Analysis of microbial community and nitrogen transition with enriched nitrifying soil microbes for organic hydroponics

Simultaneous remediation of diesel-polluted soil and promoted ryegrass growth by non-thermal plasma pretreatment

The remediation of petroleum-polluted soil has garnered significant global attention. In this study, a pot-culture experiment was conducted to assess the feasibility of using non-thermal plasma (NTP) as an efficient and economic-friendly pretreatment method in the phytoremediation of diesel-polluted soil. The remediation effectiveness was evaluated via both the removal of diesel and the ryegrass growth. Specifically, at the 50th d of ryegrass growth, the increase of diesel removal efficiency with NTP pretreatment ranged from 16 % to 30 %. Moreover, both clean and diesel-polluted soils pretreated by NTP promoted the growth of ryegrass in shoot lengths and biomass especially after the 35th d. It was found that nitrate nitrogen fixed by NTP not only stimulated the nitrate reductase activities in leaves and promoted plant growth, but also was transformed to more ammonia nitrogen for organism life activity. Subsequent investigation proved that the related nitrogen-metabolism activities of microbes were enriched in rhizosphere soils with NTP pretreatment. Furthermore, NTP treatment increased the abundance of beneficial microbial communities in diesel soil rhizosphere on the 42nd d of growth period. In addition, changes in the proportions of soil dissolved organic matter indicated enhanced nutrient cycling in soils with NTP pretreatment. These promotional effects underscored the contribution of NTP pretreatment in rapidly detoxifying diesel-contaminated soil within 10 min and accelerated the establishment of ryegrass ecosystem. This study provides valuable insights into the role of nitrogen fixation and offers an efficient and promising advanced approach for the phytoremediation of diesel-polluted soil with NTP pretreatment.

Deciphering biochar compost co-application impact on microbial communities mediating carbon and nitrogen transformation across different stages of corn development

Under current climatic conditions, developing eco-friendly and climate-smart fertilizers has become increasingly important.The co-application of biochar and compost on agricultural soils has received considerable attention recently.Unfortunately, little is known about its effects on specific microbial taxa involved in carbon and nitrogen transformation in the soil.Herein, we report the efficacy of applying biochar-based amendments on soil physicochemical indices, enzymatic activity, functional genes, bacterial community, and their network patterns in corn rhizosphere at seedling (SS), flowering (FS), and maturity (MS) stages.The applied treatments were: compost alone (COM), biochar alone (BIOC), composted biochar (CMB), fortified compost (CMWB), and the control (no fertilizer (CNTRL).The non-metric multidimensional scaling (NMDS) indicated total nitrogen (TN), pH, NO₃^--N, urease, protease, and microbial biomass C (MBC) as the dominant environmental factors driving soil bacteria in this study.The dominant N mediating genes belonged to nitrate reductase (narG) and nitronate monooxygenase (amo), while beta-galactosidase, catalase, and alpha-amylase were the dominant genes observed relating to C cycling.Interestingly, the abundance of these genes was higher in COM, CMWB, and CMB compared with the CNTRL and BIOC treatments.The bacteria network properties of CWMB and CMB indicated robust niche overlap associated with high cross-feeding between bacterial communities compared to other treatments.Path and stepwise regression analyses revealed norank_Reyranellaceae and Sphingopyxis in CMWB as the major bacterial genera and the major predictive indices mediating soil organic C (SOC), NH₄⁺-N, NO₃^--N, and TN transformation.Overall, biochar with compost amendments improved soil nutrient conditions, regulated the composition of the bacterial community, and benefited C/N cycling in the soil ecosystem.

Root Exudates of Ginger Induced by Ralstonia solanacearum Infection Could Inhibit Bacterial Wilt

Bacterial wilt caused by Ralstonia solanacearum (Rs) is one of the most important diseases found in ginger; however, the disease resistance mechanisms dependent on root bacteria and exudates are unclear. In the present study, we analyzed the changes in the composition of rhizobacteria, endobacteria, and root exudates during the pathogenesis of bacterial wilt using high-throughput sequencing and gas chromatography-mass spectrometry (GC-MS). Rs caused bacterial wilt in ginger with an incidence of 50.00% and changed the bacterial community composition in both endosphere and rhizosphere. It significantly reduced bacterial α-diversity but increased the abundance of beneficial and stress-tolerant bacteria, such as Lysobacter, Ramlibacter, Pseudomonas, and Azospirillum. Moreover, the change in rhizobacterial composition induced the changes in endobacterial and root exudate compositions. Moreover, the upregulated exudates inhibited ginger bacterial wilt, with the initial disease index (77.50%) being reduced to 40.00%, suggesting that ginger secretes antibacterial compounds for defense against bacterial pathogens.

