Building efficient biocathodes with Acidithiobacillus ferrooxidans for the high current generation

International audienceThe development of biocathodes is highly fascinating in microbial electrochemical technologies research. In this study, iron-oxidizing bacterium Acidithiobacillus ferrooxidans-based biocathodes were developed under the con-stant polarization of the electrochemical reactors at -0.2 V vs. Ag/AgCl with a pH of 2. On the 15th day of the 21-day batch experiment, A. ferrooxidans-based biocathode produced a maximum current density of-38.61 +/- 13.16 A m(-2) when the reactors were supplemented with 125 mM Fe2+ ions as an electron donor and 9 mM citrate as an iron chelator to buffer the iron-rich medium. Oxidation of Fe2+ to Fe3+ by A. ferrooxidans and its electrochemical regeneration at the cathode were mainly responsible for the high current generation. Furthermore, in the presence of iron, A. ferrooxidans develop a multi-layer biofilm on the cathode surface, which could potentially perform an indirect electron transfer mechanism

Phytobeneficial Traits under the Control of Multiple Crosstalks' Belowground

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Rhizobium alamii improves water stress tolerance in a non-legume

International audienceWith the increasing demand for alternative solutions to replace or optimize the use of synthetic fertilizers and pesticides, the inoculation of bacteria that can contribute to the growth and health of plants (PGPR) is essential. The properties classically sought in PGPR are the production of phytohormones and other growth-promoting molecules, and more rarely the production of exopolysaccharides. We compared the effect of two strains of exopolysaccharide-producing Rhizobium alamii on rapeseed grown in a calcareous silty-clay soil under water stress conditions or not. The effect of factors ‘water stress’ and ‘inoculation’ were evaluated on plant growth parameters and the diversity of microbiota associated to root and root-adhering soil compartments. Water stress resulted in a significant decrease in leaf area, shoot biomass and RAS/RT ratio (root-adhering soil/root tissues), as well as overall beta-diversity. Inoculation with R. alamii YAS34 and GBV030 under water-stress conditions produced the same shoot dry biomass compared to uninoculated treatment in absence of water stress, and both strains increased shoot biomass under water-stressed conditions (+7% and +15%, respectively). Only R. alamii GBV030 significantly increased shoot biomass under unstressed or water-stressed conditions compared to the non-inoculated control (+39% and +15%, respectively). Alpha-diversity of the root-associated microbiota after inoculation with R. alamii YAS34 was significantly reduced. Beta-diversity was significantly modified after inoculation with R. alamii GBV030 under unstressed conditions. LEfSe analysis identified characteristic bacterial families, Flavobacteriaceae and Comamonadaceae, in the RT and RAS compartments for the treatment inoculated by R. alamii GBV030 under unstressed conditions, as well as Halomonadaceae (RT) and several species belonging to Actinomycetales (RAS). We showed that R. alamii GBV030 had a PGPR effect on rapeseed growth, increasing its tolerance to water stress, probably involving its capacity to produce exopolysaccharides, and other plant growth-promoting (PGP) traits

Phytobeneficial bacteria improve saline stress tolerance in Vicia faba and modulate microbial interaction network

International audienceIncreased global warming, caused by climate change and human activities, will seriously hinder plant development, such as increasing salt concentrations in soils, which will limit water availability for plants. To ensure optimal plant growth under such changing conditions, microorganisms that improve plant growth and health must be integrated into agricultural practices. In the present work, we examined the fate of Vicia faba microbiota structure and interaction network upon inoculation with plant-nodulating rhizobia (Rhizobium leguminosarum RhOF125) and non-nodulating strains (Paenibacillus mucilaginosus BLA7 and Ensifer meliloti RhOL1) in the presence (or absence) of saline stress. Inoculated strains significantly improved plant tolerance to saline stress, suggesting either a direct or indirect effect on the plant response to such stress. To determine the structure of microbiota associated with V. faba, samples of the root-adhering soil (RAS), and the root tissues (RT) of seedlings inoculated (or not) with equal population size of RhOF125, BLA7 and RhOL1 strains and grown in the presence (or absence) of salt, were used to profile the microbial composition by 16S rRNA gene sequencing. The inoculation did not show a significant impact on the composition of the RT microbiota or RAS microbiota. The saline stress shifted the RAS microbiota composition, which correlated with a decrease in Enterobacteriaceae and an increase in Sphingobacterium, Chryseobacterium, Stenotrophomonas, Agrobacterium and Sinorhizobium. When the microbiota of roots and RAS are considered together, the interaction networks for each treatment are quite different and display different key populations involved in community assembly. These findings indicate that upon seed inoculation, community interaction networks rather than their composition may contribute to helping plants to better tolerate environmental stresses. The way microbial populations interfere with each other can have an impact on their functions and thus on their ability to express the genes required to help plants tolerate stresses

Culturing the desert microbiota

International audienceOver the last 30 years, the description of microbial diversity has been mainly based on culture-independent approaches (metabarcoding and metagenomics) allowing an in-depth analysis of microbial diversity that no other approach allows. Bearing in mind that culture-dependent approaches cannot replace culture-independent approaches, we have improved an original method for isolating strains consisting of "culturing" grains of sand directly on Petri dishes (grain-by-grain method). This method allowed to cultivate up to 10% of the bacteria counted on the surface of grains of the three sites studied in the Great Western Erg in Algeria (Timoudi, Béni Abbès, and Taghit), knowing that on average about 10 bacterial cells colonize each grain. The diversity of culturable bacteria (collection of 290 strains) predicted by 16S rRNA gene sequencing revealed that Arthrobacter subterraneus, Arthrobacter tecti, Pseudarthrobacter phenanthrenivorans, Pseudarthrobacter psychrotolerans, and Massilia agri are the dominant species. The comparison of the culture-dependent andindependent (16S rRNA gene metabarcoding) approaches at the Timoudi site revealed 18 bacterial genera common to both approaches with a relative overestimation of the genera Arthrobacter/Pseudarthrobacter and Kocuria, and a relative underestimation of the genera Blastococcus and Domibacillus by the bacterial culturing approach. The bacterial isolates will allow further study on the mechanisms of tolerance to desiccation, especially in Pseudomonadota (Proteobacteria)

A non specific Lipid Transfer Protein with potential functions in infection and nodulation

International audienceThe response of Alnus glutinosa to Frankia alni ACN14a is driven by several sequential physiological events from calcium spiking and root hair deformation to the development of the nodule. Early stages of actinorhizal symbiosis were monitored at the transcriptional level to observe plant host responses to Frankia. Forty-two genes were significantly upregulated in inoculated compared to non-inoculated roots. Most of these genes encode proteins involved in biological processes induced during microbial infection such as oxidative stress or response to stimuli but a large part of them are not differentially modulated or downregulated later in the process of nodulation. In contrast, several of them remained upregulated in mature nodules, and this included the gene most upregulated, which encodes a non-specific lipid transfer protein (nsLTP). Classified as an antimicrobial peptide, this nsLTP, was immunolocalized on the deformed root hair surfaces that are points of contact for Frankia during infection. Later in nodules, it binds to the surface of Frankia’s vesicles, which are the specialized cells for nitrogen fixation. This nsLTP, named AgLTP24, was biologically produced in a heterologous host and purified for assay on F. alni ACN14a to identify physiological effects. Thus, the activation of the plant immunity response occurs upon first contact, while the recognition of Frankia switches off part of the defense system during nodulation. AgLTP24 constitutes a part of the defense system that is maintained all along the symbiosis with potential functions such as the formation of infection threads or nodule primordia to the control of Frankia proliferation

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities