Agronomic advantage of bacterial biological nitrogen fixation on wheat plant growth under contrasting nitrogen and phosphorus regimes.

Introduction: Given their remarkable capacity to convert atmospheric nitrogen into plant-accessible ammonia, nitrogen-fixing microbial species hold promise as a sustainable alternative to chemical nitrogen fertilizers, particularly in economically significant crops like wheat. This study aimed to identify strains with optimal attributes for promoting wheat growth sustainably, with a primary emphasis on reducing reliance on chemical nitrogen fertilizers. Methods: We isolated free nitrogen-fixing strains from diverse rhizospheric soils across Morocco. Subsequently, we conducted a rigorous screening process to evaluate their plant growth-promoting traits, including nitrogen fixation, phosphate solubilization, phytohormone production and their ability to enhance wheat plant growth under controlled conditions. Two specific strains, Rhodotorula mucilaginosa NF 516 and Arthrobacter sp. NF 528, were selected for in-depth evaluation, with the focus on their ability to reduce the need for chemical nitrogen supply, particularly when used in conjunction with TSP fertilizer and natural rock phosphate. These two sources of phosphate were chosen to assess their agricultural effectiveness on wheat plants. Results and discussion: Twenty-two nitrogen-fixing strains (nif-H+) were isolated from various Moroccan rhizospheric soils, representing Bacillus sp., Pseudomonas sp., Arthrobacter sp., Burkholderia sp. and a yeast-like microorganism. These strains were carefully selected based on their potential to promote plant growth. The findings revealed that the application of Rhodotorula mucilaginosa NF 516 and Arthrobacter sp. NF 528 individually or in combination, significantly improved wheat plant growth and enhanced nutrients (N and P) uptake under reduced nitrogen regimes. Notably, their effectiveness was evident in response to both natural rock phosphate and TSP, demonstrating their important role in wheat production under conditions of low nitrogen and complex phosphorus inputs. This research underscores the significant role of nitrogen-fixing microorganisms, particularly Rhodotorula mucilaginosa NF 516 and Arthrobacter sp. NF 528, in wheat production under conditions of low nitrogen and complex phosphorus inputs. It showcases their potential to reduce chemical nitrogen fertilization requirements by up to 50% without compromising wheat plant yields. Our study emphasizes the importance of bacterial biological nitrogen fixation in meeting the remaining nitrogen requirements beyond this reduction. This underscores the vital role of microbial contributions in providing essential nitrogen for optimal plant growth and highlights the significance of biological nitrogen fixation in sustainable agriculture practices.

Current status and future developments of assessing microbiome composition and dynamics in anaerobic digestion systems using metagenomic approaches.

The metagenomic approach stands as a powerful technique for examining the composition of microbial communities and their involvement in various anaerobic digestion (AD) systems. Understanding the structure, function, and dynamics of microbial communities becomes pivotal for optimizing the biogas process, enhancing its stability and improving overall performance. Currently, taxonomic profiling of biogas-producing communities relies mainly on high-throughput 16S rRNA sequencing, offering insights into the bacterial and archaeal structures of AD assemblages and their correlations with fed substrates and process parameters. To delve even deeper, shotgun and genome-centric metagenomic approaches are employed to recover individual genomes from the metagenome. This provides a nuanced understanding of collective functionalities, interspecies interactions, and microbial associations with abiotic factors. The application of OMICs in AD systems holds the potential to revolutionize the field, leading to more efficient and sustainable waste management practices particularly through the implementation of precision anaerobic digestion systems. As ongoing research in this area progresses, anticipations are high for further exciting developments in the future. This review serves to explore the current landscape of metagenomic analyses, with focus on advancing our comprehension and critically evaluating biases and recommendations in the analysis of microbial communities in anaerobic digesters. Its objective is to explore how contemporary metagenomic approaches can be effectively applied to enhance our understanding and contribute to the refinement of the AD process. This marks a substantial stride towards achieving a more comprehensive understanding of anaerobic digestion systems.

Chromosome-scale assembly uncovers genomic compartmentation of Fusarium oxysporum f. sp. albedinis, the causal agent of Bayoud disease in date palm.

