Plant Growth-promoting Rhizobia Research Articles

Characterization of plant growth-promoting bacteria isolated from rhizosphere of lentil (Lens culinaris L.) grown in two different soil orders of eastern India.

Lentil, which is an important grain legume, can be co-inoculated with plant growth-promoting rhizobia and rhizobacteria to boost nitrogen fixation, increase biomass, and a possibility for early nodulation. The goal of the ongoing study was to identify plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of lentil growing soils in eastern India. Sixteen rhizosphere bacteria were isolated from two different soil orders, and their capacity to solubilize phosphate and generate hydrogen cyanide (HCN), siderophore, and indole acetic acid (IAA) was assessed. The three best strains were selected for compatibility study with twenty Rhizobium isolated from lentil root nodules. The isolated rhizobacteria were able to produce ammonia and different mycolytic enzymes. Isolate B3 produced the highest amount of IAA and siderophore; the highest amount of phosphate solubilized by PSB1 strain; and isolates AB1, AB2, B3, PS2, and PSB2 produced considerable amount of HCN gas. Among all the isolates, B3, PSB1, and PS2 performed better based on different plant growth-promoting abilities. These three bacterial isolates showed compatible reaction with most of the Rhizobium strains. Isolates B3, PS2, and PSB1 were identified as Bacillus subtilis (MT729775), Pseudomonas palmensis (MT729782), and Paraburkholderia caribenis (MZ956803), respectively. Lentil shoot weight, root length, nodule number, N uptake, and P uptake were increased in the pot culture experiment when inoculated with these strains. PGPR strain B3 performed best among the three strains in the pot culture experiment. Strain B3 can be used as potential biofertilizer along with compatible Rhizobium species for better production of lentil.

Combined Use of Spent Mushroom Substrate Biochar and PGPR Improves Growth, Yield, and Biochemical Response of Cauliflower (Brassica oleracea var. botrytis): A Preliminary Study on Greenhouse Cultivation

This paper investigated the impact of the combined use of spent mushroom substrate (SMS) biochar and plant-growth-promoting rhizobia (PGPR) on the growth, yield, and biochemical response of cauliflower (Brassica oleracea var. botrytis). A preliminary study was conducted under greenhouse condition using six treatments (sextuplicate) as control (no addition), T1 (PGPR), T2 (5 g/Kg biochar), T3 (5 g/Kg biochar + PGPR), T4 (10 g/Kg biochar), and T5 (10 g/Kg biochar + PGPR) under greenhouse conditions. The Scanning Electron Microscopy (SEM-Zeiss), Energy Dispersive Spectroscopy (EDS), and Fourier’s transform infrared spectroscopy (FTIR) analyses showed that biochar produced from slow pyrolysis of SMS had advantageous structural, functional, and morphological properties for agricultural use. Results showed that SMS biochar addition aids the acceleration of soil nutrient properties. SMS biochar and PGPR application also significantly (p < 0.05) improved the selected growth, yield, and biochemical parameters of cauliflower. In particular, the highest cauliflower yield (550.11 ± 10.05 g), fresh plant biomass (1.66 ± 0.04 Kg), dry plant biomass (149.40 ± 4.18 g), plant height (22.09 ± 0.14 cm), root length (11.20 ± 0.05 cm), plant spread (28.35 ± 0.18 cm), and the number of leaves (12.50 ± 0.50) were observed in T5 treatment. Similarly, the best values for biochemical parameters and enzyme activities such as total chlorophyll (TC: 3.13 ± 0.07 mg/g), superoxide dismutase (SOD: 79.12 ± 1.29 µg/g), catalase (CAT: 55.70 ± 2.52 µg/g), peroxidase (POD 30.18 ± 0.37 µg/g), total phenolics (TP: 19.50 ± 0.31 mg/g), ascorbic acid (AA: 14.18 ± 0.55 mg/g), and total carotenoids (TCT: 150.17 ± 8.20 µg/100 g) were also recorded in the T5 treatment. The application of SMS biochar and PGPR showed a positive correlation with growth, yield, and biochemical response of cauliflower, as indicated by the Pearson correlation analysis. The findings of this study suggest efficient recycling of mushroom industry waste for biochar production and the use of PGPR to improve nutrient utilization in sustainable agriculture.

