Soil pH enhancement and alterations in nutrient and Bacterial Community profiles following Pleioblastus amarus expansion in tea plantations.

BACKGROUND: The expansion of bamboo forests increases environmental heterogeneity in tea plantation ecosystems, affecting soil properties and microbial communities. Understanding these impacts is essential for developing sustainable bamboo management and maintaining ecological balance in tea plantations. METHODS: We studied the effect of the continuous expansion of Pleioblastus amarus into tea plantations, by establishing five plot types: pure P. amarus forest area (BF), P. amarus forest interface area (BA), mixed forest interface area (MA), mixed forest center area (TB), and pure tea plantation area (TF). We conducted a comprehensive analysis of soil chemical properties and utilized Illumina sequencing to profile microbial community composition and diversity, emphasizing their responses to bamboo expansion. RESULTS: (1) Bamboo expansion significantly raised soil pH and enhanced levels of organic matter, nitrogen, and phosphorus, particularly noticeable in BA and MA sites. In the TB sites, improvements in soil nutrients were statistically indistinguishable from those in pure tea plantation areas. (2) Continuous bamboo expansion led to significant changes in soil bacterial diversity, especially noticeable between BA and TF sites, while fungal diversity was unaffected. (3) Bamboo expansion substantially altered the composition of less abundant bacterial and fungal communities, which proved more sensitive to changes in soil chemical properties. CONCLUSION: The expansion of bamboo forests causes significant alterations in soil pH and nutrient characteristics, impacting the diversity and composition of soil bacteria in tea plantations. However, as expansion progresses, its long-term beneficial impact on soil quality in tea plantations appears limited.

Multi-omics analyses reveal the responses of wheat (Triticum aestivum L.) and rhizosphere bacterial community to nano(micro)plastics stress.

The pervasive existence of nanoplastics (NPs) and microplastics (MPs) in soil has become a worldwide environmental concern. N/MPs exist in the environment in a variety of forms, sizes, and concentrations, while multi-omics studies on the comprehensive impact of N/MPs with different properties (e.g. type and size) on plants remain limited. Therefore, this study utilized multi-omics analysis methods to investigate the effects of three common polymers [polyethylene-NPs (PE-NPs, 50 nm), PE-MPs (PE-MPs, 10 µm), and polystyrene-MPs (PS-MPs, 10 µm)] on the growth and stress response of wheat, as well as the rhizosphere microbial community at two concentrations (0.05 and 0.5 g/kg). PS and PE exhibited different effects for the same particle size and concentration. PE-NPs had the most severe stress effects, resulting in reduced rhizosphere bacteria diversity, plant biomass, and antioxidant enzyme activity while increasing beneficial bacteria richness. N/MPs altered the expression of nitrogen-, phosphorus-, and sulfur-related functional genes in rhizosphere bacteria, thereby affecting photosynthesis, as well as metabolite and gene levels in wheat leaves. Partial least squares pathway models (PLSPMs) indicated that concentration, size, and type play important roles in the impact of N/MPs on the plant ecological environment, which could have essential implications for assessing the environmental risk of N/MPs.

Edaphobacter paludis sp. nov., a new acidophilic representative of the Acidobacteriota isolated from fen soils.

Two new strains JP48T and JP55 affiliated with the acidobacterial class Terriglobia have been isolated from fen soil sampled in the Fichtelgebirge Mountains near Bayreuth, Germany. Both strains were Gram-stain-negative, non-motile, non-spore-forming rods that divide by binary fission, segregate exopolysaccharide-like material and form capsules. Strains JP48T and JP55 grew at 4-36 °C (optimum at 27 °C), pH 3.6-7.3 (optimum at pH 4.6-5.5) and with NaCl concentrations of 0-3% (optimum at 1.0%; w/v). Strains JP48T and JP55 grew aerobically on a wide range of organic substrates including mono- and oligosaccharides, amino acids and short-chained fatty acids. MK-8 was identified as the major respiratory quinone. The major fatty acids for strains JP48T and JP55 were iso-C15 : 0, C16 : 1 ω7c, C16 : 0 and iso-diabolic acid. Phosphatidylglycerol, phosphatidylethanolamine, diphosphatidylglycerol, lysophophatidylethanolamine, phosphatidylcholine, unidentified glyco- and glycophospholipids, and unidentified high mass lipid species were the major polar membrane lipids. The G+C content of strains JP48T and JP55 was 57.4 and 57.2 mol%, respectively. The genomes of strains JP48T and JP55 contained nine potential secondary metabolite regions encoding for the compound classes NRPS(-like), T3PKS, terpene, or lanthipeptide class IV. Phylogenetic reconstruction and 16S rRNA gene sequence similarities of 98.3 and 96.9% identified Edaphobacter dinghuensis DHF9T and Edaphobacter lichenicola DSM 104462T as the most closely related type strains to strains JP48T and JP55. Based on their phenotype, phylogeny and chemotaxonomy, we propose the novel species Edaphobacter paludis sp. nov. (type strain JP48T=DSM 109919T=CECT 30269T; additional strain JP55=DSM 109920=CECT 30268) within the class Terriglobia of the phylum Acidobacteriota.

