Soluble Phosphorus Research Articles

Solubilization effects of egg yolk granules induced by weakly alkaline treatment.

Egg yolk granules (EYGs) are water-insoluble components of egg yolk that are rich in protein and phospholipids. Improving the solubility of EYGs is crucial for their development and utilization. The solubilization of EYGs in a weak alkaline environment (pH7.5-8.5) was investigated through physicochemical properties, microstructure analysis, and metabolomics. The results reveal a significant reduction in the average particle size of EYGs, ranging from 70.49 to 91.28nm in weakly alkaline conditions. Microstructure and spectroscopic analyses indicate conformational changes in EYGs under these conditions, facilitating the solubilization of proteins, calcium, phosphorus and other components. Furthermore, metabolomics analyses confirms that depolymerization of EYGs promotes the release of glycerophospholipids. These findings underscore the beneficial effects of weakly alkaline conditions on the solubility of EYGs.

Effect of lignin carbon material on phosphorus solubilisation performance of Bacillus megaterium.

Secondary salinisation significantly compromises soil quality because of the over-application of chemical fertilisers. The combined application of biochar and microorganisms enhanced soil physicochemical properties and improved soil remediation efficiency. However, different types of biochar had varying effects on microbial growth and reproduction. A phosphate-solubilising bacterial agent (BM-LPC) was obtained by low-temperature carbonisation/activation lignin-based porous carbon (LPC) in situ culture/adsorption Bacillus megaterium (BM). The maximum soluble phosphorus capacity of BM-LPC was 744.29mg/L when 1% LPC was added. This was a 22% increase compared with BM alone. The maximum adsorption of BM by LPC was 3.66×109 colony-forming units (CFU)/g. At 150days, the viable bacterial count of BM-LPC was 2.09×109CFU/g. The abundances of -OH, -COOH, -NH2, and CO groups on the surface of LPC provided a stable environment for BM, which in turn, enhanced the solubilisation of phosphorus and extended the viability of BM. The findings of this study can help increase the added value of industrial lignin and provide a theoretical basis for soil remediation research.

Functional and genomic analyses of plant growth promoting traits in Priestia aryabhattai and Paenibacillus sp. isolates from tomato rhizosphere

This study investigated plant growth-promoting (PGP) mechanisms in Priestia aryabhattai VMYP6 and Paenibacillus sp. VMY10, isolated from tomato roots. Their genomes were initially assessed in silico through various approaches, and these observations were then compared with results obtained in vitro and in vivo. Both possess genes associated with the production of siderophores, indole acetic acid (IAA) and cytokinins (CKs), all of which have been shown to promote plant growth. The two strains were able to produce these compounds in vitro. Although both genomes harbor genes for phosphorus solubilization, only VMY10 demonstrated this ability in vitro. Genes linked to flagellar assembly and chemotaxis were identified in the two cases. Both strains were able to colonize plant roots, even though VMYP6 lacked motility and no flagella were observed microscopically. In the greenhouse, tomato plants inoculated with the strains showed increased biomass, leaf area, and root length. These findings underscore the importance of integrating in vitro assays, genomic analyses, and plant trials to gain a comprehensive insight into the PGP mechanisms of rhizobacteria like VMYP6 and VMY10. Such insight may contribute to improving the selection of strains used as biofertilizers in tomato, a major crop worldwide.

Diversity, characterization, and biotechnological potential of plant growth-promoting bacteria from Bryophyllum pinnatum (Lam.) (Crassulaceae) roots and rhizosphere soil.