Succession of the microbial community during the process of mechanical and biological pretreatment coupled with a bio-filter for removal of VOCs derived from domestic waste: a field study

Changes in the microbial community can not only reflect the efficiency of waste disposal, but also reveal the effect of odor control during the treatment process. This study aimed to evaluate the removal efficiency of volatile organic compounds (VOCs) by the process of mechanical and biological pretreatment (MBP) coupled with a bio-filter (BF). An interesting phenomenon was found that the VOCs were effectively reduced through the MBP process. To understand the removal mechanism of VOCs, the abundance and diversity of microbial bacteria and fungi in the biological dehydration (BD) process, biological fermentation process, and BF process were explored. The abundance and diversity of microbes in the BF were relatively high, of which the bacteria such as Lactobacillus, Bacillus and Candida were the dominant species for VOCs treatment. The proposed technical process and the positive effects observed in this study indicate that it could be applied to the control of VOCs in the treatment of domestic waste.

The applicability of anaerobically treated domestic wastewater as a nutrient medium in hydroponic lettuce cultivation: Nitrogen toxicity and health risk assessment

The applicability of anaerobic effluent (AE) from an anaerobic membrane bioreactor (AnMBR) treating domestic wastewater as a nutrient medium was evaluated through hydroponic cultivation of lettuce. The growth of lettuce plants on AE media was significantly inhibited to 31-40% in height and 36-48% in number of leaves compared to that on half-strength Hoagland solution (HHS) as a control. The primary cause of inhibition was nitrite toxicity as induced by partial nitrification. Therefore, the nitrification of AE as a pre-treatment step was adopted to prevent the toxicity of nitrite. The heights of lettuce grown on nitrified anaerobic effluent (NAE) and nitrified anaerobic effluent with 96 mg/L sulfate (NAES) were in the range of 11.4-11.5 cm and was comparable to that on control solution (11.4 cm). The potential health risk for heavy metals was insignificant based on health risk index (HRI < 1) and targeted hazardous quotient (THQ < 1). These results show that efficient crop production can be achieved with AE, but suitable pre-treatment steps should be followed.

Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl^- concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality.

Bioponic system for nitrogen and phosphorus recovery from chicken manure: Evaluation of manure loading and microbial communities

Bioponics integrates the biological treatment of nutrient-rich waste streams with hydroponics. However, there are several challenges of bioponics, especially nutrient availability and qualities, which affect plant yield. In this study, chicken manure based-nutrient film technique bioponics was examined at manure loadings of 200, 300, and 400 g dry wt. per bioponic system (total of 18 plants). Bioponics effectively released nitrogen and phosphorus (total ammonia nitrogen of 5.8-8.0 mgN/L, nitrate of 7.0-11.2 mgN/L, and phosphate of 48.7-74.2 mgP/L) for efficient growth of lettuce (Lactuca sativa; total yield of 1208-2030 g wet wt. per 18 plants). Nitrogen and phosphorus use efficiencies were 35.1-41.8% and 6.8-8.0%, respectively, and were comparable to aquaponics. Next-generation sequencing was used to examine the microbial communities in digested chicken manure and plant roots in bioponics. Results showed that several microbial genera were associated with organic degradation (e.g., Nocardiopsis spp., Cellvibrio spp.), nitrification (Nitrospira spp.), phosphorus solubilization, and plant growth promotion (e.g., WD2101_soil_group, and Bacillus spp.). Nocardiopsis spp., Romboutsia spp. and Saccharomonospora spp. were found at high abundances and a high degree of co-occurrences among the microbiota, suggesting that the microbial organic decomposition to nitrogen and phosphorus release could be the key factors to achieve better nutrient recovery in bioponics.

