Isolation, identification and plant growth promotion ability of endophytic bacteria associated with lupine root nodule grown in Tunisian soil

Genetic diversity, stress tolerance and phytobeneficial potential in rhizobacteria of Vachellia tortilis subsp. raddiana

BACKGROUND

Soil bacteria often form close associations with their host plants, particularly within the root compartment, playing a significant role in plant growth and stress resilience. Vachellia tortilis subsp. raddiana, (V. tortilis subsp. raddiana)a leguminous tree, naturally thrives in the harsh, arid climate of the Guelmim region in southern Morocco. This study aims to explore the diversity and potential plant growth-promoting (PGP) activities of bacteria associated with this tree.

RESULTS

A total of 152 bacterial isolates were obtained from the rhizosphere of V. tortilis subsp. raddiana. Rep-PCR fingerprinting revealed 25 distinct genomic groups, leading to the selection of 84 representative strains for further molecular identification via 16 S rRNA gene sequencing. Seventeen genera were identified, with Bacillus and Pseudomonas being predominant. Bacillus strains demonstrated significant tolerance to water stress (up to 30% PEG), while Pseudomonas strains showed high salinity tolerance (up to 14% NaCl). In vitro studies indicated variability in PGP activities among the strains, including mineral solubilization, biological nitrogen fixation, ACC deaminase activity, and production of auxin, siderophores, ammonia, lytic enzymes, and HCN. Three elite strains were selected for greenhouse inoculation trials with V. tortilis subsp. raddiana. Strain LMR725 notably enhanced various plant growth parameters compared to uninoculated control plants.

CONCLUSIONS

The findings underscore the potential of Bacillus and Pseudomonas strains as biofertilizers, with strain LMR725 showing particular promise in enhancing the growth of V. tortilis subsp. raddiana. This strain emerges as a strong candidate for biofertilizer formulation aimed at improving plant growth and resilience in arid environments.

Plant beneficial traits of endophytic bacteria associated with fennel (Foeniculum vulgare Mill.)

In this study, we used 16S rRNA gene sequence analysis to describe the diversity of cultivable endophytic bacteria associated with fennel (Foeniculum vulgare Mill.) and determined their plant-beneficial traits. The bacterial isolates from the roots of fennel belonged to four phyla: Firmicutes (BRN1 and BRN3), Proteobacteria (BRN5, BRN6, and BRN7), Gammaproteobacteria (BRN2), and Actinobacteria (BRN4). The bacterial isolates from the shoot of fennel represented the phyla Proteobacteria (BSN1, BSN2, BSN3, BSN5, BSN6, BSN7, and BSN8), Firmicutes (BSN4, BRN1, and BRN3), and Actinobacteria (BRN4). The bacterial species Bacillus megaterium, Bacillus aryabhattai, and Brevibacterium frigoritolerans were found both in the roots and shoots of fennel. The bacterial isolates were found to produce siderophores, HCN, and indole-3-acetic acid (IAA), as well as hydrolytic enzymes such as chitinase, protease, glucanase, and lipase. Seven bacterial isolates showed antagonistic activity against Fusarium culmorum, Fusarium solani, and Rhizoctonia. solani. Our findings show that medicinal plants with antibacterial activity may serve as a source for the selection of microorganisms that exhibit antagonistic activity against plant fungal infections and may be considered as a viable option for the management of fungal diseases. They can also serve as an active part of biopreparation, improving plant growth.

