The phosphate-solubilizing ability of Penicillium guanacastense and its effects on the growth of Pinus massoniana in phosphate-limiting conditions

Harnessing phosphate-solubilizing microorganisms for mitigation of nutritional and environmental stresses, and sustainable crop production

MAIN CONCLUSION

Phosphate-solubilizing microorganisms enhance nutrients availability, mitigate environmental stresses, and increase plant growth. The bioengineering of phosphate-solubilizing microbes and host plants may further improve their efficacy for increasing crop yield. Unsustainable agricultural practices are followed in current crop production systems worldwide for resolving food demand issues of ever-increasing human population. In addition, global food crop production is further affected due to continuous climatic change, erratic rains, and environmental stresses during the recent past causing threat to microbial as well as plant biodiversity. The application of plant beneficial microorganisms into agricultural practices has emerged recently as an innovative and sustainable approach to increase crop yield with limited resources and in vulnerable environment. These beneficial microbes improve crop productivity by enhancing nutrients' availability and mitigation of abiotic stresses along with suppression of plant diseases. However, there have been limited studies on the stress ameliorative role of phosphate-solubilizing microorganisms (PSMs), and there is still a need to elucidate the contribution of PSMs in improving plant health and crop productivity under harsh environmental conditions. This review summarizes the role of PSMs in improving phosphorus availability in soil through solubilization or mineralization of organic phosphate, and by assisting plants in amelioration of environmental stresses. Other beneficial activities of PSMs, such as release of phytohormones, production of ACC deaminase, strengthening of antioxidant system, and induction of systemic resistance, also contribute toward stress mitigation and plant growth promotion under stressful environments. Improvement in efficacy of PSMs and host plants using genetic engineering techniques has been discussed leading to increases in crop yields. However, further research is needed to develop sustainable climate-resilient approach by improving plant growth-promoting activities of PSMs even under environmental stresses to increase soil fertility and crop production in different agroecosystems.

Genomic Analysis of Penicillium griseofulvum CF3 Reveals Potential for Plant Growth Promotion and Disease Resistance

Penicillium griseofulvum CF3 is a fungus isolated from healthy strawberry soil, with the potential to promote the growth of plants and enhance their resistance to diseases. However, the genome sequence of P. griseofulvum CF3 remains unclear. Therefore, we performed the whole-genome CCS sequencing of P. griseofulvum CF3 using the PacBio Sequel II platform. The assembled genome comprised 104 contigs, with a total length of 37,564,657 bp, encoding 13,252 protein-coding genes. Comprehensive functional annotation was performed using various BLAST databases, including the non-redundant (Nr) protein sequence database, Gene Ontology (GO), the Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG), and the Carbohydrate-Active enZymes (CAZy) database, to identify and predict protein-coding genes, tRNAs, and rRNAs. The Antibiotics and Secondary Metabolites Analysis Shell (Antismash) analysis identified 50 biosynthetic gene clusters involved in secondary metabolite production within the P. griseofulvum CF3 genome. The whole-genome sequencing of P. griseofulvum CF3 helps us to understand its potential mechanisms in promoting plant growth and enhancing disease resistance, paving the way for the application of the CF3 strain in sustainable crop production.

Studies on the Phosphorus-Solubilizing Ability of Isaria cateinannulata and Its Influence on the Growth of Fagopyrum tataricum Plants

I. cateinannulata has been shown to promote the growth of F. tataricum. However, whether its growth-promoting capacity is related to its ability to solubilize phosphorus has not been reported. Therefore, in this study, we sought to assess the phosphorus-solubilizing ability of 18 strains of I. cateinannulata by analyzing their growth in an inorganic phosphorus culture medium. The effects of F. tataricum on growth and effective phosphorus content were analyzed through field experiments. The results showed that all 18 strains of I. cateinannulata had a phosphorus release capacity, with phosphorus solubilization ranging from 5.14 ± 0.37 mg/L to 6.21 ± 0.01 mg/L, and strain 9 exhibited the best phosphorus solubilization effect. Additionally, the field results demonstrated that I. cateinannulata positively influenced the growth, root length, and yield of F. tataricum by increasing the chlorophyll and soluble phosphorus content. This study will provide a material basis and theoretical support for investigating the interaction mechanism between I. cateinannulata and F. tataricum.

