A long-term field experiment, started in 1983, was carried out on a clay loam soil (Ferric/Haplic Luvisols, FAO) in Jurong Agricultural Institute, Jiangsu Province, China, to study changes of organic ...carbon (C) and nitrogen (N) pools in the topsoil under a rice/wheat rotation system. Treatments included conventional tillage (CT) and no tillage (NT) combined with various fertilizer treatments. The fertilizer treatments were control (no fertilizer), chemical fertilizer only, straw plus chemical fertilizer, and pig manure plus chemical fertilizer. With the exception of the control treatment, all treatments received the same level (in kg ha(-1)) of N (150), phosphorus (P) (50), and potassium (K) (155). Results showed that soil organic C, N, and microbial biomass carbon (MBC) and nitrogen (MBN) were higher in the top 5 cm layer after 18 years of no tillage than that under CT, whereas the reverse trend was observed in 5 to 10- and 10 to 20-cm layers. The application of organic manures with a reduced amount of commercial chemical fertilizer increased the content of soil organic C, total and available N, and MBC and MBN compared to the treatment with inorganic fertilizer alone. Organic C and total N contents of soils from different treatments were found in the order of pig manure plus inorganic fertilizer > straw plus inorganic fertilizer > inorganic fertilizer > control. Microbial biomass C and MBN showed a similar trend to organic C and total N. These results indicate that a combination of NT and application of pig manure is the best way to sustain soil fertility in the experiment.
Soil plays a crucial role as a significant reservoir for antibiotic resistance genes (ARGs). Despite the extensive research conducted in this area, there remains a need for further investigation, ...particularly concerning diverse types of agricultural soil. This comprehensive study examined Fusarium wilt diseased and healthy soil samples to investigate the spectrum of ARGs and identify bacteria potentially harboring these genes. The level of antibiotic resistance (AR) in the two soil types was detected by using culture plate counts (PC). We quantified and identified antibiotic resistant bacteria (ARB) against nine antibiotics. From the PC results, the relative number of ARB (number of ARB/total number culturable bacteria) resistant to erythromycin, lincomycin, sulfonamides, streptomycin sulfate, kanamycin, and enrofloxacin in the diseased soil was significantly higher than that in the healthy soil (One-way ANOVA, p < 0.01). The GeoChip (version 5.0) was employed to identify ARGs and antibiotic biosynthetic genes (ABGs). Interestingly, despite the presence of similar ARGs in both soil types, the Fusarium wilt diseased soil demonstrated a significantly elevated abundance of the tetracycline (tetX) resistance gene compared to the healthy soil. A robust correlation (r ≥ 0.8) between multidrug efflux pumps and ARGs indicates that natural antibiotics as selective pressures for transportation mechanisms. Our analysis identified diverse ARB phylotypes and multiple ARGs in both soil types. Incorporating these soil types into ARGs risk assessments and relevant monitoring is essential for a comprehensive understanding of AR dynamics in various environments.
Display omitted
•Fusarium wilt diseased soil had more ARB with antibiotics than healthy soil.•A high abundance of the tetX gene in diseased soil indicates tetracycline resistance.•Efflux pump & ARG show a strong link (r ≥ 0.8), implying antibiotic driven transport.
Volatile organic compounds (VOCs) produced by soil bacteria have been shown to exert plant pathogen biocontrol potential owing to their strong antimicrobial activity. While the impact of VOCs on soil ...microbial ecology is well established, their effect on plant pathogen evolution is yet poorly understood. Here we experimentally investigated how plant-pathogenic Ralstonia solanacearum bacterium adapts to VOC-mixture produced by a biocontrol Bacillus amyloliquefaciens T-5 bacterium and how these adaptations might affect its virulence. We found that VOC selection led to a clear increase in VOC-tolerance, which was accompanied with cross-tolerance to several antibiotics commonly produced by soil bacteria. The increasing VOC-tolerance led to trade-offs with R. solanacearum virulence, resulting in almost complete loss of pathogenicity in planta. At the genetic level, these phenotypic changes were associated with parallel mutations in genes encoding lipopolysaccharide O-antigen (wecA) and type-4 pilus biosynthesis (pilM), which both have been linked with outer membrane permeability to antimicrobials and plant pathogen virulence. Reverse genetic engineering revealed that both mutations were important, with pilM having a relatively larger negative effect on the virulence, while wecA having a relatively larger effect on increased antimicrobial tolerance. Together, our results suggest that microbial VOCs are important drivers of bacterial evolution and could potentially be used in biocontrol to select for less virulent pathogens via evolutionary trade-offs.
