Stability and Microbial Toxicity of Silver Nanoparticles under Denitrifying Conditions

While the antibacterial effect of silver nanoparticles (AgNPs) on environmentally beneficial microbes has drawn considerable attention, the stability and microbial toxicity of AgNPs in a system where nitrate reduction is the dominant terminal electron-accepting process remain understudied. Here, we explore the impact of citrate-coated AgNPs (cit-AgNPs) on the growth and metabolism of two metal-sensitive and one nonsensitive bacterial strains under denitrifying conditions. Dose-response analysis revealed that in contrast to the bacteriostatic effect exhibited at 1 ppm, 5 ppm cit-AgNPs were bactericidal to the metal-sensitive strains. It was observed that the growth of the cells initiated Ag(I) formation, and the supplement of chloride (2.7 mM) to the cultures substantially mitigated the bactericidal capacity of cit-AgNPs, indicating that AgNP dissolution to ionic Ag(I) played a key role in AgNP toxicity. Abiotic experiments confirmed that nitrite, not nitrate, had the capacity to oxidize cit-AgNPs. Transcriptomic analysis revealed that (i) the gene encoding for membrane stress was upregulated proportionally to cit-AgNP concentrations; (ii) cit-AgNPs and Ag(I) at higher levels upregulated genes involved in oxidative stress and iron-sulfur clusters, whereas expressions of the genes responsible for electron transport, ATP synthesis, and denitrification were substantially repressed; (iii) the addition of chloride significantly altered the level of transcriptional profiles of all of the genes. These results not only provide evidence of abiotic AgNP oxidation by metabolic intermediate nitrogen species but also suggest that AgNPs and Ag(I) may induce differential toxicity modes to prokaryotes. Our findings reinforce the importance of evaluating the potential ecological toxicity and risks associated with the transformation of nanomaterials.

Poly(γ-glutamic acid) Nanocoating To Enhance the Viability of Pseudomonas stutzeri NRCB010 through Cell Surface Engineering

Microbial inoculants can enhance soil quality, promote plant nutrient acquisition, and alleviate problems caused by the excessive use of chemical fertilizers. However, susceptibility to harsh conditions during transport and storage, as well as the short shelf-life of plant growth-promoting rhizobacteria (PGPR), limit industrial application. Herein, a novel strategy to form nanocoating on bacterial surfaces to enhance viability was proposed. The nanocoating was composed of N-hydroxysuccinimide (NHS)-modified poly (γ-glutamic acid) (γ-PGA) and calcium ions, which could adhere to the surface of bacteria by forming covalent bonds and ionic bonds with the bacteria. The bacteria encapsulated in the coating had better resistance against harsh conditions than bare bacteria. The viability of coated bacteria was also increased by 2.38 times compared with bare bacteria after 4 weeks of storage. The pot experiment showed that coated Pseudomonas stutzeri NRCB010 had better growth-promoting properties compared with free P. stutzeri NRCB010. These results indicate that cell surface engineering is an effective method to enhance the resistance of bacteria against harsh conditions and is expected to promote the widespread use of PGPR.

Chlorpyrifos inhibits nitrogen fixation in rice-vegetated soil containing Pseudomonas stutzeri A1501

Chlorpyrifos, a common organophosphorus pesticide, is widely used for agricultural pest control and can inhibit nitrogen-fixing bacteria biomass in paddy. In this study, the additions of chlorpyrifos (1 and 8 mg kg^-1) to soil, with or without Pseudomonas stutzeri A1501, resulted in a significant decrease in nitrogen fixation, despite insignificant effects on the abundances of P. stutzeri A1501 and bacteria in soil. Toxic effect of chlorpyrifos on P. stutzeri A1501 nitrogenase activity in medium was also observed, accompanied by a significant reduction in the expression of nitrogen-fixing related genes (nifA and nifH). Furthermore, rhizosphere colonization and biofilm formation by P. stutzeri A1501 were repressed by chlorpyrifos, leading to decreased nitrogenase activity in the rhizosphere. Biofilm formation in medium was inhibited by bacterial hyperkinesis and reduction of extracellular polymeric substance, including exopolysaccharides and proteins. Together, these findings showed that chlorpyrifos-induced production of reactive oxygen species (ROS) which was directly responsible for reduced nitrogenase activity in the medium, soil, and rhizosphere by inhibiting the expressions of nitrogen-fixing related genes. Furthermore, the inhibition of biofilm formation by chlorpyrifos or ROS likely aggravated the reduction in rhizospherere nitrogenase activity. These findings provide potentially valuable insights into the toxicity of chlorpyrifos on nitrogen-fixing bacteria and its mechanisms. Furthermore, for sustainable rice production, it is necessary to evaluate whether other pesticides affect nitrogen fixation and select pesticides that do not inhibit nitrogen fixation.

