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With the aim to select powerful microbial strains to be used for the enhancement of maize yield and resistance to abiotic and biotic stresses, we tested five endophytic bacterial strains previously isolated from maize roots. A range of different laboratory assays in regard to potential plant growth promotion was performed and strains were further evaluated for improving growth of five maize cultivars under axenic and natural soil conditions. Endophytic colonization was an additional component in our selection process as it is of high importance for an inoculant strain to efficiently colonize the plant environment. All strains had the potential to improve maize seedling growth under axenic conditions. Enterobacter sp. strain FD17 showed both the highest growth-promoting activity under axenic conditions as well as colonization capacity. FD17 was therefore selected for further plant tests in a net house, in which two different maize cultivars were grown in large pots until ripening and subjected to outdoor climatic conditions. Results showed that inoculation significantly increased plant biomass, number of leaves plant⁻¹, leaf area, and grain yield up to 39 %, 14 %, 20 %, and 42 %, respectively, as compared to the un-inoculated control. Similarly, inoculation also improved the photochemical efficiency of photosystem II (PSII) of maize plant and reduced the time needed for flowering. We also confirmed that strain FD17 is able to colonize the rhizosphere, roots and stems. Based on rigorous testing, Enterobacter sp. strain FD17 showed the highest potential to promote growth and health of maize grown under natural conditions. This study suggested that in vitro plant growth-promoting traits and potential of maize seedling growth promotion by bacterial endophytes could be used for the selection of potential inoculant strains subjected for further testing as bio-inoculant under field conditions.

Sewage sludge is a reservoir of pharmaceutically active compounds (Antibiotics), antibiotic-resistant genes and antibiotic-resistant bacteria, a potential risk to mankind and the environment. This study unravels the physicochemical aspects of sewage sludge and its valorization using bio-remediation. Assessment of physico-chemical parameters was conclusive of the fact that sludge samples were enriched with inorganic components (Chloride, Phosphate and Sulfate) and organic constituents. Sludge samples were found to be contaminated with heavy metals Cr (12.69 mg.kg-1), As (1.23 mg.kg-1), Se (0.86 mg.kg-1), Hg (1.49 mg.kg-1), and Pb (30.32 mg.kg-1), with non-adherence to prescribed limits (Haryana State Pollution Control Board). Screening for bacterial isolates capable of utilizing Cephalosporin (Cefixime:200mg) as their sole source of carbon and energy was carried out. 5 isolates exhibiting fastidious growth were characterized as Bacillus sp., Escherichia sp., Pseudomonas sp., Streptococcus sp. and Enterobacter sp. Noteworthy is the fact, isolates exhibited a broad range of tolerance as reflected by Minimum Inhibitory Concentration (MIC). This was carried out by the Agar dilution method using cefixime (10-100 mg.L-1). 0.03, 0.05, 0.07, 0.06 and 0.09% w/v were the respective Minimum Inhibitory Concentration (MIC) range. The isolate with maximum tolerance to cefixime was subjected to 16S rDNA sequencing and characterized as Enterobacter SCef1.

Background The biosynthesis of zinc oxide nanoparticles (ZnO NPs) using Enterobacter sp. and the evaluation of their antimicrobial and copper stress (Cu + 2 )-reducing capabilities in Vicia faba (L.) plants. The green-synthesized ZnO NPs were validated using X-ray powder diffraction (XRD); Fourier transformed infrared (FTIR), Ultraviolet-Visible spectroscopy (UV-Vis), Transmission electron microscope (TEM) and scanning electron microscopy (SEM) techniques. ZnO NPs could serve as an improved bactericidal agent for various biological applications. as well as these nanoparticles used in alleviating the hazardous effects of copper stress on the morphological and physiological traits of 21-day-old Vicia faba (L.) plants. Results The results revealed that different concentrations of ZnO NPs (250, 500, or 1000 mg L -1 ) significantly alleviated the toxic effects of copper stress (100 mM CuSO 4 ) and increased the growth parameters, photosynthetic efficiency (Fv/Fm), and pigments (Chlorophyll a and b) contents in Cu-stressed Vicia faba (L.) seedlings. Furthermore, applying high concentration of ZnO NPs (1000 mg L -1 ) was the best dose in maintaining the levels of antioxidant enzymes (CAT, SOD, and POX), total soluble carbohydrates, total soluble proteins, phenolic and flavonoid in all Cu-stressed Vicia faba (L.) seedlings. Additionally, contents of Malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) were significantly suppressed in response to high concentrations of ZnO NPs (1000 mg L -1 ) in all Cu-stressed Vicia faba (L.) seedlings. Also, it demonstrates strong antibacterial action (0.9 mg/ml) against various pathogenic microorganisms. Conclusions The ZnO NPs produced in this study demonstrated the potential to enhance plant detoxification and tolerance mechanisms, enabling plants to better cope with environmental stress. Furthermore, these nanoparticles could serve as an improved bactericidal agent for various biological applications.

