An overview of Parafrankia (Nod+/Fix+) and Pseudofrankia (Nod+/Fix-) interactions through genome mining and experimental modeling in co-culture and co-inoculation of Elaeagnus angustifolia.

In many frankia, the ability to nodulate host plants (Nod+) and fix nitrogen (Fix+) is a common strategy. However, some frankia within the Pseudofrankia genus lack one or two of these traits. This phenomenon has been consistently observed across various actinorhizal nodule isolates, displaying Nod- and/or Fix- phenotypes. Yet, the mechanisms supporting the colonization and persistence of these inefficient frankia within nodules, both with and without symbiotic strains (Nod+/Fix+), remain unclear. It is also uncertain whether these associations burden or benefit host plants. This study delves into the ecological interactions between Parafrankia EUN1f and Pseudofrankia inefficax EuI1c, isolated from Elaeagnus umbellata nodules. EUN1f (Nod+/Fix+) and EuI1c (Nod+/Fix-) display contrasting symbiotic traits. While the prediction suggests a competitive scenario, the absence of direct interaction evidence implies that the competitive advantage of EUN1f and EuI1c is likely contingent on contextual factors such as substrate availability and the specific nature of stressors in their respective habitats. In co-culture, EUN1f outperforms EuI1c, especially under specific conditions, driven by its nitrogenase activity. Iron-depleted conditions favor EUN1f, emphasizing iron's role in microbial competition. Both strains benefit from host root exudates in pure culture, but EUN1f dominates in co-culture, enhancing its competitive traits. Nodulation experiments show that host plant preferences align with inoculum strain abundance under nitrogen-depleted conditions, while consistently favoring EUN1f in nitrogen-supplied media. This study unveils competitive dynamics and niche exclusion between EUN1f and EuI1c, suggesting that host plant may penalize less effective strains and even all strains. These findings highlight the complex interplay between strain competition and host selective pressure, warranting further research into the underlying mechanisms shaping plant-microbe-microbe interactions in diverse ecosystems. IMPORTANCE: While Pseudofrankia strains typically lack the common traits of ability to nodulate the host plant (Nod-) and/or fix nitrogen (Fix-), they are still recovered from actinorhizal nodules. The enigmatic question of how and why these unconventional strains establish themselves within nodule tissue, thriving either alongside symbiotic strains (Nod+/Fix+) or independently, while considering potential metabolic costs to the host plant, remains a perplexing puzzle. This study endeavors to unravel the competitive dynamics between Pseudofrankia inefficax strain EuI1c (Nod+/Fix-) and Parafrankia strain EU1Nf (Nod+/Fix+) through a comprehensive exploration of genomic data and empirical modeling, conducted both in controlled laboratory settings and within the host plant environment.

Inhibitory activity of bacterial lipopeptides against Fusarium oxysporum f.sp. Strigae.

This study investigated the influence of bacterial cyclic lipopeptides (LP; surfactins, iturins, fengycins) on microbial interactions. The objective was to investigate whether the presence of bacteria inhibits fungal growth and whether this inhibition is due to the release of bacterial metabolites, particularly LP. Selected endophytic bacterial strains with known plant-growth promoting potential were cultured in the presence of Fusarium oxysporum f.sp. strigae (Fos), which was applied as model fungal organism. The extracellular metabolome of tested bacteria, with a focus on LP, was characterized, and the inhibitory effect of bacterial LP on fungal growth was investigated. The results showed that Bacillus velezensis GB03 and FZB42, as well as B. subtilis BSn5 exhibited the strongest antagonism against Fos. Paraburkholderia phytofirmans PsJN, on the other hand, tended to have a slight, though non-significant growth promotion effect. Crude LP from strains GB03 and FZB42 had the strongest inhibitory effect on Fos, with a significant inhibition of spore germination and damage of the hyphal structure. Liquid chromatography tandem mass spectrometry revealed the production of several variants of iturin, fengycin, and surfactin LP families from strains GB03, FZB42, and BSn5, with varying intensity. Using plate cultures, bacillomycin D fractions were detected in higher abundance in strains GB03, FZB42, and BSn5 in the presence of Fos. Additionally, the presence of Fos in dual plate culture triggered an increase in bacillomycin D production from the Bacillus strains. The study demonstrated the potent antagonistic effect of certain Bacillus strains (i.e., GB03, FZB42, BSn5) on Fos development. Our findings emphasize the crucial role of microbial interactions in shaping the co-existence of microbial assemblages.