Multifarious Characterization and Efficacy of Three Phosphate-Solubilizing Aspergillus Species as Biostimulants in Improving Root Induction of Cassava and Sugarcane Stem Cuttings

Several soil fungi significantly contribute to the enhancement of plant development by improving nutrient uptake and producing growth-promoting metabolites. In the present study, three strains of phosphate-solubilizing fungi, namely, Aspergillus chiangmaiensis SDBR-CMUI4, A. pseudopiperis SDBR-CMUI1, and A. pseudotubingensis SDBR-CMUO2, were examined for their plant-growth-promoting capabilities. The findings demonstrated that all fungi showed positive siderophore production, but only A. pseudopiperis can produce indole-3-acetic acid. All fungi were able to solubilize insoluble phosphate minerals [Ca3(PO4)2 and FePO4] by producing phosphatase enzymes and organic acids (oxalic, tartaric, and succinic acids). These three fungal species were grown at a water activity ranging from 0.837 to 0.998, pH values ranging from 4 to 9, temperatures between 4 and 40 °C, and 16-17% NaCl in order to evaluate their drought, pH, temperature, and salt tolerances, respectively. Moreover, the results indicated that A. pseudopiperis and A. pseudotubingensis were able to tolerate commercial insecticides (methomyl and propargite) at the recommended dosages for field application. The viability of each fungal strain in the inoculum was higher than 50% at 4 and 20 °C after 3 months of storage. Subsequently, all fungi were characterized as plant-growth-promoting strains by improving the root inductions of cassava (Manihot esculenta Crantz) and sugarcane (Saccharum officinarum L.) stem cuttings in greenhouse experiments. No symptoms of plant disease were observed with any of the treatments involving fungal inoculation and control. The cassava and sugarcane stem cuttings inoculated with fungal strains and supplemented with Ca3(PO4)2 exhibited significantly increased root lengths, shoot and root dry biomasses, chlorophyll concentrations, and cellular inorganic phosphate contents. Therefore, the application of these phosphate-solubilizing fungi is regarded as a new frontier in the induction of roots and the promotion of growth in plants.

Plant growth promotion under phosphate deficiency and improved phosphate acquisition by new fungal strain, Penicillium olsonii TLL1

Microbiomes in soil ecosystems play a significant role in solubilizing insoluble inorganic and organic phosphate sources with low availability and mobility in the soil. They transfer the phosphate ion to plants, thereby promoting plant growth. In this study, we isolated an unidentified fungal strain, POT1 (Penicillium olsonii TLL1) from indoor dust samples, and confirmed its ability to promote root growth, especially under phosphate deficiency, as well as solubilizing activity for insoluble phosphates such as AlPO4, FePO4·4H2O, Ca3(PO4)2, and hydroxyapatite. Indeed, in vermiculite containing low and insoluble phosphate, the shoot fresh weight of Arabidopsis and leafy vegetables increased by 2-fold and 3-fold, respectively, with POT1 inoculation. We also conducted tests on crops in Singapore's local soil, which contains highly insoluble phosphate. We confirmed that with POT1, Bok Choy showed a 2-fold increase in shoot fresh weight, and Rice displayed a 2-fold increase in grain yield. Furthermore, we demonstrated that plant growth promotion and phosphate solubilizing activity of POT1 were more effective than those of four different Penicillium strains such as Penicillium bilaiae, Penicillium chrysogenum, Penicillium janthinellum, and Penicillium simplicissimum under phosphate-limiting conditions. Our findings uncover a new fungal strain, provide a better understanding of symbiotic plant-fungal interactions, and suggest the potential use of POT1 as a biofertilizer to improve phosphate uptake and use efficiency in phosphate-limiting conditions.