Enterobacter sp. 638 is an endophytic plant growth promoting gamma-proteobacterium that was isolated from the stem of poplar (Populus trichocarpaxdeltoides cv. H11-11), a potentially important biofuel feed stock plant. The Enterobacter sp. 638 genome sequence reveals the presence of a 4,518,712 bp chromosome and a 157,749 bp plasmid (pENT638-1). Genome annotation and comparative genomics allowed the identification of an extended set of genes specific to the plant niche adaptation of this bacterium. This includes genes that code for putative proteins involved in survival in the rhizosphere (to cope with oxidative stress or uptake of nutrients released by plant roots), root adhesion (pili, adhesion, hemagglutinin, cellulose biosynthesis), colonization/establishment inside the plant (chemiotaxis, flagella, cellobiose phosphorylase), plant protection against fungal and bacterial infections (siderophore production and synthesis of the antimicrobial compounds 4-hydroxybenzoate and 2-phenylethanol), and improved poplar growth and development through the production of the phytohormones indole acetic acid, acetoin, and 2,3-butanediol. Metabolite analysis confirmed by quantitative RT-PCR showed that, the production of acetoin and 2,3-butanediol is induced by the presence of sucrose in the growth medium. Interestingly, both the genetic determinants required for sucrose metabolism and the synthesis of acetoin and 2,3-butanediol are clustered on a genomic island. These findings point to a close interaction between Enterobacter sp. 638 and its poplar host, where the availability of sucrose, a major plant sugar, affects the synthesis of plant growth promoting phytohormones by the endophytic bacterium. The availability of the genome sequence, combined with metabolome and transcriptome analysis, will provide a better understanding of the synergistic interactions between poplar and its growth promoting endophyte Enterobacter sp. 638. This information can be further exploited to improve establishment and sustainable production of poplar as an energy feedstock on marginal, non-agricultural soils using endophytic bacteria as growth promoting agents.

Background The release of organic acids (OAs) is considered the main mechanism used by phosphate-solubilizing bacteria (PSB) to dissolve inorganic phosphate in soil. Nevertheless, little is known about the effect of individual OAs produced by a particular PSB in a soil–plant system. For these reasons, the present work aimed at investigating the effect of Enterobacter sp. strain 15S and the exogenous application of its OAs on (i) the solubilization of tricalcium phosphate (TCP), (ii) plant growth and (iii) P nutrition of cucumber. To this purpose two independent experiments have been performed. Results In the first experiment, carried out in vitro, the phosphate solubilizing activity of Enterobacter 15S was associated with the release of citric, fumaric, ketoglutaric, malic, and oxalic acids. In the second experiment, cucumber plants were grown in a Leonard jar system consisting of a nutrient solution supplemented with the OAs previously identified in Enterobacter 15S (jar’s base) and a substrate supplemented with the insoluble TCP where cucumber plants were grown (jar’s top). The use of Enterobacter 15S and its secreted OAs proved to be efficient in the in situ TCP solubilization. In particular, the enhancement of the morpho-physiological traits of P-starved cucumber plants was evident when treated with Enterobacter 15S, oxalate, or citrate. The highest accumulation of P in roots and shoots induced by such treatments further corroborated this hypothesis. Conclusion In our study, the results presented suggest that organic acids released by Enterobacter 15S as well as the bacterium itself can enhance the P-acquisition by cucumber plants.