Cultivable microbial communities associated with plants inhabiting extreme environments have great potential in biotechnological applications. However, there is a lack of knowledge about these microorganisms from Bryophyllum pinnatum (which survives in severely barren soil) and their ability to promote plant growth. The present study focused on the isolation, identification, biochemical characterization, and potential applications of root endophytic bacteria and rhizosphere bacteria. A total of 73 bacterial isolates were obtained, with 50 derived from rhizospheric soil and 23 from root tissue. The identified strains were categorized into 16 genera, with Bacillus, Priestia, Pseudarthrobacter, Neobacillus, Mesobacillus, and Arthrobacter being the most species-rich genera. Heat stress experiments indicated that almost half (50.7%) of the selected isolates were tolerant to heat stress. Furthermore, most strains present diverse capabilities for biotechnological applications, including the potential for indole-3-acetic acid (IAA) production, organic phosphorus solubilization, inorganic phosphorus solubilization, and nitrogen fixation. Some isolates (21.92%) exhibited broad-spectrum antagonistic activity against various phytopathogenic fungi, including Fusarium spp. Agar plate assays revealed that the Cellulomonas hominis strain LS43 and Bacillus inaquosorum strain LS77 significantly increased the total fresh weight of Arabidopsis (P < 0.05), yet these strains did not significantly affect the primary root length or the number of leaves. Notably, a subset of the strains tested did not significantly increase the growth of Arabidopsis and, in fact, had inhibitory effects on certain growth parameters. This is the first investigation highlighting the potential of root endophytic bacteria and rhizosphere bacteria in association with B. pinnatum in barren soils. Thus, these isolated strains positively influence plant nutrient uptake, stress resilience, and biocontrol to reduce chemical inputs in conventional agricultural practices, highlighting the importance of their development as biofertilizers for improving the quality of barren soil.

Four Decades of Bacillus Biofertilizers: Advances and Future Prospects in Agriculture.

Over the past four decades, Bacillus biofertilizers, which are microbial formulations based on Bacillus species, have significantly contributed to sustainable agriculture by enhancing crop growth, improving soil health, and reducing the dependency on chemical fertilizers. Bacillus species, particularly known for their ability to promote plant growth, fix nitrogen, solubilize phosphorus, and produce growth-promoting substances such as phytohormones and antibiotics, have emerged as key players in the development of eco-friendly agricultural solutions. This research utilizes bibliometric analysis based on 3,242 documents sourced from the Web of Science database to map the development, key contributions, and innovation within the field from 1985 to 2023. This study identifies exponential growth in research output, particularly from 2003 onwards, indicating a robust interest and expanding research base predominantly in China, India, and the United States. We segmented the research timeline into three distinct phases, each marked by varying growth rates and research foci. This paper presents novel insights into the geographical and institutional distributions of research, highlighting the predominant role of developing countries in advancing Bacillus-based technologies. Key research hotspots have evolved from basic applications to complex interactions involving synthetic microbial communities and advanced multi-omics techniques. Our findings demonstrate a trend towards more strategic and technologically integrated approaches to developing Bacillus biofertilizers, reflecting broader shifts towards more sustainable agricultural systems. This study not only charts historical progress, but also proposes future research trajectories aimed at enhancing the application and effectiveness of microbial fertilizers across diverse ecosystems.

Intrasporangium zincisolvens sp. nov., A Novel Actinobacterium Isolated from Rhizosphere Soil.

A novel phosphate-solubilizing and zinc-solubilizing actinobacterium strain YIM S08009T was isolated from rhizosphere soil collected from Pinus yunnanensis in Wuliangshan National Nature Reserve, Pu'er City, Yunnan Province, southwest PR China. Cells of strain YIM S08009T were Gram-stain-positive, non-motile, irregular rods to cocci, and formed yellow and white colonies on nutrient agar. Growth was observed at 10-40°C (optimum 25-35°C), pH 6.0-8.5 (optimum 7), and 0-4% (w/v) NaCl (optimum 1%). The cell wall peptidoglycan contained LL-diaminopimelic acid. The whole-cell sugars were mannose, ribose, glucose, and galactose. The predominant menaquinone was MK-8(H4). Major polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, unknown lipid, and 3 unknown phospholipids. The predominant fatty acids were iso-C14:0, iso-C15:0, and iso-C16:0. The DNA G + C content was 72.6%. A phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM S08009T belonged to genus Intrasporangium, and was most closely related to Intrasporangium flavum MUSC 78T, with 99.0% 16S rRNA gene sequence similarity. Strain YIM S08009T shared 90.1% orthologous average nucleotide identity (OrthoANI) and 39.8% digital DNA-DNA hybridization (dDDH) with I. flavum MUSC 78T. The genome of strain YIM S08009T contained phosphate-solubilizing genes (SenX3, RegX3, pstSCAB, ugpBAEC, phoA) and zinc-solubilizing genes (znuABC, zupT), and the strain had also demonstrated in vitro phosphorus and zinc solubilization. Based on the genotypic and phenotypic analyses, strain YIM S08009T (= CGMCC 1.60168T = NBRC 116604T = KCTC 59021T) represents a novel Intrasporangium species, for which the name Intrasporangium zincisolvens sp. nov. is proposed.