Prevalence, diversity and applications potential of nodules endophytic bacteria: a systematic review

Legumes are renowned for their distinctive biological characteristic of forming symbiotic associations with soil bacteria, mostly belonging to the Rhizobiaceae familiy, leading to the establishment of symbiotic root nodules. Within these nodules, rhizobia play a pivotal role in converting atmospheric nitrogen into a plant-assimilable form. However, it has been discerned that root nodules of legumes are not exclusively inhabited by rhizobia; non-rhizobial endophytic bacteria also reside within them, yet their functions remain incompletely elucidated. This comprehensive review synthesizes available data, revealing that Bacillus and Pseudomonas are the most prevalent genera of nodule endophytic bacteria, succeeded by Paenibacillus, Enterobacter, Pantoea, Agrobacterium, and Microbacterium. To date, the bibliographic data available show that Glycine max followed by Vigna radiata, Phaseolus vulgaris and Lens culinaris are the main hosts for nodule endophytic bacteria. Clustering analysis consistently supports the prevalence of Bacillus and Pseudomonas as the most abundant nodule endophytic bacteria, alongside Paenibacillus, Agrobacterium, and Enterobacter. Although non-rhizobial populations within nodules do not induce nodule formation, their presence is associated with various plant growth-promoting properties (PGPs). These properties are known to mediate important mechanisms such as phytostimulation, biofertilization, biocontrol, and stress tolerance, emphasizing the multifaceted roles of nodule endophytes. Importantly, interactions between non-rhizobia and rhizobia within nodules may exert influence on their leguminous host plants. This is particularly shown by co-inoculation of legumes with both types of bacteria, in which synergistic effects on plant growth, yield, and nodulation are often measured. Moreover these effects are pronounced under both stress and non-stress conditions, surpassing the impact of single inoculations with rhizobia alone.

The Beneficial Effects of Inoculation with Selected Nodule-Associated PGPR on White Lupin Are Comparable to Those of Inoculation with Symbiotic Rhizobia

Nodule endophytes and associated bacteria are non-symbiotic bacteria that colonize legume nodules. They accompany nodulating rhizobia and can form beneficial associations, as some of them are plant growth-promoting rhizobacteria (PGPR) that are able to promote germination and plant growth and increase tolerance to biotic and abiotic stress. White lupin (Lupinus albus) is a legume crop that is gaining relevance as a suitable alternative to soybean as a plant protein source. Eleven nodule-associated bacteria were isolated from white lupin nodules grown in a Tunisian soil. They belonged to the genera Rhizobium, Ensifer, Pseudomonas and Bacillus. Their plant growth-promoting (PGP) and enzymatic activities were tested in vitro. Strains Pseudomonas sp., L1 and L12, displayed most PGP activities tested, and were selected for in planta assays. Inoculation with strains L1 or L12 increased seed germination and had the same positive effects on all plant growth parameters as did inoculation with symbiotic Bradyrhizobium canariense, with no significant differences among treatments. Inoculation with efficient nitrogen-fixing rhizobia must compete with rhizobia present in the soil that sometimes nodulate efficiently but fix nitrogen poorly, leading to a low response to inoculation. In such cases, inoculation with highly effective PGPR might represent a feasible alternative to boost crop productivity.

Isolation and Characterization of Bacterial Endophytes from Small Nodules of Field-Grown Peanut

It is evident that legume root nodules can accommodate rhizobial and non-rhizobial bacterial endophytes. Our recent nodule microbiome study in peanuts described that small nodules can harbor diverse bacterial endophytes. To understand their functional role, we isolated 87 indigenous endophytes from small nodules of field-grown peanut roots and characterized them at molecular, biochemical, and physiological levels. The amplified 16S rRNA genes and phylogenetic analysis of these isolates revealed a wide variety of microorganisms related to the genera Bacillus, Burkholderia, Enterobacter, Herbaspirillum, Mistsuaria, Pantoea, Pseudomonas, and Rhizobia. It was observed that 37% (100% identity) and 56% (>99% identity) of the isolates matched with the amplified sequence variants (ASVs) from our previous microbiome study. All of these isolates were tested for stress tolerance (high temperature, salinity, acidic pH) and phosphate (P) solubilization along with ammonia (NH3), indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate deaminase (ACCD), and siderophore production. The majority (78%) of the isolates were found to be halotolerant, thermotolerant, and acidophilic, and a few of them showed a significant positive response to the production of IAA, NH3, siderophore, ACCD, and P-solubilization. To evaluate the plant growth promotion (PGP) activity, plant and nodulation assays were performed in the growth chamber conditions for the selected isolates from both the non-rhizobial and rhizobial groups. However, these isolates appeared to be non-nodulating in the tested conditions. Nonetheless, the isolates 2 (Pantoea), 17 (Burkholderia), 21 (Herbaspirillum), 33o (Pseudomonas), and 77 (Rhizobium sp.) showed significant PGP activity in terms of biomass production. Our findings indicate that these isolates have potential for future biotechnological applications through the development of biologicals for sustainable crop improvement.