Strategies on aroma formation in Chardonnay sparkling base wine: Different Saccharomyces cerevisiae strains, co-inoculation with Torulaspora delbrueckii and utilization of bentonite.

The worldwide production of sparkling wines has been growing annually, driven by a market demand for high quality and more complex products. The present study aimed to evaluate the fermentation of Chardonnay must using two different Saccharomyces cerevisiae yeasts, either alone (from commercial brands A and B) or in combination with Torulaspora delbrueckii (ScA + Td and ScB + Td, respectively), as well as the addition of bentonite to the fermentation with ScA (ScA + Ben), to investigate their impact on aroma formation in sparkling base wine. Enological parameters, volatile composition, and sensory profile were evaluated. The results showed notable differences in total sulfur dioxide and volatile acidity among the S. cerevisiae strains. Moreover, the esters ethyl acetate, isoamyl acetate, hexyl acetate, and phenethyl acetate showed significant differences among treatments. Esters are recognized for their contribution to fruity and floral aromas, making them an essential part of the aromatic profile of wines. The descriptive analysis revealed that ScB + Td had the highest intensity of floral and tropical fruit notes, as well as aromatic clarity. The use of bentonite did not affect the aromatic composition or sensory profile of the wine. Therefore, the co-inoculation of S. cerevisiae with T. delbrueckii can lead to a base wine with a higher intensity of important volatile compounds and sensory attributes, providing an important alternative to produce winery products with a more complex aroma profile.

Co-inoculation effects of B. licheniformis and P. aeruginosa on soil Cd and As availability and rice accumulation.

There have been studies reporting the effects of multiple bacterial strains on the Cd/As immobilization and transformation in culture media. However, there is limited research to validate the effects of microbial strain combination on plant Cd/As accumulation and antioxidant system in the soil-plant system. By planting the rice (Zhefu 7) with the co-inoculation of bacterial strains (i.e. Bacillus licheniformis and Pseudomonas aeruginosa) after two months with the contaminations of Cd (2 mg/kg), As (80 mg/kg) and Cd + As (2 + 80 mg/kg), we found that the bacterial co-inoculation decreased Cd concentrations in the rhizosphere soil porewater, but had limited effects on mitigating plant Cd accumulation. By contrast, the co-inoculation did not affect the As(III) and As(V) concentrations in the rhizosphere soil porewater, but decreased As(III) and As(V) concentrations by 17% and 17% in the root respectively and by 17% and 37% in rice shoot respectively. Using DNA sequencing, we found the increased abundance in both exogenous Bacillus licheniformis and native microorganisms, indicating that the added strains had synergetic interactions with soil native microorganisms. Regarding on plant antioxidant enzyme system, the bacterial co-inoculation decreased the concentrations of superoxide dismutase (SOD), hydrogen peroxide (H2O2) and malondialdehyde (MDA) by 75%, 74% and 22%, mitigating the As damage to rice root and promote plant growth. However, under Cd and As co-stress, the effects of co-inoculation on mitigating plant As accumulation and enhancing plant stress resistance appear to be diminished. Our findings underscore the importance of microbial co-inoculation in reducing plant As accumulation and preserving plant health under heavy metal stress.

The influence of Torulaspora delbrueckii on beer fermentation.

