Mitigating sediment cadmium contamination through combining PGPR Enterobacter ludwigii with the submerged macrophyte Vallisneria natans.

Sediment cadmium contamination poses risks to aquatic ecosystems. Phytoremediation is an environmentally sustainable method to mitigate cadmium contamination. Submerged macrophytes are affected by cadmium stress, but plant growth-promoting rhizobacteria (PGPR) can restore the health status of submerged macrophytes. Herein, we aimed to reduce sediment cadmium concentration and reveal the mechanism by which the combined application of the PGPR Enterobacter ludwigii and the submerged macrophyte Vallisneria natans mitigates cadmium contamination. Sediment cadmium concentration decreased by 21.59% after submerged macrophytes were planted with PGPR, probably because the PGPR colonized the rhizosphere and roots of the macrophytes. The PGPR induced a 5.09-fold increase in submerged macrophyte biomass and enhanced plant antioxidant response to cadmium stress, as demonstrated by decreases in oxidative product levels (reactive oxygen species and malondialdehyde), which corresponded to shift in rhizosphere metabolism, notably in antioxidant defence systems (i.e., the peroxidation of linoleic acid into 9-hydroperoxy-10E,12Z-octadecadienoic acid) and in some amino acid metabolism pathways (i.e., arginine and proline). Additionally, PGPR mineralized carbon in the sediment to promote submerged macrophyte growth. Overall, PGPR mitigated sediment cadmium accumulation via a synergistic plantmicrobe mechanism. This work revealed the mechanism by which PGPR and submerged macrophytes control cadmium concentration in contaminated sediment.

Solid-state fermentation of brown seaweeds for the production of alginate lyase using marine bacterium Enterobacter tabaci RAU2C.

Alginate lyases have countless potential for application in industries and medicine particularly as an appealing biocatalyst for the production of biofuels and bioactive oligosaccharides. Solid-state fermentation (SSF) allows improved production of enzymes and consumes less energy compared to submerged fermentation. Seaweeds can serve as the most promising biomass for the production of biochemicals. Alginate present in the seaweed can be used by alginate lyase-producing bacteria to support growth and can secrete alginate lyase. In this perspective, the current study was directed on the bioprocessing of brown seaweeds for the production of alginate lyase using marine bacterial isolate. A novel alginate-degrading marine bacterium Enterobacter tabaci RAU2C which was previously isolated in the laboratory was used for the production of alginate lyase using Sargassum swartzii as a low-cost solid substrate. Process parameters such as inoculum incubation period and moisture content were optimized for alginate lyase production. SSF resulted in 33.56 U/mL of alginate lyase under the static condition maintained with 75% moisture after 4 days. Further, the effect of different buffers, pH, and temperature on alginate lyase activity was also analyzed. An increase in alginate lyase activity was observed with an increase in moisture content from 60 to 75%. Maximum enzyme activity was perceived with phosphate buffer at pH 7 and 37 °C. Further, the residual biomass after SSF could be employed as biofertilizer for plant growth promotion based on the preliminary analysis. To our knowledge, this is the first report stating the usage of seaweed biomass as a substrate for the production of alginate lyase using solid-state fermentation.

Community Structure of Nitrifying and Denitrifying Bacteria from Effluents Discharged into Lake Victoria, Kenya.

An active microbial community of nitrifying and denitrifying bacteria is needed for efficient utilization of nitrogenous compounds from wastewater. In this study, we explored the bacterial community diversity and structure within rivers, treated and untreated wastewater treatment plants (WWTPs) discharging into Lake Victoria. Water samples were collected from rivers and WWTPs that drain into Lake Victoria. Physicochemical analysis was done to determine the level of nutrients or pollutant loading in the samples. Total community DNA was extracted, followed by Illumina high throughput sequencing to determine the total microbial community and abundance. Enrichment and isolation were then done to recover potential nitrifiers and denitrifiers. Physicochemical analysis pointed to high levels total nitrogen and ammonia in both treated and untreated WWTPs as compared to the samples from the lake and rivers. A total of 1,763 operational taxonomic units (OTUs) spread across 26 bacterial phyla were observed with the most dominant phylum being Proteobacteria. We observed a decreasing trend in diversity from the lake, rivers to WWTPs. The genus Planktothrix constituted 19% of the sequence reads in sample J2 collected from the lagoon. All the isolates recovered in this study were affiliated to three genera: Pseudomonas, Klebsiella and Enterobacter in the phylum Proteobacteria. A combination of metagenomic analysis and a culture-dependent approach helped us understand the relative abundance as well as potential nitrifiers and denitrifiers present in different samples. The recovered isolates could be used for in situ removal of nitrogenous compounds from contaminated wastewater.

