Genus Of Plant Growth-promoting Rhizobacteria Research Articles

Biochar + AD exerts a biostimulant effect in the yield of horticultural crops and improves bacterial biodiversity and species richness in the rhizosphere

Organic fertilisers are gaining prominence in advanced agri-systems due to the need for alternatives to the most pollutant agricultural inputs, contributing to sustainable agriculture. The objective of this study was to analyse the agronomic effect of a biochar non-additivated and additivated with anaerobic digestate (AD) on the soil microbiome in melon and pepper crops at the field scale, hypothesising that the synergy between biochar and the additive confers additional benefits to the crop. Two doses of biochar (250 and 500 kg ha−1) and two doses of additive with respect to biochar (5 and 10% v:w) were tested. The highest yield was observed for a reduced dose of mineral fertilisation (NPK −20%) with biochar + AD at the highest dose of additive: a biochar dose of 250 kg/ha with 10% AD for the melon crop and a biochar dose of 500 kg ha−1 with 10% AD for the pepper crop. Specifically, the yield increase compared with the control, which only received NPK, was a 33% increase in melon and 18% in pepper. The microbiome of the bulk soil was not modified by biochar + AD, but the composition of the rhizosphere microbiome changed, emerging plant growth-promoting rhizobacteria (PGPR) or increasing its relative abundance (e.g. Arthrobacter, Mitsuaria or Bacillus genus). We have demonstrated a positive correlation between yield and fruit quality parameters, and the presence of cluster of bacteria with predominance of known PGPR genera, that have been boosted by the treatments with biochar + AD. Thus, we hypothesize that the improved yield and fruit quality is in part due to the rhizosphere bacteria community enhancement.

Multifaceted Impacts of Plant-Beneficial Pseudomonas spp. in Managing Various Plant Diseases and Crop Yield Improvement.

The modern agricultural system has issues with the reduction of agricultural productivity due to a wide range of abiotic and biotic stresses. It is also expected that in the future the entire world population may rapidly increase and will surely demand more food. Farmers now utilize a massive quantity of synthetic fertilizers and pesticides for disease management and to increase food production. These synthetic fertilizers badly affect the environment, the texture of the soil, plant productivity, and human health. However, agricultural safety and sustainability depend on an ecofriendly and inexpensive biological application. In contrast to synthetic fertilizers, soil inoculation with plant-growth-promoting rhizobacteria (PGPR) is one of the excellent alternative options. In this regard, we focused on the best PGPR genera, Pseudomonas, which exists in the rhizosphere as well as inside the plant's body and plays a role in sustainable agriculture. Many Pseudomonas spp. control plant pathogens and play an effective role in disease management through direct and indirect mechanisms. Pseudomonas spp. fix the amount of atmospheric nitrogen, solubilize phosphorus and potassium, and also produce phytohormones, lytic enzymes, volatile organic compounds, antibiotics, and secondary metabolites during stress conditions. These compounds stimulate plant growth by inducing systemic resistance and by inhibiting the growth of pathogens. Furthermore, pseudomonads also protect plants during different stress conditions like heavy metal pollution, osmosis, temperature, oxidative stress, etc. Now, several Pseudomonas-based commercial biological control products have been promoted and marketed, but there are a few limitations that hinder the development of this technology for extensive usage in agricultural systems. The variability among the members of Pseudomonas spp. draws attention to the huge research interest in this genus. There is a need to explore the potential of native Pseudomonas spp. as biocontrol agents and to use them in biopesticide development to support sustainable agriculture.

Study of the plant growth-promoting capacity of Pseudomonas putida 1046 in a model plant system

Plant Growth Promoting Rhizobacteria (PGPR) represent a microbial community that exerts growth-promoting capabilities in plants by various mechanisms. Among the PGPR genera, Pseudomonas spp. deserves special attention. It is due to its characteristic traits, like the production of phytohormones and siderophores, solubilization of minerals and phosphates, and plant protection from biotic and abiotic stress. These PGPR properties depend on the microorganism and its plant counterpart. The use of microbial strains as bioinoculants must consider the physiological and economic aspects of the process, and the plant growth stimulating effect has to be checked and proved. This study aimed to explore the PGP capacity of Pseudomonas putida 1046 strain in a model plant system of the economically important corn culture (Zea mays). The effect of the strain’s metabolic status on the plant germination capacity was evaluated. Bacterial cultures, grown 16 h and 48 h, were explored for the treatment of the corn seeds at three experimental concentrations: 0.1, 0.2, and 0.4%, and monitoring of their germination capacity through the growth indicators length of the radicle, length of the coleoptile, and the number of lateral roots. The data obtained outline the positive effect of Pseudomonas putida 1046 on the germination capacity of corn when applied at 0.2% concentration. The in vitro treatment of the model plants with 0.2% suspension resulted in a 22.87%–28.33% increase in the length of the radicle, a 35.96%–49.56% increase in the length of the coleoptile, and a 5.41–16.67% increase in the number of the lateral roots. High values of the vigour index (2125 for 16 h and 2721 for 48 h culture) were also registered. The strain’s ability to produce siderophores of hydroximate type and exhibit phosphate solubilizing activity is proved. The optimal treatment parameters of the corn seeds comprise the application of 0.2% suspension of 16 h grown Pseudomonas putida 1046 strain for five days.