Screening of plant growth-promoting Rhizobium tarimense from root nodules of chickpea (Cicer arietinum)

Plant growth-promoting rhizobacteria (PGPR) are favourable bacteria that colonize the plant roots and enhance plant growth by direct and/or indirect mechanisms. This study aimed to screen rhizobial isolates of chickpea and evaluate their multiple plant growth-promoting traits. A total of twelve rhizobia-like-bacterial isolates were collected from the root nodules of chickpea (Cicer arietinum L.) from different regions of Madhya Pradesh, India, characterized by morphological, biochemical, and identified by the 16S rRNA gene sequencing. Out of twelve, one rhizobial isolate designated as RH17 was confirmed as Rhizobium tarimense by 16S rRNA gene sequencing, which showed 98% similarity with the strain PL-41. The phylogenetic study was done by using MEGA-X to confirm the identity of RH17 isolate and the nucleotide sequence of the 16S rRNA gene of RH17 isolate was submitted to the National Center for Biotechnology Information (NCBI) database under Genbank with accession number OM996100. The RH17 isolate showed multiple plant growth-promoting traits like nitrogen fixation, solubilization of phosphate (15mm), indole acetic acid (IAA) production (1µg/ml), 1-aminocyclopropane-1-carboxylate (ACC) deaminase (0.5nmol), ammonia (NH3), siderophore, hydrogen cyanide (HCN) production and antagonism against phytopathogenic fungi Fusarium oxysporum and Macrophomina phaseolina. Therefore, the present study suggests that R. tarimense (RH17) isolate can be used as PGP bacteria and a biocontrol agent to enhance the growth, productivity and yield of chickpea.

Endofungal Rhizobium species enhance arsenic tolerance in colonized host plant under arsenic stress.

Arsenic (As) is a toxic metalloid that is present in natural surroundings in many forms with severe consequences to sustainable agriculture and human health. Plant growth-promoting Rhizobia have been found involved in the induction of plant tolerance under various biotic and abiotic stresses. An endofungal Rhizobium species associated with arbuscular mycorrhizal fungi (AMF) Serendipita indica deploy beneficial role in the promotion of plant growth and tolerance against various biotic and abiotic stresses. In the current study, we have determined the role of endofungal Rhizobium species in protection of host plant growth under As stress. We observed that endofungal Rhizobium species strain Si001 tolerate AsV up to 25mM and its inoculation enhances tomato seed germination and seedling growth. A hyper-colonization of Rhizobium species Si001 in tomato roots was observed under As stress and results in modulation of GSH and proline content with reduced ROS. Rhizobium species Si001 colonization in host plant recovered pigment contents (chlorophyll-a and chlorophyll-b up to 189.5% and 192%, respectively), photosynthesis (157%), and water use efficiency (166%) compared to As-treated plants. Interestingly, bacterial colonization results in 40% increased As accumulation in the root, while a reduction in As translocation from root to shoot up to 89% was observed as compared to As treated plants. In conclusion, endofungal Rhizobium species Si001 association with the host plant may improve plant health and tolerance against As stress with reduced As accumulation in the crop produce.