Blended soil amendments: A viable strategy to reduce soluble phosphorus in soils.

Phosphorus (P) loss from soils can contribute significantly toward P enrichment in water bodies, impairing water quality. Application of soil amendments is a viable strategy to decrease soluble P in surface soils. Since soluble P is reduced through different mechanisms that are amendment-specific, blended amendments could be a better approach than single amendment applications; however, very little information is available on blended amendment effects in reducing P loss from soils. We compared the effectiveness of gypsum (CaSO4·2H2O), Epsom salt (MgSO4·7H2O), and alum [Al2(SO4)3·18H2O] applied singly or blended in different ratios in reducing water-extractable P (WEP) and Mehlich-3 P of two soils (0- to 15-cm depth) with contrasting P status (Mehlich-3 P of 7.1 mg kg-1 and 202 mg kg-1) from the Red River Valley region in MB, Canada. Ten treatments used for the laboratory incubation study were unamended control, gypsum or Epsom salt at 2.5 or 5 Mg ha-1, alum at 2.5 Mg ha-1, and four blended treatments of gypsum: alum or Epsom salt: alum at 1:1 or 2:1. Treated soils were saturated and incubated for 2 weeks and analyzed for WEP (an indicator of risk of P loss) and Mehlich-3 P (plant-available P) concentrations. All amendments significantly reduced the WEP concentrations compared to control in both soils. The blended amendments, particularly gypsum-alum blends, performed better than unblended amendments in reducing the potential risk of P loss. Mehlich-3 P concentration was not influenced by amended treatments, suggesting no significant decrease in plant-available P with amendments in both soils.

Synergistic Chemical Modification and Physical Adsorption for the Efficient Curing of Soluble Phosphorus/Fluorine in Phosphogypsum

Phosphogypsum (PG), a by-product of phosphoric acid production, contains high levels of fluorine and phosphorus impurities, which negatively impact the strength and setting time of PG-based cement materials and pose environmental risks. This study explores a dual approach combining physical adsorption using zeolite powder and chemical modification with quicklime (CaO) to immobilize these impurities. The composition of 90 wt.% PG, 5 wt.% zeolite powder, and 5 wt.% quicklime reduces the soluble phosphorus to below the detection limits and significantly lowers the free water content in the PG. Through SEM, XRD, and FT-IR analyses, it was found that zeolite powder adsorbs fluorine and phosphorus through encapsulation, while quicklime chemically reacts to form insoluble calcium phosphate and calcium fluoride. This transformation decreases the solubility, mitigating potential environmental contamination. The combination of physical adsorption and chemical conversion provides a sustainable strategy to reduce environmental hazards and enhance PG’s suitability for cement-based materials. The findings from this research offer a promising pathway for the sustainable utilization of PG, providing a mechanism for its safe incorporation into building materials, while addressing both environmental and material performance concerns.

Bioprospecting of a Native Plant Growth-Promoting Bacterium Bacillus cereus B6 for Enhancing Uranium Accumulation by Sudan Grass (Sorghum sudanense (Piper) Stapf).