Transcriptome sequencing analysis of gene expression in phosphate-solubilizing bacterium 'N3' and grafted watermelon plants coping with toxicity induced by cadmium.

Cadmium (Cd) is a harmful metal in soil, and reducing Cd accumulation in plants has become a vital prerequisite for maintaining food safety. Phosphate-solubilizing bacteria (PSB) can not only improve plant growth but also inhibit the transportation of metals to roots. However, data on gene expression in PSB Burkholderia sp. strain 'N3' and grafted watermelon plants dealing with Cd remain to be elucidated. In this study, core genes and metabolic pathways of strain 'N3' and grafted plants were analyzed by Illumina sequencing. Results showed that 356 and 2527 genes were upregulated in 'N3' and grafted watermelon plants, respectively, whereas 514 and 1540 genes were downregulated in 'N3' and grafted watermelon plants, respectively. Gene ontology enrichment analysis showed that signal transduction, inorganic ion transport, cell motility, amino acid transport, and metabolism pathways were marked in 'N3'. However, pathways such as secondary metabolite biosynthesis, oxidation-reduction process, electron transfer activity, and channel regulator activity were marked in the grafted plants. Six genes related to pentose phosphate, glycolysis, and gluconeogenesis metabolism were upregulated in the grafted plants. This study paves the way for developing potential strategies to improve plant growth under Cd toxicity.

Taxonomic and genomic attributes of oligotrophic soil bacteria.

Not all bacteria are fast growers. In soil as in other environments, bacteria exist along a continuum-from copiotrophs that can grow rapidly under resource-rich conditions to oligotrophs that are adapted to life in the "slow lane." However, the field of microbiology is built almost exclusively on the study of copiotrophs due, in part, to the ease of studying them in vitro. To begin understanding the attributes of soil oligotrophs, we analyzed three independent datasets that represent contrasts in organic carbon availability. These datasets included 185 samples collected from soil profiles across the USA, 950 paired bulk soil and rhizosphere samples collected across Europe, and soils from a microcosm experiment where carbon availability was manipulated directly. Using a combination of marker gene sequencing and targeted genomic analyses, we identified specific oligotrophic taxa that were consistently more abundant in carbon-limited environments (subsurface, bulk, unamended soils) compared to the corresponding carbon-rich environment (surface, rhizosphere, glucose-amended soils), including members of the Dormibacterota and Chloroflexi phyla. In general, putative soil oligotrophs had smaller genomes, slower maximum potential growth rates, and were under-represented in culture collections. The genomes of oligotrophs were more likely to be enriched in pathways that allow oligotrophs to metabolize a range of energy sources and store carbon, while genes associated with energy-intensive functions like chemotaxis and motility were under-represented. However, few genomic attributes were shared, highlighting that oligotrophs likely use a range of different metabolic strategies and regulatory pathways to thrive in resource-limited soils.

A Comparative Analysis of Bacterial and Fungal Communities in Coastal and Inland Pecan Plantations.