Promoting the growth of Sulla flexuosa L. by endophytic root nodule bacteria authors and affiliations

Legume plants rely upon multipartite interactions between rhizobia and bacterial endophytes within root nodules to facilitate plant growth. This study aimed to isolate and identify indigenous endophytic bacteria from root nodules of Sulla aculeolata L. in Northeast Morocco. Based on their tri-calcium phosphate (TCP) solubilization capacity, five endophytes were chosen for further evaluation of their plant growth traits. All isolates were hydrogen cyanide (HCN) and siderophore producers, while only BCH24 tested positive for ACC deaminase activity. Indole-3-acetic acid (IAA) synthesis ranged from 1.27 mgL^- 1 to 2.89 mgL^- 1, while soluble phosphate concentrations was between 7.99 mg L^- 1 and 110.58 mg L^- 1. Additionally, all the endophytes were able to produce more than two lytic enzymes. Based on the analysis of 16 S rRNA gene sequences five isolates were identified as Enterobacter sp (BCH13, BCH2), Pseudomonas sp (BCH16, BCH24), and Serratia sp (BCH10). The strains inhibited the growth of three phytopathogenic fungi, with BCH13 exhibiting the highest rate against Aspergillus ochraceus (45%), followed by BCH24 against Fusarium oxysporum (40%) and Botrytis cinerea (35%), respectively. In vivo inoculation of halotolerant strains Enterobacter hormaechei (BCH13) and Pseudomonas moraviensis (BCH16) under gnotobiotic conditions revealed that co-inoculation with Rhizobium sullae KS6 improved plant development compared to single inoculation, making it a promising eco-friendly bio-inoculant for legume Sulla flexuosa L. production.

Fe-Based Nanomaterial-Induced Root Nodulation Is Modulated by Flavonoids to Improve Soybean (Glycine max) Growth and Quality

Innovative technology to increase efficient nitrogen (N) use while avoiding environmental damages is needed because of the increasing food demand of the rapidly growing global population. Soybean (Glycine max) has evolved a complex symbiosis with N-fixing bacteria that forms nodules to fix N. Herein, foliar application of 10 mg L^-1 Fe₇(PO₄)₆ and Fe₃O₄ nanomaterials (NMs) (Fe-based NMs) promoted soybean growth and root nodulation, thus improving the yield and quality over that of the unexposed control, EDTA-control, and 1 and 5 mg L^-1 NMs. Mechanistically, flavonoids, key signaling molecules at the initial signaling steps in nodulation, were increased by more than 20% upon exposure to 10 mg L^-1 Fe-based NMs, due to enhanced key enzyme (phenylalanine ammonia-lyase, PAL) activity and up-regulation of flavonoid biosynthetic genes (GmPAL, GmC4H, Gm4CL, and GmCHS). Accumulated flavonoids were secreted to the rhizosphere, recruiting rhizobia for colonization. Fe₇(PO₄)₆ NMs increased Allorhizobium by 87.3%, and Fe₃O₄ NMs increased Allorhizobium and Mesorhizobium by 142.2% and 34.9%, leading to increased root nodules by 50.0% and 35.4% over the unexposed control, respectively. Leghemoglobin content was also noticeably improved by 8.2-46.5% upon Fe-based NMs. The higher levels of nodule number and leghemoglobin content resulted in enhanced N content by 15.5-181.2% during the whole growth period. Finally, the yield (pod number and grain biomass) and quality (flavonoids, soluble protein, and elemental nutrients) were significantly increased more than 14% by Fe-based NMs. Our study provides an effective nanoenabled strategy for inducing root nodules to increase N use efficiency, and then both yield and quality of soybean.

