Indole-3-acetic acid biosynthetic pathway and aromatic amino acid aminotransferase activities in Pantoea dispersa strain GPK

Unveiling the duality of Pantoea dispersa: A mini review

Pantoea dispersa is a Gram-negative bacterium that exists in a variety of environments and has potential in many commercial and agricultural applications, such as biotechnology, environmental protection, soil bioremediation, and plant growth stimulation. However, P. dispersa is also a harmful pathogen to both humans and plants. This "double-edged sword" phenomenon is not uncommon in nature. To ensure survival, microorganisms respond to both environmental and biological stimuli, which could be beneficial or detrimental to other species. Therefore, to harness the full potential of P. dispersa, while minimizing potential harm, it is imperative to unravel its genetic makeup, understand its ecological interactions and underlying mechanisms. This review aims to provide a comprehensive and up-to-date overview of the genetic and biological characteristics of P. dispersa, in addition to potential impacts on plants and humans, as well as to provide insights into potential applications.

Plant Protection Mediated Through an Array of Metabolites Produced by Pantoea dispersa Isolated from Pitcher Plant

In the study, the bacterial isolate NhPB54 purified from the pitcher of Nepenthes plant was observed to have activity against Pythium aphanidermatum by dual culture and well diffusion. Hence, it was subjected to 16S rDNA sequencing and BLAST analysis, where the NhPB54 was found to have 100% identity to Pantoea dispersa. Upon screening for the plant beneficial properties, Pantoea dispersa NhPB54 was found to be positive for phosphate, potassium and zinc solubilization, nitrogen fixation, indole-3-acetic acid, ammonia, 1-aminocyclopropane-1-carboxylate deaminase, biofilm and biosurfactant production. Further to this, Solanum lycopersicum seedlings primed with P. dispersa NhPB54 were studied for the improved plant growth and disease protection. Here, the seedlings pre-treated with the NhPB54 culture supernatant were found to have enhanced plant growth and protection from damping off and fruit rot caused by P. aphanidermatum. From the LC-QTOF-MS/MS and GC MS analysis, P. dispersa NhPB54 was found to produce a blend of chemicals including 1-hydroxyphenazine, surfactin, and other bioactive metabolites with the likely basis of its observed antifungal and plant growth-promoting properties. From the results of the study, plants with unique adaptations can expect to harbor microbial candidates with beneficial applications.

Characterization of Bacillus velezensis RDA1 as a Biological Control Agent against White Root Rot Disease Caused by Rosellinia necatrix

White root rot disease, caused by Rosellinia necatrix, poses a threat to several tree crops; hence, effective and sustainable strategies to control this disease remain warranted. This study identified an effective R. necatrix biocontrol agent by isolating 32 strains from soil samples collected from white root rot-infested organic pear orchards, among which RDA1 exhibited the most potent growth-inhibitory effects. Microbiological and 16S rRNA gene sequencing analyses revealed that the bacterial isolate belonged to the Bacillus genus and exhibited 100% nucleotide sequence similarity with Bacillus velezensis species in the GenBank. This strain showed strong antifungal activity against four Rosellinia necatrix strains and harbored genes essential for lipopeptide, polyketide, and tripeptide bacilysin biosynthesis. RDA1 produced volatile compounds that suppressed the development of phytopathogens and possessed plant growth-promoting traits, such as phosphate solubilization, and indole-3-acetic acid and siderophore production. B. velezensis RDA1 has a significant potential application in sustainable agriculture and can be used to suppress white root rot disease infections and to improve plant growth.

Identification of Plant Growth Promoting Rhizobacteria That Improve the Performance of Greenhouse-Grown Petunias under Low Fertility Conditions

The production of greenhouse ornamentals relies on high fertilizer inputs to meet scheduling deadlines and quality standards, but overfertilization has negative environmental impacts. The goals of this study were to identify plant-growth-promoting rhizobacteria (PGPR) that can improve greenhouse ornamental crop performance with reduced fertilizer inputs, and to identify the best measurements of plant performance for assessing the beneficial impact of PGPR on ornamentals. A high-throughput greenhouse trial was used to identify 14 PGPR isolates that improved the flower/bud number and shoot dry weight of Petunia × hybrida ‘Picobella Blue’ grown under low fertility conditions in peat-based media. These 14 PGPR were then applied to petunias grown under low fertility conditions (25 mg L⁻¹ N). PGPR-treated plants were compared to negative (untreated at 25 mg L⁻¹ N) and positive (untreated at 50, 75, 100, and 150 mg L⁻¹ N) controls. Multiple parameters were measured in the categories of flowering, vegetative growth, and vegetative quality to determine the best measurements to assess improvements in ornamental plant performance. Caballeronia zhejiangensis C7B12-treated plants performed better in almost all parameters and were comparable to untreated plants fertilized with 50 mg L⁻¹ N. Genomic analysis identified genes that were potentially involved in plant growth promotion. Our study identified potential PGPR that can be used as biostimulants to produce high-quality greenhouse ornamentals with lower fertilizer inputs.