Pecan forests (Carya illinoinensis) are significant contributors to both food and oil production, and thrive in diverse soil environments, including coastal regions. However, the interplay between soil microbes and pecan forest health in coastal environments remains understudied. Therefore, we investigated soil bacterial and fungal diversity in coastal (Dafeng, DF) and inland (Guomei, GM) pecan plantations using high-throughput sequencing. The results revealed a higher microbial diversity in the DF plantation than in the GM plantation, significantly influenced by pH and edaphic factors. The dominant bacterial phyla were Proteobacteria, Acidobacteriota and Bacteroidota in the DF plantation, and Acidobacteriota, Proteobacteria, and Verrucomicrobiota in the GM plantation. Bacillus, Nitrospira and UTCFX1 were significantly more abundant bacterial genera in DF soil, whereas Candidatus Udaeobacter, HSB_OF53-F07 and ADurbBin063-1 were more prevalent in GM soil. Basidiomycota dominated fungal sequences in the GM plantation, with a higher relative abundance of Ascomycota in the DF plantation. Significant differences in fungal genus composition were observed between plantations, with Scleroderma, Hebeloma, and Naucoria being more abundant in DF soil, and Clavulina, Russula, and Inocybe in GM soil. A functional analysis revealed greater carbohydrate metabolism potential in GM plantation bacteria and a higher ectomycorrhizal fungi abundance in DF soil. Significantly positive correlations were detected between certain bacterial and fungal genera and pH and total soluble salt content, suggesting their role in pecan adaptation to coastal environments and saline-alkali stress mitigation. These findings enhance our understanding of soil microbiomes in coastal pecan plantations, and are anticipated to foster ecologically sustainable agroforestry practices and contribute to coastal marshland ecosystem management.

Comparison of Bacterial Communities in Five Ectomycorrhizal Fungi Mycosphere Soil.

Ectomycorrhizal fungi have huge potential value, both nutritionally and economically, but most of them cannot be cultivated artificially. To better understand the influence of abiotic and biotic factors upon the growth of ectomycorrhizal fungi, mycosphere soil and bulk soil of five ectomycorrhizal fungi (Calvatia candida, Russula brevipes, Leucopaxillus laterarius, Leucopaxillus giganteus, and Lepista panaeola) were used as research objects for this study. Illumina MiSeq sequencing technology was used to analyze the community structure of the mycosphere and bulk soil bacteria of the five ectomycorrhizal fungi, and a comprehensive analysis was conducted based on soil physicochemical properties. Our results show that the mycosphere soil bacteria of the five ectomycorrhizal fungi are slightly different. Escherichia, Usitatibacter, and Bradyrhizobium are potential mycorrhizal-helper bacteria of distinct ectomycorrhizal fungi. Soil water content, soil pH, and available potassium are the main factors shaping the soil bacterial community of the studied ectomycorrhizal fungi. Moreover, from the KEGG functional prediction and LEfSe analysis, there are significant functional differences not only between the mycosphere soil and bulk soil. 'Biosynthesis of terpenoidsand steroids', 'alpha-Linolenic acid metabolism', 'Longevity regulating pathway-multiple species', 'D-Arginine and D-ornithine metabolism', 'Nitrotoluene degradation' and other functions were significantly different in mycosphere soil. These findings have pivotal implications for the sustainable utilization of ectomycorrhizal fungi, the expansion of edible fungus cultivation in forest environments, and the enhancement of derived economic benefits.

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress.

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Small Interfering RNAs (siRNAs) Negatively Impact Growth and Gene Expression of Environmentally Relevant Bacteria in In Vitro Conditions.

Rising global populations have amplified food scarcity and ushered in the development of genetically modified (GM) crops containing small interference RNAs (siRNAs) that control gene expression to overcome these challenges. The use of RNA interference (RNAi) in agriculture remains controversial due to uncertainty regarding the unintended release of genetic material and downstream nontarget effects, which have not been assessed in environmental bacteria to date. To evaluate the impacts of siRNAs used in agriculture on environmental bacteria, this study assessed microbial growth and viability as well as transcription activity with and without the presence of environmental stressors. Results showed a statistically significant reduction in growth capacity and maximum biomass achieved when bacteria are exposed to siRNAs alone and with additional external stress (p < 0.05). Further transcriptomic analysis demonstrated that nutrient cycling gene activities were found to be consistently and significantly altered following siRNA exposure, particularly among carbon (xylA, FBPase, limEH, Chitinase, rgl, rgh, rgaE, mannanase, ara) and nitrogen (ureC, nasA, narB, narG, nirK) cycling genes (p < 0.05). Decreases in carbon cycling gene transcription profiles were generally significantly enhanced when siRNA exposure was coupled with nutrient or antimicrobial stress. Collectively, findings suggest that certain conditions facilitate the uptake of siRNAs from their surrounding environments that can negatively affect bacterial growth and gene expression activity, with uncertain downstream impacts on ecosystem homeostasis.