Chitin, a natural organic compound with content slightly lower than cellulose, is also known for chitosan, a substance derived from chitin through deacetylation. In this experiment, preliminary screening was conducted using the plate discoloration circle method, leading to the selection of a high-yield CDA-producing strain from 28 candidates through rescreening. Morphological characteristics and 16S rDNA sequence analysis revealed 99.93% homology with Enterobacter sichuanensis strain N24, thus naming this strain Enterobacter strain ZCDA27. Initial fermentation of the strain yielded CDA activity of 9.29 U/mL. Single-factor optimization was then performed, followed by a PB test to screen for significant factors affecting enzyme production. The response surface method was used to further optimize the fermentation conditions. The optimal fermentation conditions for the carbon source, nitrogen source, metal ion, fermentation temperature, time, liquid volume, and initial pH were explored. Significant factors affecting enzyme production, including MgSO 4 , initial medium pH, and fructose levels, were identified using the PB test. Finally, the fermentation conditions of ZCDA27 were optimized using the Box-Behnken design combined with RSM, which comprised fructose at 1.020%, magnesium sulfate at 0.016%, and peptone at 1%. The fermentation conditions included a temperature of 37, initial pH of 7.1, rotation speed of 140 ×  g , fermentation time of 28 h, inoculation amount of 2%, and liquid volume of 40%. Under these conditions, the enzyme activity of ZCDA27 reached 14.52 U/mL, a 1.6-fold increase from the pre-optimization levels. In summary, this study provides an experimental foundation for further development and application of Enterobacter spp. ZCDA27 CDA.

Plant growth-promoting rhizobacteria (PGPRs) that produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase are capable of reducing limits to plant growth due to water-deficient conditions. Here, seven PGPR strains that can produce ACC deaminase were successfully obtained from the rhizosphere soil of grapevine ( Vitis vinifera L.) in arid regions of China. The strains belonged to three different genera: Pseudomonas , Enterobacter , and Achromobacter , according to their 16S rDNA sequencing analysis. A drought tolerance experiment revealed two PGPR strains (DR3 and DR6) with exceptionally high phosphate solubilization, nitrogen fixation, indoleacetic acid (IAA), and exopolysaccharides secretion potential. Both strains were selected for use in a pot experiment to evaluate their growth-promoting effects on grapevines under drought conditions. Each of these two PGPRs and their mixed inoculation into grapevines were expected to alleviate the comprehensive growth inhibition of grapevines caused by drought stress. The mixed inoculation was hypothesized to elicit the best growth-promoting effects. Inoculation with the PGPRs not only enhanced the root-adhering soil/root tissue ratios and soil aggregate stability, but it also increased the nitrogen and phosphorus levels in the soil and plant leaves. Further, inoculation with PGPRs significantly altered the plant height, biomass of shoot and root organs, relative water contents, and net photosynthetic rate of leaves, enabling grapevines to better cope with drought. Moreover, the contents of IAA, abscisic acid, and malondialdehyde in these grapevines under drought stress were significantly changed by PGPRs. They indirectly affected biochemical and physiological properties of grapevines to alleviate their drought stress. Taken together, these results demonstrate that the DR3 and DR6 PGPRs might be useful for effectively weakening the growth inhibition caused by drought in grapevines. The strains might also be applied as effective bioinoculants to maintain the quality of wine grapes.