Multifunctional potential of endophytic bacteria from Anacardium othonianum Rizzini in promoting in vitro and ex vitro plant growth

Anacardium othonianum Rizzini, a cashew tree native to the Brazilian Cerrado, is economically important due to its applications in the food, chemical and pharmaceutical industries. However, A. othonianum yields a crop with low productivity due to a number of factors, such as nutritionally poor soils, drought and losses due to pests and diseases. Brazil is one of the nine largest cashew nut producers worldwide, and sustainable technologies are needed to increase the productivity of this crop. In this context, the use of endophytic microorganisms could promote plant growth and provide protection against phytopathogens. In this study, the isolation of the root endophytic community of A. othonianum led to the characterization of 22 distinct bacterial strains with multifunctional traits for plant growth promotion. The results of in vitro assays to assess auxin synthesis, phosphate solubilization, phosphatase and siderophore production and biocontrol against Fusarium oxysporum led to the selection of Acinetobacter lwoffii Bac109 and Pantoea agglomerans Bac131 as the most promising strains. The reinoculation of the Bac109 and Bac131 strains onto A. othonianum seeds showed that the treatment containing a mixture of these strains was the most effective in promoting increases in the biometric parameters of early plant growth. Thus, this study highlights the biotechnological potential of a consortium of A. lwoffii Bac109 and P. agglomerans Bac131 for future applications in sustainable cashew cultivation.

Auxins of microbial origin and their use in agriculture

To maintain the world population demand, a sustainable agriculture is needed. Since current global vision is more friendly with the environment, eco-friendly alternatives are desirable. In this sense, plant growth-promoting rhizobacteria could be the choice for the management of soil-borne diseases of crop plants. These rhizobacteria secrete chemical compounds which act as phytohormones. Indole-3-acetic acid (IAA) is the most common plant hormone of the auxin class which regulates various processes of plant growth. IAA compound, in which structure can be found a carboxylic acid attached through a methylene group to the C-3 position of an indole ring, is produced both by plants and microorganisms. Plant growth-promoting rhizobacteria and fungi secrete IAA to promote the plant growth. In this review, IAA production and mechanisms of action by bacteria and fungi along with the metabolic pathways evolved in the IAA secretion and commercial prospects are revised.Key points• Many microorganisms produce auxins which help the plant growth promotion.• These auxins improve the plant growth by several mechanisms.• The auxins are produced through different mechanisms.

Pyridoxal 5'-Phosphate-Dependent Enzymes at the Crossroads of Host-Microbe Tryptophan Metabolism

The chemical processes taking place in humans intersects the myriad of metabolic pathways occurring in commensal microorganisms that colonize the body to generate a complex biochemical network that regulates multiple aspects of human life. The role of tryptophan (Trp) metabolism at the intersection between the host and microbes is increasingly being recognized, and multiple pathways of Trp utilization in either direction have been identified with the production of a wide range of bioactive products. It comes that a dysregulation of Trp metabolism in either the host or the microbes may unbalance the production of metabolites with potential pathological consequences. The ability to redirect the Trp flux to restore a homeostatic production of Trp metabolites may represent a valid therapeutic strategy for a variety of pathological conditions, but identifying metabolic checkpoints that could be exploited to manipulate the Trp metabolic network is still an unmet need. In this review, we put forward the hypothesis that pyridoxal 5′-phosphate (PLP)-dependent enzymes, which regulate multiple pathways of Trp metabolism in both the host and in microbes, might represent critical nodes and that modulating the levels of vitamin B6, from which PLP is derived, might represent a metabolic checkpoint to re-orienteer Trp flux for therapeutic purposes.