Effect of Altitude Gradients on the Spatial Distribution Mechanism of Soil Bacteria in Temperate Deciduous Broad-Leaved Forests.

Soil bacteria are an important part of the forest ecosystem, and they play a crucial role in driving energy flow and material circulation. Currently, many uncertainties remain about how the composition and distribution patterns of bacterial communities change along altitude gradients, especially in forest ecosystems with strong altitude gradients in climate, vegetation, and soil properties. Based on dynamic site monitoring of the Baiyun Mountain Forest National Park (33°38'-33°42' N, 111°47'-111°51' E), this study used Illumina technology to sequence 120 soil samples at the site and explored the spatial distribution mechanisms and ecological processes of soil bacteria under different altitude gradients. Our results showed that the composition of soil bacterial communities varied significantly between different altitude gradients, affecting soil bacterial community building by influencing the balance between deterministic and stochastic processes; in addition, bacterial communities exhibited broader ecological niche widths and a greater degree of stochasticity under low-altitude conditions, implying that, at lower altitudes, community assembly is predominantly influenced by stochastic processes. Light was the dominant environmental factor that influenced variation in the entire bacterial community as well as other taxa across different altitude gradients. Moreover, changes in the altitude gradient could cause significant differences in the diversity and community composition of bacterial taxa. Our study revealed significant differences in bacterial community composition in the soil under different altitude gradients. The bacterial communities at low elevation gradients were mainly controlled by stochasticity processes, and bacterial community assembly was strongly influenced by deterministic processes at middle altitudes. Furthermore, light was an important environmental factor that affects differences. This study revealed that the change of altitude gradient had an important effect on the development of the soil bacterial community and provided a theoretical basis for the sustainable development and management of soil bacteria.

Effects of Organic Fertilizer Addition to Vegetation and Soil Bacterial Communities in Saline-Alkali-Degraded Grassland with Photovoltaic Panels.

The Songnen grassland is an important resource for livestock production in China. Due to the intensification of anthropogenic activities in recent years, vegetation degradation has worsened, and the salinization of grassland has become increasingly serious, which severely affects the sustainable development of grassland animal husbandry. In this study, organic fertilizer addition was carried out at saline-and-alkaline-degraded Songnen grassland sites with photovoltaic panels, and we investigated the effects of organic fertilizer treatments on the vegetation and soil bacteria in these areas. The results showed that both organic fertilizer treatments increased the community composition and diversity indices of plants (p < 0.05); they also had significant effects on soil electrical conductivity and rapidly available potassium (p < 0.05). In the dominant phylum of bacteria, the relative abundance of Firmicutes increased without adding organic fertilizer under the photovoltaic panel; the addition of organic fertilizer had a significant effect on the relative abundance of Firmicutes and Desulfobacterota (p < 0.05), reducing their relative abundance, respectively. There were differences in the number of bacteria at the genus level under different treatments compared to the control, with the highest enrichment of bacteria occurring at the OFE position, and a significant difference (p < 0.05) being found between the control and the other four groups at the genus level of g_norank_f_norank_o_Actinomarinales. Organic fertilizer had a significant effect on the bacterial Simpson diversity index, with the most significant increasing trend found in OFE (the front eaves of the photovoltaic panel in fertilization area). The results of a correlation analysis showed that pH, electrical conductivity, and total nitrogen were the main factors affecting the soil bacterial community.

Variation in soil bacterial community characteristics inside and outside the West Ordos National Nature Reserve, northern China.