New application of rutin: Repair the toxicity of emerging perfluoroalkyl substance to Pseudomonas stutzeri

Per- and polyfluoroalkyl substances (PFASs) are toxic to microorganisms, thereby affecting microbial communities in sludge and soil, but how to repair the toxicity of microorganisms remains unclear. In this study, rutin, an antioxidant, was added into a culture medium with an aerobic denitrification bacteria, Pseudomonas stutzeri, under the exposure of sodium perfluorononyloxy-benzenesulfonate (OBS) to evaluate the repair mechanisms of rutin to the toxicity of OBS to the bacteria. The results showed that rutin could repair the damage of OBS to cell structures, and reduce the death rates of the bacteria under OBS exposure. The dosage of rutin reduced the effect on the inhibition of denitrification ability of P. stutzeri under OBS exposure. Compared with the bacteria exposed to single OBS, the dosage of rutin resulted in that the death rates recovered from 96.2% to 66.4%, the growth inhibition rate decreased from 46.5% to 15.8%, the total nitrogen removal rate recovered from 66.9% to 100%, and the NO₂^- content recovered from 34.5 mg/L to 0.22 mg/L. The expressions of key denitrification genes (napA, nirS, norB, nosZ) were recovered after adding rutin under OBS exposure. Rutin changed the positive rate of reactive oxygen species, the relative superoxide dismutase and catalase activities in the bacteria which exposed to OBS. The mechanism by which rutin repaired the toxicity of OBS to P. stutzeri related to inhibiting the activities of antioxidant and denitrification enzymes rather than affecting the expressions of genes involved in these enzymes. This study sheds light on the repair method of micro-organics and reveals the repair mechanisms under PFASs exposure.

Novel Metal Cation Resistance Systems from Mutant Fitness Analysis of Denitrifying Pseudomonas stutzeri

Metal ion transport systems have been studied extensively, but the specificity of a given transporter is often unclear from amino acid sequence data alone. In this study, predicted Cu(2+) and Zn(2+) resistance systems in Pseudomonas stutzeri strain RCH2 are compared with those experimentally implicated in Cu(2+) and Zn(2+) resistance, as determined by using a DNA-barcoded transposon mutant library. Mutant fitness data obtained under denitrifying conditions are combined with regulon predictions to yield a much more comprehensive picture of Cu(2+) and Zn(2+) resistance in strain RCH2. The results not only considerably expand what is known about well-established metal ion exporters (CzcCBA, CzcD, and CusCBA) and their accessory proteins (CzcI and CusF), they also reveal that isolates with mutations in some predicted Cu(2+) resistance systems do not show decreased fitness relative to the wild type when exposed to Cu(2+) In addition, new genes are identified that have no known connection to Zn(2+) (corB, corC, Psest_3226, Psest_3322, and Psest_0618) or Cu(2+) resistance (Mrp antiporter subunit gene, Psest_2850, and Psest_0584) but are crucial for resistance to these metal cations. Growth of individual deletion mutants lacking corB, corC, Psest_3226, or Psest_3322 confirmed the observed Zn-dependent phenotypes. Notably, to our knowledge, this is the first time a bacterial homolog of TMEM165, a human gene responsible for a congenital glycosylation disorder, has been deleted and the resulting strain characterized. Finally, the fitness values indicate Cu(2+)- and Zn(2+)-based inhibition of nitrite reductase and interference with molybdenum cofactor biosynthesis for nitrate reductase. These results extend the current understanding of Cu(2+) and Zn(2+) efflux and resistance and their effects on denitrifying metabolism.

