbon (native SOC) without biochar carbon sequestration in situ remain largely unknown. Here, an 11-year field experiment was carried out to examine different biochar application rates (0, 30, 60, and 90 Mg ha−1) on native SOC pools (native labile SOC pool I and II, and native recalcitrant SOC) and microbial activities in calcareous soil across an entire winter wheat–maize rotation. The proportions of C3 and C4-derived native SOC mineralization were quantified using soil basal respiration (SBR) combined with 13C natural isotope abundance measurements. The results showed that 39–51% of the biochar remained in the top 30 cm after 11 years. Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC [native labile SOC pool I and II, dissolved organic carbon (DOC), and microbial biomass carbon (MBC)]. Biochar application tended to increase the indicators of microbial activities associated with SOC degradation, such as SBR, fluorescein diacetate hydrolysis activity, and metabolic quotient (qCO2). Meanwhile, higher biochar application rates (B60 and B90) significantly increased the C4-derived CO2 proportion of the SBR and enhanced C4-derived native SOC mineralization. The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0–15 cm layer, however, there were no significant differences at 15–30 cm. Soil depth also significantly increased native labile SOC pool I and II contents and decreased qCO2. In conclusion, the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC, and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions, which has important implications for long-term agricultural soil organic carbon sequestration.Graphical

Eight-year impacts of conservation agriculture on soil quality, carbon storage, and carbon emission footprint

The conventional method of intensive tillage alters the soil environment, destroys soil aggregates, depletes soil organic carbon (SOC), emits more carbon, requires higher energy, alters microbial activities and ultimately degrades the soil health. These ill-effects of conventional tillage can be severe in rainfed soils with poor workability such as Vertisols of Central India. To minimize these negative effects of conventional tillage (CT), conservation agricultural (CA) practices such as reduced tillage (RT) and no-till (NT) with crop residue retentions are advocated as sustainable practices that can improve the soil health. Four cropping systems [soybean+pigeonpea (CS1); soybean–wheat (CS2); maize–chickpea (CS3); maize+pigeonpea (CS4)] were established as sub-plots under CT, RT and NT management. Soil samples were collected at 0–10 cm, 10–20 cm and 20–30 cm depths. The effects of 8 years of continuous use of CA were evaluated on soil physical, chemical and biological properties in Vertisol of Central India. After that, 20 key soil properties were subjected to calculating soil quality indices (SQI) in each tillage systems. Results indicated that mean weight diameter (MWD) and water-stable aggregates (WSA) were significantly higher (P < 0.05) in NT (1.57 mm and 79.4%) and RT (1.05 mm and 76.2%) than CT (0.71 mm and 63.8%) at 0–10 cm depth, respectively. The soil under NT had the highest SOC concentration (1.12%) followed by that under RT (1.02%), and the least was found in CT (0.91%) at 0–10 cm depth. The proportion of large macro-aggregates (LM) was the highest under NT than CT (P < 0.05) whereas that of micro-aggregates was highest under CT. The aggregate associated organic C (AOC) tended to decrease with the decrease of aggregate size. Soil dehydrogenase activity, fluorescein diacetate hydrolysis activity, β-glucosidase activity and easily extractable glomalin content were significantly higher under NT than CT (P < 0.05). The soil quality index was significantly highest in NT, followed by RT and CT at all soil depths. CA based practices favoured carbon storage, lowered carbon emission, foot print and soil quality compared to conventional farming. Therefore, under Vertisols, 8 years of CA practices likely to improve several soil quality indicators, allowing a positive trend for soil preservation.