Nature reserves are crucial for protecting biological habitats and maintaining biodiversity. Soil bacterial community plays an irreplaceable role in the structure and function of ecosystem. However, the impact of nature reserves on soil bacterial communities is still unclear. To explore the effects of desert grassland nature reserve management on soil microbial communities, we compared the differences in soil bacterial community composition, α-diversity and community structure inside and outside a desert grassland nature reserve, and explored the correlation between soil bacterial communities and plant biomass and soil chemical index. We found that (1) the relative abundance of Acidobacteriota is highest in the soil both inside and outside the nature reserve in shrub grassland; (2) the Chao1 index of soil bacterial communities in the core protected zone and general control zone of the reserve was significantly higher than that outside the reserve (p < 0.05) in the shrub grassland. Similarly, in the herbaceous grassland, the Shannon index of soil bacterial communities was significantly higher in the core protected zone of the reserve than that outside the reserve (p < 0.05). (3) While we found no significant difference in soil bacterial community structure between inside and outside the reserve in the shrub grassland, we found that the soil bacterial community structure in the core protected zone was significantly different from that outside the reserve in the herbaceous grassland (p < 0.05); (4) we also found that higher plant productivity and soil nutrients promoted most soil dominant bacterial phyla, while higher soil pH and salinity inhibited most soil dominant bacterial phyla. Our findings thus help better understand the influencing factors of and the mechanisms behind variation in soil bacterial communities inside and outside desert grassland nature reserves.

Use of plant growth-promoting bacteria to facilitate phytoremediation.

Here, phytoremediation studies of toxic metal and organic compounds using plants augmented with plant growth-promoting bacteria, published in the past few years, were summarized and reviewed. These studies complemented and extended the many earlier studies in this area of research. The studies summarized here employed a wide range of non-agricultural plants including various grasses indigenous to regions of the world. The plant growth-promoting bacteria used a range of different known mechanisms to promote plant growth in the presence of metallic and/or organic toxicants and thereby improve the phytoremediation ability of most plants. Both rhizosphere and endophyte PGPB strains have been found to be effective within various phytoremediation schemes. Consortia consisting of several PGPB were often more effective than individual PGPB in assisting phytoremediation in the presence of metallic and/or organic environmental contaminants.

Priority establishment of soil bacteria in rhizosphere limited the spread of tetracycline resistance genes from pig manure to soil-plant systems based on synthetic communities approach.

The spread of antibiotic resistance genes (ARGs) in agroecosystems through the application of animal manure is a global threat to human and environmental health. However, the adaptability and colonization ability of animal manure-derived bacteria determine the spread pathways of ARG in agroecosystems, which have rarely been studied. Here, we performed an invasion experiment by creating a synthetic communities (SynCom) with ten isolates from pig manure and followed its assembly during gnotobiotic cultivation of a soil-Arabidopsis thaliana (A. thaliana) system. We found that Firmicutes in the SynCom were efficiently filtered out in the rhizosphere, thereby limiting the entry of tetracycline resistance genes (TRGs) into the plant. However, Proteobacteria and Actinobacteria in the SynCom were able to establish in all compartments of the soil-plant system thereby spreading TRGs from manure to soil and plant. The presence of native soil bacteria prevented the establishment of manure-borne bacteria and effectively reduced the spread of TRGs. Achromobacter mucicolens and Pantoea septica were the main vectors for the entry of tetA into plants. Furthermore, doxycycline stress promoted the horizontal gene transfer (HGT) of the conjugative resistance plasmid RP4 within the SynCom in A. thaliana by upregulating the expression of HGT-related mRNAs. Therefore, this study provides evidence for the dissemination pathways of ARGs in agricultural systems through the invasion of manure-derived bacteria and HGT by conjugative resistance plasmids and demonstrates that the priority establishment of soil bacteria in the rhizosphere limited the spread of TRGs from pig manure to soil-plant systems.

Tebuconazole promotes spread of a multidrug-resistant plasmid into soil bacteria to form new resistant bacterial strains.

The development of antibiotic resistance threatens human and environmental health. Non-antibiotic stressors, including fungicides, may contribute to the spread of antibiotic resistance genes (ARGs). We determined the promoting effects of tebuconazole on ARG dissemination using a donor, Escherichia coli MG1655, containing a multidrug-resistant fluorescent plasmid (RP4) and a recipient (E. coli HB101). The donor was then incorporated into the soil to test whether tebuconazole could accelerate the spread of RP4 into indigenous bacteria. Tebuconazole promoted the transfer of the RP4 plasmid from the donor into the recipient via overproduction of reactive oxygen species (ROS), enhancement of cell membrane permeability and regulation of related genes. The dissemination of the RP4 plasmid from the donor to soil bacteria was significantly enhanced by tebuconazole. RP4 plasmid could be propagated into more genera of bacteria in tebuconazole-contaminated soil as the exposure time increased. These findings demonstrate that the fungicide tebuconazole promotes the spread of the RP4 plasmid into indigenous soil bacteria, revealing the potential risk of tebuconazole residues enhancing the dissemination of ARGs in soil environments.