Bacillus velezensis SQR9 (former B. amyloliquefaciens SQR9) is a plant-growth-promoting rhizobacterium (PGPR) that promotes plant growth and health. The colonization of PGPR strains along plant roots ...is a prerequisite for them to execute their specific functions. However, one problem of microbial introduction in practice is that the applied PGPR strains do not always successfully colonize the rhizosphere. In Bacillus spp., two-component signal transduction system (TCS) DegS/U regulates flagellar motility, biofilm formation and antibiotic production. Phosphorylation of DegU by DegS is positively affected by DegQ protein. In this study, we constructed a xylose-inducible degQ genetically engineered strain SQR9XYQ to improve the biocontrol activity. The results from in vitro, root in situ, greenhouse experiments and RT-qPCR studies demonstrate that (i) the phosphorylation of DegU in SQR9XYQ can be gradually activated by xylose, which is a component of both cucumber and tomato root exudates, and (ii) biofilm formation, antibiotic expression, colonization activity, and biocontrol efficiency were improved in SQR9XYQ compared with the wild-type strain SQR9. These results suggest that colonization trait is important to biocontrol strains for maintenance of plant health.
Inadequately managed solid organic waste generation poses a threat to the environment and human health globally. Biotransformation with the black soldier fly larvae (BSFL) is emerging as talent ...technology for solid waste management. However, there is a lack of understanding of whether BSFL can effectively suppress potential pathogenic microorganisms during management and the underlying mechanisms. In this study, we investigated the temporal variations of microorganisms in two common types of solid waste, i.e., kitchen waste (KW) and pig manure (PM). Natural composting and composting with BSFL under three different pH levels (pH 5, 7, and 9) were established to explore their impact on microbial communities in compost and the gut of BSFL. The results showed that the compost of kitchen waste and pig manure led to an increase in relative abundance of various potentially pathogenic bacteria. Temporal gradient analyses revealed that the most substantial reduction in the relative abundance and diversity of potentially pathogenic microorganisms occurred when the initial pH of both two wastes were adjusted to 7 upon the introduction of BSFL. Through network and pls-pm analysis, it was discovered that the gut microbiota of BSFL occupied an ecological niche in the compost, inhibiting the proliferation of potentially pathogenic microorganisms. This study has revealed the potential of BSFL in reducing public health risks during the solid waste management process, providing robust support for sustainable waste management.
Display omitted
•BSFL could reduce pathogenic microorganisms during organic solid waste management.•The potential pathogenic microorganisms could not enrich in BSFL gut.•The BSFL brings ecological niches to promote growth of beneficial microorganisms.
Anthropogenic activities such as long-term fertilizer application are known to lead to losses in above and belowground biodiversity, thereby negatively impacting ecosystem function. However, our ...understanding of the relative sensitivity of different soil organisms groups to increasing fertilizer application levels remains largely unknown. To address this knowledge gap, we investigated the impacts of different long-term fertilization regimes, and the associated changes in plant communities, on a broad range of soil organisms, including bacteria, fungi, protists, and nematodes, in the alpine meadow ecosystem of the Qinghai-Xizang Plateau. Results showed that the community composition of protists was the most sensitive to different fertilization regimes as compared to those of bacteria, fungi, and nematodes. Changes in the protist community were also most strongly linked to changes in plant richness and biomass under prolonged fertilization. Nitrogen fertilizer addition leads to more deterministic community assembly processes for protist communities, while phosphorus fertilizer application leads to more stochastic assembly processes. Together, our results suggest that protists may be among the most susceptible soil organisms concerning the impact of human disturbances like fertilizer application, highlighting their potential importance as sensitive ecological indicators of human-induced disturbances in terrestrial ecosystems.
•Protists was more sensitive to fertilization regimes compared to bacteria, fungi and nematode.•Protists were highly linked to changes in plant richness and biomass.•Nitrogen fertilizer addition led to deterministic processes in protist community assembly.•Phosphorus fertilizer application led to more stochastic assembly processes in protist community assembly.
High-affinity K
+
(HAK)/K
+
uptake (KUP)/K
+
transporters (KT) play crucial roles in the regulation of cellular K
+
levels. However, little is known about these genes in the Rosaceae family. In this ...study, 56 putative HAK/KUP/KT genes were identified in genome sequences from
Pyrus bretschneideri, Fragaria vesca
, and
Vitis vinifera
, 21 of which were from
P. bretschneideri
(designated
PbHAK1-21
). HAK/KUP/KTs from these species, as well as from
Arabidopsis
and rice, were grouped into five major clusters with eight subclades. Whole-genome duplication/segmental duplication and dispersed duplication largely accounts for the expansion of HAK/KUP/KT families in these five species. Orthologous relationships between pear and
Arabidopsis
genes suggest that some
PbHAKs
function as high-affinity K
+
transporters or mediators of abiotic stress responses. Cis-regulatory motifs upstream of
PbHAK
genes also suggest that members of this family respond to environment changes.
PbHAK2
and
PbHAK12
mRNAs are abundant in roots exposed to normal levels of K
+
and are rapidly up-regulated under conditions of K
+
deficiency, suggesting that they have crucial roles in K
+
uptake, especially at low K
+
concentrations.