Phytoremediation technology is viewed as a potential solution for addressing soil uranium contamination. Sudan grass (Sorghum sudanense (Piper) Stapf.), noted for its robust root structure and resilience to heavy metals, has garnered significant attention. This paper investigates a strain of uranium-tolerant bacterium, B6, obtained from the inter-root environment of native plants in soil contaminated with uranium tailings. The bacterium was identified as Bacillus cereus. Genomic analyses and assessment of uranium tolerance-promoting properties showed that strain B6 not only exhibited high uranium tolerance, but also possessed beneficial properties such as phosphorus solubilization and iron-producing carriers. In this study, we used strain B6 as an inoculant in combination with Sudan grass for germination and potting experiments. The findings demonstrated that Bacillus cereus B6 could substantially mitigate the adverse effects of uranium stress on Sudan grass, boost the plant's antioxidant response, significantly increase the root length and dry biomass of Sudan grass, and facilitate the accumulation of uranium in the roots, as well as its translocation to the aboveground portions. The study showed that PGPB strain B6 can significantly enhance the effect of plant accumulation of uranium and increase the potential of Sudan grass to become a uranium-rich plant, which provides an important scientific basis and application prospect for the use of microbial-assisted Sudan grass remediation technology to treat uranium-contaminated soil.

Integrated Nutrient Management Strategies for Red Gram, Sorghum and Blackgram-Based Intercropping Systems

A field experiment was conducted at the National Pulses Research Centre, Vamban, Pudukkottai District, during the kharif seasons of 2022 and 2023 to evaluate integrated nutrient management strategies for redgram-based intercropping systems. The study included two intercropping treatments: (I₁) Redgram + Sorghum (1:2) and (I₂) Redgram + Blackgram (1:2), along with three organic fertilizer treatments: (F₁) Recommended Dose of Fertilizer (RDF), (F₂) RDF + Vermicompost @ 2.5 t ha-1, and (F₃) RDF + Farmyard Manure (FYM) @ 5 t ha-1. Two biofertilizer treatments were also evaluated: (B₁) without Phosphorus Solubilizing Bacteria (PSB) and (B₂) with PSB. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. The study utilized the red gram variety VBN 3, intercropped with the sorghum variety K 11 and the black gram variety VBN 6. Results indicated that the redgram + blackgram (1:2) intercropping system produced the highest redgram plant height (347.6 cm), branches per plant (21.2), and number of pods (295.8 per plant). This system also achieved the highest redgram seed yield (858 kg ha-1), redgram grain equivalent yield (1139 kg ha-1), and benefit-cost ratio (2.69). The application of RDF + vermicompost at 2.5 t ha-1 produced the tallest redgram plants (348.8 cm) and the highest number of branches (21.6), with significantly higher pod numbers (300.6 per plant) and seed yield (856 kg ha-1). PSB application further enhanced seed yields, with the highest redgram grain equivalent yield (1122 kg ha-1) and benefit-cost ratio (2.76). The study concluded that the combination of redgram + blackgram intercropping, RDF + vermicompost, and PSB application offers an effective integrated nutrient management strategy, optimizing both grain yields and profitability.

Mechanisms of Rhizosphere Microorganisms in Regulating Plant Root System Architecture in Acidic Soils

Red soil occupies an important position in China's agriculturally cultivated land resources. However, its low pH value, high aluminum concentration, and inefficient phosphorus utilization limit the productivity of acidic red soil farmland. Plant roots exhibit remarkable plasticity, capable of absorbing water and nutrients and modulating root system architecture in response to biotic and abiotic stresses, either autonomously or through rhizosphere microorganisms. This study primarily investigates the regulatory effects of rhizosphere microorganisms, including plant growth-promoting rhizobacteria, such as arbuscular mycorrhizal fungi and rhizobia, and synthetic microbial consortia, on plant root system architecture. These regulatory mechanisms encompass the production of hormones, the release of volatile organic compounds, nitrogen fixation, phosphorus solubilization, and the improvement of rhizospheric soil structure. Such mechanisms can influence root biomass, branching, lateral roots, and root hair growth. Furthermore, we summarize new visualization methods for plant root system architecture and rhizosphere microorganisms, providing technical support for studying the regulation of root system architecture by rhizosphere microbes. Under acidic soil conditions, rhizosphere microorganisms serve as a crucial regulatory strategy. By adjusting plant root system architecture, they can enhance the productivity of acidic soils, representing a potential solution for ameliorating the constraints of acidic soils.