Plant growth-promoting rhizobacteria for orphan legume production: Focus on yield and disease resistance in Bambara groundnut

Orphan legumes are now experiencing growing demand due to the constraints on available major food crops. However, due to focus on major food crops, little research has been conducted on orphan legumes compared to major food crops, especially in microbiome application to improve growth and yield. Recent developments have demonstrated the enormous potential of beneficial microbes in growth promotion and resistance to stress and diseases. Hence, the focus of this perspective is to examine the potential of plant growth promoting rhizobacteria (PGPR) to improve Bambara groundnut yield and quality. Further insights into the potential use of PGPR as a biological control agent in the crop are discussed. Finally, three PGPR genera commonly associated with plant growth and disease resistance (Bacillus, Pseudomonas, and Streptomyces) were highlighted as case studies for the growth promotion and disease control in BGN production.

Bradyrhizobium japonicum, B. elkanii and B. diazoefficiens Interact with Rice (Oryza sativa), Promote Growth and Increase Yield.

Bradyrhizobium is a genus of plant growth-promoting rhizobacteria (PGPR) that have been studied for several decades mainly for the ability to fix diazotrophic nitrogen after having been established endosymbiotically inside root nodules of the legumes of Fabaceae. The aim of this work was to evaluate the capability of Bradyrhizobium to promote the growth of crops belonging to other families, in this case, rice (Oryza sativa), both in laboratory and in field trials. For laboratory test, surface-sterilized rice seeds were soaked with cultures of each strain and planted in pots. Plant length and dry weight were measured after 35days. For the field test, rice seeds of varieties Yeruá La Plata and Gurí INTA were inoculated with the three best strains observed in the laboratory test and planted in plots. After 60days of growth, plant length and dry weight were measured. At harvest time, we measured the dry weight of the aerial part, yield and thousand-grain weight. Inoculation with any of the three species described provoked significant increments compared to the uninoculated control at least in one of the parameters measured, both in the laboratory and in the field tests. Bradyrhizobium japonicum E109 was the strain that promoted rice growth the most in the lab while Bradyrhizobium elkanii SEMIA 587 was the strain that promoted rice growth the most in the field, with increments in yield of approximately 1000kg/ha. Data obtained suggest that the Bradyrhizobium species promoted all rice growth and yield.

Predictive comparative antibiotic resistance (AMR) profiles of rhizobacteria genes using CARD: a bioinformatics approach

Members of the Plant Growth Promoting Rhizobacteria (PGPR) have been severally implicated as excellent growth enhancers, yield promoters as well as bio-fertilizers. A study on antibiotics surveillance of PGPR is urgently needed as caution towards its continued usage in Bio-science and Agro-allied. Antimicrobial resistance has become a great concern in agriculture and public health. The detection and characterization of antimicrobial resistance move from targeted culture and enzyme-based reaction to high-throughput metagenomics; acceptable resources for the analysis of large-scale information area unit as an expected rescue. The excellent bioinformatics tool newly curated for Antibiotic Resistance information (CARD; https://card.mcmaster.ca) could be a curated hub and resource-providing-referenced server for deoxyribonucleic acid and protein sequences as well as detection models on the molecular radar for antimicrobial resistance. This study employed CARD as pathogenomics repertoires for high-quality reference information on retrieving antibiotics resistance information on twenty-two carefully-selected members of Rhizobacter from NCBI. NCBI and CARD on-line platform were employed in polishing of antiobitics resistance info of selected PGPR genera such as Leguminosarum, Azotobacter, Azospirillum, Erwinia, Mesorhizobium, Flavobacterium Paenibacillus Polymyxa, Bacilli mycoides, B. subtilis, and Burkholderia pseudomallei among others. The data generated showed evidence that these rhizobacteria could be resistant to certain drug classes under a different Antimicrobial Resistance (AMR) Gene families using different phyto-pathogenic genes (ARO terms) using different resistance mechanisms. This distinctive platform provides bioinformatics tool that bridges antibiotic resistance considerations, which could be a fallback for policies in healthcare, agriculture and the environment.

The Plant Growth-Promoting Rhizobacterium Variovorax boronicumulans CGMCC 4969 Regulates the Level of Indole-3-Acetic Acid Synthesized from Indole-3-Acetonitrile.