Deep Learning Approach for Detection of Underground Natural Gas Micro-Leakage Using Infrared Thermal Images

The leakage of underground natural gas has a negative impact on the environment and safety. Trace amounts of gas leak concentration cannot reach the threshold for direct detection. The low concentration of natural gas can cause changes in surface vegetation, so remote sensing can be used to detect micro-leakage indirectly. This study used infrared thermal imaging combined with deep learning methods to detect natural gas micro-leakage areas and revealed the different canopy temperature characteristics of four vegetation varieties (grass, soybean, corn and wheat) under natural gas stress from 2017 to 2019. The correlation analysis between natural gas concentration and canopy temperature showed that the canopy temperature of vegetation increased under gas stress. A GoogLeNet model with Bilinear pooling (GLNB) was proposed for the classification of different vegetation varieties under natural gas micro-leakage stress. Further, transfer learning is used to improve the model training process and classification efficiency. The proposed methods achieved 95.33% average accuracy, 95.02% average recall and 95.52% average specificity of stress classification for four vegetation varieties. Finally, based on Grad-Cam and the quasi-circular spatial distribution rules of gas stressed areas, the range of natural gas micro-leakage stress areas under different vegetation and stress durations was detected. Taken together, this study demonstrated the potential of using thermal infrared imaging and deep learning in identifying gas-stressed vegetation, which was of great value for detecting the location of natural gas micro-leakage.

Microbiome profiling reveals that Pseudomonas antagonises parasitic nodule colonisation of cheater rhizobia in Lotus

Nodule microbiota are dominated by symbiotic nitrogen-fixing rhizobia, however, other non-rhizobial bacteria also colonise this niche. Although many of these bacteria harbour plant-growth-promoting functions, it is not clear whether these less abundant nodule colonisers impact root-nodule symbiosis. We assessed the relationship between the nodule microbiome and nodulation as influenced by the soil microbiome, by using a metabarcoding approach to characterise the communities inside nodules of healthy and starved Lotus species. A machine learning algorithm and network analyses were used to identify nodule bacteria of interest, which were re-inoculated onto plants in controlled conditions to observe their potential functionality. The nodule microbiome of all tested species differed according to inoculum, but only that of Lotus burttii varied with plant health. Amplicon sequence variants representative of Pseudomonas species were the most indicative non-rhizobial signatures inside healthy L. burttii nodules and negatively correlated with Rhizobium sequences. A representative Pseudomonas isolate co-colonised nodules infected with a beneficial Mesorhizobium, but not with an ineffective Rhizobium isolate and another even reduced the number of ineffective nodules induced on Lotus japonicus. Our results show that nodule endophytes influence the overall outcome of the root-nodule symbiosis, albeit in a plant host-specific manner.

Plant-Growth-Promoting Rhizobacteria Emerging as an Effective Bioinoculant to Improve the Growth, Production, and Stress Tolerance of Vegetable Crops

Vegetable cultivation is a promising economic activity, and vegetable consumption is important for human health due to the high nutritional content of vegetables. Vegetables are rich in vitamins, minerals, dietary fiber, and several phytochemical compounds. However, the production of vegetables is insufficient to meet the demand of the ever-increasing population. Plant-growth-promoting rhizobacteria (PGPR) facilitate the growth and production of vegetable crops by acquiring nutrients, producing phytohormones, and protecting them from various detrimental effects. In this review, we highlight well-developed and cutting-edge findings focusing on the role of a PGPR-based bioinoculant formulation in enhancing vegetable crop production. We also discuss the role of PGPR in promoting vegetable crop growth and resisting the adverse effects arising from various abiotic (drought, salinity, heat, heavy metals) and biotic (fungi, bacteria, nematodes, and insect pests) stresses.