Isolating, identifying and evaluating of oil degradation strains for the air-assisted microbial enhanced oil recovery process.

Due to the inefficient reproduction of microorganisms in oxygen-deprived environments of the reservoir, the applications of microbial enhanced oil recovery (MEOR) are restricted. To overcome this problem, a new type of air-assisted MEOR process was investigated. Three compounding oil degradation strains were screened using biochemical experiments. Their performances in bacterial suspensions with different amounts of dissolved oxygen were evaluated. Water flooding, microbial flooding and air-assisted microbial flooding core flow experiments were carried out. Carbon distribution curve of biodegraded oil with different oxygen concentration was determined by chromatographic analysis. The long-chain alkanes are degraded by microorganisms. A simulation model was established to take into account the change in oxygen concentration in the reservoir. The results showed that the optimal dissolved oxygen concentration for microbial growth was 4.5~5.5mg/L. The main oxygen consumption in the reservoir happened in the stationary and declining phases of the microbial growth systems. In order to reduce the oxygen concentration to a safe level, the minimum radius of oxygen consumption was found to be about 145m. These results demonstrate that the air-assisted MEOR process can overcome the shortcomings of traditional microbial flooding techniques. The findings of this study can help for better understanding of microbial enhanced oil recovery and improving the efficiency of microbial oil displacement.

Applying Pb2+ to probe the dissolution of carbonated hydroxylapatite by Enterobacter sp.: A new insight into the bioerosion of tooth mineral.

Dental caries is one of the most common disorders in dentistry. Typically, it is caused by the dissolution of the tooth mineral due to cariogenic organisms. Bioapatite is vulnerable to acid-etching ascribed to a variety of substitutions. This study applied Pb2+ cations to probe the dissolution of synthetic carbonated hydroxylapatite (CHAp) in the acidic environment induced by Enterobacter sp. It indicated a decreasing tendency of crystallite size (from ∼400 nm to 10-20 nm) during gradual incorporation of carbonate (from 2.5 to 13.8 wt %). Meanwhile, the shape of CHAp crystals was transformed from elongated to plate-like. Addition of Enterobacter sp. enhanced P release from CHAp (especially for the CHAp with ∼8 wt % CO3 ) around 10 times. Moreover, the bacterium provided a moderately acidic environment to cause more formation of stable pyromorphite over other Pb-minerals, for example, Pb3 (PO4 )2 , and PbCO3 . Then, transmission electron microscopy-energy dispersive X-Ray spectroscopy mapping successfully confirmed the Pb labeling on the newly formed phosphate mineral as Pb (with high-atomic weight) has strong signal under electron microscopy. This study therefore elucidated that Pb labeling has a bright future to explore the degradation of tooth mineral by microorganisms, as well as to evaluate the resistance of calcium phosphate dental restorative materials.

Efficacy of soil-borne Enterobacter sp. for carbofuran degradation: HPLC quantitation of degradation rate.