Variovorax is a metabolically diverse genus of plant growth-promoting rhizobacteria (PGPR) that engages in mutually beneficial interactions between plants and microbes. Unlike most PGPR, Variovorax cannot synthesize the phytohormone indole-3-acetic acid (IAA) via tryptophan. However, we found that Variovorax boronicumulans strain CGMCC 4969 can produce IAA using indole-3-acetonitrile (IAN) as the precursor. Thus, in the present study, the IAA synthesis mechanism of V. boronicumulans CGMCC 4969 was investigated. V. boronicumulans CGMCC 4969 metabolized IAN to IAA through both a nitrilase-dependent pathway and a nitrile hydratase (NHase) and amidase-dependent pathway. Cobalt enhanced the metabolic flux via the NHase/amidase, by which IAN was rapidly converted to indole-3-acetamide (IAM) and in turn to IAA. IAN stimulated metabolic flux via the nitrilase, by which IAN was rapidly converted to IAA. Subsequently, the IAA was degraded. V. boronicumulans CGMCC 4969 can use IAN as the sole carbon and nitrogen source for growth. Genome sequencing confirmed the IAA synthesis pathways. Gene cloning and overexpression in Escherichia coli indicated that NitA has nitrilase activity and IamA has amidase activity to respectively transform IAN and IAM to IAA. Interestingly, NitA showed a close genetic relationship with the nitrilase of the phytopathogen Pseudomonas syringae Quantitative PCR analysis indicated that the NHase/amidase system is constitutively expressed, whereas the nitrilase is inducible. The present study helps our understanding of the versatile functions of Variovorax nitrile-converting enzymes that mediate IAA synthesis and the interactions between plants and these bacteria.IMPORTANCE We demonstrated that Variovorax boronicumulans CGMCC 4969 has two enzymatic systems-nitrilase and nitrile hydratase/amidase-that convert indole-3-acetonitrile (IAN) to the important plant hormone indole-3-acetic acid (IAA). The two IAA synthesis systems have very different regulatory mechanisms, affecting the IAA synthesis rate and duration. The nitrilase was induced by IAN, which was rapidly converted to IAA; subsequently, IAA was rapidly consumed for cell growth. The nitrile hydratase (NHase) and amidase system was constitutively expressed and slowly but continuously synthesized IAA. In addition to synthesizing IAA from IAN, CGMCC 4969 has a rapid IAA degradation system, which would be helpful for a host plant to eliminate redundant IAA. This study indicates that the plant growth-promoting rhizobacterium V. boronicumulans CGMCC 4969 has the potential to be used by host plants to regulate the IAA level.

The benefits of foliar inoculation with Azospirillum brasilense in soybean are explained by an auxin signaling model

Azospirillum sp. is one of the most studied genera of plant growth-promoting rhizobacteria (PGPR). The ability of Azospirillum sp. to promote plant growth has been associated with its ability to produce several phytohormones, such as auxins, gibberellins and cytokinins, but mainly indole-3-acetic acid (IAA). It has been propoosed that the production of IAA explains the positive effects of co-inoculation with Azospirillum sp. on the rhizobia-legume symbiosis. In this study, we constructed an IAA-deficient mutant of A. brasilense Az39 (ipdC − ) by using a restriction-free cloning method. We inoculated soybean seeds with 1·106 cfu·seed−1 of Bradyrhizobium japonicum E109 and co-inoculating leaves at the V3 stage with 1·108 cfu.plant−1 of A. brasilense Az39 wt or ipdC − or inoculated leaves with 20 μg.plant−1 synthetic IAA. The results confirmed soybean growth promotion as there was increased total plant and root length, aerial and root dry weight, number of nodules on the primary root, and an increase in the symbiosis established with B. japonicum E109. Nodule weight also increased after foliar co-inoculation with the IAA- producer A. brasilense Az39. The exogenous application of IAA decreased aerial and root length, as well as the number of nodules on primary roots in comparison with the Az39 wt strain. These results allow us to propose a biological model of response to foliar co-inoculation of soybean with IAA-producing rhizobacteria. This model clearly shows that both the presence of microorganism as part of the colonization process and the production of IAA in situ are co-responsible, via plant signaling molecules, for the positive effects on plant growth and symbiosis establishment.

