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Unveiling the Secrets of Calcium-Dependent Proteins in Plant Growth-Promoting Rhizobacteria: An Abundance of Discoveries Awaits.

ABSTRACT: The role of Calcium ions (Ca²⁺) is extensively documented and comprehensively understood in eukaryotic organisms. Nevertheless, emerging insights, primarily derived from studies on human pathogenic bacteria, suggest that this ion also plays a pivotal role in prokaryotes. In this review, our primary focus will be on unraveling the intricate Ca²⁺ toolkit within prokaryotic organisms, with particular emphasis on its implications for plant growth-promoting rhizobacteria (PGPR). We undertook an in silico exploration to pinpoint and identify some of the proteins described in the existing literature, including prokaryotic Ca²⁺ channels, pumps, and exchangers that are responsible for regulating intracellular Calcium concentration ([Ca²⁺]_i), along with the Calcium-binding proteins (CaBPs) that play a pivotal role in sensing and transducing this essential cation. These investigations were conducted in four distinct PGPR strains: Pseudomonas chlororaphis subsp. aurantiaca SMMP3, P. donghuensis SVBP6, Pseudomonas sp. BP01, and Methylobacterium sp. 2A, which have been isolated and characterized within our research laboratories. We also present preliminary experimental data to evaluate the influence of exogenous Ca²⁺ concentrations ([Ca²⁺]_ex) on the growth dynamics of these strains.

SUBMITTER: Agaras BC

PROVIDER: S-EPMC10574481 | biostudies-literature | 2023 Sep

REPOSITORIES: biostudies-literature

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Unveiling the Secrets of Calcium-Dependent Proteins in Plant Growth-Promoting Rhizobacteria: An Abundance of Discoveries Awaits.

Agaras Betina Cecilia BC Grossi Cecilia Eugenia María CEM Ulloa Rita María RM

Plants (Basel, Switzerland) 20230926 19

The role of Calcium ions (Ca2+) is extensively documented and comprehensively understood in eukaryotic organisms. Nevertheless, emerging insights, primarily derived from studies on human pathogenic bacteria, suggest that this ion also plays a pivotal role in prokaryotes. In this review, our primary focus will be on unraveling the intricate Ca2+ toolkit within prokaryotic organisms, with particular emphasis on its implications for plant growth-promoting rhizobacteria (PGPR). ...[more]

PMID: 37836138

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Project description:The profound negative effect of inorganic chemical fertilizer application on rhizobacterial diversity has been well documented using 16S rRNA gene amplicon sequencing and predictive metagenomics. We aimed to measure the function and relative abundance of readily culturable putative plant growth-promoting rhizobacterial (PGPR) isolates from wheat root soil samples under contrasting inorganic fertilization regimes. We hypothesized that putative PGPR abundance will be reduced in fertilized relative to unfertilized samples. Triticum aestivum cv. Cadenza seeds were sown in a nutrient depleted agricultural soil in pots treated with and without Osmocote® fertilizer containing nitrogen-phosphorous-potassium (NPK). Rhizosphere and rhizoplane samples were collected at flowering stage (10 weeks) and analyzed by culture-independent (CI) amplicon sequence variant (ASV) analysis of rhizobacterial DNA as well as culture-dependent (CD) techniques. Rhizosphere and rhizoplane derived microbiota culture collections were tested for plant growth-promoting traits using functional bioassays. In general, fertilizer addition decreased the proportion of nutrient-solubilizing bacteria (nitrate, phosphate, potassium, iron, and zinc) isolated from rhizocompartments in wheat whereas salt tolerant bacteria were not affected. A "PGPR" database was created from isolate 16S rRNA gene sequences against which total amplified 16S rRNA soil DNA was searched, identifying 1.52% of total community ASVs as culturable PGPR isolates. Bioassays identified a higher proportion of PGPR in non-fertilized samples [rhizosphere (49%) and rhizoplane (91%)] compared to fertilized samples [rhizosphere (21%) and rhizoplane (19%)] which constituted approximately 1.95 and 1.25% in non-fertilized and fertilized total community DNA, respectively. The analyses of 16S rRNA genes and deduced functional profiles provide an in-depth understanding of the responses of bacterial communities to fertilizer; our study suggests that rhizobacteria that potentially benefit plants by mobilizing insoluble nutrients in soil are reduced by chemical fertilizer addition. This knowledge will benefit the development of more targeted biofertilization strategies.

Project description:Arabidopsis thaliana transcriptome analysis in response to plant growth promoting rhizobacteria (PGPR) Experiment 1 : Changes in gene expression profile triggered during root architecture response to Phyllobacterium. Biological question : Which genes are up- or down-regulated in Arabidopsis thaliana cultivated in vitro with increased lateral root development in response to Phyllobacterium STM196 inoculation. Experiment description: Seeds of wild-type Arabidopsis thaliana (ecotype Columbia) were surface-sterilized and sown on agar mineral medium (see below). 4 days after storage in the dark at 4C, seedling were cultivated 6 days in a growth chamber (16 h daily, 20-22C) and then transferred on a fresh agar mineral medium inoculated or not with Phyllobacterium STM196 (2.108 cfu/ml). 6 days later, root and leaves were collected, froze on liquid nitrogen and stored at -80C. Experiment 2 : Changes in gene expression profile triggered during induced systemic resistance (ISR) Biological question : Which genes are up- or down-regulated during the ISR triggered by a rhizobacteria, in comparison with those affected by a pathogenic interaction. Experiment description: Seeds were sown on 0.8% (W/V) agar mineral medium (see below). 4 days after storage in the dark at 4C, seedling were cultivated 6 days in a growth chamber (16 h daily, 20-22C) and then transferred on soil inoculated or not with 107 cfu.g-1 of Bradyrhizobium strain ORS278. Three weeks later, 3 leaves per plant were infiltrated with a suspension of Pseudomonas syringae pv. tomato (2.105 cfu.ml-1) or with MgSO4 10 mM alone for control plants. Infiltrated leaves were collected 24h later. Experiment 3 : Comparison of the effects of 3 rhizobacteria on Arabidopsis thaliana transcriptome Biological question : which genes are specifically induced or repressed in Arabidopsis thaliana by inoculation of the soil with a PGPR vs a bacteria that has the ability to trigger nodule formation in a Legume. Experiment description: Seeds of wild-type Arabidopsis thaliana (ecotype Columbia) were surface-sterilized and sown on agar mineral medium. Four days after storage in the dark at 4C, seedlings were cultivated 6 days in a growth chamber (16 h daily, 20-22C) and then transferred on soil inoculated or not with 108 cfu.g-1 of Mesorhizobium loti, or 108 cfu.g-1 of Phyllobacterium STM196, or 107 cfu.g-1 of Bradyrhizobium ORS278.