Isolation and Identification of a Phosphate-Solubilizing Pantoea dispersa with a Saline-Alkali Tolerance and Analysis of Its Growth-Promoting Effects on Silage Maize Under Saline-Alkali Field Conditions

Phosphate-solubilizing bacteria (PSB) are microorganisms that can dissolve insoluble phosphorus (P) to accessible forms. This study aimed to screen saline-alkali-tolerant PSB and analyze its growth promoting properties, and evaluate its effects on the growth, quality, soil nutrient balance, and enzyme activities of silage maize in the field. We isolated six phosphate-solubilizing strains from rhizosphere soil of silage maize planted in saline-alkali land, and FC-1 with the best P-solubilizing effect was used for further study. The morphological, physiological and biochemical analysis, and 16S rDNA and housekeeping gene atpD sequencing were performed for identification. FC-1 was identified as Pantoea dispersa and had high P solubility. The phosphate solubility of FC-1 using four P sources ranged from 160.79 to 270.22 mg l-1. FC-1 produced indole-3-acetic acid (IAA) and decreased the pH of the growth media by secreting organic acids, including citric acid, malic acid, succinic acid, and acetic acid. The results of a field experiment indicated that FC-1 treatment increased the height, stem diameter, fresh weight, dry weight, starch content, crude protein content, and total P content of silage maize by 9.8, 9.2, 12.6, 11.7, 12.6, 18.3, and 17.4%, respectively. The nitrogen, potassium, phosphorus, and organic matter contents in the rhizosphere soil of silage maize increased by 29.8, 17.1, 17.9, and 25.3%, respectively; urease, catalase, sucrase, and alkaline phosphatase levels also increased by 24.7, 26.7, 24.0, and 19.5%, respectively. FC-1 promoted the growth of silage maize by improving nutrient metabolism and enzyme activities in saline-alkali soil and may be an effective alternative to fertilizers.

Drivers to improve metal(loid) phytoextraction with a focus on microbial degradation of dissolved organic matter in soils

Bioaugmentation of soils can increase the mobilization of metal(loid)s from the soil-bearing phases. However, once desorbed, these metal(loid)s are mostly complexed to the dissolved organic matter (DOM) in the soil solution, which can restrict their availability to plants (roots mainly taking up the free forms) and then the phytoextraction performances. Firstly the main drivers influencing phytoextraction are reminded, then the review focuses on the DOM role. After having reminding the origin, the chemical structure and the lability of DOM, the pool of stable DOM (the most abundant in the soil) most involved in the complexation of metal(loid)s is addressed in particular by focusing on carboxylic and/or phenolic groups and factors controlling metal(loid) complexation with DOM. Finally, this review addresses the ability of microorganisms to degrade metal(loid)-DOM complexes as an additional lever for increasing the pool of free metal(loid) ions, and then phytoextraction performances, and details the origin of microorganisms and how they are selected. The development of innovative processes including the use of these DOM-degrading microorganisms is proposed in perspectives.

Date Palm Waste Compost Application Increases Soil Microbial Community Diversity in a Cropping Barley (Hordeum vulgare L.) Field

Application of date palm waste compost is quite beneficial in improving soil properties and crop growth. However, the effect of its application on soil microbial communities is less understood. High-throughput sequencing and quantitative real-time PCR (qPCR) were used to evaluate the effect of compost application on the soil microbial composition in a barley field during the tillering, booting and ripening stages. The results showed that compost treatment had the highest bacterial and fungal abundance, and its application significantly altered the richness (Chao1 index) and α-diversity (Shannon index) of fungal and bacterial communities. The dominant bacterial phyla found in the samples were Proteobacteria and Actinobacteria while the dominant fungal orders were Ascomycota and Mortierellomycota. Interestingly, compost enriched the relative abundance of beneficial microorganisms such as Chaetomium, Actinobacteriota, Talaromyces and Mortierella and reduced those of harmful microorganisms such as Alternaria, Aspergillus and Neocosmospora. Functional prediction based on Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) showed that amplicon sequence variant (ASV) sequences related to energy metabolism, amino acid metabolism and carbohydrate metabolism were associated with compost-treated soil. Based on Fungi Functional Guild (FUNGuild), identified fungi community metabolic functions such as wood saprotroph, pathotroph, symbiotroph and endophyte were associated with compost-treated soil. Overall, compost addition could be considered as a sustainable practice for establishing a healthy soil microbiome and subsequently improving the soil quality and barley crop production.