Plant Growth-Promoting Rhizobium Nepotum Phenol Utilization: Characterization and Kinetics

Phenol is a severe pollutant that harms the environment and, potentially, human health. This study aimed to investigate the biodegradability of phenol by the plant growth-promoting bacterium R. nepotum. That included studying the growth kinetics and the effects of growth conditions such as incubation temperature, pH, and the use of different substrate concentrations. As the primary substrate, six different starting concentrations of phenol were utilized. The ability of these cells to biodegrade phenol was greatly influenced by the culture conditions. After 36 and 96 hours of incubation at pH 7 and a temperature of 28 C, this organism grew the fastest and had the highest phenol biodegradation. The biodegradation rate is much higher at 700 mg/L, the highest of the six concentrations tried. In less than 96 hours of incubation, more than 90% of the phenol (700 mg/L) had been eliminated. The Haldane model has been the most accurate for determining the relationship between the initial concentration of phenol and growth rate. In contrast, the refined Gompertz model provided the most accurate depiction of phenol biodegradation over time. As predicted by the Haldane equation, the highest specific growth rate, half-saturation coefficient, and Haldane's growth kinetics inhibition coefficient are 0.7161 h1, 15.8 parts per million (ppm), and 292 parts per million (ppm), respectively. The equation of Haldane successfully fitted the experimental data by reducing the SSR (sum of squared errors) to 3.8x10 3. According to the results of the analysis by GC-MS for the bacterial culture sample, the hydroxylase enzyme was the first to convert the phenol molecule into catechol. The catechol was subsequently broken down into 2-hydroxymucconic semialdehyde by the 2,3-dioxygenase enzyme, which occurred through the meta-pathway. It is the first study showing that R. nepotum, a plant growth promoter, has high efficiency of phenol. In phenol-stressed conditions, this could help with rhizoremediation and crop yield preservation.

Combined Use of Sewage Sludge and Plant Growth-Promoting Rhizobia Improves Germination, Biochemical Response and Yield of Ridge Gourd (Luffa acutangula (L.) Roxb.) under Field Conditions

This research investigated the combined use of sewage sludge (SS) and plant growth-promoting rhizobia (PGPR) for Ridge gourd (Luffa acutangula (L.) Roxb.) cultivated under field conditions. The different treatments of SS and PGPR such as 0% (soil as control), 5% SS, 5% SS + PGPR, 10% SS, and 10% SS + PGPR were applied to assess their impacts on seedling growth, biochemical response, and yield performance of Ridge gourd. The results showed that the highest seedling emergence (92.3 ± 2.1%), fresh biomass (9.6 ± 0.3 g), growth rate (1.4 ± 0.1 g/day), seedling length (15.5 ± 0.3 cm), root length (10.4 ± 0.3 cm), total chlorophyll (3.2 ± 0.1 mg/g), crop yield (13.8 ± 0.1 kg/plant), and average crop yield per harvest (2.8 ± 0.1 kg/plant) were observed in 10% SS + PGPR treatment. The enzyme activities of superoxide dismutase (SOD; µg/g) and catalase (CAT: µg/g) were significantly lowered after PGPR inoculation in higher SS treatments. The results of principal component (PC) and Euclidian clustered distance analyses showed a positive influence of SS dose on soil nutrient availability and Ridge gourd’s growth, biochemical responses, and yield performance. Moreover, the elemental analysis showed that the bioaccumulation factor (BAF < 0.90) and health risk index (HRI < 0.40) of selected metal elements (Cd, Cr, Cu, Fe, Mn, and Zn) were within the permissible limits, indicating consumption of Ridge gourd fruits was safe. The outcomes of this study suggest the potential use of SS and PGPR for improved Ridge gourd production and contribution towards sustainable development goal (SDG) 12 on responsible consumption and production of vegetable crops.