PbHAK12
(orthologous to
AtHAK5
from
Arabidopsis
) is predominately localized in the plasma membrane, consistent with a role in mediating K
+
uptake. Some
PbHAK
mRNA levels also change in response to abiotic stresses such as salt, cold, and drought. Our data reveals potential candidate genes for further functional characterization, and may be useful for breeding pear rootstocks that utilize potassium more efficiently.
Dihydrofolate reductase (DHFR) is an essential enzyme in the folate pathway and has been recognized as a well-known target for antibacterial and antifungal drugs. We discovered eight compounds from ...the ZINC database using virtual screening to inhibit Rhizoctonia solani (R. solani), a fungal pathogen in crops. These compounds were evaluated with in vitro assays for enzymatic and antifungal activity. Among these, compound Hit8 is the most active R. solani DHFR inhibitor, with the IC50 of 10.2 μM. The selectivity of inhibition is 22.3 against human DHFR with the IC50 of 227.7 μM. Moreover, Hit8 has higher antifungal activity against R. solani (EC50 of 38.2 mg L–1) compared with validamycin A (EC50 of 67.6 mg L–1), a well-documented fungicide. These results suggest that Hit8 may be a potential fungicide. Our study exemplifies a computer-aided method to discover novel inhibitors that could target plant pathogenic fungi.
Although the precipitation and dissolution of iron (Fe)-containing-minerals are driven by microbially-mediated iron-redox cycling, we still have a limited understanding of complex response of such ...microbial communities to fertilisation. Here, using chemical and synchrotron-based spectral analyses, we show that the distribution of poorly crystalline Fe minerals and crystalline Fe minerals is different in organically- and inorganically-fertilised soils, and that compared to no fertilisation (Control), Fe redox cycling bacteria were present at higher abundance and diversity in organically-fertilised soils but lower in inorganically-fertilised soil. During Fe(III) reduction, Geobacter were important active Fe(III) reducers, with a higher relative abundance in both organically- and inorganically-fertilised soils than in Control, and their higher abundance was responsible for greater dissolution of ferrihydrite in inorganically-fertilised soil than in organically-fertilised soil. However, during the Fe(II) oxidation, Pseudomonas and Anaerolinea were more abundant, and produced higher levels of poorly crystalline Fe oxides under organic fertilisation. Thus, for the first time, we demonstrate that inorganic and organic fertilisation regimes have contrasting effects on the Fe redox bacterial communities, which then influence Fe cycling in soils.
•Synchrotron spectroscopy and Illumina sequencing were combined in this study.•Fertilisation regimes had contrasting effects on the Fe redox bacterial communities.•Fe redox bacteria were present at higher abundance in organically-fertilised soils.•Geobacter were strongly involved for dissolution of ferrihydrite in soils.
Core Ideas
Organic fertilization increased the oxalate extractable iron oxides.
Oxalate extractable iron oxides contributed to soil organic carbon sequestration.
Soil organic carbon from 20 to 40 cm ...was more labile than that from 0 to 20 cm.
Oxalate extractable iron oxides preferentially preserved aromatic compounds.
Carbon sequestration in paddy soils through organic fertilization is of great importance for soil quality improvement in subtropical Asia. This study explored the effect of oxalate extractable iron oxides (Feo) on soil organic carbon (SOC) sequestration in response to different fertilization treatments. Soil samples were collected from 0‐ to 10‐cm, 10‐ to 20‐cm, and 20‐ to 40‐cm depth intervals in June 2016 after a wheat (Triticum aestivum L.) harvest. This study involved five treatments: control with no fertilizer (CK), chemical fertilizer (NPK), 50% chemical fertilizer plus manure (NPKM), 100% chemical fertilizer plus straw (NPKS), and 30% chemical fertilizer plus manure organic‐inorganic compound fertilizer (NPKMOI). Organic fertilization significantly (P < 0.05) increased the SOC content and the Feo concentration compared with chemical fertilization alone. The specific C mineralization rate (SCMR, rate per unit SOC) increased with increasing soil depths, suggesting that SOC at the 20‐ to 40‐cm depth was more labile than that from 0 to 20 cm. The percentage of SOC present as microbial biomass carbon (MBC) was significantly (P < 0.001) positively correlated with SCMR, indicating that soil microorganisms influenced the potential SOC mineralization. Furthermore, the alternation of drying and wetting in paddy soils drives the biogeochemical cycles of iron and SOC, during which organic fertilization promotes the accumulation of Feo possibly by forming organo‐iron complexes as indicated by the higher Feo content in NPKM than in NPK. The Feo was significantly (P < 0.001) positively correlated with SOC and the percentage of aromatic C, indicating that Feo may play an important role in preserving SOC, especially the aromatic compounds. Therefore, the enhancement of Feo by organic fertilization, especially organic manure that is enriched in aromatic compounds, improved the SOC sequestration potential in the rice (Oryza sativa)–wheat rotation system.
PDF