IMPORTANCE

In this study, genome-wide mutant fitness data in P. stutzeri RCH2 combined with regulon predictions identify several proteins of unknown function that are involved in resisting zinc and copper toxicity. For zinc, these include a member of the UPF0016 protein family that was previously implicated in Ca(2+)/H(+) antiport and a human congenital glycosylation disorder, CorB and CorC, which were previously linked to Mg(2+) transport, and Psest_3322 and Psest_0618, two proteins with no characterized homologs. Experiments using mutants lacking Psest_3226, Psest_3322, corB, corC, or czcI verified their proposed functions, which will enable future studies of these little-characterized zinc resistance determinants. Likewise, Psest_2850, annotated as an ion antiporter subunit, and the conserved hypothetical protein Psest_0584 are implicated in copper resistance. Physiological connections between previous studies and phenotypes presented here are discussed. Functional and mechanistic understanding of transport proteins improves the understanding of systems in which members of the same protein family, including those in humans, can have different functions.

Influence of copper on expression of nirS, norB and nosZ and the transcription and activity of NIR, NOR and N2 OR in the denitrifying soil bacteria Pseudomonas stutzeri

Reduction of the potent greenhouse gas nitrous oxide (N(2)O) occurs in soil environments by the action of denitrifying bacteria possessing nitrous oxide reductase (N(2)OR), a dimeric copper (Cu)-dependent enzyme producing environmentally benign dinitrogen (N(2)). We examined the effects of increasing Cu concentrations on the transcription and activity of nitrite reductase (NIR), nitric oxide reductase (NOR) and N2 OR in Pseudomonas stutzeri grown anaerobically in solution over a 10-day period. Gas samples were taken on a daily basis and after 6 days, bacterial RNA was recovered to determine the expression of nirS, norB and nosZ encoding NIR, NOR and N(2)OR respectively. Results revealed that 0.05 mM Cu caused maximum conversion of N(2)O to N(2) via bacterial reduction of N(2)O. As soluble Cu generally makes up less than 0.001% of total soil Cu, extrapolation of 0.05 mg l(-l) soluble Cu would require soils to have a total concentration of Cu in the range of, 150-200 μg g(-1) to maximize the proportion of N(2)O reduced to N(2). Given that many intensively farmed agricultural soils are deficient in Cu in terms of plant nutrition, providing a sufficient concentration of biologically accessible Cu could provide a potentially useful microbial-based strategy of reducing agricultural N(2)O emissions.

Toxicity of TiO₂ nanoparticle to denitrifying strain CFY1 and the impact on microbial community structures in activated sludge

The antibacterial activity of titanium dioxide nanoparticles (TiO2 NPs) is well described, but little is known of their impact on specific microbial functions such as denitrification, nor on microbial community structure. In this study, a denitrifier (named as Pseudomonas stutzeri CFY1), which was isolated from the activated sludge and could remove up to 111.68 mg/L of NO3(-)-N under aerobic conditions, was utilized to evaluate the influences of TiO2 NPs on its nitrogen removal ability and associated gene expression under aerobic conditions. The variations of the bacterial diversity of activated sludge were also observed. The results showed that antibacterial activity increased with increasing concentrations of TiO2 NPs. Increased production of reactive oxygen species was responsible for TiO2 NPs toxicity. An up-regulation of denitrification genes was observed with increasing concentrations of TiO2 NPs under aerobic conditions. Accordingly, denitrification by P. stutzeri was accelerated when the concentration of TiO2 NPs was increased to 50 mg/L. However, the denitrification of CFY1 was inhibited at low concentrations of TiO2 NPs (5-25 mg/L), indicating that assimilatory and dissimilatory denitrification were synchronized in P. stutzeri CFY1; the latter process plays a major role in denitrification. Further study of the community using 454 pyrosequencing showed that after 7 days of exposure to 50 mg/L TiO2 NPs, the microbial composition of the activated sludge was significantly different and had a lower diversity compared to the controls.

Multiple phenotypic changes associated with large-scale horizontal gene transfer

Horizontal gene transfer often leads to phenotypic changes within recipient organisms independent of any immediate evolutionary benefits. While secondary phenotypic effects of horizontal transfer (i.e., changes in growth rates) have been demonstrated and studied across a variety of systems using relatively small plasmids and phage, little is known about the magnitude or number of such costs after the transfer of larger regions. Here we describe numerous phenotypic changes that occur after a large-scale horizontal transfer event (∼1 Mb megaplasmid) within Pseudomonas stutzeri including sensitization to various stresses as well as changes in bacterial behavior. These results highlight the power of horizontal transfer to shift pleiotropic relationships and cellular networks within bacterial genomes. They also provide an important context for how secondary effects of transfer can bias evolutionary trajectories and interactions between species. Lastly, these results and system provide a foundation to investigate evolutionary consequences in real time as newly acquired regions are ameliorated and integrated into new genomic contexts.