Potential of Coupling Heavy Metal (HM) Phytoremediation by Bioenergy Plants and Their Associated HM-Adapted Rhizosphere Microbiota (Arbuscular Mycorrhizal Fungi and Plant Growth Promoting Microbes) for Bioenergy Production

There is growing concern for the contamination of our soils and waters worldwide with heavy metals (HMs), as a result of indiscriminate use of agrochemicals for feeding growing population which require optimal use of resources and sustainable agricultural strategies. This can be simultaneously achieved by using microbes as bio-fertilizers, bio-protectants, and bio-stimulants, and suitable phytoremediation- plant capable of removing heavy metals contaminants from contaminated sites. There is a growing need to adopt such environmentally safe, attractive, and economical techniques that can remove most HMs contaminants as well as yield high biomass for bioenergy production. Phytoremediation and the microbes associated with the roots and inhabiting rhizospheres of the plants used for this purpose, has emerged as an alternative strategy. This article reviews the principles and application of this strategy, and provides an overview of the use of fast growing, non-food bioenergy plants, like Vetiver grass and industrial hemp, and their root-associated microbiota such as Arbuscular Mycorrhizal Fungi (AMF), Mycorrhiza Helping Bacteria (MHB), and Plant–Growth–Promoting-Rhizobia (PGPR) that can both tolerate and immobilize HMs in the roots, i.e. sequestrate contaminant HMs thereby protecting plants from metal toxicity. This mini-review also focuses on other phytoextraction strategies involving rhizosphere microbes, such as (1) inoculating plants used for phytoremediation of HMs contaminated soil and water with rhizobial microflora, and (2) managing their population in the rhizospheres by using a consortium of site specific AMF, PGPR, and MHB, and N-fixing rhizobia as biofertilizers to Phyto-remediate derelict contaminated sites. Various crop management strategies such as Crop Sequencing and Intercropping or Co-cropping of, for example, mycorrhizal and non-mycorrhizal crops, or leguminous and non-leguminous crops, etc., can be employed for improved plant growth. Another possible strategy to exploit soil microbes is to employ pre-cropping with mycotrophic crops to exploit AMF for mycorrhizo-remediation strategy.

In-Vitro Plant Growth Promotion of Rhizobium Strains Isolated from Lentil Root Nodules under Abiotic Stresses

Plant growth-promoting rhizobia are known to improve crop performance by multiple mechanisms. However, the interaction between host plants and Rhizobium strains is highly influenced by growing conditions, e.g., heat, cold, drought, soil salinity, nutrient scarcity, etc. The present study was undertaken to assess the use of Rhizobium as plant growth promoters under abiotic stress conditions. Fifteen Rhizobium strains isolated from lentil root nodules were tested for phosphate solubilization activity (PSA) and phytohormones production under salt and drought conditions. The results showed that 15 Rhizobium strains were significant phosphate solubilizers, and indole acedic acid (IAA) and gibberellic acid (GA3) producers based on least significant difference (LSD) analysis (p ≤ 0.05). The highest rate of PSA was attributed to three strains namely, 1145N5, 1159N11, and 1159N32 with a range of 144.6 to 205.6 P2O5 (µg/mL). The highest IAA production was recorded in the strain 686N5 with 57.68 ± 4.25 µg/mL as compared to 50.8667 ± 1.41 µg/mL and 37.32 ± 12.59 µg/mL for Rhizobium tropici CIAT 899 and Azospirillum brasilense DSM-1690, respectively. Strain 318N2111 produced 329.24 ± 7.84 µg/mL of GA3 as against 259.84 ± 25.55 µg/mL for A. brasilense DSM-1690. R. tropici CIAT 899 showed tolerance to salt (5% NaCl) and drought (ψ = −2.6 MPa) stress, whereas strain 686N5 showed an extremely high level of salt-tolerance (5% NaCl) and moderate level of drought tolerance (ψ = −0.75 MPa). These results indicate different pathways for drought and salt tolerance mechanisms. The assessment of plant growth promoting (PGP) activities of Rhizobium showed differences between bacterial viability and bacterial PGP activity in terms of abiotic stress tolerance where bacterial PGP activity is interrupted before reaching the bacterial tolerance threshold. These results integrate a new concept of PGPR screening based on PGP activity under abiotic stress.