Date palm (Phoenixdactylifera) is the most significant crop across North Africa and the Middle East. However, the crop faces a severe threat from Bayoud disease caused by the fungal pathogen Fusarium oxysporum f. sp. albedinis (FOA). FOA is a soil-borne fungus that infects the roots and vascular system of date palms, leading to widespread destruction of date palm plantations in North Africa over the last century. This is considered the most devastating pathogen of oasis agriculture in North Africa and responsible for loss of 13 million trees in Algeria and Morocco alone. In this study, we present a chromosome-scale high-quality genome assembly of the virulent isolate Foa 44, which provides valuable insights into understanding the genetic basis of Bayoud disease. The genome assembly consists of 11 chromosomes and 40 unplaced contigs, totalling 65,971,825 base pairs in size. It exhibits a GC ratio of 47.77% and a TE (transposable element) content of 17.30%. Through prediction and annotation, we identified 20,416 protein-coding genes. By combining gene and repeat densities analysis with alignment to Fusarium oxysporum f. sp. lycopersici (FOL) 4287 isolate genome sequence, we determined the core and lineage-specific compartments in Foa 44, shedding light on the genome structure of this pathogen. Furthermore, a phylogenomic analysis based on the 3,292 BUSCOs core genome revealed a distinct clade of FOA isolates within the Fusarium oxysporum species complex (FOSC). Notably, the genealogies of the five identified Secreted In Xylem (SIX) genes (1, 6, 9, 11 and 14) in FOA displayed a polyphyletic pattern, suggesting a horizontal inheritance of these effectors. These findings provide a valuable genomics toolbox for further research aimed at combatting the serious biotic constraints posed by FOA to date palm. This will pave the way for a deeper understanding of Bayoud disease and facilitate the development of effective diagnostic tools and control measures.

Effect of Arbuscular Mycorrhizal Fungi Isolated From Rock Phosphate Mine and Agricultural Soil on the Improvement of Wheat Plant Growth.

The improvement of plant growth and yield becomes crucial to feed the rising world population, especially in harsh conditions, drought, salt stress, lack of nutrition, and many other challenges. To cope with these stresses, plants developed an adaptation strategy (mycorrhiza), which is an efficient way to reinforce their growth and resistance. For this purpose, we studied the influence of mycorrhizal fungi isolated from a natural rock phosphate mine in the vicinity of some native plants and agricultural soil to assess their capacity in increasing the growth, nutritional profile improvement, and biochemical parameters in the inoculated wheat plants. Results showed a high diversity of isolated arbuscular mycorrhizal fungi (AMF) spores in the agricultural soil, and less diversity in the natural phosphate samples, where three main genera were identified: glomus, gigaspora, and acaulospora. The chlorophyll content increased by 116% in the native inoculum (NM) flowed by Glomus sp2 from agricultural soil (98%) compared to non-mycorrhized plants, which significantly impact the growth and plant biomass (an increase of 90 and 73%, respectively). The same rate of change was shown on total phenolic compounds with an increase of 64% in the plants inoculated with Glomus sp2 in the presence of TSP, compared to the non-mycorrhized plants. In conclusion, the inoculation of wheat plants with AMF spores improved plants' growth via the increase in the density of the root system, which implies better assimilation of nutrients, especially in mycorrhizal plants with phosphorus fertilization regime, triple superphosphate (TSP) or natural rock phosphate (RP). This improvement of the physiological and biochemical parameters (chlorophyll contents and phenolic compound) of the treated plants reflected the positive impact of AMF, especially those originating from RP. AMF in phosphate mine could be an important source of inoculum to improve plant nutrient efficiency with the direct use of RP as fertilizer.

Investigation of bacterial diversity using 16S rRNA sequencing and prediction of its functionalities in Moroccan phosphate mine ecosystem.

Native plants in extreme environments may harbor some unique microbial communities with particular functions to sustain their growth and tolerance to harsh conditions. The aim of this study was to investigate the bacterial communities profiles in some native plants and samples of the Moroccan phosphate mine ecosystem by assessing the percentages of taxonomic identification using six hypervariable regions of the 16S rRNA. The rhizosphere of the three wild plants in the Moroccan phosphate mine is characterized by interesting bacterial diversity including Proteobacteria (62.24%, 71.15% and 65.61%), Actinobacteria (22.53%, 15.24%, 22.30%), Bacteroidetes (7.57%; 4.23%; 7.63%), and Firmicutes (5.82%; 1.17%; 2.83%). The bulk phosphate mine samples were dominated by Actinobacteria with average relative abundance of 97.73% that are different from those inferred in the rhizosphere samples of the native plants. The regions V3, V4 and V67 performed better in the taxonomic profiling at different taxonomic levels. Results indicated that both plant genotype and mainly soil conditions may be involved in the shaping of bacterial diversity. Such indication was also confirmed by the prediction of functional profiles that showed enrichment of many functions related to biological nitrogen fixation in the rhizosphere of native plants and the stress related functions in the bulk phosphate mine in comparison with the wheat rhizosphere samples.

Complete mitochondrial genome and phylogeny of the causal agent of Bayoud disease on date palm, Fusarium oxysporum f. sp. albedinis.

The complete mitogenome of Fusarium oxysporum f. sp. albedinis (FOA), the causal agent of the destructive fusarium wilt in date palm, is sequenced and assembled. The circular mitogenome of isolate Foa44 is 51,601 bp in length and contains 26 transfer RNA (tRNA) genes, one ribosomal RNA (rRNA), and 28 protein-coding genes. A mitogenome-based phylogenetic analysis of Fusarium revealed that FOA is congruent with previous nuclear-gene phylogenetic results.

