Effects of different fertilizers on residues of oxytetracycline and microbial activity in soil

Interactions between Sugarcane Leaf Return and Fertilizer Reduction in Soil Bacterial Network in Southern China Red Soil

Microbes may play an important role in the sugarcane leaf degradation and nutrient conversion process. Soil bacterial communities are more or less involved in material transformation and nutrient turnover. In order to make better use of the vast sugarcane leaf straw resources and reduce the overuse of chemical fertilizers in the subtropical red soil region of Guangxi, a pot experiment, with three sugarcane leaf return (SLR) amounts [full SLR (FS), 120 g/pot; half SLR (HS), 60 g/pot; and no SLR (NS)] and three fertilizer reduction (FR) levels [full fertilizer (FF), 4.50 g N/pot, 3.00 g P2O5/pot, and 4.50 g K2O/pot; half fertilizer (HF), 2.25 g N/pot, 1.50 g P2O5/pot, and 2.25 g K2O/pot; and no fertilizer (NF)], was conducted to assess the interactions of different SLR amounts and chemical FR levels in the soil bacterial network and the relationship between the soil properties and bacterial network by using Illumina Miseq high-throughput sequencing technology. According to the results of the soil bacterial community compositions and diversity, the soil bacterial network was changed during maize growth. SLR exerted a stronger effect on soil bacterial function than FR. Returning the sugarcane leaf to the field increased the diversity of the soil bacteria network. The bacterial communities were consistently dominated by Acidobacteria, Actinobacteria, and Bacteroidetes across all treatments, among which Actinobacteria was the most abundant bacteria type by almost 50% at the phylum level. The analysis results of the experimental factor on maize growth showed that the effect of SLR was lower than that of FR; however, this was opposite in the soil bacterial community structure and diversity. The soil bacterial network was significantly correlated with the soil total K, available N and organic matter contents, and EC. The soil bacteria community showed different responses to SLR and FR, and the FF in combination with FS partly increased the complexity of the soil bacteria network, which can further benefit crop production and soil health in the red soil region.

Toxicity and bioremediation of the lead: a critical review

Lead is a naturally occurring, bluish-gray metal that is found in small quantities in the earth's crust. The existing literature demonstrates that non-biodegradable character and continuous use results in accumulation of lead concentration in the environment and causes various ill effects such as neurotoxicity, change in psychological and behavioral development of different organisms. Nowadays the most effective technique in the revival of the environment is bioremediation and it is environmentally friendly and cost-effective. Bacterial strains such as Oceanobacillus profundus and Lactobacillus acidophilus ATCC4356 have the ability to reduce lead 97% and 73.9%, respectively. Similarly some species of algae and fungal strains also showed lead removal efficiency as 74% (spirulina), 97.1% (Chlorella kessleri), 95.5% (Penicillium janthinillum) and 86% (Aspergillus flavus). Biodegradation of lead by various microbes would be the most efficient and sustainable approach. This review focuses on toxicity, fate of lead in the environment and its microbial degradation.

The single and combined effects of sulfamethazine and cadmium on soil nitrification and ammonia-oxidizing microorganisms

The coexistence of antibiotics and heavy metals in soil has attracted increasing attention due to their negative effects on microorganisms. However, how antibiotics and heavy metals affect functional microorganisms related to nitrogen cycle remains unclear. The goals of this work were to explore the individual and combined effects of sulfamethazine (SMT) and cadmium (Cd), selected as target pollutants in soil, on potential nitrification rates (PNR) and ammonia oxidizers (ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB)) structure and diversity by 56-day cultivation experiment. Results showed that PNR in Cd- or SMT-treated soil decreased at the beginning of the experiment and then increased over time. PNR was significantly correlated with AOA and AOB-amoA relative abundance (P < 0.01). SMT addition (10 and 100 mg kg^-1) significantly improved AOA activity by 13.93% and 17.93%, respectively, and had no effect on AOB at day 1. Conversely, Cd at 10 mg kg^-1 significantly inhibited AOA and AOB by 34.34% and 37.39%, respectively. Moreover, the relative abundance of AOA and AOB in combined SMT and Cd addition clearly higher relative to single Cd at 1 day. The single and combined Cd and SMT increased and reduced the community richness of AOA and AOB, respectively, but reduced the diversity of both after 56 days. Cd and SMT treatments significantly changed the relative abundance of AOA phylum levels and AOB genus levels in the soil. It was mainly manifested in reducing the relative abundance of AOA Thaumarchaeota, and increasing the relative abundance of AOB Nitrosospira. Besides, AOB Nitrosospira was more tolerant to the compound addition of both than single application.