Distribution pattern and influencing factors of bacterial communities in different soil depths of Caragana jubata shurb in Luya Mountain, China.

Soil microorganisms are important components of terrestrial ecosystems, affecting soil formation and fertility, plant growth and stress tolerance, nutrient turnover and carbon storage. In this study, we collected soil samples (humus layer, 0-10 cm, 10-20 cm, 20-40 cm, and 40-80 cm) from Caragana jubata shrubland in Shanxi subalpine to explore the composition, diversity, and assembly of soil bacterial communities at different depths across the soil profile. The results showed that Actinomycota (19%-28%), Chloromycota (10%-36%) and Acidobacteria (15%-24%), and Proteobacteria (9%-25%) were the dominant bacterial phyla. α-diversity of soil bacterial community significantly decreased with the increases of soil depth. Soil bacterial ß-diversity varied across different soil depths. Soil pH, water content, and enzyme activity were the main ecological factors affecting the distribution of soil bacterial communities. Soil bacterial communities had more complex interactions in humus layer and 0-10 cm layer. On the whole, soil bacterial communities were dominated by coexistence in C. jubata shrubland, and the soil bacterial community assembly was driven by random process.

Effects of Root-Root Interactions on the Physiological Characteristics of Haloxylon ammodendron Seedlings.

The root traits and response strategies of plants play crucial roles in mediating interactions between plant root systems. Current research on the role of root exudates as underground chemical signals mediating these interactions has focused mainly on crops, with less attention given to desert plants in arid regions. In this study, we focused on the typical desert plant Haloxylon ammodendron and conducted a pot experiment using three root isolation methods (plastic film separation, nylon mesh separation, and no separation). We found that (1) as the degree of isolation increased, plant biomass significantly increased (p < 0.05), while root organic carbon content exhibited the opposite trend; (2) soil electrical conductivity (EC), soil total nitrogen (STN), soil total phosphorus (STP), and soil organic carbon (SOC) were significantly greater in the plastic film and nylon mesh separation treatments than in the no separation treatment (p < 0.05), and the abundance of Proteobacteria and Actinobacteriota was significantly greater in the plastic film separation treatment than in the no separation treatment (p < 0.05); (3) both plastic film and nylon mesh separations increased the secretion of alkaloids derived from tryptophan and phenylalanine in the plant root system compared with that in the no separation treatment; and (4) Pseudomonas, Proteobacteria, sesquiterpenes, triterpenes, and coumarins showed positive correlations, while both pseudomonas and proteobacteria were significantly positively correlated with soil EC, STN, STP, and SOC (p < 0.05). Aurachin D was negatively correlated with Gemmatimonadota and Proteobacteria, and both were significantly correlated with soil pH, EC, STN, STP, and SOC. The present study revealed strong negative interactions between the root systems of H. ammodendron seedlings, in which sesquiterpenoids, triterpenoids, coumarins, and alkaloids released by the roots played an important role in the subterranean competitive relationship. This study provides a deeper understanding of intraspecific interactions in the desert plant H. ammodendron and offers some guidance for future cultivation of this species in the northwestern region of China.

Sesame bacterial wilt significantly alters rhizosphere soil bacterial community structure, function, and metabolites in continuous cropping systems.

