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The global market of sweet potato (Ipomoea batatas (L.) Lam.) is continuously growing and, consequently, demands greater productivity from the agricultural sector. The use of biofertilizers facilitates plant growth by making essential nutrients available to crops or providing resistance against different abiotic and biotic factors. The strains Bacillus safensis T052-76 and Bacillus velezensis T149-19 have previously been inoculated in the sweet potato cultivar Ourinho, showing positive effects on plant shoot growth and inhibiting the phytopathogen Plenodomus destruens. To elucidate the effects of these strains on sweet potato growth, four different cultivars of sweet potato were selected: Capivara, IAPAR 69, Rosinha de Verdan and Roxa. The plants were grown in pots in a greenhouse and inoculated with the combined strains according to a randomized block design. A control (without the inoculation of both strains) was also used. A slight positive effect of the inoculation of the two Bacillus strains was observed on the aerial parts of some of the cultivars. An increase in the fresh weight of the sweet potatoes of the inoculated plants was obtained, varying from 2.7 to 11.4 %. The number of sweet potatoes obtained from the inoculated cultivars IAPAR 69 and Roxa increased 15.2 % and 16.7 %, respectively. The rhizosphere soil of each cultivar was further sampled for DNA extraction, and the 16S rRNA gene metabarcoding technique was used to determine how the introduction of these Bacillus strains influenced the rhizosphere bacterial community. The bacterial communities of the four different cultivars were dominated by Actinobacteria, Proteobacteria and Firmicutes. Nonmetric multidimensional scaling (NMDS) revealed that the rhizosphere bacterial communities of plants inoculated with Bacillus strains were more similar to each other than to the bacterial communities of uninoculated plants. This study highlights the contribution of these Bacillus strains to the promotion of sweet potato growth.

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In this study, we have identified and characterized three genomes from bacteria isolated from the rhizosphere of Triticum aestivum. Streptomyces virginiae CMAA1738 and Paenibacillus ottowii CMAA1739 were obtained from the wheat landrace Iran 1-29-11334, and Pseudomonas inefficax CMAA1741 was isolated from the wheat landrace Karakilcik.

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Due to its adsorption with aluminum and iron hydroxides, phosphorus viability is low in acidic soils; thus, the aim of this study was to isolate and identify bacteria from the rhizosphere of four legumes growing in acidic soils of the Cumbaza Sub-basin, San Martín, Peru, as well as to characterize their ability to solubilize aluminum phosphate and iron phosphate. The isolation process was conducted on TSA medium and the isolates were classified based on their origin and morphocolonial characteristics, with the bacillary shape being the most frequent, followed by cocci. To assess the solubilization of aluminum and iron phosphates, the liquid medium GELP was employed. Sixteen strains were selected, among which three stood out for their effectiveness in solubilizing AlPO4 (Sfcv-098-02, 22.65 mg L-1; Sfc-093-04, 26.50 mg L-1; and Sfcv-041-01-2, 55.98 mg L-1) and one for its ability to solubilize FePO4 (Sfcr-043-02, 32.61 mg L-1). These four strains were molecularly characterized, being identified as Enterobacter sp., Pseudomonas sp., and Staphylococcus sp. Additionally, a decrease in pH was observed in the reactions, with values ranging from 5.23 to 3.29, which enhanced the phosphate of solubilization. This suggests that the selected bacteria could be used to improve phosphorus availability in agricultural soils.

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Plant-fungus symbioses have functional relevance during plant growth and development. However, it is still unknown whether the endosphere fungi in mature plants originated from soils or seeds. To elucidate the origination of endosphere fungi in mature rice roots, the fungal communities in surface sterilized roots and shoots of mature rice plants germinated in soils, rhizosphere soils and seedlings germinated under sterile conditions were analyzed by Illumina-based sequencing and compared. Total 62 fungal OTUs shared in the seedlings, shoots and roots, 126 OTUs shared in the rhizosphere soils, shoots and roots. Fungal OTUs coexisted in the four types of samples belonged to genera of Rhizophagus, Trichoderma, Fusarium, Atractiella, Myrmecridium, Sporothrix, Microdochium, Massariosphaeria, and Phialemonium. The principle component analysis (PCA) and NMDS plot suggested that the fungal community structure in rhizosphere soils was different from that in seedlings significantly. Rhizosphere soil, shoot and root contained more similar fungal community. The fungal community in seedling was similar to that in shoot and root of mature plants. The results suggested that endophytic fungal communities in mature rice plants originated from both seedlings and rhizosphere soils, and more fungal taxa originated from rhizosphere soils. Mature rice plants contain mycobiome transmitted vertically from seeds, which suggests that inoculation of endophytic fungi isolated from seedlings might be an effective way to introduce beneficial fungal inoculants into rice plants successfully.