Nematophagous Fungi: A Review of Their Phosphorus Solubilization Potential

Nematophagous fungi (NF) are a group of diverse fungal genera that benefit plants. The aim of this review is to increase comprehension about the importance of nematophagous fungi and their role in phosphorus solubilization to favor its uptake in agricultural ecosystems. They use different mechanisms, such as acidification in the medium, organic acids production, and the secretion of enzymes and metabolites that promote the bioavailability of phosphorus for plants. This study summarizes the processes of solubilization, in addition to the mechanisms of action and use of NF on crops, evidencing the need to include innovative alternatives for the implementation of microbial resources in management plans. In addition, it provides information to help understand the effect of NF to make phosphorus available for plants, showing how these biological means promote phosphorus uptake, thus improving productivity and yield.

Metabolic characterization of phosphate solubilizing microorganisms and their role in improving soil phosphate solubility, yield of upland rice (Oryza sativa L.), and phosphorus fertilizers efficiency

Phosphate solubilizing microbes (PSM) can improve soil P availability by P dissolution. These microbes can make substances that regulate plant growth, which promotes plant growth. The present study aimed to characterize PSM and determine how PSM application affected P solubilization, soil phosphatase activity, and upland rice yield. The greenhouse experiment used a factorial randomized block design (RBD) with two factors and three replications. The first factor was PSM isolates, which came in four different forms: without microbes, with microbes (Burkholderia sp.), with fungus (Penicillium sp.), and with a combination of microbes (Burkholderia sp. and Penicillium sp.). The PSM isolates were characterized to analyze the production of organic acids, phosphatase enzymes, and phytohormones. The second factor was the superphosphate fertilizer dose, which has four levels: 0, 50, 75, and 100 kg P ha−1. According to the PSM characterization, it produced organic acids such as lactate acid, oxalate acid, citric acid, and acetate acid, as well as phytohormones (IAA) and the enzyme phosphatase. The pot experiment results show that the PSM inoculation raised the available P and soil phosphatase, P content of the plant, decreased soil organic P, and increased upland rice production. For improving available P, phosphatase activity, P content of the plant, and upland rice yields, mixed inoculants of phosphate-solubilizing bacteria and fungi performed better. The availability of soil P, the activity of the enzyme phosphatase, and the upland rice yields were all improved by applying P fertilizer at 75 kg P ha−1. This study showed that PSM as a biofertilizer reduced the dosage of inorganic fertilizers by up to 25%.