Microbiological properties of soils are sensitive to changes provided by organic cultivation of banana ‘BRS Princesa’ in the semi-arid region

Soil microbiota has a key role in the dynamics of natural and agro-ecosystems and is sensitive to changes in these environments. This study evaluated changes in the microbiological properties of soils under an organic production system of banana ‘BRS Princesa’ (Musa spp.). The experimental design consisted of completely randomized blocks, with four replications. Treatments consisted of 1) soil cover with green manure and agricultural gypsum at a dose of 2,820 kg ha−1, 2) soil cover with green manure without gypsum application, 3) soil cover with weeds and agricultural gypsum at a dose of 2,820 kg ha−1, 4) soil cover with spontaneous plants without gypsum application, and two controls: 5) soil under native Caatinga and 6) soil under regenerating forest (capoeira). The evaluated properties were β-glucosidase, arylsulfatase, acid phosphatase, fluorescein diacetate hydrolysis activities (FDA), carbon and phosphorus contents in microbial biomass, basal soil respiration, microbial and metabolic quotients, and arbuscular mycorrhizal fungi spore density. Soil samples were collected from the 0–0.20m depth layer in two seasons. No parameter could distinguish the treatments. Spontaneous plants provided conditions equivalent to those under green manure. Agricultural gypsum application also did not influence the microbial biomass and microbiota activity, in the analyzed soil depth. However, β-glucosidase and arylsulfatase activities, the carbon content in microbial biomass, and metabolic and microbial quotients were sensitive to land-use changes and could distinguish areas under organic cultivation from those under native vegetation. Therefore, these properties can be considered good indicators for monitoring the quality of these soils. Furthermore, microbial communities of soils under organic cultivation responded with arylsulfatase activity corresponding to that found in soils under regenerating forest, which may indicate that organic management tends to provide the microbiota with a condition similar to that found under situations that are little disturbing to edaphic living.

Fluorescein diacetate hydrolytic activity as a sensitive tool to quantify nitrogen/sulfur gene content in urban river sediments in China.

The relative abundance of functional genes used to quantify the abundance of functional genes in communities is controversial. Quantitative PCR (qPCR) technology offers a powerful tool for quantifying functional gene abundance. However, humic substances can inhibit qPCR in sediment/soil samples. Therefore, finding a convenient and effective quantitative analysis method for sediment/soil samples is necessary. The functional genes and physicochemical properties in sediments with different-level pollutions were analyzed in this study. Correlations between physicochemical properties and the relative abundance of functional genes were used to test whether relative abundance in gene prediction quantifies the abundance of functional genes. The abundance of functional genes could be corrected by multiplying the fluorescein diacetate (FDA) hydrolytic rates by the relative abundance of functional genes since the FDA assay has been widely used as a rapid and sensitive method for quantifying microbial activity in sediments. Redundancy analysis showed significant interrelations between the functional genes and the physicochemical properties of sediments. The relative abundance of functional genes is unreliable for quantifying the abundance of functional genes because of the weak correlation (R < 0.5, P < 0.05) between different pollutants and the relative abundance of functional genes. However, a significant positive correlation between concentrations of different pollutants and the activities of associated enzymes was obtained (R > 0.933, P < 0.05), which revealed that the abundance of functional genes could be reliably quantified by the relative abundance and FDA hydrolytic rate. This study proposed an alternative method besides qPCR to quantify the absolute abundance of functional genes, which overcomes the problem of humic interference in the quantitative analysis of sediment/soil samples.

Development of novel kinetic model based on microbiome and biochar for in-situ remediation of total petroleum hydrocarbons (TPHs) contaminated soil