Influence of PGPB Inoculation on HSP70 and HMA3 Gene Expression in Switchgrass under Cadmium Stress

This study aimed to evaluate the gene expression of HSP70 and HMA3 in the switchgrass inoculated with plant-growth-promoting-bacteria (PGPB) under cadmium (Cd) stress and to observe the benefit of PGPB in plant growth and development. Plants were grown in hydroponic culture and treated with PGPB inoculants: Pseudomonas grimontii, Pantoea vagans, Pseudomonas veronii, and Pseudomonas fluorescens with the strains Bc09, So23, E02, and Oj24, respectively. The experimental results revealed that HSP70 and HMA3 genes expressed highly in the PGPB-inoculated plants under Cd stress. In addition, the expression of HSP70 and HMA3 genes was considerably higher in the first two days after successive four-day exposure of Cd in plants compared to the last two days of exposure. Increased biomass and indole-3-acetic-acid production with reduced Cd accumulation were observed in the PGPB-inoculated plants under Cd stress compared to the Cd-control plants. These PGPB, with their beneficial mechanisms, protect plants by modifying the gene expression profile that arises during Cd-toxic conditions and increased the healthy biomass of switchgrass. This demonstrates there is a correlation among the growth parameters under Cd stress. The PGPB in this study may help to intensify agriculture by triggering mechanisms to encourage plant growth and development under heavy metal stress.

Characterization of Indole-3-acetic Acid Biosynthesis and the Effects of This Phytohormone on the Proteome of the Plant-Associated Microbe Pantoea sp. YR343

Indole-3-acetic acid (IAA) plays a central role in plant growth and development, and many plant-associated microbes produce IAA using tryptophan as the precursor. Using genomic analyses, we predicted that Pantoea sp. YR343, a microbe isolated from Populus deltoides, synthesizes IAA using the indole-3-pyruvate (IPA) pathway. To better understand IAA biosynthesis and the effects of IAA exposure on cell physiology, we characterized proteomes of Pantoea sp. YR343 grown in the presence of tryptophan or IAA. Exposure to IAA resulted in upregulation of proteins predicted to function in carbohydrate and amino acid transport and exopolysaccharide (EPS) biosynthesis. Metabolite profiles of wild-type cells showed the production of IPA, IAA, and tryptophol, consistent with an active IPA pathway. Finally, we constructed an Δ ipdC mutant that showed the elimination of tryptophol, consistent with a loss of IpdC activity, but was still able to produce IAA (20% of wild-type levels). Although we failed to detect intermediates from other known IAA biosynthetic pathways, this result suggests the possibility of an alternate pathway or the production of IAA by a nonenzymatic route in Pantoea sp. YR343. The Δ ipdC mutant was able to efficiently colonize poplar, suggesting that an active IPA pathway is not required for plant association.

A Carotenoid-Deficient Mutant in Pantoea sp. YR343, a Bacteria Isolated from the Rhizosphere of Populus deltoides, Is Defective in Root Colonization

The complex interactions between plants and their microbiome can have a profound effect on the health and productivity of the plant host. A better understanding of the microbial mechanisms that promote plant health and stress tolerance will enable strategies for improving the productivity of economically important plants. Pantoea sp. YR343 is a motile, rod-shaped bacterium isolated from the roots of Populus deltoides that possesses the ability to solubilize phosphate and produce the phytohormone indole-3-acetic acid (IAA). Pantoea sp. YR343 readily colonizes plant roots and does not appear to be pathogenic when applied to the leaves or roots of selected plant hosts. To better understand the molecular mechanisms involved in plant association and rhizosphere survival by Pantoea sp. YR343, we constructed a mutant in which the crtB gene encoding phytoene synthase was deleted. Phytoene synthase is responsible for converting geranylgeranyl pyrophosphate to phytoene, an important precursor to the production of carotenoids. As predicted, the ΔcrtB mutant is defective in carotenoid production, and shows increased sensitivity to oxidative stress. Moreover, we find that the ΔcrtB mutant is impaired in biofilm formation and production of IAA. Finally we demonstrate that the ΔcrtB mutant shows reduced colonization of plant roots. Taken together, these data suggest that carotenoids are important for plant association and/or rhizosphere survival in Pantoea sp. YR343.

Draft Genome Sequence of Pantoea sp. Strain MBLJ3, Isolated in a Laboratory Environmental Control Study

This report describes the draft genome sequence of a newly isolated strain, Pantoea sp. MBLJ3. The genome is 4.8 Mb in size, with a G+C content of 54.27%, and it contains 4,522 protein-coding sequences, 69 tRNA genes, and 5 rRNA genes.