Excessive use of pesticides in agricultural fields is a matter of great concern for living beings as well as the environment across the world, in particular, the third world countries. Therefore, there is an urgent need to find out an effective way to degrade these hazardous chemicals from the soil in an environment-friendly way. In the current project, a bacterial species were isolated through enrichment culture from carbofuran-supplemented rice-field soil and identified as a carbofuran degrader. The rate of carbofuran degradation by this bacterial species was evaluated using reverse-phase high-performance liquid chromatography (RP-HPLC), which confirmed the ability to utilize as a carbon source up to 4 µg/ml of 99% technical grade carbofuran. The morphological, physiological, biochemical characteristics and phylogenetic analysis of the 16S rRNA sequence showed that this strain belongs to the genus of Enterobacter sp. (sequence accession number LC368285 in DDBJ), and the optimum growth condition for the isolated strain was 37°C at pH 7.0. Moreover, an antibiotic sensitivity test showed that it was susceptible to azithromycin, penicillin, ceftazidime, ciprofloxacin, and gentamycin, and the minimal inhibitory concentration value of gentamycin was 400 µg/ml against the bacteria. It shows beyond doubt from the RP-HPLC quantification that the isolated bacterium has the ability to detoxify carbofuran (99% pure). Finally, the obtained results imply that the isolated strain of Enterobacter can be used as a potential and effective carbofuran degrader for bioremediation of contaminated sites through bioaugmentation.

Root colonization by heavy metal resistant Enterobacter and its influence on metal induced oxidative stress on Cajanus cajan.

BACKGROUND: Heavy metal resistant bacterium Enterobacter sp. C1D was evaluated for cadmium (Cd) mediated exopolysaccharide production, biofilm formation and legume root colonization ability under Cd stress to alleviate metal induced stress. RESULTS: The plant was sensitive to Cd (IC50 3-4 µg mL-1 ), whereas the bacterium showed high Cd tolerance (MIC99 120 µg mL-1 ). Confocal laser scanning microscopy of the Cajanus cajan roots showed heavy loads of green fluorescence protein labelled Enterobacter sp. C1D on the surface of plant root, specifically at the point of root hair/lateral root formation along with cortex, even under metal stress. The root colonizing ability of Enterobacter sp. C1D was not affected by the presence of Rhizobium and the bacteria could be observed after 30 days of incubation in soil. Various plant growth parameters, antioxidant metabolites and oxidative stress indicator were significantly influenced by bacterial treatment, which, overall, reduced the adverse effect of Cd. CONCLUSION: Heavy metal tolerant bacteria may be a good choice for the development of biofertilizers and may work well with the native soil microbes such as Rhizobium under the metal polluted soil. © 2019 Society of Chemical Industry.

Evaluation of seven chemical pesticides by mixed microbial culture (PCS-1): Degradation ability, microbial community, and Medicago sativa phytotoxicity.

Environmental problems caused by the large-scale use of chemical pesticides are becoming more and more serious, and the removal of chemical pesticides from the ecological environment by microbial degradation has attracted wide attention. In this study, using enrichment screening with seven chemical pesticides as the sole carbon source, a mixed microbial culture (PCS-1) was obtained from the continuous cropping of strawberry fields. The microbial community composition, degradation ability, and detoxification effect of PCS-1 was determined for the seven pesticides. Inoculation with PCS-1 showed significant degradation of and tolerance to the seven pesticides. Microbial community composition analysis indicated that Pseudomonas, Enterobacter, Aspergillus, and Rhodotorula were the dominant genera for the degradation of the seven pesticides by PCS-1. The concentration of the seven pesticides was 10 mg L-1 in hydroponic and soil culture experiments. The fresh weight, plant height, and root length of PCS-1-inoculated alfalfa (Medicago sativa) significantly increased compared with those of non-PCS-1-inoculated M. sativa. PCS-1 not only effectively degraded the residual content of the seven pesticides in water and soil but also reduced the pesticide residues in the roots, stems, and leaves of M. sativa. This study shows that PCS-1 may be important in environmental remediation involving the seven pesticides.

Biochemical and nutritional characterization of the medfly gut symbiont Enterobacter sp. AA26 for its use as probiotics in sterile insect technique applications.