Effects of integrated biocontrol on bacterial wilt and rhizosphere bacterial community of tobacco

Bacterial wilt as a soil-borne disease was caused by Ralstonia solanacearum, and seriously damages the growth of tobacco. Integrated biocontrol method was explored to control bacterial wilt. Nevertheless, the long-term effects of the integrated biocontrol method on soil bacterial community, soil physicochemical properties and the incidence of bacterial wilt are not well understood. In this study, B. amyoliquefaciens ZM9, calcium cyanamide and rice bran were applied to tobacco fields in different ways. The disease index and incidence of tobacco bacterial wilt (TBW), soil physicochemical properties, colonization ability of B. amyoliquefaciens ZM9, and rhizopshere bacterial community were investigated. The results showed that the integrated application of B. amyoliquefaciens ZM9, rice bran and calcium cyanamide had the highest control efficiency of TBW and bacteria community diversity. Additionally, the integrated biocontrol method could improve the colonization ability of B. amyoliquefaciens ZM9. Furthermore, the integrated biocontrol method could effectively suppress TBW by regulating soil physicochemical properties, promoting beneficial bacteria and antagonistic bacteria of rhizopshere soil. This strategy has prospect of overcoming the defects in application of a single antagonistic bacteria and provides new insights to understand how to improve the colonization capacity of antagonistic bacteria and control efficacy for TBW.

Computational analysis of successional changes in the microbial population and community diversity of the immobilized marine nitrifying bacterial consortium in a nitrifying packed bed bioreactor

Nitrifying bioreactor (NBR) connected to the recirculating aquaculture system (RAS), has a greater emphasis on the biological treatment of wastewater. Nitrifying bacterial consortium (NBC) formed bio-film on the substratum activating the NBR, and it was observed with high nitrification potential in shrimp maturation systems. Scanning Electron Microscopy (SEM) revealed the integrity of the biofilm substantiated with biomineralization. The fate of the matured bio-film population on subsequent operation under RAS, and the aggregated population at different points of RAS, including the rearing water were determined using fingerprints of Denaturing Gradient Gel Electrophoresis (DGGE). Altogether, 38 OTUs of biofilm sample and 35 OTUs of water samples represented the bacterial communities; the shared and unique OTUs indicated the diversity of the population at different time intervals in the operation of the NBR. The mathematical (range-weighted richness) and statistical (diversity indices) interpretation unveiled the OTUs based high bacterial diversity in the biofilm supporting the compositional changes and determined the distance between the community cluster. Ordination analyses indicated the population shift and stability of the activated bio-film till the matured biofilm community got established in the RAS. The DGGE with mathematical and statistical analysis revealed microbial diversity (high Shannon index, species richness and evenness), abundance (relative intensity), consecutive change in the population composition (OTUs, Rr index), and the dynamics (Δt) in the system during the operation.

Inhibitory effect of phenol on wastewater ammonification

This study aimed to elucidate inhibitory effect of phenol on ammonification of dissolved organic nitrogen (DON) in wastewater. Laboratory incubation experiments were conducted using primary and secondary effluent samples spiked with phenol (100-1000 mg/L) and inoculated with mixed cultures, pure strains of phenol-degrading bacteria (Acinetobacter sp. and Pseudomonas putida F1), and/or an ammonia oxidizing bacterium (Nitrosomonas europaea). DON concentration was monitored with incubation time. Phenol suppressed the ammonification rate of DON up to 62.9%. No or minimal ammonification inhibition was observed at 100 mg/L of phenol while the inhibition increased with increasing phenol concentration from 250 to 1000 mg/L. The inhibition was curtailed by the presence of the phenol-degrading bacteria. DON was ammonified in the samples inoculated with only N. europaea and the ammonification was also inhibited by phenol. The findings suggest that high phenol in wastewater could result in low ammonification and high DON in the effluent.