Project description:BackgroundThe 'Microphenotron' is an automated screening platform that uses 96-well microtiter plates to test the response of seedlings to natural products. This system allows monitoring the phenotypic effect of a large number of small molecules. Here, this model system was used to study the effect of phytohormones produced by plant growth-promoting rhizobacteria (PGPR) on the growth of wild-type and mutant lines of Arabidopsis thaliana.MethodsIn the present study, high-throughput screening based on 'Microphenotron' was used to screen PGPRs. Rhizobacteria were isolated from the rhizosphere of Acacia Arabica, which was growing in saline habitats. The phylogeny of these rhizobacteria was determined by 16S rRNA gene sequencing. Strains were screened for plant growth-promoting traits such as auxin production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and phosphate solubilization. Ultra-Performance Liquid Chromatography (UPLC) was used to detect the presence of different indolic compounds. Finally, PGPR were evaluated to enhance the growth of A. thaliana in the 'Microphenotron' system and pot trials.ResultsSelected rhizobacteria strains showed positive results for multiple plant-growth promoting traits. For instance, strain (S-6) of Bacillus endophyticus exhibited the highest ACC-deaminase activity. UPLC analysis indicated the presence of different indolic compounds in bacterial extracts that included indole lactic acid (ILA), indole carboxylic acid (ICA), and indole-3-acetic acid (IAA). Two strains (S-7 and S-11) of Psychrobacter alimentarius produced the most IAA, ICA and ILA. A screening bioassay through 96-well microtiter plates with wild-type Col. N6000 showed an increase in root growth and proliferation. The highest twofold increase was recorded in root growth with B. thuringiensis S-26 and B. thuringiensis S-50. In pot trials, mutant lines of A. thaliana impaired for auxin signaling showed that B. endophyticus S-6, Psy. alimenterius S-11, Enterobacter asburiae S-24 and B. thuringiensis S-26 used auxin signaling for plant growth promotion. Similarly, for ethylene insensitive mutant lines (ein2.5 and etr1), Prolinoborus fasciculus S-3, B. endophyticus S-6, Psy. alimenterius S-7, E. asburiae S-24, and B. thuringiensis S-26 showed the involvement of ethylene signaling. However, the growth promotion pattern for most of the strains indicated the involvement of other mechanisms in enhancing plant growth. The result of Microphenotron assays generally agreed with pot trials with mutant and wild type A. thaliana varieties. Bacterial strains that induced the highest growth response by these cultivars in the 'Microphenotron' promoted plant growth in pot trials. This suggests that Microphenotron can accelerate the evaluation of PGPR for agricultural applications.

Project description:Constraint-based modeling has risen as an alternative for characterizing metabolism of communities. Adaptations of flux balance analysis have been proposed to model metabolic interactions, which in most cases consider the maximization of biomass production as their objective. In nature, novel essential functions are not directly related to cell growth force communities to display suboptimal growth rates. These suboptimal states allow a degree of plasticity in their metabolism, thus allowing quick shifts between alternative flux distributions as an initial response to environmental changes. In this work, we introduce the abundance-growth space as a representation of metabolic phenotypes of a community. This space is defined by the composition of a community, represented by its members' relative abundances, and their growth rate. The analysis of this space allows us to pinpoint how critical reactions respond to shifts of the environment, showing where changes in community plasticity occur. Interestingly, it highlights the relevance of the relative abundance of its members in the lost or gain of plasticity. This method is applied to two simple communities that exchange metabolites. A synthetic community of two mutant Escherichia coli strains and an environmental bioleaching community composed by Acidithiobacillus ferrooxidans Wenelen and Sulfobacillus thermosulfidooxidans Cutipay, where only Cutipay consumes organic matter disposed of by the community.IMPORTANCEIn nature, organisms live in communities and not as isolated species, and their interactions provide a source of resilience to environmental disturbances. Despite their importance in ecology, human health, and industry, understanding how organisms interact in different environments remains an open question.In this work, we provide a novel approach that, only using genomic information, studies the metabolic phenotype exhibited by communities, where the exploration of suboptimal growth flux distributions and the composition of a community allows to unveil its capacity to respond to environmental changes, shedding light of the degrees of metabolic plasticity inherent to the community.

Dataset Information

Unveiling the Secrets of Calcium-Dependent Proteins in Plant Growth-Promoting Rhizobacteria: An Abundance of Discoveries Awaits.

Publications

Unveiling the Secrets of Calcium-Dependent Proteins in Plant Growth-Promoting Rhizobacteria: An Abundance of Discoveries Awaits.

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