Diversity and biological activity of culturable endophytic bacteria associated with marigold (Calendula officinalis L.)

Endophytes colonizing plant tissue play an essential role in plant growth, development, stress tolerance and plant protection from soil-borne diseases. In this study, we report the diversity of cultivable endophytic bacteria associated with marigold (Calendula officinalis L.) by using 16S rRNA gene analysis and their plant beneficial properties. A total of 42 bacterial isolates were obtained from plant tissues of marigold. They belonged to the genera Pantoea, Enterobacter, Pseudomonas, Achromobacter, Xanthomonas, Rathayibacter, Agrobacterium, Pseudoxanthomonas, and Beijerinckia. Among the bacterial strains, P. kilonensis FRT12, and P. rhizosphaerae FST5 showed moderate or vigorous inhibition against three tested plant pathogenic fungi, F. culmorum, F. solani and R. solani. They also demonstrated the capability to produce hydrolytic enzymes and indole-3-acetic acid (IAA). Five out of 16 isolates significantly stimulated shoot and root growth of marigold in a pot experiment. The present study reveals that more than half of the bacterial isolates associated with marigold (C. officinalis L.) provided antifungal activity against one or more plant pathogenic fungi. Our findings suggest that medicinal plants with antimicrobial activity could be a source for selecting microbes with antagonistic activity against fungal plant pathogens or with plant growth stimulating potential. These isolates might be considered as promising candidates for the improvement of plant health.

A Comprehensive Analysis Using Colorimetry, Liquid Chromatography-Tandem Mass Spectrometry and Bioassays for the Assessment of Indole Related Compounds Produced by Endophytes of Selected Wheat Cultivars

Liquid chromatography–tandem mass spectrometry (LC–MS/MS), colorimetry, and bioassays were employed for the evaluation of the ability of endophytic bacterial strains to synthesize indole-related compounds (IRCs) and in particular indole-3-acetic acid (IAA). A total of 54 endophytic strains belonging to seven bacterial genera isolated from tissues of common and spelt wheat cultivars were studied. The endophytic bacteria isolated from different tissues of the tested wheat types were capable of IRCs production, including IAA, which constituted from 1.75% to 52.68% of all IRCs, in in vitro conditions via the tryptophan dependent pathway. The selected post-culture medium was also examined using a plant bioassay. Substantial growth of wheat coleoptile segments treated with the bacterial post-culture medium was observed in several cases. Our data suggest that the studied endophytic bacteria produce auxin-type compounds to support plant development. Summarizing, our approach to use three complementary methods for estimation of IRCs in different endophytic strains provides a comprehensive picture of their effect on wheat growth.

The Endophytic Microbiome as a Hotspot of Synergistic Interactions, with Prospects of Plant Growth Promotion

The plant root is the primary site of interaction between plants and associated microorganisms and constitutes the main components of plant microbiomes that impact crop production. The endophytic bacteria in the root zone have an important role in plant growth promotion. Diverse microbial communities inhabit plant root tissues, and they directly or indirectly promote plant growth by inhibiting the growth of plant pathogens, producing various secondary metabolites. Mechanisms of plant growth promotion and response of root endophytic microorganisms for their survival and colonization in the host plants are the result of complex plant-microbe interactions. Endophytic microorganisms also assist the host to sustain different biotic and abiotic stresses. Better insights are emerging for the endophyte, such as host plant interactions due to advancements in 'omic' technologies, which facilitate the exploration of genes that are responsible for plant tissue colonization. Consequently, this is informative to envisage putative functions and metabolic processes crucial for endophytic adaptations. Detection of cell signaling molecules between host plants and identification of compounds synthesized by root endophytes are effective means for their utilization in the agriculture sector as biofertilizers. In addition, it is interesting that the endophytic microorganism colonization impacts the relative abundance of indigenous microbial communities and suppresses the deleterious microorganisms in plant tissues. Natural products released by endophytes act as biocontrol agents and inhibit pathogen growth. The symbiosis of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) affects plant symbiotic signaling pathways and root colonization patterns and phytohormone synthesis. In this review, the potential of the root endophytic community, colonization, and role in the improvement of plant growth has been explained in the light of intricate plant-microbe interactions.