In this study, the effect of five different Torulaspora delbrueckii strains in combination with an ale type Saccharomyces cerevisiae on physical, chemical, microbiological, aroma composition, and sensory profiles of beer were examined. The ethyl alcohol content of produced beers ranged from 5.46% (v/v) to 5.93% (v/v), while the highest alcohol amount was obtained using a pure culture of S. cerevisiae. The major volatiles among beer aroma compounds was acetaldehyde, n-propanol, 3-methyl-butanol, 2-methyl-butanol, ethyl acetate, isoamyl acetate, 2,3-butanedione, and 2,3-pentanedione. It was ascertained that the total amount of higher alcohols was higher in the S. cerevisiae control beer compared to all mixed fermentations. Total ester levels were higher in all the mixed culture beers than the control beer. Sensory evaluation showed that all the mixed cultures of S. cerevisiae and T. delbrueckii positively influenced the sensory profile of the beers. Strain Y1031 was the most preferred and was characterized as rich in hop aroma and full bodied. It is therefore a suitable strategy to use T. delbrueckii in mixed fermentations with S. cerevisiae to produce beer with a distinctive flavor. The results demonstrate that, T. delbrueckii strains isolated or commercialized for winemaking can be equally employed as well in brewing.

Inoculation with Trichoderma harzianum and Azospirillum brasilense increases nutrition and yield of hydroponic lettuce.

The use of beneficial fungi and bacteria stimulate plant growth and serve to improve yield and food quality in a sustainable manner. The electrical conductivity of nutrients solution is closely linked to better nutrition of vegetable plants in a hydroponic system. Therefore, objectives of current study were to evaluate the effect of isolated and combined inoculation with Azospirillum brasilense and Trichoderma harzianum under two electrical conductivities on growth, nutrition, and yield of lettuce in hydroponic cultivation. The experiment was designed in a strip-plot block with five replications in a 4 × 2 factorial scheme. The treatments were consisted of four microbial inoculations (without, A. brasilense, T. harzianum and co-inoculation) and electrical conductivities (1.2 and 1.4 dS m-1). Inoculation with A. brasilense and T. harzianum increased lettuce root growth by 47% and 20%, respectively. The single inoculation of T. harzianum provided higher fresh leaves yield (24%) at electrical conductivity of 1.2 dS m-1, while single inoculation with A. brasilense increased fresh leaves yield by 17% at electrical conductivity 1.4 dS m-1. The lowest shoot NO3- accumulation (40%) was observed with inoculation of A. brasilense and highest (28%) with inoculation T. harzianum in both electrical conductivities. Inoculation with A. brasilense increased leaf accumulation of K, P, Ca, Mg, Fe, Mn, Cu, and Zn, which are essential for human nutrition and being recommended to improve yield of lettuce plants in hydroponics. It is recommended to use EC 1.4 dS m-1 of the nutrients solution to improve accumulation of K, Mn, Cu, and Zn, regardless of inoculations for biofortification of lettuce with application of fertilizers.

Remediation of copper-contaminated soils using Tagetes patula L., earthworms and arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal fungi (AMF) and earthworms have potential uses in the bioremediation of contaminated soils. In recent years, heavy metal-contaminated sites have been remediated by adding plants and AMF or earthworms to the soil. However, there are few studies on remediation using combinations of plants, animals, and microbes, especially for the remediation of Cu-contaminated soil. The present study investigated the separate and combined effects of AMF and earthworms on Cu-contaminated soil in which Tagetes patula L. was grown. The results show that the combined application of AMF and earthworms markedly increased the biomass of plant shoots and roots by more than 100%. It also increased Cu extraction by T. patula by 270%. The combined treatment was effective in increasing the CEC, contents of OM, and available Cu, P and K, but reduced the soil pH. Furthermore, the combined treatment significantly increased the abundance and diversity of the soil microbial community. In particular, the abundances of the bacteria Bacteroides, Proteobacteria, and Actinobacteria were increased, with the genera Flavobacterium, Pedobacter, Algoriphagus, Gaetbulibacter, Pseudomonas, Luteimonas, and Arthrobacter dominating. Meanwhile, the abundance of the fungus Zygomycota was increased, with Mortierella dominating. Moreover, inoculation with earthworms greatly improved the structure of the soil microbial community.