Interactions of Fungi and Algae from the Greenland Ice Sheet

Heavily pigmented glacier ice algae Ancylonema nordenskiöldii and Ancylonema alaskanum (Zygnematophyceae, Streptophyta) reduce the bare ice albedo of the Greenland Ice Sheet, amplifying melt from the largest cryospheric contributor to eustatic sea-level rise. Little information is available about glacier ice algae interactions with other microbial communities within the surface ice environment, including fungi, which may be important for sustaining algal bloom development. To address this substantial knowledge gap and investigate the nature of algal-fungal interactions, an ex situ co-cultivation experiment with two species of fungi, recently isolated from the surface of the Greenland Ice Sheet (here proposed new species Penicillium anthracinoglaciei Perini, Frisvad and Zalar, Mycobank (MB 835602), and Articulospora sp.), and the mixed microbial community dominated by glacier ice algae was performed. The utilization of the dark pigment purpurogallin carboxylic acid-6-O-β-D-glucopyranoside (C₁₈H₁₈O₁₂) by the two fungi was also evaluated in a separate experiment. P. anthracinoglaciei was capable of utilizing and converting the pigment to purpurogallin carboxylic acid, possibly using the sugar moiety as a nutrient source. Furthermore, after 3 weeks of incubation in the presence of P. anthracinoglaciei, a significantly slower decline in the maximum quantum efficiency (F_v/F_m, inverse proxy of algal stress) in glacier ice algae, compared to other treatments, was evident, suggesting a positive relationship between these species. Articulospora sp. did uptake the glycosylated purpurogallin, but did not seem to be involved in its conversion to aglycone derivative. At the end of the incubation experiments and, in conjunction with increased algal mortality, we detected a substantially increasing presence of the zoosporic fungi Chytridiomycota suggesting an important role for them as decomposers or parasites of glacier ice algae.

Fine Identification and Classification of a Novel Beneficial Talaromyces Fungal Species from Masson Pine Rhizosphere Soil

Rhizosphere fungi have the beneficial functions of promoting plant growth and protecting plants from pests and pathogens. In our preliminary study, rhizosphere fungus JP-NJ4 was obtained from the soil rhizosphere of Pinus massoniana and selected for further analyses to confirm its functions of phosphate solubilization and plant growth promotion. In order to comprehensively investigate the function of this strain, it is necessary to ascertain its taxonomic position. With the help of genealogical concordance phylogenetic species recognition (GCPSR) using five genes/regions (ITS, BenA, CaM, RPB1, and RPB2) as well as macro-morphological and micro-morphological characters, we accurately determined the classification status of strain JP-NJ4. The concatenated phylogenies of five (or four) gene regions and single gene phylogenetic trees (ITS, BenA, CaM, RPB1, and RPB2 genes) all show that strain JP-NJ4 clustered together with Talaromyces brevis and Talaromyces liani, but differ markedly in the genetic distance (in BenA gene) from type strain and multiple collections of T. brevis and T. liani. The morphology of JP-NJ4 largely matches the characteristics of genes Talaromyces, and the rich and specific morphological information provided by its colonies was different from that of T. brevis and T. liani. In addition, strain JP-NJ4 could produce reduced conidiophores consisting of solitary phialides. From molecular and phenotypic data, strain JP-NJ4 was identified as a putative novel Talaromyces fungal species, designated T. nanjingensis.

Cultivated and wild pearl millet display contrasting patterns of abundance and co-occurrence in their root mycobiome

Fungal communities associated with roots play a key role in nutrient uptake and in mitigating the abiotic and biotic stress of their host. In this study, we characterized the roots mycobiome of wild and cultivated pearl millet [Pennisetum glaucum (L.) R. Br., synonym: Cenchrus americanus (L.) Morrone] in three agro-ecological areas of Senegal following a rainfall gradient. We hypothesized that wild pearl millet could serve as a reservoir of endophytes for cultivated pearl millet. We therefore analyzed the soil factors influencing fungal community structure and whether cultivated and wild millet shared the same fungal communities. The fungal communities associated with pearl millet were significantly structured according to sites and plant type (wild vs cultivated). Besides, soil pH and phosphorus were the main factors influencing the fungal community structure. We observed a higher fungal diversity in cultivated compared to wild pearl millet. Interestingly, we detected higher relative abundance of putative pathotrophs, especially plant pathogen, in cultivated than in wild millet in semi-arid and semi-humid zones, and higher relative abundance of saprotrophs in wild millet in arid and semi-humid zones. A network analysis based on taxa co-occurrence patterns in the core mycobiome revealed that cultivated millet and wild relatives had dissimilar groups of hub taxa. The identification of the core mycobiome and hub taxa of cultivated and wild pearl millet could be an important step in developing microbiome engineering approaches for more sustainable management practices in pearl millet agroecosystems.