A novel kinetic model has been developed to explain the degradation of total petroleum hydrocarbons. Microbiome engineered biochar amendment may result in a synergistic impact on degradation of total petroleum hydrocarbons (TPHs). Therefore, the present study analyzed the potential of hydrocarbon-degrading bacteria A designated as Aeromonas hydrophila YL17 and B as Shewanella putrefaciens Pdp11 morphological characterized as rod shaped, anaerobic and gram-negative immobilized on biochar, and the degradation efficiency was measured by gravimetric analysis and gas chromatography-mass spectrometry (GC-MS). Whole genome sequencing of both strains revealed the existence of genes responsible for hydrocarbon degradation. In 60 days remediation setup, the treatment consisting of immobilization of both strains on biochar proved more efficient with less half-life and better biodegradation potentials compared to biochar without strains for decreasing the content of TPHs and n-alkanes (C12–C18). Enzymatic content and microbiological respiration showed that biochar acted as a soil fertilizer and carbon reservoir and enhanced microbial activities. The removal efficiency of hydrocarbons was found to be a maximum of 67% in soil samples treated with biochar immobilized with both strains (A + B), followed by biochar immobilized with strain B 34%, biochar immobilized with strain A 29% and with biochar 24%, respectively. A 39%, 36%, and 41% increase was observed in fluorescein diacetate (FDA) hydrolysis, polyphenol oxidase and dehydrogenase activities in immobilized biochar with both strains as compared to control and individual treatment of biochar and strains. An increase of 35% was observed in the respiration rate with the immobilization of both strains on biochar. While a maximum colony forming unit (CFU/g) was found 9.25 with immobilization of both strains on biochar at 40 days of remediation. The degradation efficiency was due to synergistic effect of both biochar and bacteria based amendment on the soil enzymatic activity and microbial respiration.

The Effects of Atrazine, Diuron, Fluazifop-P-butyl, Haloxyfop-P-methyl, and Pendimethalin on Soil Microbial Activity and Diversity

Understanding the impacts of herbicides on soil microbial communities is important, as these organisms mediate a wide range of ecosystem services. Here, we investigated whether the diversity and function of soil microbial communities were significantly influenced by one-off applications of atrazine, diuron, fluazifop-P-butyl, haloxyfop-P-methyl and pendimethalin as pure compounds at their recommended doses over multiple time points (1, 3, 7, 14, 30 and 60 days). Phylogenetic marker gene sequencing revealed that none of the herbicides influenced the numbers of bacterial and archaeal taxa or the evenness of their abundances. Similarly, none of the herbicides influenced the composition of bacterial and archaeal communities, except for diuron, fluazifop-P-methyl and pendimethalin, which were associated with larger relative abundances of a small number of OTUs on day 30 only. Functionally, none of the herbicides significantly influenced fluorescein diacetate hydrolysis (FDA) and beta-glucosidase activities or the induced respiratory responses of soil microbial communities to a range of substrates. These data indicate that the active herbicide ingredients tested may have minimal non-target effects when applied once at their recommended dose. Given their frequent use, it is important to next consider whether these herbicides have more pronounced effects at higher doses and application frequencies.

A method for soil quality assessment in the metropolitan greenery: A comprehensive view of ecosystem services and soil functions

The soils in urban greenery considerably contribute to providing ecosystem services. However, appropriate tools to assess and manage urban soil quality under consideration of ecosystem services and soil functions are unavailable. In this study, we aimed to 1) provide detailed instructions for assessing a novel urban soil quality index (uSQI) and 2) propose the application of uSQI in urban soil quality management. The uSQI is the average of the scores for six soil functions. Each soil function was estimated by several measurable indicators that have high correlation with soil functions. The measurable soil indicators are bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay + silt content, inorganic nitrogen concentration, fluorescein diacetate hydrolytic activity, cation exchange capacity, concentrations of potentially toxic elements, and pH. The uSQI effectively identified the soils with low quality due to disturbances. The radar chart of six soil functions comprising uSQI could suggest the direction of management for urban stakeholders.•The uSQI represents soil functions necessary for urban greenery to provide ecosystem services.•The uSQI successfully identified the soils with low quality due to disturbances.