Legacy Effects of Phytoremediation on Plant-Associated Prokaryotic Communities in Remediated Subarctic Soil Historically Contaminated with Petroleum Hydrocarbons

Phytoremediation of petroleum hydrocarbons in subarctic regions relies on the successful establishment of plants that stimulate petroleum-degrading microorganisms, which can be challenging due to the extreme climate, limited nutrients, and difficulties in maintaining sites in remote locations. A long-term phytoremediation experiment was initiated in Alaska in 1995 with the introduction of grasses and/or fertilizer to petroleum hydrocarbon (PHC)-contaminated soils that were subsequently left unmanaged. In 2011, the PHC concentrations were below detection limits in all soils tested and the originally planted grasses had been replaced by volunteer plant species that had colonized the site. Here, we sought to understand how the original treatments influenced the structure of prokaryotic communities associated with plant species that colonized the soils and to assess the interactions between the rhizospheric and endophytic communities of the colonizing vegetation 20 years after the experiment was established. Metataxonomic analysis performed using 16S rRNA gene sequencing revealed that the original type of contaminated soil and phytoremediation strategy influenced the structure of both rhizospheric and endophytic communities of colonizing plants, even 20 years after the treatments were applied and following the disappearance of the originally planted grasses. Our findings demonstrate that the choice of initial phytoremediation strategy drove the succession of microorganisms associated with the colonizing vegetation. The outcome of this study provides new insight into the establishment of plant-associated microbial communities during secondary succession of subarctic areas previously contaminated by PHCs and indicates that the strategies for restoring these ecosystems influence the plant-associated microbiota in the long term. IMPORTANCE Subarctic ecosystems provide key services to local communities, yet they are threatened by pollution caused by spills and disposal of petroleum waste. Finding solutions for the remediation and restoration of subarctic soils is valuable for reasons related to human and ecosystem health, as well as environmental justice. This study provides novel insight into the long-term succession of soil and plant-associated microbiota in subarctic soils that had been historically contaminated with different sources of PHCs and subjected to distinct phytoremediation strategies. We provide evidence that even after the successful removal of PHCs and the occurrence of secondary succession, the fingerprint of the original source of contamination and the initial choice of remediation strategy can be detected as a microbial legacy in the rhizosphere, roots, and shoots of volunteer vegetation even 2 decades after the contamination had occurred. Such information needs to be borne in mind when designing and applying restoration approaches for PHC-contaminated soils in subarctic ecosystems.

Individual and combined contamination of oxytetracycline and cadmium inhibited nitrification by inhibiting ammonia oxidizers

Introduction

The large-scale development of animal husbandry and industrialization lead to more and more serious co-contamination from heavy metals and antibiotics in soils. Ecotoxic effects of residues from antibiotics and heavy metals are of increasing concern.

Materials and Methods

In this study, oxytetracycline (OTC) and cadmium (Cd) were selected as target pollutants to evaluate the individual and combined effects on nitrification process using four different soil types sampled from North to South China through a 56-day incubation experiment.

Results and Discussion

The results demonstrated that the contaminations of OTC and Cd, especially combined pollution had significant inhibitory effects on net nitrification rates (NNRs) as well as on AOA and AOB abundance. The toxic effects of contaminants were greatly enhanced with increasing OTC concentration. AOB was more sensitive than AOA to exogenous contaminants. And the interaction effects of OTC and Cd on ammonia oxidizers were mainly antagonistic. Furthermore, Cd contaminant (with or without OTC) had indirect effects on nitrification activity via inhibiting mineral N and AOA/AOB, while OTC alone indirectly inhibited nitrification activity by inhibiting ammonia oxidizers. The results could provide theoretical foundation for exploring the eco-environmental risks of antibiotics and heavy metals, as well as their toxic effects on nitrification processes.