Nitrogen Fixing Azotobacter Species as Potential Soil Biological Enhancers for Crop Nutrition and Yield Stability.

Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic "Nitrogenase" conversion of atmospheric nitrogen (N2) into ammonium readily absorbable by roots. N2-fixing microorganisms collectively termed as "diazotrophs" are able to fix biologically N2 in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N2-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance of Azotobacter species was highlighted as both important free-living N2-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we described Azotobacter beneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features of Azotobacter that are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed out Azotobacter based-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculant Azotobacter cysts. Furthermore, Azotobacter species still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.

Bioformulation of Microbial Fertilizer Based on Clay and Alginate Encapsulation.

This study aims to develop new formulations for microbial fertilizers Pseudomonas fluorescens Ms-01 (Pf) and Azosprillum brasilense DSM1690 (Ab) using two kinds of clay minerals. The studied formulations were prepared as hybrid materials based on halloysite and alginate [Ha-Ag] or montmorillonite and alginate polymers [Mt-Ag] and were applied to the bacterial strains to develop low cost, efficient, and slow-release capsules. Their efficiency was evaluated in comparison with alginate [Ag] as the control. The produced capsules were spherical in shape and were chemically and physically characterized and further analyzed for their swelling ratios, soil biodegradability, release kinetics of microbial cells, and their survival stability over 3 months of storage under different conditions (room temperature vs 4 °C). The effect of the capsules on the growth of wheat plants was also investigated. Results showed that both formulations were able to preserve bacterial survival which reached 14.8 log CFU g-1 after 3 months storage in the halloysite formulation. The swelling ratios were ranged between 61.5 ± 1.35% and 36.5 ± 5% for the montmorillonite and the halloysite formulations, respectively. The release kinetics revealed the slow-release capacity of the capsules mainly with the halloysite formulation which significantly released bacterial cells after 15 days of incubation in saline water (15.24 log CFU mL-1). The application of the capsules to wheat plants significantly increased root and shoot biomasses and nitrogen content in the roots. In conclusion, halloysite minerals seem to be more adapted as additive to alginate in microbial encapsulation.

Role of Inorganic Phosphate Solubilizing Bacilli Isolated from Moroccan Phosphate Rock Mine and Rhizosphere Soils in Wheat (Triticum aestivum L) Phosphorus Uptake.

This work aimed to assess the ability of plant growth-promoting Bacilli isolated from wheat rhizosphere and rock phosphate mine soils to convert inorganic phosphate (Pi) from Moroccan natural phosphate (NP) to soluble forms. The effect of these bacteria on wheat plants in order to increase their phosphorus (P) uptake in vitro was also investigated. Bacteria were isolated from wheat rhizosphere and natural rock phosphate soils and screened for their ability to solubilize Tri-Calcium Phosphate (TCP) and Natural Rock Phosphate (NP), to produce indole-3-acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Isolates were identified by 16S rRNA sequencing and tested for their capacity to increase wheat plants growth and their phosphorus uptake.Twenty-four strains belonging to Bacillus genus isolated from both biotopes were screened for their ability to solubilize Pi. The highest NP solubilization was showed by strains isolated from wheat rhizosphere. Solubilization of Pi was accompanied by organic acid production. Strains produce IAA, siderophore and ACC deaminase. Inoculation assays using efficient NP-solubilizing bacilli strains from both sources showed the ability of these isolates to increase wheat growth and the phosphorus uptake under in vitro conditions. Bacilli strains isolated from rhizosphere soil and natural rock phosphorus soil showed effective solubilization of Pi from rock phosphate. Phosphate solubilizing Bacilli were evaluated for their plant growth promotion under in vitro conditions. Results revealed the positive effect of all strains on biometric parameters and P content of wheat seedlings.

Bio-active nanocomposite films based on nanocrystalline cellulose reinforced styrylquinoxalin-grafted-chitosan: Antibacterial and mechanical properties.

In this study, active nanocomposite films based on cellulose nanocrystalline (NCC) reinforced styrylquinoxalin-grafted-chitosan are prepared by solvent-casting process. The structures of the two styrylquinoxaline derivatives were confirmed by FT-IR, 1H, 13C NMR spectral data and the study of the antibacterial activity against Escherichia coli (EC), Staphylococcus aureus (SA), Bacillus subtilis (BS) and Pseudomonas Aeruginosa (PA) exhibits that they have a good antibacterial activity against (PA). On their side, the styrylquinoxalin-g-chitosan films are able to inhibit the growth of (PA) through their contact area without being damaged by the antibacterial test conditions. The addition of 5wt% of NCCs as nano-reinforcements revealed no change at the level of antibacterial activity but led to an important improvement of the mechanical properties (more than 60% and 90% improvement in Young's modulus and tensile strength, respectively) of the modified-chitosan films. Thereby, the present nanocomposite films are prepared by a simple way and featured by good mechanical and antibacterial properties which enhance the possibility to use them as bio-based products for biomedical and food packaging.