Utilization of Biochar for Eliminating Residual Pharmaceuticals from Wastewater Used in Agricultural Irrigation: Application to Ryegrass

Biochar is known to be a promising material for the treatment of contaminants in wastewater and soil. In this research, wastewater samples collected at the tertiary stage from a WWTP located in the North Bohemia region of Czechia and containing 20 pharmaceutical contaminants were treated with the same biochar (wood and maize cob feedstocks, pyrolysis temperature of 470 °C), but of different doses (0.1 g L−1, 0.25 g L−1, 0.5 g L−1). In this case study, we aimed to verify the impacts of biochar application and/or concentration on the sorption of pharmaceuticals in water. The treated water was later used for irrigating planted (ryegrass taken as the plant model) and unplanted agricultural soils in a pot experiment. Soils and ryegrass samples were examined again for potential pharmaceutical existence, and the soil microbial activities were determined through fluorescein diacetate hydrolytic activities (FDHA). Results showed that most pharmaceuticals concentrations were significantly, but not totally, reduced from the wastewater upon biochar addition. Contaminants such as 3-hydroxycarbamazepine and metoprolol were entirely removed from the wastewater after 0.25 g L−1, whilst bezafibrate did not decline even at 0.5 g L−1. Moreover, the concentrations of pharmaceuticals in ryegrass biomass and soils were dominantly below detection limits or at very low doses. Finally, there were no significant differences in the microbial activities of the soils. This implicates that biochar could be approached as a good substrate for eliminating pharmaceuticals from wastewaters used for agricultural irrigation; however, more similar studies need to be carried out.

Ascomycetous isolates promote soil biological and nutritional attributes in corn and soybeans in sandy and clayey soils

Biological inputs are environmentally friendly agriculture practices for conserving natural resources in the face of the world's increasing demand for food, fiber and biofuels. The effects of beneficial non-mycorrhizal fungi on soil and plants are multifactorial and mostly unknown. In this regard, we aimed to assess the effects of five ascomycetous isolates, namely Beauveria bassiana, Metarhizium anisopliae, Pochonia chlamydosporia, Purpureocillium lilacinum and Trichoderma asperellum, on the biology and fertility of sandy and clayey soils from the Cerrado biome under corn and soybeans grown in a greenhouse. The fungal treatments produced some differences in soil microbial biomass, enzyme activity and fertility and consistently promoted arbuscular mycorrhiza (AM) colonization in both soils under corn and soybeans. Fungal applications significantly increased colonization efficacy of arbuscular mycorrhiza fungi (AMF) by 28%–72% in corn and from 57% to 105% in soybeans, relative to a control. A combination of principal component analysis and correlation analysis showed that applications of any of the five ascomycetous fungi increased AM colonization, and shoot concentrations of P, K, S and Cu in the corn assays, and shoot concentrations of K and phosphatase and fluorescein diacetate hydrolysis activity in the soil of the soybean assays. Thus, the application of fungal isolates, with the stimulation of root colonization, nutrient absorption and soil biological activity, may have effects on soil function and quality in the medium and long term. These findings can contribute to the development and adoption of more sustainable agricultural practices.

Diversification of Rice-Based Cropping System for Improving System Productivity and Soil Health in Eastern Gangetic Plains of India

Mono-cropping in the farming system decline in farm profit, climate change, and food insecurity are some of the major concerns that lead to unsustainability in the agricultural production system in the Eastern Gangetic Plains. A study was conducted for three years from June 2019 to June 2022 at Dr. Rajendra Prasad Central Agricultural University, Pusa, Bihar, India, to assess the profitable and best rice-based cropping system through crop diversification for sustainable agriculture. Ten different cropping sequences were exploited using randomised block design and replicated thrice, with the system productivity ranging from 8.70 to 24.95 t ha−1 under the different cropping sequences. The system productivity was increased by 187% and profitability by 299.52% in the maize − Cole crops − sesame cropping system over the rice − wheat cropping system. A diversified cropping system with black gram − maize + vegetable pea − sesbania possessed significantly more soil organic carbon (0.49%), bacterial population (47.85 × 106 cfu/g soil), azotobacter population (42.96 × 104 cfu/g soil), phosphate solubilising bacteria (20.72 × 106 cfu/g soil), dehydrogenase activity (4.39 µg TPF/g/h), fluorescein diacetate hydrolytic activity (17.28 µg fluorescein/g/h) and acid phosphatase activity (451.46 µg pNP/g/h), as well as urease activity (47.21 µg NH4+/g/h), relative to the rice–wheat cropping system. Therefore, the adoption of vegetables and legumes as diversified crops are viable options for enhancing productivity, profitability and soil health in the EGPs.