BACKGROUND: Enterobacter sp. AA26 was recently isolated from the midgut of Ceratitis capitata (Wiedemann) and it was shown to have positive effects in rearing efficiency when used as larval probiotics. In this study, biomass production was carried out in bench-scale bioreactors to elucidate the biokinetic properties of Enterobacter sp. AA26 and its nutritional value. RESULTS: Strain AA26 is a psychrotolerant, halotolerant, facultatively anaerobic bacterium with broad pH range for growth (pH 4 to 10.2), which possessed the typical biochemical profile of Enterobacter spp. The specific oxygen uptake rate (SOUR) was calculated as 63.2 ± 1.26 and 121 ± 1.73 mg O2 g- 1 VSS h- 1, with the yield coefficients in acetate and glucose being equal to 0.62 ± 0.03 and 0.67 ± 0.003 g biomass produced/g substrate consumed, respectively. The maximum specific growth rate (µmax) of strain AA26 grown in fill-and-draw bioreactors at 20 °C and 35 °C was 0.035 and 0.069 h- 1, respectively. Strain AA26 grew effectively in agro-industrial wastewaters, i.e. cheese whey wastewater (CWW), as alternative substrate for replacing yeast-based media. Biomass of strain AA26 could provide all the essential amino acids and vitamins for the artificial rearing of C. capitata. Greater intracellular α- and ß-glucosidase activities were observed during growth of strain AA26 in CWW than in yeast-based substrate, although the opposite pattern was observed for the respective extracellular activities (p < 0.01). Low protease activity was exhibited in cells grown in yeast-based medium, while no lipase activities were detected. CONCLUSIONS: The ability of strain AA26 to grow in agro-industrial wastes and to provide all the essential nutrients can minimize the cost of commercial media used for mass rearing and large scale sterile insect technique applications.

A New Strategy for Effective Succinic Acid Production by Enterobacter sp. LU1 Using a Medium Based on Crude Glycerol and Whey Permeate.

The newly-isolated strain Enterobacter sp. LU1, which has previously been shown to be an effective producer of succinic acid on glycerol with the addition of lactose, was used for further intensive works aimed at improving the production parameters of the said process. The introduction of an initial stage of gentle culture aeration allowed almost 47 g/L of succinic acid to be obtained after 168 h of incubation, which is almost two times faster than the time previously taken to obtain this amount. Furthermore, the replacement of glycerol with crude glycerin and the replacement of lactose with whey permeate allowed the final concentration of succinic acid to be increased to 54 g/L. Considering the high content of yeast extract (YE) in the culture medium, tests were also performed with a reduced YE content via its partial substitution with urea. Although this substitution led to a deterioration of the kinetic parameters of the production process, using the fed-batch strategy, it allowed a succinic acid concentration of 69 g/L to be obtained in the culture medium, the highest concentration ever achieved using this process. Furthermore, the use of microaerophilic conditions meant that the addition of lactose to the medium was not required, with 37 g/L of succinic acid being produced on crude glycerol alone.

Characteristics of White-rot Fungus Phlebia brevispora TMIC33929 and Its Growth-Promoting Bacterium Enterobacter sp. TN3W-14 in the Decolorization of Dye-Contaminated Water.

The dye decolorization potential of the white-rot fungus Phlebia brevispora TMIC33929 when grown alone or in coculture with its growth-promoting bacterium Enterobacter sp. TN3W-14 was evaluated in low nitrogen liquid medium at different pHs. Axenic fungus removed a similar amount of Congo red and crystal violet at pH 4.5 and 7.0, respectively. The bacterium alone achieved only slightly better decolorization of crystal violet than the fungus at pH 9.0. Compared with axenic fungus, cocultures provided no increased crystal violet removal but achieved higher removal of crystal violet in mixed dye at all pHs, and the best-mixed dye decolorization at pH 9.0. Unlike bacterial growth on dyes, growth of fungal mycelia was not inhibited by the dyes at all pH but the cocultures gave comparably higher mycelial growth.

Enterobacter oligotrophica sp. nov., a novel oligotroph isolated from leaf soil.