Functional Analysis and Genome Mining Reveal High Potential of Biocontrol and Plant Growth Promotion in Nodule-Inhabiting Bacteria Within Paenibacillus polymyxa Complex

Bacteria belonging to the genus Paenibacillus were frequently isolated from legume nodules. The nodule-inhabiting Paenibacillus as a resource of biocontrol and plant growth-promoting endophytes has rarely been explored. This study explored the nodule-inhabiting Paenibacillus' antifungal activities and biocontrol potentials against broad-spectrum important phytopathogenic fungi. We collected strains which were isolated from nodules of Robinia pseudoacacia, Dendrolobium triangulare, Ormosia semicastrata, Cicer arietinum, Acacia crassicarpa, or Acacia implexa and belong to P. peoriae, P. kribbensis, P. endophyticus, P. enshidis, P. puldeungensis, P. taichungensis, or closely related to P. kribbensis, or P. anseongense. These nodule-inhabiting Paenibacillus showed diverse antagonistic activities against five phytopathogenic fungi (Fusarium graminearum, Magnaporthe oryzae, Rhizoctonia solani, Sclerotinia sclerotiorum, and Botrytis cinerea). Six strains within the P. polymyxa complex showed broad-spectrum and potent activities against all the five pathogens, and produced multiple hydrolytic enzymes, siderophores, and lipopeptide fusaricidins. Fusaricidins are likely the key antimicrobials responsible for the broad-spectrum antifungal activities. The nodule-inhabiting strains within the P. polymyxa complex were able to epiphytically and endophytically colonize the non-host wheat plants, produce indole acetic acids (IAA), and dissolve calcium phosphate and calcium phytate. P. peoriae strains RP20, RP51, and RP62 could fix N2. P. peoriae RP51 and Paenibacillus sp. RP31, which showed potent plant colonization and plant growth-promotion competence, effectively control fungal infection in planta. Genome mining revealed that all strains (n = 76) within the P. polymyxa complex contain ipdC gene encoding indole-3-pyruvate decarboxylase for biosynthesis of IAA, 96% (n = 73) contain the fus cluster for biosynthesis of fusaricidins, and 43% (n = 33) contain the nif cluster for nitrogen fixation. Together, our study highlights that endophytic strains within the P. polymyxa complex have a high probability to be effective biocontrol agents and biofertilizers and we propose an effective approach to screen strains within the P. polymyxa complex.

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.

Genome-based reclassification of Paenibacillus panacisoli DSM 21345T as Paenibacillus massiliensis subsp. panacisoli subsp. nov. and description of Paenibacillus massiliensis subsp. massiliensis subsp. nov