Plant Growth-promoting Bacteria Alleviate the Toxic Effects of Soil Microplastics and Heavy Metal Complex Pollution in Hybrid pennisetum

The coexistence of microplastics and heavy metals in soil can lead to more intricate environmental effects. While plant growth-promoting bacteria have been widely recognized for enhancing the remediation of heavy metal-contaminated soils, little research has been conducted to investigate whether they can alleviate the stress of microplastic-heavy metal composite contamination on plants. We investigated the effects of isolated and screened plant growth-promoting bacteria on the growth and cadmium （Cd） accumulation of Hybrid pennisetum under the composite pollution of Cd and polypropylene （PP） with different particle sizes （6.5 and 830 μm） in pot experiments and analyzed their effects on the composition of rhizosphere bacterial communities using high-throughput sequencing. Seven strains of bacteria were isolated and screened from soil contaminated with heavy metal-microplastic composites, identified as Enterobacter and Bacillus spp. All exhibited plant growth-promoting characteristics, including IAA production, siderophores, phosphorus solubilization, and potassium solubilization. Inoculation of plant growth-promoting bacteria increased the length and dry weight of H. pennisetum, effectively alleviating the stress caused by PP+Cd compound pollution. Plant growth-promoting bacteria increased soil available potassium and available phosphorus content, mitigating the decrease in soil mineral nutrients caused by PP+Cd composite pollution. PP+Cd compound pollution and plant growth-promoting bacterial inoculation affected the composition of the rhizosphere bacterial community of H. pennisetum, influencing dominant populations such as Proteobacteria, Firmicutes, and Actinobacteria. This study observed that the isolated and screened plant growth-promoting bacteria can effectively alleviate the plastic-heavy metal complex pollution caused by H. pennisetum. This provides a theoretical basis and data support for the remediation of microplastic heavy metal complex-contaminated soil biological pollution.

Modeling aerobic granules in continuously flowing wastewater-treatment processes.

Continuously flowing wastewater-treatment processes can be configured for biological and physical selection to form and retain large biological aggregates (LBAs), along with suspended biomass that contains ordinary biological flocs and biomass that has detached from the LBAs. Suspended biomass and LBAs have different solids residence times (SRTs) and mass-transport resistances. Here, mathematical sub-models that describe metabolic processes, a 1-D biofilm, and spherical carriers that can migrate throughout a wastewater-treatment process were combined to simulate a full-scale demonstration train having anaerobic, anoxic, and oxic zones, as well as side-stream enhanced biological phosphorus removal. Hydrocyclones were utilized for physical selection. Simulation results and experimental observations agreed for soluble chemical oxygen demand, nitrogen, and phosphorus removals, as well as mixed liquor concentration and characteristics. The model outputs demonstrated that suspended biomass was responsible for most of the transformations in the bioreactor, but LBAs contributed importantly to P accumulation as polyphosphate. The simulated LBAs accumulated a higher density of phosphorus-storing bacteria, polyphosphate, and total- and protein-extracellular polymeric substances (EPS), particularly near their core. Protein-EPS accumulated near the substratum because protein-EPS hydrolyzed more slowly than carbohydrate-EPS, while the SRT in each layer increased from the surface layer to the layer adjacent to the LBA core. PRACTITIONER POINTS: Combined models well represented observed solids components in a full-scale demonstration train as A2O with S2EBPR. Simulations described aerobic-granule structure and function consistent with what is known about aerobic granules in BNR processes. Suspended biomass dominated most of the simulated transformation rates, but the LBAs accumulated ~2000 mg P/L as polyphosphosphate. The simulated aerobic granules did not intensify WWT overall but should have improved the net solids-settling characteristics. Aerobic granules had more EPS than the suspended biomass and protein-EPS accumulated inside the LBA by slower hydrolysis kinetics.