Compared with phytoremediation or microbial remediation alone, combined remediation was considered to be a more efficient remediation strategy. This study describes the effects of the combined remediation of T. patula, AMF, and earthworms on the physiochemical properties and microbial community of Cu-contaminated soil. This provides a comprehensive strategy to improve the phytoremediation efficiency in Cu-contaminated soil.

Microbiome of Nodules and Roots of Soybean and Common Bean: Searching for Differences Associated with Contrasting Performances in Symbiotic Nitrogen Fixation.

Biological nitrogen fixation (BNF) is a key process for the N input in agriculture, with outstanding economic and environmental benefits from the replacement of chemical fertilizers. However, not all symbioses are equally effective in fixing N2, and a major example relies on the high contribution associated with the soybean (Glycine max), contrasting with the low rates reported with the common bean (Phaseolus vulgaris) crop worldwide. Understanding these differences represents a major challenge that can help to design strategies to increase the contribution of BNF, and next-generation sequencing (NGS) analyses of the nodule and root microbiomes may bring new insights to explain differential symbiotic performances. In this study, three treatments evaluated in non-sterile soil conditions were investigated in both legumes: (i) non-inoculated control; (ii) inoculated with host-compatible rhizobia; and (iii) co-inoculated with host-compatible rhizobia and Azospirillum brasilense. In the more efficient and specific symbiosis with soybean, Bradyrhizobium presented a high abundance in nodules, with further increases with inoculation. Contrarily, the abundance of the main Rhizobium symbiont was lower in common bean nodules and did not increase with inoculation, which may explain the often-reported lack of response of this legume to inoculation with elite strains. Co-inoculation with Azospirillum decreased the abundance of the host-compatible rhizobia in nodules, probably because of competitiveness among the species at the rhizosphere, but increased in root microbiomes. The results showed that several other bacteria compose the nodule microbiomes of both legumes, including nitrogen-fixing, growth-promoters, and biocontrol agents, whose contribution to plant growth deserves further investigation. Several genera of bacteria were detected in root microbiomes, and this microbial community might contribute to plant growth through a variety of microbial processes. However, massive inoculation with elite strains should be better investigated, as it may affect the root microbiome, verified by both relative abundance and diversity indices, that might impact the contribution of microbial processes to plant growth.

Medicago-Sinorhizobium-Ralstonia: A Model System to Investigate Pathogen-Triggered Inhibition of Nodulation.

How plants deal with beneficial and pathogenic microorganisms and how they can tolerate beneficial ones and face pathogens at the same time are questions that remain puzzling to plant biologists. Legume plants are good models to explore those issues, as their interactions with nitrogen-fixing bacteria called rhizobia results in a drastic and easy-to-follow phenotype of nodulation. Intriguingly, despite massive and chronic infection, legume defense reactions are essentially suppressed during the whole symbiotic process, raising a question about a potential negative effect of plant immune responses on the establishment of nodulation. In the present study, we used the model legume, Medicago truncatula, coinoculated with mutualistic and phytopathogenic bacteria, Sinorhizobium medicae and Ralstonia solanacearum, respectively. We show that the presence of R. solanacearum drastically inhibits the nodulation process. The type III secretion system of R. solanacearum, which is important for the inhibition of pathogen-associated molecular pattern-triggered immunity (PTI), strongly contributes to inhibit nodulation. Thus, our results question the negative effect of PTI on nodulation. By including a pathogenic bacterium in the interaction system, our study provides a new angle to address the influence of the biotic environment on the nodulation process.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Response of intercropped barley and fenugreek to mono- and co-inoculation with Sinorhizobium meliloti F42 and Variovorax paradoxus F310 under contrasting agroclimatic regions.