Soil Enzyme Activity Behavior after Urea Nitrogen Application.

Understanding how fertilizer application (particularly N, the most used chemical fertilizer worldwide) interacts with soil microbes is important for the development of best management practices that target improved microbial activity to enhance sustainable food production. This study was conducted to determine whether urea N rate and time of application to maize (Zea mays) influenced soil enzyme activity. Enzyme activity was determined by monitoring fluorescein diacetate (FDA) hydrolysis, ß-glucosidase, acid-phosphomonoesterase, and arylsulfatase activities. Experiments were conducted from 2014 through 2016 to compare single (fall or spring applications) and split applications of N at varying N rates under irrigation (Becker) and rainfed conditions (Lamberton and Waseca) in MN, USA. Nitrogen rates varied by location and were based on University of Minnesota guidelines. Soil samples were collected seven times each season. Nitrogen application split into two applications increased FDA activity by 10% compared with fall and spring applied N at Waseca. Fall or spring N application decreased arylsulfatase activity by 19% at Becker and by between 13% and 16% at Lamberton. ß-Glucosidase and acid-phosphomonoesterase activities were unaffected by N application. Sampling time and year had the greatest impact on enzyme activity, but the results varied by location. A negative linear relationship occurred between FDA and ß-glucosidase activity at all three sites. In summary, urea N application had small effects on enzyme activity at the sites studied, suggesting that some form of organic N could be more important than the ammonium provided by urea.

Biochar Additions Alter the Abundance of P-Cycling-Related Bacteria in the Rhizosphere Soil of Portulaca oleracea L. under Salt Stress

Numerous reports confirm a positive impact of biochar amendments on soil enzyme activities, nutrient cycles, and, finally, plant growth and development. However, reports explaining the process behind such diverse observations are scarce. The aim of the present study was (1) to evaluate the effect of biochar on the growth of purslane (Portulaca oleracea L.) and nutrients; (2) to determine the response of rhizosphere enzyme activities linked to soil phosphorus cycling after bio-char amendment under non–saline and saline soil conditions. Furthermore, we investigate whether adding biochar to soil alters the abundance of P-cycling-related bacteria. Two rates of biochar (2% and 4%) were applied in pot experiments. Biochar addition of 2% significantly increased plant growth under non-saline and saline soil conditions by 21% and 40%, respectively. Moreover, applying biochar increased soil microbial activity as observed by fluorescein diacetate (FDA) hydrolase activity, as well as phosphomonoesterase activities, and the numbers of colony-forming units (CFU) of P-mobilizing bacteria. Soil amended with 2% biochar concentration increased total soil nitrogen (Nt), phosphorus (P), and total carbon (Ct) concentrations by 18%, 15%, and 90% under non-saline soil conditions and by 29%, 16%, and 90% in saline soil compared the control, respectively. The soil FDA hydrolytic activity and phosphatase strongly correlate with soil Ct, Nt, and P contents. The rhizosphere soil collected after biochar amendment showed a higher abundance of tricalcium phosphate-solubilizing bacteria than the control soil without biochar. Overall, this study demonstrated that 2% maize-derived biochar positively affects halophyte plant growth and thus could be considered for potential use in the reclamation of degraded saline soil.