A novel oligotrophic bacterium, designated strain CCA6, was isolated from leaf soil collected in Japan. Cells of the strain were found to be a Gram-negative, non-sporulating, motile, rod-shaped bacterium. Strain CCA6 grew at 10-45°C (optimum 20°C) and pH 4.5-10.0 (optimum pH 5.0). The strain was capable of growth in poor-nutrient (oligotrophic) medium, and growth was unaffected by high-nutrient medium. The major fatty acid and predominant quinone system were C16:0 and ubiquinone-8. Phylogenetic analysis based on 16S rRNA gene sequences indicated strain CCA6 presented as a member of the family Enterobacteriaceae. Multilocus sequence analysis (MLSA) based on fragments of the atpD, gyrB, infB, and rpoB gene sequences was performed to further identify strain CCA6. The MLSA showed clear branching of strain CCA6 with respect to Enterobacter type strains. The complete genome of strain CCA6 consisted of 4,476,585 bp with a G+C content of 54.3% and comprising 4,372 predicted coding sequences. The genome average nucleotide identity values between strain CCA6 and the closest related Enterobacter type strain were <88.02%. Based on its phenotypic, chemotaxonomic and phylogenetic features, strain CCA6 (=HUT 8142T =KCTC 62525T ) can be considered as a novel species within the genus Enterobacter with the proposed name Enterobacter oligotrophica.

Enrichment of phosphate solubilizing bacteria during late developmental stages of eggplant (Solanum melongena L.).

Understanding the ecology of phosphate solubilizing bacteria (PSBs) is critical for developing better strategies to increase crop productivity. In this study, the diversity of PSBs and of the total bacteria in the rhizosphere of eggplant (Solanum melongena L.) cultivated in organic, integrated and conventional farming systems was compared at four developmental stages of its lifecycle. Both selective culture and high-throughput sequencing analysis of 16S rRNA amplicons indicated that Enterobacter with strong or very strong in vivo phosphate solubilization activities was enriched in the rhizosphere during the fruiting stage. The high-throughput sequencing analysis results demonstrated that farming systems explained 23% of total bacterial community variation. Plant development and farming systems synergistically shaped the rhizospheric bacterial community, in which the degree of variation influenced by farming systems decreased over the plant development phase from 56% to 26.3% to 16.3%, and finally to no significant effect as the plant reached at fruiting stage. Pangenome analysis indicated that two-component and transporter systems varied between the rhizosphere and soil PSBs. This study elucidated the complex interactions among farming systems, plant development and rhizosphere microbiomes.

Coculturing Bacteria Leads to Reduced Phenotypic Heterogeneities.

Isogenic bacterial populations are known to exhibit phenotypic heterogeneity at the single-cell level. Because of difficulties in assessing the phenotypic heterogeneity of a single taxon in a mixed community, the importance of this deeper level of organization remains relatively unknown for natural communities. In this study, we have used membrane-based microcosms that allow the probing of the phenotypic heterogeneity of a single taxon while interacting with a synthetic or natural community. Individual taxa were studied under axenic conditions, as members of a coculture with physical separation, and as a mixed culture. Phenotypic heterogeneity was assessed through both flow cytometry and Raman spectroscopy. Using this setup, we investigated the effect of microbial interactions on the individual phenotypic heterogeneities of two interacting drinking water isolates. Through flow cytometry we have demonstrated that interactions between these bacteria lead to a reduction of their individual phenotypic diversities and that this adjustment is conditional on the bacterial taxon. Single-cell Raman spectroscopy confirmed a taxon-dependent phenotypic shift due to the interaction. In conclusion, our data suggest that bacterial interactions may be a general driver of phenotypic heterogeneity in mixed microbial populations.IMPORTANCE Laboratory studies have shown the impact of phenotypic heterogeneity on the survival and functionality of isogenic populations. Because phenotypic heterogeneity plays an important role in pathogenicity and virulence, antibiotic resistance, biotechnological applications, and ecosystem properties, it is crucial to understand its influencing factors. An unanswered question is whether bacteria in mixed communities influence the phenotypic heterogeneity of their community partners. We found that coculturing bacteria leads to a reduction in their individual phenotypic heterogeneities, which led us to the hypothesis that the individual phenotypic diversity of a taxon is dependent on the community composition.

Enhanced biodegradation of atrazine by Arthrobacter sp. DNS10 during co-culture with a phosphorus solubilizing bacteria: Enterobacter sp. P1.