In the present research, we aimed to select efficient rhizobia and plant growth-promoting rhizobacteria (PGPR) from fenugreek nodules and assess their performance as bio-inoculum for intercropped fenugreek and barley. Inoculation effects with selected bacteria were investigated firstly on fenugreek plants under greenhouse experiment and secondly on intercropped fenugreek and barley under three different agro-environmental conditions for two consecutive years. Sinorhizobium meliloti F42 was selected due to its ability to nodulate fenugreek and effectively improve plant growth. Among non-nodulating endophytic bacteria, Variovorax paradoxus F310 strain was selected regarding its plant growth-promoting traits showed in vitro and confirmed in vivo under greenhouse experiment. Field inoculation trials revealed a significant improvement in fenugreek nodulation (up to + 97%) as well as in soil enzymes activities (up to + 209%), shoot N content (up to + 18%), shoot dry weight (up to + 40%), photosynthetic assimilation (up to + 34%) and chlorophyll content of both intercropped plants in response to the mono-inoculation with Sinorhizobium meliloti F42, compared to the un-inoculated treatment at the SBR and JBS sites. Variovorax paradoxus F310 inoculation significantly increased shoot P content of both intercropped plants at the three experimental sites compared to the un-inoculated treatment (up to + 48%). It was shown that bacterial inoculation was more efficient at the low-rainfall region than the high-rainfall region. The co-inoculation with Sinorhizobium meliloti F42 and Variovorax paradoxus F310 resulted in a significant reduction in fenugreek nodulation and shoot N content. This survey showed the benefits of rhizobial and PGPR inoculation as efficient bio-inoculums to promote the cereal-legume intercropping system and highlights the influence of site-specific environmental factors on Rhizobium-PGPR-plant interactions.

Application of Azospirillum on seeds and leaves, associated with Rhizobium inoculation, increases growth and yield of common bean.

Association of rhizobia with other plant growth-promoting bacteria (PGPB), such as Azospirillum, have the potential to increase crop yields. This work aimed to assess how Rhizobium tropici and Azospirillum brasilense alone or in combination, affect the growth and yields of common bean grains (Phaseolus vulgaris L.). In a field experiment, R. tropici and A. brasilense were inoculated on seeds, alone or in combination, associated or not with foliar spraying of A. brasilense. Shoot biomass, nitrogen accumulation, thousand-grain weight, and grain yield were evaluated. Application of A. brasilense, on seed or by foliar spraying, and seed inoculation of R. tropici, had an additive effect, increasing biomass and accumulated nitrogen, thousand-grain weight, and grain yield.

Early adaptation strategies of Saccharomyces cerevisiae and Torulaspora delbrueckii to co-inoculation in high sugar grape must-like media.

Torulaspora delbrueckii and Saccharomyces cerevisiae are yeast species found concurrently in wine. In order to commence fermentation, they adapt to the initial harsh environment, maintaining cellular homeostasis and promoting metabolism. These actions involve an intricate regulation of stress tolerance, growth and metabolic genes. Their phenotypes are influenced by the fermentation environment and physiological state of the cell, but such gene-environment interactions are poorly understood. This study aimed to compare the cell physiology of the two species, through genome-wide analysis of gene expression, coupling Oxford Nanopore MinION and Illumina Hiseq sequencing platforms. The early transcriptional responses to stress, nutrients and cell-to-cell communication were analysed. Particular attention was given to the fundamental gene modulations, leading to an understanding of the physiological changes needed to maintain cellular homeostasis, exit the quiescent state and establish dominance in the fermentation. Our findings suggest the existence of species-specific adaptation strategies in response to growth in a high sugar synthetic grape juice medium.

Co-inoculation of Bacillus sp. and Pseudomonas putida at different development stages acts as a biostimulant to promote growth, yield and nutrient uptake of tomato.

AIMS: This study builds upon the premise that roots culture distinct bacteria at specific stages of plant growth to benefit of specific microbial services needed at that particular growth stage. Accordingly, we hypothesized that the co-inoculation of beneficial microbes with distinct properties at specific stages of plant development would enhance plant performance. METHODS AND RESULTS: The chosen microbes were Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus mojavensis and Pseudomonas putida. These microbes were selected based on their specific services ranging from nutrient solubilization, root growth promotion and disease resistance, and were applied to the roots of tomato plants at specific time points when those services were needed the most by the plant. Laboratory and greenhouse studies were conducted to evaluate the effects of co-inoculation at specific stages of development compared to single microbial applications. CONCLUSION: In general, the combination of three microbes gave the highest biomass and yield without the presence of disease. Applications of three microbes showed the highest root/shoot ratio, and applications of four microbes the lowest ratio. Pseudomonas putida significantly increased fruit macronutrient and micronutrient contents. SIGNIFICANCE AND IMPACT OF THE STUDY: Our studies suggest that co-inoculation of three or four microbes is a good strategy for healthy crop production.