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BACKGROUND: Bacillus subtilis is well known for promoting plant growth and reducing abiotic and biotic stresses. Mutant gene-defective models can be created to understand important traits associated with rhizosphere fitness. This study aimed to analyze the role of exopolymeric genes in modulating tomato rhizosphere microbiome assembly under a gradient of soil microbiome diversities using the B. subtilis wild-type strain UD1022 and its corresponding mutant strain UD1022eps-TasA, which is defective in exopolysaccharide (EPS) and TasA protein production. RESULTS: qPCR revealed that the B. subtilis UD1022eps-TasA- strain has a diminished capacity to colonize tomato roots in soils with diluted microbial diversity. The analysis of bacterial ß-diversity revealed significant differences in bacterial and fungal community structures following inoculation with either the wild-type or mutant B. subtilis strains. The Verrucomicrobiota, Patescibacteria, and Nitrospirota phyla were more enriched with the wild-type strain inoculation than with the mutant inoculation. Co-occurrence analysis revealed that when the mutant was inoculated in tomato, the rhizosphere microbial community exhibited a lower level of modularity, fewer nodes, and fewer communities compared to communities inoculated with wild-type B. subtilis. CONCLUSION: This study advances our understanding of the EPS and TasA genes, which are not only important for root colonization but also play a significant role in shaping rhizosphere microbiome assembly. Future research should concentrate on specific microbiome genetic traits and their implications for rhizosphere colonization, coupled with rhizosphere microbiome modulation. These efforts will be crucial for optimizing PGPR-based approaches in agriculture.

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The Peruvian Amazonian native cacao faces ongoing challenges that significantly undermine its productivity. Among them, frosty pod rot disease and cadmium accumulation result in losses that need for effective and environmentally safe strategies, such as those based on bacteria. To explore the biological resources in the cacao soil, a descriptive study was conducted to assess the diversity of culturable bacteria across three production districts in the Amazonas region: La Peca, Imaza, and Cajaruro. The study also focused on the functional properties of these bacteria, particularly those related to the major issues limiting cacao cultivation. For this purpose, 90 native bacterial isolates were obtained from the cacao rhizosphere. According to diversity analysis, the community was composed of 19 bacterial genera, with a dominance of the Bacillaceae family and variable distribution among the districts. This variability was statistically supported by the PCoA plots and is related to the pH of the soil environment. The functional assessment revealed that 56.8% of the isolates showed an antagonism index greater than 75% after 7 days of confrontation. After 15 days of confrontation with Moniliophthora roreri, 68.2% of the bacterial population demonstrated this attribute. This capability was primarily exhibited by Bacillus strains. On the other hand, only 4.5% were capable of removing cadmium, highlighting the biocontrol potential of the bacterial community. In addition, some isolates produced siderophores (13.63%), solubilized phosphate (20.45%), and solubilized zinc (4.5%). Interestingly, these traits showed an uneven distribution, which correlated with the divergence found by the beta diversity. Our results revealed a diverse bacterial community inhabiting the Amazonian cacao rhizosphere, showcasing crucial functional properties related to the biocontrol of M. roreri. The information generated serves as a significant resource for the development of further biotechnological tools that can be applied to native Amazonian cacao.

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To investigate the impact of Poa alpigena Lindm on rhizosphere and bulk soil microorganisms in Haixin Mountain, Qinghai Lake, this study employed metagenomics technology to analyze the microbial communities of the samples. Results showed that 65 phyla, 139 classes, 278 orders, 596 families, 2376 genera, and 5545 species of soil microorganisms were identified from rhizosphere and bulk soil samples. Additionally, a microbial gene library specific to Poa alpigena Lindm was established for Qinghai Lake. Through α-diversity analysis, the richness and diversity of bulk microorganisms both significantly had a higher value than that in rhizosphere soil. The indicator microorganisms of rhizosphere and bulk soil at class level were Actinobacteria and Alphaproteobacteria, respectively. KEGG pathway analysis indicated that Carotenoid biosynthesis, Starch and sucrose metabolism, Bacterial chemotaxis, MAPK signaling pathway, Terpenoid backbone biosynthesis, and vancomycin resistance were the key differential metabolic pathways of rhizosphere soil microorganisms; in contrast, in bulk soil, the key differential metabolic were Benzoate degradation, Glycolysis gluconeogenesis, Aminobenzoate degradation, ABC transporters, Glyoxylate and dicarboxylate metabolism, oxidative phosphorylation, Degradation of aromatic compounds, Methane metabolism, Pyruvate metabolism and Microbial metabolism diverse environments. Our results indicated that Poa alpigena Lindm rhizosphere soil possessed selectivity for microorganisms in Qinghai Lake Haixin Mountain, and the rhizosphere soil also provided a suitable survival environment for microorganisms.