Rhizobium as plant probiotic for strawberry production under microcosm conditions

There is increasing interest in the use of plant growth-promoting rhizobacteria (PGPR) as environmental-friendly and healthy biofertilizers. Strawberries (Fragraria x ananassa) are mainly consumed fresh and hence any PGPRs used for biofertilization must be safe for humans, which is the case for members of the genus Rhizobium. In this study, the effects of inoculation of strawberry plants with Rhizobium sp. strain PEPV16, which belongs to the phylogenetic group of R. leguminosarum, and whose plant growth promotion ability has been reported previously for lettuce (Lactuca sativa) and carrots (Daucus carota), was examined. The results demonstrated that PEPV16 promotes strawberry growth through significant increases in the number of stolons, flowers and fruits as compared with uninoculated controls. Compared to uninoculated controls, the fruits of the inoculated plants had higher concentrations of Fe, Zn, Mn and Mo, and they also had higher concentrations of organic acids, such as citric and malic acid, and lower amounts of ascorbic acid than fruits. Although decreases in ascorbic acid have previously been described after the inoculation of strawberry with strains from different PGPR genera, this is the first study to report increases in organic acids after PGPR inoculation.

Rice Sheath Blight: A Review of Disease and Pathogen Management Approaches

Rice is an important food grain and is a staple food for majority of the world’s population. To meet increasing global demand and consumption, rice productivity must be enhanced. However, biotic stresses such as diseases have impeded rice cultivation both in the tropics and subtropics. Of them, sheath blight is a major soil borne disease causing economic losses to rice cultivation. This article summarizes sheath blight (ShB) of rice, disease etiology and economics. Elaborative and updated accounts of various management options and their efficacy for ShB control are given. Specifically, the effects of popular cultural practices influencing ShB incidence, various chemical fungicides, and biological control individually and their combined effect on ShB are presented. The role of Plant Growth-Promoting Rhizobacteria (PGPR) and various genera of PGPR in ShB suppression are discussed. The present review also showed various aspects relating to ShB suppression by PGPR such as antagonism, competition for space and essential nutrients, and induction of systemic resistance. Integrated management of ShB involving all the compatible combinations is included in this review.

Azospirillum, a free-living nitrogen-fixing bacterium closely associated with grasses: genetic, biochemical and ecological aspects.

Azospirillum represents the best characterized genus of plant growth-promoting rhizobacteria. Other free-living diazotrophs repeatedly detected in association with plant roots, include Acetobacter diazotrophicus, Herbaspirillum seropedicae, Azoarcus spp. and Azotobacter. Four aspects of the Azospirillum-plant root interaction are highlighted: natural habitat, plant root interaction, nitrogen fixation and biosynthesis of plant growth hormones. Each of these aspects is dealt with in a comparative way. Azospirilla are predominantly surface-colonizing bacteria, whereas A. diazotrophicus, H. seropedicae and Azoarcus sp. are endophytic diazotrophs. The attachment of Azospirillum cells to plant roots occurs in two steps. The polar flagellum, of which the flagellin was shown to be a glycoprotein, mediates the adsorption step. An as yet unidentified surface polysaccharide is believed to be essential in the subsequent anchoring phase. In Azoarcus sp. the attachment process is mediated by type IV pili. Nitrogen fixation structural genes (nif) are highly conserved among all nitrogen-fixing bacteria, and in all diazotrophic species of the class of proteobacteria examined, the transcriptional activator NifA is required for expression of other nif genes in response to two major environmental signals (oxygen and fixed N). However, the mechanisms involved in this control can vary in different organisms. In Azospirillum brasilense and H. seropedicae (alpha- and beta-subgroup, respectively), NifA is inactive in conditions of excess nitrogen. Activation of NifA upon removal of fixed N seems to involve, either directly or indirectly, the signal transduction protein P(II). The presence of four conserved cysteine residues in the NifA protein might be an indication that NifA is directly sensitive to oxygen. In Azotobacter vinelandii (gamma-subgroup) nifA is cotranscribed with a second gene nifL. The nifL gene product inactivates NifA in response to high oxygen tension and cellular nitrogen-status. NifL was found to be a redox-sensitive flavoprotein. The relief of NifL inhibition on NifA activity, in response to N-limitation, is suggested to involve a P(II)-like protein. Moreover, nitrogenase activity is regulated according to the intracellular nitrogen and O(2) level. In A. brasilense and Azospirillum lipoferum posttranslational control of nitrogenase, in response to ammonium and anaerobiosis, involves ADP-ribosylation of the nitrogenase iron protein, mediated by the enzymes DraT and DraG. At least three pathways for indole-3-acetic acid (IAA) biosynthesis in A. brasilense exist: two Trp-dependent (the indole-3-pyruvic acid and presumably the indole-3-acetamide pathway) and one Trp-independent pathway. The occurrence of an IAA biosynthetic pathway not using Trp (tryptophan) as precursor is highly unusual in bacteria. Nevertheless, the indole-3-pyruvate decarboxylase encoding ipdC gene is crucial in the overall IAA biosynthesis in Azospirillum. A number of genes essential for Trp production have been isolated in A. brasilense, including trpE(G) which codes for anthranilate synthase, the key enzyme in Trp biosynthesis. The relevance of each of these four aspects for plant growth promotion by Azospirillum is discussed.