Bacterial wilt is the leading disease of sesame and alters the bacterial community composition, function, and metabolism of sesame rhizosphere soil. However, its pattern of change is unclear. Here, the purpose of this study was to investigate how these communities respond to three differing severities of bacterial wilt in mature continuously cropped sesame plants by metagenomic and metabolomic techniques, namely, absence (WH), moderate (WD5), and severe (WD9) wilt. The results indicated that bacterial wilt could significantly change the bacterial community structure in the rhizosphere soil of continuously cropped sesame plants. The biomarker species with significant differences will also change with increasing disease severity. In particular, the gene expression levels of Ralstonia solanacearum in the WD9 and WD5 treatments increased by 25.29% and 33.61%, respectively, compared to those in the WH treatment (4.35 log10 copies g-1). The occurrence of bacterial wilt significantly altered the functions of the bacterial community in rhizosphere soil. KEEG and CAZy functional annotations revealed that the number of significantly different functions in WH was greater than that in WD5 and WD9. Bacterial wilt significantly affected the relative content of metabolites, especially acids, in the rhizosphere soil, and compared with those in the rhizosphere soil from WH, 10 acids (including S-adenosylmethionine, N-acetylleucine, and desaminotyrosine, etc.) in the rhizosphere soil from WD5 or WD9 significantly increased. In comparison, the changes in the other 10 acids (including hypotaurine, erucic acid, and 6-hydroxynicotinic acid, etc.) were reversed. The occurrence of bacterial wilt also significantly inhibited metabolic pathways such as ABC transporter and amino acid biosynthesis pathways in rhizosphere soil and had a significant impact on two key enzymes (1.1.1.11 and 2.6.1.44). In conclusion, sesame bacterial wilt significantly alters the rhizosphere soil bacterial community structure, function, and metabolites. This study enhances the understanding of sesame bacterial wilt mechanisms and lays the groundwork for future prevention and control strategies against this disease.

Survival of a microbial inoculant in soil after recurrent inoculations.

Microbial inoculants are attracting growing interest in agriculture, but their efficacy remains unreliable in relation to their poor survival, partly due to the competition with the soil resident community. We hypothesised that recurrent inoculation could gradually alleviate this competition and improve the survival of the inoculant while increasing its impact on the resident bacterial community. We tested the effectiveness of such strategy with four inoculation sequences of Pseudomonas fluorescens strain B177 in soil microcosms with increasing number and frequency of inoculation, compared to a non-inoculated control. Each sequence was carried out at two inoculation densities (106 and 108 cfu.g soil-1). The four-inoculation sequence induced a higher abundance of P. fluorescens, 2 weeks after the last inoculation. No impact of inoculation sequences was observed on the resident community diversity and composition. Differential abundance analysis identified only 28 out of 576 dominants OTUs affected by the high-density inoculum, whatever the inoculation sequence. Recurrent inoculations induced a strong accumulation of nitrate, not explained by the abundance of nitrifying or nitrate-reducing microorganisms. In summary, inoculant density rather than inoculation pattern matters for inoculation effect on the resident bacterial communities, while recurrent inoculation allowed to slightly enhance the survival of the inoculant and strongly increased soil nitrate content.

Screening biosurfactant-producing actinomycetes: Identification of Streptomyces sp. RP1 as a potent species for bioremediation.

This study aimed to isolate biosurfactant-producing and hydrocarbon-degrading actinomycetes from different soils using glycerol-asparagine and starch-casein media with an antifungal agent. The glycerol-asparagine agar exhibited the highest number of actinomycetes, with a white, low-opacity medium supporting pigment production and high growth. Biosurfactant analyses, such as drop collapse, oil displacement, emulsification, tributyrin agar test, and surface tension measurement, were conducted. Out of 25 positive isolates, seven could utilize both olive oil and black oil for biosurfactant production, and only isolate RP1 could produce biosurfactant when grown in constrained conditions with black oil as the sole carbon source and inducer, demonstrating in situ bioremediation potential. Isolate RP1 from oil-spilled garden soil is Gram-staining-positive with a distinct earthy odor, melanin formation, and white filamentous colonies. It has a molecular size of ~621 bp and 100% sequence similarity to many Streptomyces spp. Morphological, biochemical, and 16 S rRNA analysis confirmed it as Streptomyces sp. RP1, showing positive results in all screenings, including high emulsification activity against kerosene (27.2%) and engine oil (95.8%), oil displacement efficiency against crude oil (7.45 cm), and a significant reduction in surface tension (56.7 dynes/cm). Streptomyces sp. RP1 can utilize citrate as a carbon source, tolerate sodium chloride, resist lysozyme, degrade petroleum hydrocarbons, and produce biosurfactant at 37°C in a 15 mL medium culture, indicating great potential for bioremediation and various downstream industrial applications with optimization.