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This study aimed to investigate the phytochemistry of lemongrass (Cymbopogon citratus) inoculated with Azospirillum brasilense and grown in lead (Pb)-contaminated soil to assess its responses to inoculation under different Pb levels. The experimental design was completely randomized in a 2 × 5 factorial scheme: two levels of A. brasilense (absence or presence) and five Pb levels. After four months of treatment, the following were analyzed: total and reducing sugars, total phenolic content, flavonoids, antioxidant activity, antioxidant enzymes, proline, and essential oil (EO) content and composition. Soil Pb levels and A. brasilense inoculation affected phytochemicals in lemongrass plants. Azospirillum inoculation reduced total sugars in the roots at all soil Pb levels, while increasing Pb levels favored a rise in sugar contents. There was an increase in flavonoid content in treatments associated with Pb and inoculated with A. brasilense. Antioxidant capacity was lower at lower Pb levels, regardless of bacterial inoculation. Enzymatic response was mainly affected by Pb concentrations between 50 and 100 mg kg-1 soil. EO content was influenced by soil Pb levels, with higher EO production at 500 mg Pb kg-1 soil and without A. brasilense inoculation. Overall, lemongrass cultivation in Pb-contaminated areas can be an alternative to phytoremediation and EO production for the industry.

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To investigate the biocatalytic potential of Amazonian actinomycetes for monoterpenes biotransformation. To carry out the present study, eleven actinomycetes of the genus Streptomyces isolated from inga-cipó (Inga edulis Mart.) rhizospheres were tested for their ability to bioconvert the substrates R-(+)-limonene, S-(-)-limonene, 1S-(-)-α-pinene, and (-)-ß-pinene as sole carbon and energy source. According to gas chromatography-mass spectrometry analysis, three strains, LabMicra B270, LaBMicrA B310, and LaBMicrA B314, were able to biotransform 1S-(-)-α-pinene after 96 h of growth. However, Streptomyces LaBMicrA B270 was the most promising since it converted after only 72 h all the 1S-(-)-α-pinene mainly into cis-verbenol (74.9±1.24%) and verbenone (18.2±1.20%), compounds that have important biological activities and great industrial interest as additives in foods and cosmetics. These findings can stimulate the development of natural aromas using naturally abundant monoterpenes, ratify the potential of microorganisms from almost unexplored niches such as the Amazonian rhizosphere, and reinforce the importance of preserving those niches.

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Azospirillum sp. is a plant growth-promoting rhizobacteria largely recognized for its potential to increase the yield of different important crops. In this work, we present a thorough genomic and phenotypic analysis of A. argentinense Az39T to provide new insights into the beneficial mechanisms of this microorganism. Phenotypic analyses revealed the following in vitro abilities: growth at 20-38 °C (optimum, 28 °C), pH 6.0-8.0 (optimum, pH 6.8), and in the presence of 1% (w/v) NaCl; production of variable amounts of PHB as intracellular granules; nitrogen fixation under microaerophilic conditions; IAA synthesis in the presence of L-tryptophan. Through biochemical (API 20NE) and carbon utilization profiling (Biolog) assays, we proved that A. argentinense Az39T is able to use 15 substrates and metabolize 19 different carbon substrates. Lipid composition indicated a predominance of medium and long-chain saturated fatty acids. A total of 6 replicons classified as one main chromosome, three chromids, and two plasmids, according to their tRNA and core essential genes contents, were identified. Az39T genome includes genes associated with multiple plant growth-promoting (PGP) traits such as nitrogen fixation and production of auxins, cytokinin, abscisic acid, ethylene, and polyamines. In addition, Az39T genome harbor genetic elements associated with physiological features that facilitate its survival in the soil and competence for rhizospheric colonization; this includes motility, secretion system, and quorum sensing genetic determinants. A metadata analysis of Az39T agronomic performance in the pampas region, Argentina, demonstrated significant grain yield increases in wheat and maize, proving its potential to provide better growth conditions for dryland cereals. In conclusion, our data provide a detailed insight into the metabolic profile of A. argentinense Az39T, the strain most widely used to formulate non-legume inoculants in Argentina, and allow a better understanding of the mechanisms behind its field performance.

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