Mixture Compound Fertilizer and Super Absorbent Polymer Application Significantly Promoted Growth and Increased Nutrient Levels in Pinus massoniana Seedlings and Soil in Seriously Eroded Degradation Region of Southern China

Pinus massoniana is the pioneer tree species in the red soil regions of southern China, however, the serious understory soil erosion and nutrient deficiency in that region are the main factors restricting the growth of P. massoniana. This field study examined the effects of compound fertilizer and super absorbent polymer (SAP) on the physiology, growth characteristics, biomass, soil nutrient, plant nutrient content, and nutrient uptake efficiency of 1-year-old P. massoniana seedlings for 2 years at Changting, Fujian in South China. One control (no fertilizer, CK) and fertilization treatments were established, namely, single compound fertilizer application (0.94, 1.89, and 3.56 g⋅plant^-1) and mixture compound fertilizer and SAP application (0.94 + 1.01, 1.89 + 1.01, and 3.56 + 1.01 g⋅plant^-1). Fertilization significantly improved the physiological performance, root collar diameter growth, height growth, biomass, and nutrient uptake of the seedlings. Compared with other fertilization treatments, the mixture compound fertilizer and SAP application significantly improved the seedling photosynthesis, which meant that the SAP had a significant effect on promoting photosynthesis. Under the mixture compound fertilizer and SAP application, the whole biomass of the seedlings was higher than that of all other treatments. Fertilization significantly increased the nitrogen (N), phosphorus (P), and potassium (K) content in the soils, leaves, stems, and roots of the seedlings, respectively. The P content was the main factor affecting growth characteristics and contributed to 58.03% of the total variation in seedling growth characteristics (P < 0.01). The N:P ratio of CK in the soils, leaves, and stems were higher than that of all the fertilization treatments, indicating that the severely eroded and degraded region had little P and required much of P. The principal component analysis indicated that the F2S (1.89 + 1.01 g) was the optimum fertilization amount and method in this experiment. These results provide a theoretical basis for the fertilization management of P. massoniana forests with severely eroded and degraded red soil regions.

Sorghum-Phosphate Solubilizers Interactions: Crop Nutrition, Biotic Stress Alleviation, and Yield Optimization

Sweet sorghum [Sorghum bicolor (L.) Moench] is a highly productive, gluten-free cereal crop plant that can be used as an alternative energy resource, human food, and livestock feed or for biofuel-ethanol production. Phosphate fertilization is a common practice to optimize sorghum yield but because of high cost, environmental hazards, and soil fertility reduction, the use of chemical P fertilizer is discouraged. Due to this, the impetus to search for an inexpensive and eco-friendly microbiome as an alternative to chemical P biofertilizer has been increased. Microbial formulations, especially phosphate solubilizing microbiome (PSM) either alone or in synergism with other rhizobacteria, modify the soil nutrient pool and augment the growth, P nutrition, and yield of sorghum. The use of PSM in sorghum disease management reduces the dependence on pesticides employed to control the phytopathogens damage. The role of PSM in the sorghum cultivation system is, however, relatively unresearched. In this manuscript, the diversity and the strategies adopted by PSM to expedite sorghum yield are reviewed, including the nutritional importance of sorghum in human health and the mechanism of P solubilization by PSM. Also, the impact of solo or composite inoculations of biological enhancers (PSM) with nitrogen fixers or arbuscular mycorrhizal fungi is explained. The approaches employed by PSM to control sorghum phytopathogens are highlighted. The simultaneous bio-enhancing and biocontrol activity of the PS microbiome provides better options for the replacement of chemical P fertilizers and pesticide application in sustainable sorghum production practices.