Improving Wastewater Nitrogen Removal and Reducing Effluent NOx - -N by an Oxygen-Limited Process Consisting of a Sequencing Batch Reactor and a Sequencing Batch Biofilm Reactor

A series of reactors including a sequencing batch reactor (SBR) and a sequencing batch biofilm reactor (SBBR) were used for nitrogen removal. The aim of this study was simultaneous removal of NH4+-N and NOx–-N from synthetic wastewater. In the novel proposed method, the effluent from SBR was sequentially introduced into SBBR, which contained 0.030 m3 biofilm carriers, so the system operated under a paired sequence of aerobic-anoxic conditions. The effects of different carbon sources and aeration conditions were investigated. A low dissolved oxygen (DO) level in the biofilm depth of the fixed-bed process (SBBR) simulated the anoxic phase conditions. Accordingly, a portion of NH4+-N that was not converted to NO3–-N by the SBR process was converted to NO3–-N in the outer layer of the biofilm in the SBBR process. Further, simultaneous nitrification and denitrification (SND) was achieved in the SBBR where NO2–-N was converted to N2 directly, before NO3–-N conversion (partial nitrification). The level of mixed liquid suspended solids (MLSS) was 2740 mg/l at the start of the experiments. The required carbon source (C: N ratio of 4) was provided by adding an internal carbon source (through step feeding) or ethanol. Firstly, as part of the system (SBR and SBBR), SBR operated at a DO level of 1 mg/l while SBBR operated at a DO concentration of 0.3 mg/l during Run-1. During Run-2, the system operated at the low DO concentration of 0.3 mg/l. When the source of carbon was ethanol, the nitrogen removal rate (RN) was higher than the operation with an internal carbon source. When the reactors were operated at the same DO concentration of 0.3 mg/l, 99.1 % of the ammonium was removed. The NO3–-N produced during the aerobic SBR operation of the novel method was removed in SBBR reactor by 8.3 %. The concentrations of NO3--N and NO2–-N in the SBBR effluent were reduced to 2.5 and 5.5 mg/l, respectively. Also, the total nitrogen (TN) removal efficiency was 97.5 % by adding ethanol at the DO level of 0.3 mg/l.

When C:N adjustment was carried out SND efficiency at C:N ratio of 6.5 reached to 99 %. The increasing nitrogen loading rate (NLR) to 0.554 kg N/m3 d decreased SND efficiency to 80.7 %.

Cobalt-dependent inhibition of nitrite oxidation in Nitrobacter winogradskyi

Nitrobacter winogradskyi is an abundant, intensively studied autotrophic nitrite-oxidizing bacterium, which is frequently used as a model strain in the two-step nitrification of ammonia (NH₃) to nitrate (NO₃^-) via nitrite (NO₂^-), either in activated sludge, agricultural field studies or more recently in artificial microbial consortia for organic hydroponics. We observed a hitherto unknown cobalt ion-dependent inhibition of cell growth and NO₂^- oxidation activity of N. winogradskyi in a mineral medium, which strongly depended on accompanying Ca²⁺ and Mg²⁺ concentrations. This inhibition was bacteriostatic, but susceptible to natural chelators. l-Histidine effectively restored cell growth and NO₂^- oxidation activity of N. winogradskyi in mineral media containing Co²⁺ with >90% recovery. Our results suggest that Co²⁺ competed with alkaline earth metals during uptake and that its toxicity was significantly reduced by complexation.

Microbial community composition is related to soil biological and chemical properties and bacterial wilt outbreak

Soil microbes play important roles in plant growth and health. Little is known about the differences of soil microbes between healthy and bacterial wilt infected soils with Ralstonia solanacearum. By Illumina-MiSeq sequencing of 16S rRNA and 18S rRNA gene amplicons, we found the soil microbial composition and diversity were distinct between healthy and bacterial wilt infected soils. Soil microbial community varied at different plant growth stages due to changes of root exudates composition and soil pH. Healthy soils exhibited higher microbial diversity than the bacterial wilt infected soils. More abundant beneficial microbes including Bacillus, Agromyces, Micromonospora, Pseudonocardia, Acremonium, Lysobacter, Mesorhizobium, Microvirga, Bradyrhizobium, Acremonium and Chaetomium were found in the healthy soils rather than the bacterial wilt infected soils. Compared to bacterial wilt infected soils, the activities of catalase, invertase and urease, as well as soil pH, available phosphorous and potassium content, were all significantly increased in the healthy soils. In a conclusion, the higher abundance of beneficial microbes are positively related the higher soil quality, including better plant growth, lower disease incidence, and higher nutrient contents, soil enzyme activities and soil pH.