The interaction between pure culture microorganisms has been evaluated allowing for the enhanced biodegradation of various kinds of pollutants. Arthrobacter sp. DNS10 previously enriched in an atrazine-containing soil was capable of utilizing atrazine as the sole nitrogen source for growth, and Enterobacter sp. P1 is a phosphorus-solubilizing bacterium that releases various kinds of organic acids but lacks the ability to degrade atrazine. Whether strain P1 could enhance atrazine biodegradation by the degrader strain DNS10 was investigated in this experiment. Gas chromatography and high-performance liquid chromatography results showed that co-culture of both strains degraded 99.18 ±â€¯1.00% of the atrazine (initial concentration was 100 mg L-1), while the single strain DNS10 only degraded 38.57 ±â€¯7.39% after a 48 h culture, and the resulting concentration of the atrazine final metabolite cyanuric acid were 63.91 ±â€¯3.34 mg L-1 and 26.60 ±â€¯3.87 mg L-1, respectively. In addition, the expression of the atrazine degradation-related genes trzN, atzB and atzC in co-culture treatments was 6.61, 1.81 and 3.09 times that of the single strain DNS10 culture treatment. A substrates utilization test showed that the atrazine-degrading metabolites ethylamine and isopropylamine could serve as the nitrogen source to support strain P1 growth, although strain P1 cannot degrade atrazine or utilize atrazine for growth. Furthermore, the pH of the medium was significantly decreased when strain P1 utilized ethylamine and isopropylamine as the nitrogen source for growth. The results suggest that nondegrader strain P1 could promote the atrazine biodegradation when co-cultured with strain DNS10. This phenomenon is due to metabolite exchange between the two strains. Culturing these two strains together is a new biostimulation strategy to enhance the biodegradation of atrazine by culturing these two strains together.

A newly isolated Enterobacter sp. strain produces 2,3-butanediol during its cultivation on low-cost carbohydrate-based substrates.

2,3-Butanediol (BDO) is an important platform chemical with a wide range of applications in various industries. In the present study, a newly isolated wild Enterobacter sp. strain (FMCC-208) was evaluated towards its ability to produce BDO on media composed of sugars derived from sucrose refinery plant. Optimum values of temperature and pH as well as substrate inhibition were determined through batch experiments. The ability of the strain to convert various monosaccharides was also investigated. Maximum BDO concentrations of 90.3 and 10 g l-1 of acetoin were obtained during a fed-batch bioreactor experiment with cane molasses and sucrose employed as substrates. A high volumetric productivity was noted in a fed-batch experiment using molasses and sucrose as carbon sources at T = 37°C, in which 73.0 g l-1 of BDO together with 12.4 g l-1 of acetoin was produced where 1.15 g l-1 h-1 of diol/acetoin was produced. In previously pasteurized media, 70.0 g l-1 of BDO and 5.0 g l-1 of acetoin were produced (yield = 0.39 g g-1). Finally, besides BDO production, growth on molasses was accompanied by non-negligible decolorization (25-35%) of the residue. Therefore, the strain is a promising candidate for the conversion of sucrose-based materials into BDO.

In vitro activity of tigecycline and comparators (2014-2016) among key WHO 'priority pathogens' and longitudinal assessment (2004-2016) of antimicrobial resistance: a report from the T.E.S.T. study.

We report contemporary (2014-2016) Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) global data on activity of tigecycline and comparators against WHO 'priority pathogens', and global trends (2004-2016) in antimicrobial resistance. MICs were determined using CLSI broth microdilution methodology. Antimicrobial resistance was determined using CLSI breakpoints (FDA breakpoints for tigecycline). Data are reported for Africa, Asia, Europe, North America and South America. From 2014-2016, Africa, Asia and South America reported highest resistance rates among Acinetobacter baumannii; North America lowest (all antimicrobials tested). The tigecycline MIC90 against A. baumannii was 2 mg/L in all regions except South America (1 mg/L). Among Enterobacteriaceae, meropenem resistance was low and tigecycline resistance was ≤1.3% in all regions (Escherichia coli, 0.0-0.3%; Klebsiella pneumoniae 0.0-1.3%; Enterobacter spp. 0.5-1.1%; Serratia marcescens 0.0-1.3%). Ceftriaxone resistance among E. coli ranged from 14.5% (North America) to 54.7% (Asia), and among K. pneumoniae from 9.1% (North America) to 54.0% (South America). North America reported highest rates of vancomycin-resistant Enterococcus faecium (64.6%); Europe lowest (17.7%). The tigecycline MIC90 against methicillin-resistant Staphylococcus aureus (MRSA) ranged from 0.12 mg/L (Africa and North America) to 0.5 mg/L (Asia). From 2004-2016, carbapenem resistance increased among A. baumannii (all regions), reaching 92.3% in Africa and 85.7% in South America (2016). Rates of ceftriaxone-resistant E. coli increased in all regions except Asia. Ceftriaxone resistance in K. pneumoniae increased in Europe. Rates of vancomycin-resistant E. faecium and MRSA were highest in North America and South America (and Asia for MRSA); lowest in Europe.