The Effects of Host Plant Genotype and Environmental Conditions on Fungal Community Composition and Phosphorus Solubilization in Willow Short Rotation Coppice

Phosphorus (P) is an essential plant nutrient. Low availability of P in soil is mainly caused by high content of Fe2O3 in the clay fraction that binds to P making it unavailable. Beneficial microbes, such as P solubilizing microorganisms can increase the available P in soil and improve plant growth and productivity. In this study, we evaluated the effects of environmental conditions (climate, soil parameters), plant genotype, and level of plant association (rhizosphere or endophytic root organism) on the abundance and diversity of phosphorus solubilizing microorganisms in a Salix production system. We hypothesized that a lower number of endophytic fungi may possess the ability to solubilize P compared to the number of rhizosphere fungi with the same ability. We also expect that the plant genotype and the experimental site with its environmental conditions will influence fungal diversity. Two Salix genotypes grown in pure and mixed cultures were investigated for their fungal microbiome community and diversity in the rhizosphere and endosphere during two growing seasons. We found that the rhizosphere fungal community was more diverse. A general dominance of Ascomycota (Dothideomycetes) and Basidiomycota (Tremellomycetes) was observed. The classes Agaricomycetes and Pezizomycetes were more frequent in the endosphere, while Tremellomycetes and Mortierellomycetes were more abundant in the rhizosphere. Plot-specific soil properties (pH, total organic carbon, and nitrogen) significantly influenced the fungal community structure. Among the culturable fungal diversities, 10 strains of phosphate solubilizing fungi (PSFs) from roots and 12 strains from rhizosphere soil were identified using selective media supplemented with di-calcium and tri-calcium phosphates. The fungal density and the number of PSF were much higher in the rhizosphere than in the endosphere. Penicillium was the dominant genus of PSF isolated from both sites; other less frequent genera of PSFs were Alternaria, Cladosporium, and Clonostachys. Overall the main factors controlling the fungal communities (endophytic vs. rhizosphere fungi) were the soil properties and level of plant association, while no significant influence of growing season was observed. Differences between Salix genotypes were observed for culturable fungal diversity, while in metagenomic data analysis, only the class Dothideomycetes showed a significant effect from the plant genotype.

Streptomyces strains modulate dynamics of soil bacterial communities and their efficacy in disease suppression caused by Phytophthora capsici

The responses of rhizosphere bacterial communities of Streptomyces (SS14 and IT20 stains) treated-pepper plants following inoculation by Phytophthora capsici (PC) was investigated using Illumina MiSeq sequencing. Distinct modulation of the bacteriome composition was found for PC samples with the highest relative abundance (RA) of Chitinophaga (22 ± 0.03%). The RA of several bacterial operational taxonomic units (OTUs) was affected and caused changes in alpha and beta-diversity measures. In IT20, the RA of Cyanobacteria was enriched compared to SS14 (72%) and control samples (47%). Phylotypes belonging to Devosia, Promicromonospora, Kribbella, Microbacterium, Amylocolatopsis, and Pseudomonas genera in the rhizosphere were positively responding against the pathogen. Our findings show that the phosphate solubilizing strain IT20 has higher microbial community responders than the melanin-producing strain SS14. Also, positive interactions were identified by comparing bacterial community profiles between treatments that might allow designing synthetic bio-inoculants to solve agronomic problems in an eco-friendly way.

The Status of Soil Microbiome as Affected by the Application of Phosphorus Biofertilizer: Fertilizer Enriched with Beneficial Bacterial Strains

Regarding the unfavourable changes in agroecosystems resulting from the excessive application of mineral fertilizers, biopreparations containing live microorganisms are gaining increasing attention. We assumed that the application of phosphorus mineral fertilizer enriched with strains of beneficial microorganisms contribute to favourable changes in enzymatic activity and in the genetic and functional diversity of microbial populations inhabiting degraded soils. Therefore, in field experiments conditions, the effects of phosphorus fertilizer enriched with bacterial strains on the status of soil microbiome in two chemically degraded soil types (Brunic Arenosol - BA and Abruptic Luvisol - AL) were investigated. The field experiments included treatments with an optimal dose of phosphorus fertilizer (without microorganisms - FC), optimal dose of phosphorus fertilizer enriched with microorganisms including Paenibacillus polymyxa strain CHT114AB, Bacillus amyloliquefaciens strain AF75BB and Bacillus sp. strain CZP4/4 (FA100) and a dose of phosphorus fertilizer reduced by 40% and enriched with the above-mentioned bacteria (FA60). The analyzes performed included: the determination of the activity of the soil enzymes (protease, urease, acid phosphomonoesterase, β-glucosidase), the assessment of the functional diversity of microorganisms with the application of BIOLOGTM plates and the characterization of the genetic diversity of bacteria, archaea and fungi with multiplex terminal restriction fragment length polymorphism and next generation sequencing. The obtained results indicated that the application of phosphorus fertilizer enriched with microorganisms improved enzymatic activity, and the genetic and functional diversity of the soil microbial communities, however these effects were dependent on the soil type.