The present study evaluated the performance of microalgae Chlorella vulgaris in an Enterobacter sp. MN17-assisted textile industry wastewater treatment system for decolorization, removal of heavy metals (Cu, Cr, Pb, and Cd), and chemical oxygen demand (COD). Different dilutions (5, 10, and 20%) of wastewater were prepared to decrease the pollutant toxicity for culturing microalgae and bacteria. Reduction of color, COD, and metal contents by microalgal treatment of wastewater varied greatly, while removal efficiency (RE) was significantly enhanced when endophytic bacterial strain MN17 inoculum was applied. Most notable, results were found at a 5% dilution level by Enterobacter sp. MN17-inoculated C. vulgaris medium, as chromium (Cr), cadmium (Cd), copper (Cu), and lead (Pb) concentrations were decreased from 1.32 to 0.27 mg L−1 (79% decrease), 0.79–0.14 mg L−1 (93% decrease), 1.33–0.36 mg L−1 (72% decrease), and 1.2–0.25 mg L−1 (79% decrease), respectively. The values of COD and color were also significantly decreased by 74% and 70%, respectively, by a C. vulgaris–Enterobacter sp. MN17 consortium. The present investigation revealed that bacterial inoculation of microalgae significantly enhanced the removal of coloring agents and heavy metals from textile wastewater by stimulating the growth of algal biomass. This study manifested the usefulness of microalgae–bacterial mutualism for the remediation of heavy metals, COD, and color in industrial effluents. Microalgae consortia with growth promoting bacteria could be a breakthrough for better bioremediation and bioprocess economy. Thus, further studies are needed for successful integration of microalgae–plant growth promoting bacterial (PGPB) consortium for wastewater treatments.

This study was designed to test the ability of some plant growth-promoting bacteria to adverse the effects of salinity on soybean growth. The effect of Bacillus MAP3 and Enterobacter Delta PSK, along with Bradyrhizobium japonicum was studied on soybean at two levels of NaCl salinization (50 and 100 mM). The physical growth parameters of bacterized soybean (21 days old), particularly plants co-inoculated with Bradyrhizobium japonicum  +  Enterobacter Delta PSK, were significantly enhanced compared to control plants. The shoot length, leaf area, root length, and chlorophyll a content increased by 49.58%, 78.58%, 20.19%, and 57.35%, respectively, indicating the promoting activity of this bacterial combination. After 19 days following the onset of salinity stress, the retarded growth parameters in controls improved significantly due to bacterial treatments, especially by Bradyrhizobium japonicum  +  Enterobacter DeltaPSK, which increased the values of all growth parameters significantly regardless of the salinity level. Additionally, electrolyte leakage, the amounts of malondialdehyde and hydrogen peroxide decreased considerably due to this combined bacterial treatment . Overall, the combination treatment of Enterobacter Delta PSK and the original symbiont B. japonicum enhanced soybean growth under salt stress, indicating the ability of Enterobacter Delta PSK to mitigate osmotic stress. The effect of this strain on soybean yield should be further evaluated to pave the way for its use as a biofertilizer along with B. japonicum, especially under salt stress.

Aims Polygonum hydropiper L. and Polygonum lapathifolium L. are two of the well-known indigenous Mn-hyperaccumulators. Enterobacter sp. FM-1 is a plant growth-promoting bacterium (PGPB) that we found in our previous study. We intended to develop a novel strategy to improve Mn and Cd co-contaminated soil phytoremediation by using a Mn and Cd-resistant bacterium for soil bioaugmentation. Methods We carried out this study to investigate the effects of different Enterobacter sp. FM-1 inoculation concentrations (0, 5.0 × 10 5 , 1.0 × 10 6 and 1.4 × 10 6  CFU g −1 soil) on the phytoremediation of Mn and Cd by Polygonum hydropiper L. and Polygonum lapathifolium L. in two types of Mn-Cd co-contaminated soil. Results In both soils, inoculation with Enterobacter sp. FM-1 promoted the growth of both plants. Moreover, inoculation with Enterobacter sp. FM-1 (≥1.0 × 10 6  CFU g −1 soil) significantly increased soil Mn and Cd bioavailability and decreased the soil pH. Therefore, inoculation with Enterobacter sp. FM-1 (1.4 × 10 6  CFU g −1 soil) improved Mn and Cd accumulation in both plants. Polygonum hydropiper L. presented excellent Mn accumulation in both soils. Additionally, both plants exhibited strong translocation and excellent phytoextraction and bioaccumulation abilities for Mn and Cd. Conclusions Our findings indicated that Enterobacter sp. FM-1 is a potent bioaugmentation agent that facilitates Mn and Cd phytoextraction in Polygonum hydropiper L. and Polygonum lapathifolium L.