Comparison of the interest of four types of organic mulches to reclaim degraded areas (Part 2): Microbial activities and abiotic factors

A field experimentation conducted in a wooded degraded area and contaminated by metals, aimed to compare the effectiveness of four types of organic mulches: Ramial Chipped Wood (RCW), crushed Miscanthus, dead leaves and wheat straw regarding the ecosystem's functionality. We likewise tested the plastic sheeting regularly used to forestall weed development in green spaces as well as a negative control which consisted in soil without mulch. For this purpose, microbial activities (Fluorescein diacetate hydrolyzing activity, Laccases and Urease) and abiotic factors (moisture, temperature, metal concentrations, C/N rate and organic carbon content) were monitored in the organo-mineral horizon of soil surface for 13 months. The degradation rate of the different mulches has also been taken into account. The results revealed that the organic mulching technique could provide habitats for many organisms and micro-organisms of soil with favorable microclimate and/or alternative food source (fungi) in peri-urban and planted area, not only in agricultural areas. In the current context of climate change, the mulching technique could limit desiccation stress in terrestrial ecosystems by offering more favorable temperature conditions (≈2 °C lower on average than a surface soil without mulching) and this from the very first cm of the soil. In view of the indicators followed (high temperatures, low microbial activity and low biodiversity), the plastic sheeting present the most hostile reception conditions to the soil organisms. Every one of the organic mulch examined has its advantages and limitations and the decision of the kind of mulch to be utilized requires thinking as indicated by the fixed goals. However, Miscanthus seemed to be the most suitable compromise obtaining the higher score according to our evaluation criteria: it degraded slowly, it has low metal content and fungi were very active which is favorable to functionality of the ecosystem and to the soil organisms.

Biochar-based microbial agent reduces U and Cd accumulation in vegetables and improves rhizosphere microecology

Microbial remediation of heavy metals in soil has been widely studied. However, bioremediation efficiency is limited in practical applications because of nutritional deficiency, low efficiency, and competition with indigenous microorganisms. Herein, we prepared a biochar-based microbial agent (BMA) by immobilizing the microbial agent (MA, containing Bacillus subtilis, Bacillus cereus, and Citrobacter sp.) on biochar for the remediation of U and Cd in soil. The results showed that BMA increased soil organic matter, cation exchange capacity, and fluorescein diacetate hydrolysis activity and dehydrogenase activity by 58.7%, 38.2%, 42.9%, and 51.1%. The availability of U and Cd were significantly decreased by 67.4% and 54.2% in BMA amended soil, thereby reducing their accumulation in vegetables. BMA greatly promoted vegetable growth. Additionally, BMA significantly altered the structure and function of rhizosphere soil microbial communities. Coincidently, more abundant ecologically beneficial bacteria like Nitrospira, Nitrosomonas, Lysobacter, and Bacillus were observed, whereas plant pathogenic fungi like Fusarium and Alternaria reduced in BMA amended soil. The network analysis revealed that BMA amendment increased the tightness and complexity of microbial communities. Importantly, the compatibility of niches and microbial species within co-occurrence network was enhanced after BMA addition. These findings provide a promising strategy for suppressing heavy metal accumulation in vegetables and promoting their growth.

Ecosystem services-based soil quality index tailored to the metropolitan environment for soil assessment and management

The soils in urban greenery provide essential ecosystem services. However, only a few studies have assessed urban soil quality based on a comprehensive view of ecosystem services and soil multi-functionality. In this study, we suggest an urban soil quality index (uSQI) to evaluate soil status in various spatial types of urban greenery. Our objectives are 1) to develop an uSQI incorporating a range of urban soil ecosystem services in metropolitan environments and 2) to test the efficacy of the developed uSQI by applying it to nine different sites. To fully consider ecosystem services provided by the urban soil, a DPSC (drivers and pressures, state, and changes) framework was constructed. Drivers and pressures are influencing factors that continuously alter the state of the urban greenery, eventually leading to changes in ecosystem services and soil functions. The six soil functions considered were physical stability and support, water storage and infiltration, habitat provision, organic matter stabilization, nutrient supply and retention, and pollutant immobilization and decomposition. These functions were measured using ten soil indicators which can be quantified: bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay+silt content, fluorescein diacetate hydrolytic activity, cation exchange capacity, inorganic nitrogen concentration, pH, and concentrations of potentially toxic elements. The uSQI was calculated as the arithmetic mean of the scores of the six soil functions, obtained through the fuzzy logic functions. The uSQI successfully identified the low soil quality sites among nine urban greeneries with different spatial types (point, line, and polygon). In addition, we could examine the degraded soil function of each site and suggest a management guideline using our uSQI. Our novel index can help urban stakeholders evaluate and monitor the soil quality of urban greenery.