Bioremediation model of oil-contaminated soil in Lapindo mud using multisymbiotic organism

PurposeThe study aimed at developing the bioremediation model of Lapindo mud through multisymbiotic organism.Design/methodology/approachThe research was conducted using completely randomized design. The model plants chosen in this research were soybean. The interaction pattern during the treatment was used to develop the bioremediation model based on the parameters.FindingsThe results showed that there was an effect of the type of organism on the parameters, namely: the growth of plant (biomass, height, length of root, and number of leaves), the biomass of root nodules, the percentage of mycorrhizal infection, the content of water, nitrogen, phosphorus, and total petroleum hydrocarbons (TPHs). There was a pattern of multisymbiotic interaction between each organism and roles of each symbiont in that interaction. Therefore, the plants were capable of surviving in the environment of Sidoarjo Lapindo mud. This pattern can be named as the bioremediation model proposed, which is the analogy of tripartite symbiosis between plants, mycorrhizae, and Rhizobium but also adding plant growth bacteria such as phosphate-solubilizing bacteria and hydrocarbon degradation bacteria. The implementation of this model can be used to treat oil-contaminated soil in order to be used as a plant growth medium.Originality/valuePhytoremediation is a new and promising approach to remove contaminants in the environment but using plants alone for remediation confronts many limitations. Therefore, the application of plant-growth-promoting rhizobia (PGPR) has been extended to remediate contaminated soils in association with plants (Zhuang et al., 2007). The development of the model will use the analogy of tripartite symbiosis between plants, mycorrhizae, and Rhizobium. The developed model will be based on the interaction pattern on each parameters obtained. Bioremediation is chosen because it is considered an effective technique to transform toxic components into less toxic products without disrupting the surrounding environment. Besides, bioremediation is cheaper and environment-friendly because it utilizes microorganisms to clean pollutants from the environment (Nugroho, 2006).

Effect of rice husk biochar, carpet waste, farm yard manure and plant growth promoting rhizobium on the growth and yield of rice (Oryza sativa)

The present investigation was aimed for improving growth and yield of crop using waste products of differ-ent activities and also useful in ecological stability of soil environment. This objective is not only an economic option for poor farmer but also an effective strategy for increasing yield. The experiment was conducted in the organic farm-ing plot of the Institute of Agricultural Sciences, BHU, Varanasi during kharif season of rice crop in 2014. The field experiment was laid out in randomized block design (RBD) with 10 treatments and three replications. Application of graded level of biochar, carpet waste farm yard manure (FYM) and plant growth promoting rhizobium (PGPR) was found to significantly enhance the grain and straw yield of rice by 57.70% and 56.08% over control, respectively.

Effect of Cd-tolerant plant growth-promoting rhizobium on plant growth and Cd uptake by Lolium multiflorum Lam. and Glycine max (L.) Merr. in Cd-contaminated soil

Plant growth-promoting rhizobacteria (PGPR) have been widely studied for agricultural applications. One aim of this study was to isolate cadmium (Cd)-tolerant bacteria from nodules of Glycine max (L.) Merr. grown in heavy metal-contaminated soil in southwest of China. The plant growth-promoting (PGP) traits and the effects of the isolate on plant growth and Cd uptake by legume and non-legume plants in Cd-polluted soil were investigated. Cd-tolerant bacteria were isolated by selective media. The isolates were identified by 16S rRNA gene and phylogenetic analysis. The PGR traits of the isolates were evaluated in vitro. Cd in soil and plant samples was determined by ICP-MS. One of the most Cd-tolerant bacteria simultaneously exhibited several PGP traits. Inoculation with the PGPR strain had positive impacts on contents of photosynthesis pigments and mineral nutrients (Fe or Mg) in plant leaves. The shoot dry weights of Lolium multiflorum Lam. increased significantly compared to uninoculated control. Furthermore, inoculation with the PGPR strain increased the Cd concentrations in root of L. multiflorum Lam. and extractable Cd concentrations in the rhizosphere, while the Cd concentrations in root and shoot of G. max (L.) Merr. significantly decreased. This study indicates that inoculation with Cd-tolerant PGPR can alleviate Cd toxicity to the plants, increase Cd accumulation in L. multiflorum Lam. by enhancing Cd availability in soils and plant biomass, but decrease Cd accumulation in G. max (L.) Merr. by increasing Fe availability, thus highlighting new insight into the exploration of PGPR on Cd-contaminated soil.