Screening and Identification of Cold-Tolerant Phosphorus and Potassium Solubilizing Bacteria and Their Growth-Promoting Effects on Soybean in Cold Regions

In this study, we collected soybean inter-root soil (clay soil) from the cold region of Heilongjiang Province, China, screening for cold-tolerant phosphorus- and potassium-solubilizing bacteria by the gradient-cooling-directed screening and design of mixed bacterial agents. This study screened cold-tolerant phosphorus-solubilizing and potassium-solubilizing bacteria by gradient-cooling-directed screening and constructed mixed bacterial agents. We analyzed the strain’s phosphorus/potassium solubilizing capacity, as well as its organic acid secretion ability, to reveal its mechanism of detoxification of phosphorus and potassium. Clay soil from the cold region of Heilongjiang, China, was collected for soybean potting trials. The soybean pot experiment was used to investigate the growth-promoting effects of cold-tolerant strains applied to soybeans and to analyze the effects of changes in soil bacterial activity on soybean growth. A dominant phosphorus-solubilizing bacteria strain P-5 (Pantoea ananatis) was screened, and the amount of phosphorus-solubilizing bacteria was 34.94 mg/L with a PSI (Phosphorus Solubilization Index) of 1.80 for 7 days of incubation at 15 °C. The OD600 value (optical density of 600 nm) on the 10th day was 0.61. The dominant potassium-solubilizing bacteria, K-1 (Rahnella aquatilis), solubilized 23.02 mg/L of potassium under the same culture conditions, with a KSI (Potassium Solubilization) of 1.51 and an OD600 value of 0.59 on day 10. The dominant mixed bacterial agents H-5 (25% P-5 and 75% K-1), designed with the above two, detoxified phosphorus at 62.58 mg/L and potassium at 37.59 mg/L under the same culture conditions. It was shown that P-2 secretes gluconic acid and P-5 secretes lactic acid to degrade insoluble phosphorus at low temperatures and that K-1 secretes citric acid to degrade insoluble potassium. The soybean pot experiment study showed that the application of phosphorus-solubilizing bacteria (PSB), potassium-solubilizing bacteria (KSB), and mixed bacterial agents (MSB) alone could enhance the relative abundance of Pseudomonas, Rhizobium, and other bacterial genera in the soybean planting soil, compared with the control treatment without bacterial agents (BLK). Indirectly, they can enhance the accumulation of phosphorus and potassium in various organs of soybean, promote the development of soybean leaves and stems, and achieve the effect of promoting production and increasing income. This study has important theoretical value for the replacement of chemical fertilizer application by microbial agents in the cold region of China, and it has important practical and strategic significance for the promotion of income green safety in China’s main grain-producing areas.

Diversity and Plant Growth-Promoting Properties of Rhodiola rosea Root Endophytic Bacteria.

Plants inhabiting environments with suboptimal growth conditions often have a more pronounced capacity to attract and sustain microbial communities that improve nutrient absorption and expand abiotic stress tolerance. Rhodiola rosea L. is a succulent plant of the Crassulaceae family adapted to survive in sandy or rocky soils or dry tundra. The aim of the present study was to investigate the diversity and plant growth-stimulating potential of R. rosea endophytic microbiota. Metataxonomic analysis of the bacterial diversity in the rhizome of R. rosea revealed 108 families. Among these, three families were found exclusively in the core microbiome of 1-year-old plants, while nine families were unique to the core microbiome of mature plants grown in the field for more than 4 years. Seventy-three endophytic bacteria isolates were obtained from the rhizome of R. rosea plants and were assigned into 14 distinct bacterial genera of Firmicutes (26%) or Proteobacteria (74%) phyla. Screening for functional genes related to the nitrogen cycle, phosphorus mineralisation or dissolution, and traits associated with nitrogen fixation (56% of isolates), siderophore production (40%), inorganic phosphorus solubilisation (30%), and production of indole-related compounds (51%) led to the classification of the isolates into 16 distinct clusters. Co-cultivation of 45 selected isolates with germinating Arabidopsis seedlings revealed 18 and 5 isolates that resulted in more than a 20% increase in root or shoot growth, respectively. The study results established the complexity of the succulent R. rosea endophytic microbiome and identified isolates for potential plant growth-stimulating applications.

Is Pseudofrankia, the non-nitrogen-fixing and/or non-nodulating actinorhizal nodule dweller, mutualistic or parasitic? Insights from genome-predictive analysis.