Impact of co-inoculation with plant-growth-promoting rhizobacteria and rhizobium on the biochemical responses of alfalfa-soil system in copper contaminated soil.

The effects and regulatory mechanisms of co-inoculation of plant-growth-promoting rhizobacteria (PGPRs) and rhizobium in plant-soil systems remain unclear, despite numerous reports that PGPRs or rhizobium can alleviate metal toxicity. We used the co-inoculation of the PGPR Paenibacillus mucilaginosus and the metal-resistant rhizobium Sinorhizobium meliloti for exploring the physiological and biochemical responses of the plant-soil system in metal-contaminated soil. The co-inoculation with the PGPR and rhizobium significantly increased the nutrient (N, P, and K) contents in plant tissues and promoted plant growth in soil contaminated with copper (Cu). Stress from Cu-induced reactive oxygen species and lipid peroxidation were largely attenuated by the co-inoculation by increasing the activities of antioxidant enzymes. The contents and uptake of Cu in plant tissues increased significantly in the co-inoculation treatment compared with the uninoculated control and individual inoculation treatment. Co-inoculation with PGPR and rhizobium significantly increased soil microbial biomass, enzymatic activities, total nitrogen, available phosphorus, and soil organic matter contents compared with the uninoculated control. Interestingly, co-inoculation also affected the composition of the rhizospheric microbial community, and slightly increased rhizospheric microbial diversity. These improvements of the soil fertility and biological activity also had a beneficial impact on plant growth under Cu stress. Our results suggested that alfalfa co-inoculated with PGPR and rhizobium could increase plant growth and Cu uptake in metal-contaminated soil by alleviating plant Cu stress and improving soil biochemical properties. These results indicate that the co-application of PGPR and rhizobium can have a positive effect on the biochemical responses of alfalfa-soil systems in soil contaminated by heavy metals and can provide an efficient strategy for the phytomanagement of metal-contaminated land.

Quorum sensing communication: Bradyrhizobium-Azospirillum interaction via N-acyl-homoserine lactones in the promotion of soybean symbiosis.

Quorum-sensing (QS) mechanisms are important in intra- and inter-specific communication among bacteria. We investigated QS mechanisms in Bradyrhizobium japonicum strain CPAC 15 and Azospirillum brasilense strains Ab-V5 and Ab-V6, used in commercial co-inoculants for the soybean crop in Brazil. A transconjugant of CPAC 15-QS with partial inactivation of N-acyl-homoserine lactones (AHLs) was obtained and several parameters were evaluated; in vitro, CPAC 15 and the transconjugant differed in growth, but not in biofilm formation, and no differences were observed in the symbiotic performance in vivo. The genome of CPAC 15 carries functional luxI and luxR genes and low amounts of three AHL molecules were detected: 3-OH-C12-AHL, 3-OH-C14-AHL, and 3-oxo-C14-AHL. Multiple copies of luxR-like genes, but not of luxI are present in the genomes of Ab-V5 and Ab-V6, and differences in gene expression were observed when the strains were co-cultured with B. japonicum; we may infer that the luxR-genes of A. brasilense may perceive the AHL molecules of B. japonicum. Soybean symbiotic performance was improved especially by co-inoculation with Ab-V6, which, contrarily to Ab-V5, did not respond to the AHLs of CPAC 15. We concluded that A. brasilense Ab-V5, but not Ab-V6, responded to the QS signals of CPAC 15, and that the synergistic interaction may be credited, at least partially, to the QS interaction. In addition, we confirmed inter- and intra-species QS communication between B. japonicum and A. brasilense and, for Azospirillum, at the strain level, impacting several steps of the symbiosis, from cell growth to plant nodulation and growth.