Bioaugmentation of Enterobacter cloacae AKS7 causes an enhanced degradation of low-density polyethylene (LDPE) in soil: a promising approach for the sustainable management of LDPE waste.

Enterobacter cloacae AKS7 was previously reported to degrade UV-treated low-density polyethylene (LDPE) more efficiently than UV-untreated LDPE. However, the degradation of LDPE by Enterobacter cloacae AKS7 at the LDPE-contaminated soil remained unaddressed. To address this issue, soil microcosms were prepared in which an equal amount of either UV-treated or UV-untreated LDPE was added. Then, the microcosms were either augmented with AKS7 or left non-augmented. We observed that the bioaugmented microcosms exhibited approximately twofold greater polymer degradation than non-bioaugmented microcosms. To investigate the underlying cause, we found that the abundance of LDPE-degrading organisms got increased by approximately fivefold in bioaugmented microcosms than non-bioaugmented microcosms. The microbial biomass carbon and nitrogen content got enhanced by approximately twofold in bioaugmented microcosms as contrasted to non-bioaugmented microcosms. Furthermore, the bioaugmented microcosms showed almost twofold increase in the level of dehydrogenase and fluorescein diacetate (FDA) hydrolyzing activity than the non-bioaugmented microcosms. To add on, Shannon-diversity index and Gini coefficient were determined in each microcosm to measure the microbial richness and evenness, respectively, using the results of carbon source utilization pattern of BiOLOG ECO plate. The bioaugmented microcosms exhibited ~ 30% higher functional richness and ~ 30% enhanced functional evenness than the non-bioaugmented microcosms indicating the formation of an enriched ecosystem that could offer various functions including polymer degradation. Taken together, the results suggested that Enterobacter cloacae AKS7 could be used as a promising bioaugmenting agent for the sustainable degradation of LDPE waste at a contaminated site.

Improved degradation of petroleum hydrocarbons by co-culture of fungi and biosurfactant-producing bacteria

Microbial remediation has proven to be an effective technique for the cleanup of crude-oil contaminated sites. However, limited information exists on the dynamics involved in defined co-cultures of biosurfactant-producing bacteria and fungi in bioremediation processes. In this study, a fungal strain (Scedosporium sp. ZYY) capable of degrading petroleum hydrocarbons was isolated and co-cultured with biosurfactant-producing bacteria (Acinetobacter sp. Y2) to investigate their combined effect on crude-oil degradation. Results showed that the surface tension of the co-culture decreased from 63.12 to 47.58 mN m−1, indicating the secretion of biosurfactants in the culture. Meanwhile, the degradation rate of total petroleum hydrocarbon increased from 23.36% to 58.61% at the end of the 7-d incubation period. In addition, gas chromatography – mass spectrometry analysis showed a significant (P < 0.05) degradation from 3789.27 mg/L to 940.33 mg/L for n-alkanes and 1667.33 μg/L to 661.5 μg/L for polycyclic aromatic hydrocarbons. Moreover, RT-qPCR results revealed the high expression of alkB and CYP52 genes by Acinetobacter sp. Y2 and Scedosporium sp. ZYY respectively in the co-culture, which corelated positively (P < 0.01) with n-alkane removal. Finally, microbial growth assay which corresponded with Fluorescein diacetate hydrolysis activity, highlighted the synergistic behavior of both strains in tackling the crude oil. Findings in this study suggest that the combination of fungal strain and biosurfactant-producing bacteria effectively enhances the degradation of petroleum hydrocarbons, which could shed new light on the improvement of bioremediation strategies.