Draft Genome Sequence of Plant Growth-Promoting Rhizobium Mesorhizobium amorphae, Isolated from Zinc-Lead Mine Tailings

Here, we describe the draft genome sequence of Mesorhizobium amorphae strain CCNWGS0123, isolated from nodules of Robinia pseudoacacia growing on zinc-lead mine tailings. A large number of metal(loid) resistance genes, as well as genes reported to promote plant growth, were identified, presenting a great future potential for aiding phytoremediation in metal(loid)-contaminated soil.

Salt tolerance in Zea mays (L). following inoculation with Rhizobium and Pseudomonas

This study aimed to investigate the effect of inoculation with plant growth-promoting Rhizobium and Pseudomonas species on NaCl-affected maize. Two cultivars of maize (cv. Agaiti 2002 and cv. Av 4001) selected on the basis of their yield potential were grown in pots outdoors under natural conditions during July. Microorganisms were applied at seedling stage and salt stress was induced 21 days after sowing and maintained up to 50% flowering after 120 days of stress. The salt treatment caused a detrimental effect on growth and development of plants. Co-inoculation resulted in some positive adaptative responses of maize plants under salinity. The salt tolerance from inoculation was generally mediated by decreases in electrolyte leakage and in osmotic potential, an increase in osmoregulant (proline) production, maintenance of relative water content of leaves, and selective uptake of K ions. Generally, the microbial strain acted synergistically. However, under unstressed conditions, Rhizobium was more effective than Pseudomonas but under salt stress the favorable effect was observed even if some exceptions were also observed. The maize cv. Agaiti 2002 appeared to be more responsive to inoculation and was relatively less tolerant to salt compared to that of cv. Av 4001.

Effect of metal-tolerant plant growth-promoting Rhizobium on the performance of pea grown in metal-amended soil.

The nickel- and zinc-tolerant plant growth-promoting (PGP) Rhizobium sp. RP5 was isolated from nodules of pea, grown in metal-contaminated Indian soils. The PGP potentials of strain RP5 was assessed under in vitro conditions. Strain RP5 displayed a high level of tolerance to nickel (350 microg ml(-1)) and zinc (1500 microg ml(-1)) and showed PGP activity under in vitro conditions. The PGP activity of this strain was further assessed with increasing concentrations of nickel and zinc, using pea as a test crop. The bio-inoculant enhanced the dry matter, nodule numbers, root N, shoot N, leghemoglobin, seed yield, and grain protein (GP) by 19%, 23%, 26%, 47%, 112%, 26%, and 8%, respectively, at 290 mg Ni kg(-1) while at 4890 mg Zn kg(-1) soil, it increased the dry matter, nodule numbers, leghemoglobin, seed yield, GP, and root and shoot N by 18%, 23%, 78%, 26%, 7%, 25%, and 42%, respectively, compared to plants grown in soil amended with metal only. The bio-inoculant increased the glutathione reductase activity of roots and nodules by 46% and 65% at 580 mg Ni kg(-1) and 47% and 54% at 9780 mg Zn kg(-1) soil, respectively, compared to uninoculated plants. The inoculated strain decreased the concentration of nickel and zinc in plant organs. The intrinsic abilities of nitrogen fixation, growth promotion, and the ability to reduce the toxicity of nickel and zinc of the tested strain could be of practical importance in augmenting the growth and yield of pea, in nickel- and zinc-polluted soils.