Mining alfalfa (Medicago sativa L.) nodules for salinity tolerant non-rhizobial bacteria to improve growth of alfalfa under salinity stress.

There are fewer reports on plant growth promoting (PGP) bacteria living in nodules as helper to tolerance to abiotic stress such as salinity and drought. The study was conducted to isolate rhizobial and non-rhizobial drought and salinity tolerant bacteria from the surface sterilized root nodules of alfalfa, grown in saline soils, and evaluate the effects of effective isolates on plant growth under salt stress. Based on drought and salinity tolerance of bacterial isolates and having multiple PGP traits, two non-rhizobial endophytic isolates and one rhizobial endophytic isolate were selected for further identification and characterization. Based on partial sequences of 16 S rRNA genes, non-rhizobial isolates and rhizobial isolate were closely related to Klebsiella sp., Kosakonia cowanii, and Sinorhizobium meliloti, respectively. None of the two non-rhizobial strains were able to form nodules on alfalfa roots under greenhouse and in vitro conditions. Co-inoculation of alfalfa plant with Klebsiella sp. A36, K. cowanii A37, and rhizobial strain S. meliloti ARh29 had a positive effect on plant growth indices under salinity stress. In addition, the single inoculation of non-rhizobial strains without rhizobial strain resulted in an increase in alfalfa growth indices compared to the plants non-inoculated and the ones inoculated with S. meliloti ARh29 alone under salinity stress, indicating that nodule non-rhizobial strains have PGP potentials and may be a promising way for improving effectiveness of Rhizobium bio-fertilizers in salt-affected soils.

Does co-inoculation of Lactuca serriola with endophytic and arbuscular mycorrhizal fungi improve plant growth in a polluted environment?

Phytoremediation of polluted sites can be improved by co-inoculation with mycorrhizal and endophytic fungi. In this study, the effects of single- and co-inoculation of Lactuca serriola with an arbuscular mycorrhizal (AM) fungus, Rhizoglomus intraradices, and endophytic fungi, Mucor sp. or Trichoderma asperellum, on plant growth, vitality, toxic metal accumulation, sesquiterpene lactone production and flavonoid concentration in the presence of toxic metals were evaluated. Inoculation with the AM fungus increased biomass yield of the plants grown on non-polluted and polluted substrate. Co-inoculation with the AM fungus and Mucor sp. resulted in increased biomass yield of plants cultivated on the polluted substrate, whereas co-inoculation with T. asperellum and the AM fungus increased plant biomass on the non-polluted substrate. In the presence of Mucor sp., mycorrhizal colonization and arbuscule richness were increased in the non-polluted substrate. Co-inoculation with the AM fungus and Mucor sp. increased Zn concentration in leaves and roots. The concentration of sesquiterpene lactones in plant leaves was decreased by AM fungus inoculation in both substrates. Despite enhanced host plant costs caused by maintaining symbiosis with numerous microorganisms, interaction of wild lettuce with both mycorrhizal and endophytic fungi was more beneficial than that with a single fungus. The study shows the potential of double inoculation in unfavourable environments, including agricultural areas and toxic metal-polluted areas.

Co-inoculation of Lolium perenne with Funneliformis mosseae and the dark septate endophyte Cadophora sp. in a trace element-polluted soil.