Plant-soil-microbes: A tripartite interaction for nutrient acquisition and better plant growth for sustainable agricultural practices

Plants can achieve their proper growth and development with the help of microorganisms associated with them. Plant-associated microbes convert the unavailable nutrients to available form and make them useful for plants. Besides nutrient acquisition, soil microbes also inhibit the pathogens that cause harm to plant growth and induces defense response. Due to the beneficial activities of soil nutrient-microbe-plant interactions, it is necessary to study more on this topic and develop microbial inoculant technology in the agricultural field for better crop improvement. The soil microbes can be engineered, and plant growth-promoting rhizobacteria (PGPR) and plant growth-promoting bacteria (PGPB) technology can be developed as well, as its application can be improved for utilization as biofertilizer, biopesticides, etc., instead of using harmful chemical biofertilizers. Moreover, plant growth-promoting microbe inoculants can enhance crop productivity. Although, scientists have discussed several tools and techniques by omics and gene editing approaches for crop improvement to avoid biotic and abiotic stress and make the plant healthier and more nutritive. However, beneficial soil microbes that help plants with the nutrient acquisition, development, and stress resistance were ignored, and farmers started utilizing chemical fertilizers. Thus, this review attempts to summarize the interaction system of plant microbes, the role of beneficiary soil microbes in the rhizosphere zone, and their role in plant health promotion, particularly in the nutrition acquisition of the plant. The review will also provide a better understanding of soil microbes that can be exploited as biofertilizers and plant growth promoters in the field to create environmentally friendly, sustainable agriculture systems.

Diversity Shifts in the Root Microbiome of Cucumber Under Different Plant Cultivation Substrates

Application of plant artificial cultivation substrates lead to alteration of rhizosphere environment. Whether this alteration could lead to root microbiome variation was limitedly investigated. This work aims to determine the diversity shifts in the root microbiome of cucumber under different plant cultivation substrates and predict corresponding function of these different root bacterial microbiota. Cucumber root samples cultivated with two artificial cultivation substrates and greenhouse soils were prepared. Subsequently, high throughput sequencing and bioinformatics analysis were applicated to compare the root bacterial diversity of cucumber cultivated in different substrates and their corresponding function. In total, 311,039 sequences were obtained, and they were annotated to 42 operational taxonomic units (OTUs), belonging to 28 genera, 18 families, 12 orders, four classes, and three phyla. The α and β diversity of samples from the two cultivation substrates and greenhouse soils were significantly different. Only 2-3 bacterial species were found to be discrepancy between cucumber root samples from artificial cultivation substrates and from greenhouse soils. The relative abundance of genus Asticcacaulis, Methylophilus, Massilia, Dyella, and Devosia in samples of artificial cultivation substrates was significantly higher than that of soils, while the relative abundance of genus Phenylobacterium, Noviherbaspirillum, and Arenimonas was significantly lower than that of soils. Besides, compared to cucumber root bacterial community cultivated in soils, the abundance of synthetic pathways for flavonoids and flavonols, bile acids, indole alkaloids, lactose, and neolactose increased by 41.6-, 28.7-, 5.9-, and 5.5-fold, respectively, in the bacterial community of the substrate 1-cultivated roots, and the abundance of clavulanic acid, receptor interaction, sesquiterpenoid, bile acid, flavonoid and flavonol, indole alkaloid, lactose, and neolactose synthetic pathways increased by 42.3-, 32.4-, 32.4-, 13.9-, 10.3-, 6.3-, and 5.2-fold, respectively, in the bacterial community of the substrate two-cultivated roots. This paper verified the diversity shifts in the root microbiome of cucumber under different plant cultivation substrates. Besides, the corresponding function difference of these different root bacterial microbiota was predicted. This work would provide theoretical support for discovering microbial resources and building artificial microbial flora.

Applications of Heterogeneous Photocatalysis to the Degradation of Oxytetracycline in Water: A Review

Photocatalytic processes are being studied extensively as potential advanced wastewater treatments for the removal of pharmaceuticals, pesticides and other recalcitrant micropollutants from the effluents of conventional wastewater treatment plants (WWTPs). Oxytetracycline (OTC) is a widespread antibiotic which is frequently detected in surface water bodies as a recalcitrant and persistent micropollutant. This review provides an update on advances in heterogeneous photocatalysis for the degradation of OTC in water under UV light, sunlight and visible-light irradiation. Photocatalysts based on pure semiconducting oxides are rarely used, due to the problem of rapid recombination of electron–hole pairs. To overcome this issue, a good strategy could be the coupling of two different semiconducting compounds with different conduction and valence bands. Several methods are described to enhance the performances of catalysts, such as doping of the oxide with metal and/or non-metal elements, surface functionalization, composites and nano-heterojunction. Furthermore, a discussion on non-oxidic photocatalysts is briefly provided, focusing on the application of graphene-based nanocomposites for the effective treatment of OTC.