This study re-evaluates Pseudofrankia strains, traditionally regarded as parasitic dwellers of actinorhizal root nodules due to their inability to fix nitrogen (Fix -) and/or nodulate (Nod -), as potential plant growth-promoting bacteria (PGPB). We compared plant growth-promoting traits (PGPTs) between Pseudofrankia strains, including one newly sequenced strain BMG5.37 in this study and typical (Fix + /Nod +) Frankia, Protofrankia, and Parafrankia, as well as non-frankia actinorhizal species Nocardia and Micromonospora, and the phytopathogenic Streptomyces. Although lacking nitrogen-fixing genes typically found in mutualistic Frankiaceae strains, Pseudofrankia may compensate through predicted pathways for denitrification and nitrate utilization. Functional profiling suggests potential for phosphorus solubilization, gibberellin production, and vitamin metabolism, as well as bioremediation of pollutants. Pseudofrankia strains are predicted to show moderate resistance to heavy metals, with a stronger tolerance to arsenic and tellurium compared to Frankia. Furthermore, they are anticipated to exhibit significant biotic and abiotic stress resistance, including oxidative and osmotic stress. Predictive data also indicate that Pseudofrankia strains may have root colonization abilities and may play a role in plant signaling and phytohormone production, particularly in auxin and gibberellin pathways. Secretion systems, especially CE-Type VI, are predicted to be highly developed in Pseudofrankia, suggesting potential for effective plant interactions. These findings position Pseudofrankia strains as promising candidates for plant growth promotion, although experimental validation and the integration of transcriptomic or proteomic data are needed to confirm these predictions.

The phospho-ferrozine assay: a tool to study bacterial redox-active metabolites produced at the plant root.

Soil microbial communities are pivotal to plant health and nutrient acquisition. It is becoming increasingly clear that many interactions, both among and between microbes and plants, are governed by small bioactive molecules or "secondary metabolites" that can aid in communication, competition, and nutrient uptake. Yet, secondary metabolite biogeography - who makes what, where, and why-is in its infancy. Further, secondary metabolite biosynthesis genes are often silent or weakly expressed under standard laboratory conditions, making it incredibly difficult to study these small molecules. To begin to address these dual challenges, we focused on redox-active metabolites (RAMs), a specific class of small molecules, and took advantage of recent findings that many RAMs aid in acquiring phosphorus and that their production is frequently stimulated by stress for this macronutrient. We developed a screen for RAM-producing bacteria that leverages phosphorus limitation to stimulate metabolite biosynthesis and uses a colorimetric (ferrozine) iron-reduction assay to identify redox activity. We isolated 557 root-associated bacteria from grasses collected at sites across the United States (Santa Rita Experimental Range [AZ], Konza Prairie Biological Station [KS], and Harvard Forest [MA]) and from commercial tomato plants and screened them for RAM production. We identified 128 soil isolates of at least 19 genera across Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes that produced RAMs under phosphorus stress. Our work reveals that the production of RAMs under phosphorus stress is common across diverse soil bacteria and provides an approach to screen for these small molecules rapidly.IMPORTANCEBy secreting secondary metabolites, bacteria at the plant root can defend against diseases and help acquire essential nutrients. However, the genes that synthesize secondary metabolites are typically inactive or are weakly expressed under standard laboratory conditions. This fact makes it difficult to study these small molecules and hinders the discovery of novel small molecules that may play crucial roles in agricultural and biomedical settings. Here, we focus on redox-active metabolites (RAMs), a class of secondary metabolites that can help bacteria solubilize phosphorus and are often produced when phosphorus is limited. We developed a screen that rapidly identifies RAM-producing bacteria by utilizing a colorimetric iron-reduction assay in combination with phosphorus limitation to stimulate biosynthesis. The screen reveals that RAM-producing bacteria are far more prevalent in soil than previously appreciated and that this approach can be used to identify RAM producers.