The presence of dark septate endophytes (DSEs) or arbuscular mycorrhizal fungi (AMF) in plant roots and their effects on plant fitness have been extensively described. However, little is known about their interactions when they are simultaneously colonizing a plant root, especially in trace element (TE)-polluted soils. We therefore investigated the effects of Cadophora sp. and Funneliformis mosseae on ryegrass (Lolium perenne) growth and element uptake in a Cd/Zn/Pb-polluted soil. The experiment included four treatments, i.e., inoculation with Cadophora sp., inoculation with F. mosseae, co-inoculation with Cadophora sp. and F. mosseae, and no inoculation. Ryegrass biomass and shoot Na, P, K, and Mg concentrations significantly increased following AMF inoculation as compared to non-inoculated controls. Similarly, DSE inoculation increased shoot Na concentration, whereas dual inoculation significantly decreased shoot Cd concentration. Moreover, oxidative stress determined by ryegrass leaf malondialdehyde concentration was alleviated both in the AMF and dual inoculation treatments. We used quantitative PCR and microscope observations to quantify colonization rates. They demonstrated that DSEs had no effect on AMF colonization, while AMF colonization slightly decreased DSE frequency. We also monitored fluorescein diacetate (FDA) hydrolysis and alkaline phosphatase (AP) activity in the rhizosphere soils. FDA hydrolysis remained unchanged in the three inoculated treatments, but AMF colonization increased AP activity and P mobility in the soil whereas DSE colonization did not alter AP activity. In this experiment, we unveiled the interactions between two ecologically important fungal groups likely to occur in roots which involved a decrease of oxidative stress and Cd accumulation in shoots. These results open promising perspectives on the fungal-based phytomanagement of TE-contaminated sites by the production of uncontaminated and marketable plant biomass.

Effect of Pb-resistant plant growth-promoting rhizobacteria inoculation on growth and lead uptake by Lathyrus sativus.

In search of efficient and resistant plant growth-promoting rhizobacteria (PGPR) strains with multiple activities, a total of twelve bacterial belonging to R. leguminosarum, S. meliloti, Pseudomonas sp., P. fluorescens, Luteibacter sp., Variovorax sp., B. simplex, and B. megaterium were isolated from root nodules of grass pea (Lathyrus sativus L.) grown in contaminated soils. Upon screening, all test strains were able to synthesize indoleacetic acid; more than 90% were siderophore producers and 75% showed varying levels of phosphate solubilizing ability. The gaseous metabolite biosynthesis showed that 42% of strains were cyanogenic. The lead (Pb) bioaccumulation differs with incubation times between cell wall and cytoplasm. Indeed, the most part of Pb was adsorbed to cell surface. A pot experiment was conducted for investigating the capability of combined bacteria to promote plant growth of Lathyrus sativus under controlled conditions. Subsequently, the performance of symbiosis Lathyrus sativus-PGPR (I4: R. leguminosarum (M5) + B. simplex + Luteibacter sp. + Variovorax sp.) was investigated under lead stress using hydroponic culture to elucidate the effect of bacterial inoculation on Pb uptake as well as plant growth. Results showed that under 0.5 mM Pb, inoculation with I4 significantly increased shoots and roots biomass by 59% and 56%, respectively, and improved Pb uptake in both shoots and roots by 39% and 47%, respectively, as compared to uninoculated plants. The inoculation of Lathyrus sativus with efficient and Pb resistant PGPR is a promising symbiosis that having significant potential to improve phytoremediation of Pb-polluted soils.

Effects of Different Techniques of Malolactic Fermentation Induction on Diacetyl Metabolism and Biosynthesis of Selected Aromatic Esters in Cool-Climate Grape Wines.

The effects of different malolactic bacteria fermentation techniques on the bioconversion of aromatic compounds in cool-climate grape wines were examined. During three wine seasons, red and white grape wines were produced using various malolactic fermentation induction techniques: Coinoculation, sequential inoculation, and spontaneous process. Volatile compounds (diacetyl and the products of its metabolism, and selected ethyl fatty acid esters) were extracted by solid phase microextraction. Compounds were identified with a multidimensional gas chromatograph-GC × GC-ToFMS with ZOEX cryogenic (N2) modulator. Sensory evaluation of the wines was also performed. It was found that the fermentation-derived metabolites studied were affected by the malolactic bacteria inoculation regime. Quantitatively, ethyl lactate, diethyl succinate, and ethyl acetate dominated as esters with the largest increase in content. The total concentration of ethyl esters was highest for the coinoculation technique, while the highest concentration of diacetyl was noted for the spontaneous technique. Controlled malolactic fermentation, especially using the coinoculation technique, can be proposed as a safe and efficient enological practice for producing quality cool-climate grape wines enriched with fruity, fresh, and floral aromas.