Bacteria of the genus Paenibacillus are relevant to humans, animals and plants. The species Paenibacillus massiliensis and Paenibacillus panacisoli are Gram-stain-positive and endospore-forming bacilli isolated from a blood culture of a leukemia patient and from soil of a ginseng field, respectively. Comparative analyses of their 16S rRNA genes revealed that the two Paenibacillus species could be synonyms (99.3% sequence identity). In the present study we performed different genomic analyses in order to evaluate the phylogenetic relationship of these micro-organisms. Paenibacillus massiliensis DSM 16942T and P. panacisoli DSM 21345T presented a difference in their G+C content lower than 1 mol%, overall genome relatedness index values higher than the species circumscription thresholds (average nucleotide identity, 95.57 %; genome-wide ANI, =96.51 %; and orthologous ANI, 96.25 %), and a monophyletic grouping pattern in the phylogenies of the 16S rRNA gene and the proteome core. Considering that these strains present differential biochemical capabilities and that their computed digital DNA–DNA hybridization value is lower than the cut-off for bacterial subspecies circumscription, we suggest that each of them form different subspecies of P. massiliensis , Paenibacillus massiliensis subsp. panacisoli subsp. nov. (type strain DSM 21345T) and Paenibacillus massiliensis subsp. massiliensis subsp. nov. (type strain DSM 16942T).

Effect of Applying Struvite and Organic N as Recovered Fertilizers on the Rhizosphere Dynamics and Cultivation of Lupine (Lupinus angustifolius)

Intensive agriculture and horticulture heavily rely on the input of fertilizers to sustain food (and feed) production. However, high carbon footprint and pollution are associated with the mining processes of P and K, and the artificial nitrogen fixation for the production of synthetic fertilizers. Organic fertilizers or recovered nutrients from different waste sources can be used to reduce the environmental impact of fertilizers. We tested two recovered nutrients with slow-release patterns as promising alternatives for synthetic fertilizers: struvite and a commercially available organic fertilizer. Using these fertilizers as a nitrogen source, we conducted a rhizotron experiment to test their effect on plant performance and nutrient recovery in lupine plants. Plant performance was not affected by the fertilizer applied; however, N recovery was higher from the organic fertilizer than from struvite. As root architecture is fundamental for plant productivity, variations in root structure and length as a result of soil nutrient availability driven by plant-bacteria interactions were compared showing also no differences between fertilizers. However, fertilized plants were considerably different in the root length and morphology compared with the no fertilized plants. Since the microbial community influences plant nitrogen availability, we characterized the root-associated microbial community structure and functionality. Analyses revealed that the fertilizer applied had a significant impact on the associations and functionality of the bacteria inhabiting the growing medium used. The type of fertilizer significantly influenced the interindividual dissimilarities in the most abundant genera between treatments. This means that different plant species have a distinct effect on modulating the associated microbial community, but in the case of lupine, the fertilizer had a bigger effect than the plant itself. These novel insights on interactions between recovered fertilizers, plant, and associated microbes can contribute to developing sustainable crop production systems.

Inoculation of Lupinus albus with the nodule-endophyte Paenibacillus glycanilyticus LJ121 improves grain nutritional quality

Metabolic changes occurring in white lupine grain were investigated in response to Plant Growth Promoting Rhizobacteria (PGPR) root inoculation under field condition. We precisely targeted lipids and phenolics changes occurring in white lupine grain in response to Pseudomonas brenneri LJ215 and/or Paenibacillus glycanilyticus LJ121 inoculation. Lipids and phenolic composition were analyzed using an Ultra High-Performance Liquid Chromatography/Tandem Mass Spectrometry Methods. As compared to grain of un-inoculated control plant, Paenibacillus glycaniliticus inoculation highly increased the total lipids content (from 232.55 in seeds of un-inoculated control plant to 944.95 mg/kg) and the relative percentage of several fatty acid such as oleic acid (+20.95%) and linoleic acid (+14.28%) and decreased the relative percentage of glycerophospholipids (- 13.11%), sterol (- 0.2% and - 0.34% for stigmasterol and campesterol, respectively) and prenol (- 17.45%) class. Paenibacillus glycaniliticus inoculation did not affect total phenolic content, while it modulated content of individual phenolic compounds and induced the accumulation of "new" phenolics compounds such as kaempferol. Paenibacillus glycanilyticus LJ121 can be a useful bio-fertilizer to enhance nutritional quality of white lupine grain.