Bioremediation by earthworms on soil microbial diversity and partial nitrification processes in oxytetracycline-contaminated soil

A large proportion (60-90%) of ingested tetracyclines are released to slurry, soils, surface waters and ground water, which has raised extensive concerns and may pose a risk to the soil ecosystem. A 56-day experiment was conducted to study the bioremediation by earthworms on soil microbial diversity and partial nitrification processes in oxytetracycline (OTC)-contaminated soil. The results showed that high OTC concentration significantly decreased the activity of soil bacteria, ammonia-oxidizing bacteria (AOB) and archaea (AOA). Earthworms were found to accelerate the degradation efficiency and rate of OTC, and its main metabolites were 4-epi-oxytetracycline (EOTC) and 2-acetyl-2-decarboxamido-oxytetracycline (ADOTC). Earthworms had an important role in the bioremediation of soil microbial diversity by degrading OTC and its metabolite (EOTC), especially in the high OTC condition. Additionally, the results indicated that the effects of earthworms on the degradation of OTC could remediate the abundances of 16S rRNA and AOB amoA genes and the NO₃^- content in both low and high OTC-contaminated soils. The structural equation model suggested that earthworms could remediate the microbial diversity, the abundances of 16s rRNA and AOB amoA genes by accelerating the degradation of OTC, which contributed to the bioremediation by earthworms on soil microbial diversity and partial nitrification processes in oxytetracycline-contaminated soil.

Impact of spent mushroom substrate on Cd immobilization and soil property

This study aims to evaluate the potential of fresh spent mushroom substrate (SMS) in Cd immobilization and soil improvement, compared with spent mushroom substrate biochar (SMSB) and spent mushroom substrate compost (SMSC). A simulating remediation experiment was conducted with soil at Cd concentration of 0.6, 1.2, 1.8, and 2.4 mg kg^-1 and amendment addition ratio of 0.5%, 1%, 2%, and 4% for 90 days. At the end of incubation, it was found that 4%SMS addition showed the best effect both on Cd immobilization and soil improvement. It decreased Cd exchangeable fraction ratio by 52.77% (16.30% higher than 4%SMSC) and increased residual fraction ratio by 65.28% (36.34% and 49.64% higher than 4%SMSB and 4%SMSC, respectively); increased soil pH, EC, and CEC by 10.43% (3.83% higher than 4%SMSC), 11.54%, and 29.72%; and increased urease activity, sucrase activity, and catalase activity by 125.61% (43.90% and 8.54% higher than 4%SMSB and 4%SMSC, respectively), 79.46% (35.35% and 14.02% higher than 4%SMSB and 4%SMSC, respectively), and 75.68% (29.73% higher than 4%SMSB), compared with control treatment (CK) respectively. The results demonstrate that 4%SMS can be used as amendments for cadmium-contaminated soils.

Integration of poultry manure and phosphate solubilizing bacteria improved availability of Ca bound P in calcareous soils

A laboratory incubation experiment was executed to examine the role of phosphate solubilizing bacteria (with PSB and without PSB) and poultry manure (4, 8 and 12 t PM ha^-1) in improving P mobilization/mineralization under four different lime regimes (4.78, 10, 15 and 20% CaCO₃ M/M) for 56 days using three factorial complete randomized design (CRD) with triplicates. Phosphorus availability progressively increased over time irrespective of PSB inoculation, PM and lime levels. The PSB and PM (4-12 t ha^-1) addition into soil significantly increased Olsen P at all incubation intervals. Post incubation PSB survival increased by 12 and 9% with inoculation and 12 t PM ha^-1 over control and 4 t PM ha^-1, respectively. Liming ominously reduced P mobilization/mineralization by 1.3, 2.6 and 10.5% and PSB population by 6.6, 7.3 and 16.3% at 10, 15 and 20% (lime), respectively, over control at day 56. However, PSB and PM addition (with increasing rate) into soil significantly counterbalanced these ill effects of lime. Thus, the application of PSB and PM is a promising measure to enhance P availability in calcareous soils and shall be practiced.