Evaluation of the Bactericidal Activity of Plazomicin and Comparators against Multidrug-Resistant Enterobacteriaceae.

The next-generation aminoglycoside plazomicin, in development for infections due to multidrug-resistant (MDR) Enterobacteriaceae, was evaluated alongside comparators for bactericidal activity in minimum bactericidal concentration (MBC) and time-kill (TK) assays against MDR Enterobacteriaceae isolates with characterized aminoglycoside and ß-lactam resistance mechanisms. Overall, plazomicin and colistin were the most potent, with plazomicin demonstrating an MBC50/90 of 0.5/4 µg/ml and sustained 3-log10 kill against MDR Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp.

Nematicidal and Plant Growth-Promoting Activity of Enterobacter asburiae HK169: Genome Analysis Provides Insight into Its Biological Activities.

In the course of screening for microbes with nematicidal activity, we found that Enterobacter asburiae HK169 displayed promising nematicidal activity against the root-knot nematode Meloidogyne incognita, along with plant growth-promoting properties. Soil drenching of a culture of HK169 reduced gall formation by 66% while also increasing root and shoot weights by 251% and 160%, respectively, compared with an untreated control. The cell-free culture filtrate of the HK169 culture killed all juveniles of M. incognita within 48 h. In addition, the nematicidal activity of the culture filtrate was dramatically reduced by a protease inhibitor, suggesting that proteolytic enzymes contribute to the nematicidal activity of HK169. In order to obtain genomic information about the HK169 isolate related to its nematicidal and plant growth-promoting activities, we sequenced and analyzed the whole genome of the HK169 isolate, and the resulting information provided evidence that the HK169 isolate has nematicidal and plant growth-promoting activities. Taken together, these observations enable the future application of E. asburiae HK169 as a biocontrol agent for nematode control and promote our understanding of the beneficial interactions between E. asburiae HK169 and plants.

Improvement of cadmium phytoremediation by Centella asiatica L. after soil inoculation with cadmium-resistant Enterobacter sp. FM-1.

This study examined the potential of a cadmium-resistant Enterobacter sp. FM-1 to promote plant growth and assist in cadmium accumulation in both mine-type C. asiatica L. and non-mine type C. asiatica L. tissues in highly cadmium-polluted soils. The results indicated that Enterobacter sp. FM-1 significantly promoted growth and alleviated metal toxicity in both types of C. asiatica L. Meanwhile, inoculation with Enterobacter sp. FM-1 in contaminated soil can increased cadmium bioavailability in soil. Furthermore, it will increase plant uptake and the accumulation of cadmium in C. asiatica L. leaves, stems and roots compared to that in an uninoculated plant. However, mine-type C. asiatica L. had better cadmium tolerance than the non mine-type C. asiatica L. Because of its native metal-tolerant ability, which could easily grow and proliferate, and had a better performance under cadmium-contamination conditions. Additionally, inoculation with Enterobacter sp. FM-1 significantly enhanced the bioaccumulation factor (BAF) and the translocation factor (TF) values in both types of C. asiatica L. even under high cadmium concentration soil condition. Hence, based on higher BAF and TF values and strong cadmium accumulation in the leaves and stems, we concluded that inoculation with Enterobacter sp. FM-1 is potentially useful for the phytoremediation of cadmium-contaminated sites by Centella asiatica L.