Characterization of psychrophilic bacteria with phosphorus solubilization activity and plant growth promotion

La Antártida, continente que presenta uno de los ambientes más hostiles del planeta, alberga una alta biodiversidad de microorganismos que pueden ser una fuente potencial de recursos biotecnológicos, incluidos aquellos que pueden solubilizar fósforo y promover el crecimiento vegetal. El objetivo de esta investigación fue caracterizar molecularmente bacterias de la Antártida colectadas de suelo y organismos fotosintéticos durante el verano Antártico de 2023, y evaluar su efecto en la detección de sideróforos y solubilización de fosfato tricálcico en condiciones de laboratorio. Además, se indagó su efecto en la germinación de semillas de fréjol Phaseolus vulgaris L. Las bacterias aisladas pertenecieron a los géneros Pseudomonas, Sporosarcina, Sphingomonas, Arthrobacter y Moraxella. El 73% de las bacterias estudiadas poseen capacidad de producir sideróforos, y las cepas fueron capaces de solubilizar fosfato tricálcico en medio de agar Pikovskaya, siendo Arthrobacter la bacteria que presentó mejores resultados. estas bacterias promovieron el enraizamiento de P. vulgaris L. Estos resultados respaldan la posible producción y aplicación de biofertilizantes tolerantes al frío para contribuir al desarrollo de una agricultura sostenible en zonas altas.

Enhancing maize drought and heat tolerance: single vs combined plant growth promoting rhizobacterial inoculation

Maize (Zea mays L.), a key staple crop in Sub-Saharan Africa, is particularly vulnerable to concurrent drought and heat stress, which threatens crop yield and food security. Plant growth-promoting rhizobacteria (PGPR) have shown potential as biofertilizers to enhance plant resilience under such abiotic stresses. This study aimed to (1) identify PGPR isolates tolerant to drought and heat, (2) assess their capacity to mitigate the effects of these stresses on early maize growth, and (3) analyze maize gene expression changes associated with PGPR-induced tolerance. Rhizobacteria were isolated and screened for drought and heat tolerance, alongside key plant growth-promoting (PGP) traits, including phosphorus solubilization, nitrogen fixation, and indole acetic acid production. In vitro and pot trials evaluated the effects of selected isolates on maize growth under stress, using indicators such as shoot length, root and shoot biomass (wet and dry), and leaf water content. Quantitative reverse transcription PCR (qRT-PCR) was employed to profile maize stress response genes. The identified PGPR isolates included Bacillus cereus (11MN1), Bacillus pseudomycoides (21MN1B), Lelliottia amnigena (33MP1), and Leclercia adecarboxylata (36MP8). Greenhouse trials demonstrated that L. amnigena 33MP1, L. adecarboxylata 36MP8, and a mixed culture of isolates (11MN1, 21MN1B, 33MP1, 36MP8) effectively alleviated the adverse effects of concurrent drought and heat stress in maize. Notably, qRT-PCR analysis indicated that PGPR-induced tolerance may involve the modulation of stress response genes CAT2 (catalase 2) and DHN2 (dehydrin 2), which play roles in oxidative stress management and cellular protection. The PGPR isolates identified in this study represent promising bioinoculants for enhancing maize resilience under climate-induced stresses, offering a sustainable approach to improve maize productivity, conserve water, and reduce irrigation needs in drought-prone regions.

Purification Effect of Fish–Algae Coupling on Nitrogen and Phosphorus in Shrimp Aquaculture Effluent

As the scale of shrimp aquaculture continues to expand, the environmental impacts of shrimp effluents have become increasingly severe. The purification of aquaculture effluents can no longer be overlooked. Effectively reducing the discharge of aquaculture wastewater and mitigating its potential pollution risks to the surrounding aquatic ecological environment are key issues that need to be addressed to promote the industry’s development towards a greener, more environmentally friendly, and sustainable path. This study explored the purification effect of the integration of tilapia and Spirulina on tail water from a zero-water-exchange aquaculture of whiteleg shrimp (Litopenaeus vannamei) in seawater, with the aim of assessing the growth performance of tilapia and the efficacy of the fish–algae integration in purifying tail water from the perspective of tail water resource utilisation. The study found that the removal rates of the biofloc sedimentation volume and total suspended particle concentration in the fish–algae group were 42.6% and 29.6%, respectively. The removal rates of phosphate and total phosphorus in the fish–algae group were 26.3% and 20.8%, respectively. Research indicates that tilapia effectively removes suspended organic matter from water. Introducing Spirulina into this water body aids in the removal of soluble nitrogen and phosphorus from the effluent, and tilapia exhibit a favourable feeding response to Spirulina.