Screening of Phosphate-Solubilizing Fungi From Air and Soil in Yunnan, China: Four Novel Species in Aspergillus, Gongronella, Penicillium, and Talaromyces

Phosphate-solubilizing fungi (PSF) play an important role in increasing the bioavailability of phosphorus in soils for plants. Thirteen fungal strains, one collected from air and 12 from soil, were screened and described here in detail. These fungal strains were tested for their ability to solubilize tricalcium phosphate (TCP) on both solid and liquid Pikovskaya (PVK) media in vitro. The airborne fungal strain KUMCC 18-0196 (Aspergillus hydei sp. nov.) showed the most significant phosphate solubilizing activity on a solid PVK medium with the solubilization index (SI) (2.58 ± 0.04 cm) and the highest solubilized phosphates (1523.33 ± 47.87 μg/mL) on a liquid PVK medium. To the best of our knowledge, A. hydei sp. nov. is the first phosphate-solubilizing fungus reported from air. We also provide the identification especially for Aspergillus, Penicillium and Talaromyces, generally reported as PSF. It is important to not only screen for PSF but also identify species properly so that researchers have a clearer taxonomic picture for identifying potential taxa for future plant growth-promoting applications. Herein, A. hydei (section Nigri), Gongronella hydei, Penicillium soli (section Lanata-Divaricata) and Talaromyces yunnanensis (section Talaromyces) are fully described and introduced as new to science. These four new species are identified based on both morphological characteristics and multigene phylogenetic analyses, including the genealogical concordance phylogenetic species recognition method where necessary. Penicillium austrosinense is considered to be a synonym of P. guaibinense.

Evaluation of Pantoea eucalypti FBS135 for pine (Pinus massoniana) growth promotion and its genome analysis

AIMS

Pinus massoniana is one of the most widely distributed forest plants in China. In this study, we isolated a bacterial endophyte (designated FBS135) from apical buds and needles of P. massoniana. Investigations were performed to understand the effects of the strain on pine growth, its genomic features and the functions of the plasmids it carries.

METHODS AND RESULTS

Based on its morphological features and 16S rRNA sequence, strain FBS135 was primarily identified as Pantoea eucalypti. We found that FBS135 not only promoted the growth of P. massoniana seedlings, but also significantly increased the survival rate of pine seedlings. The whole genome of FBS135 was sequenced, which revealed that the bacterium carries one chromosome and four plasmids. Its chromosome is 4 023 751 bp in size and contains dozens of genes involved in plant symbiosis. Curing one of the four plasmids, pPant1, resulted in a decrease in the size of the FBS135 colonies and the loss of the ability to synthesize yellow pigment, indicating that this plasmid may be very important for FBS135.

CONCLUSIONS

Pantoea eucalypti FBS135 has a genomic basis to be implicated in plant-associated lifestyle and was established to have the capability to promote pine growth.

SIGNIFICANCE AND IMPACT OF THE STUDY

To the best of our knowledge, this is the first report that such a bacterial species, P. eucalypti, was isolated from pine trees and evidenced to have pine beneficial activities. Our results elucidate the ecological effects of endophytes on forest plants as well as endophyte-plant interaction mechanisms.