Molecular stress responses to nano-sized zero-valent iron (nZVI) particles in the soil bacterium Pseudomonas stutzeri

Nanotoxicological studies were performed in vitro using the common soil bacterium Pseudomonas stutzeri to assess the potentially toxic impact of commercial nano-sized zero-valent iron (nZVI) particles, which are currently used for environmental remediation projects. The phenotypic response of P. stutzeri to nZVI toxicity includes an initial insult to the cell wall, as evidenced by TEM micrographs. Transcriptional analyses using genes of particular relevance in cellular activity revealed that no significant changes occurred among the relative expression ratios of narG, nirS, pykA or gyrA following nZVI exposure; however, a significant increase in katB expression was indicative of nZVI-induced oxidative stress in P. stutzeri. A proteomic approach identified two major defence mechanisms that occurred in response to nZVI exposure: a downregulation of membrane proteins and an upregulation of proteins involved in reducing intracellular oxidative stress. These biomarkers served as early indicators of nZVI response in this soil bacterium, and may provide relevant information for environmental hazard assessment.

Impacts of silver nanoparticles on cellular and transcriptional activity of nitrogen-cycling bacteria

The widespread use of silver nanoparticles (AgNPs) raises the potential for environmental releases that could impact microbial ecosystem services. In the present study, the authors address how the AgNPs and Ag(+) that they release may impact nitrogen-cycling bacteria. The authors studied the cellular and transcriptional response of the denitrifier Pseudomonas stutzeri, the nitrogen fixer Azotobacter vinelandii, and the nitrifier Nitrosomonas europaea exposed to 35 nm (carbon-coated) AgNPs or to Ag(+) (added as AgNO3 ). Based on minimum inhibitory concentrations (MICs), Ag(+) was 20 times to 48 times more toxic to the tested strains than AgNPs (including Ag(+) released during exposure). Exposure to sublethal concentrations of AgNPs or Ag(+) (representing 10% of the respective MIC for AgNO3 ) resulted in no significant effect on the expression of the denitrifying genes narG, napB, nirH, and norB in P. stutzeri or the nitrogen-fixing genes nifD, nifH, vnfD, and anfD in A. vinelandii, whereas nitrifying genes (amoA1 and amoC2) in N. europaea were upregulated (2.1- to 3.3-fold). This stimulatory effect disappeared at higher silver concentrations (60% of the Ag(+) MIC), and toxicity was exerted at concentrations higher than 60% of the Ag(+) MIC. The MIC for N. europaea was 8 times to 24 times lower than for the other strains, indicating higher susceptibility to AgNPs. This was corroborated by the lower half-lethal concentration for N. europaea (87 µg/L) compared with P. stutzeri (124 µg/L) and A. vinelandii (>250 µg/L) when cells were exposed with Ag(+) for 24 h in 1 mM bicarbonate buffer. This suggests that ammonia oxidation would be the most vulnerable nitrogen-cycling process in wastewater treatment plants receiving AgNPs and in agricultural soils amended with biosolids that concentrate them.

Metal accumulation in cell wall: a possible mechanism of cadmium resistance by Pseudomonas stutzeri

A heavy metal resistant strain, Pseudomonas stutzeri (MTCC 101) has been investigated for its cadmium tolerance properties along with its antibiotic resistance. The organism could tolerate cadmium up to 1,200 μg/mL with LD50 value 700 μg/mL. The gene(s) involved in such high resistance appear(s) to be induced in the presence of the metal. Increasing concentrations of cadmium successively prolonged the lag phase of growth with delayed attainment of the stationary phase. Transmission electron microscope and scanning electron microscope-energy dispersive analysis of X-ray spectroscope analysis showed cadmium adsorption on the bacterial surface with morphological distortion. Atomic absorption spectrometric study corroborated this data, showing highest cadmium accumulation in the cell wall fraction of the bacteria. Additionally, the cell wall fraction showed synthesis of new proteins when grown under metal stress.

Antibacterial and antiplasmodial constituents of Beilschmiedia cryptocaryoides

Four new beilschmiedic acid derivatives, cryptobeilic acids A-D (1-4), and tsangibeilin B (5) have been isolated from the bark of Beilschmiedia cryptocaryoides collected from Madagascar. Their structures were elucidated using detailed spectroscopic and spectrometric methods. Cryptobeilic acid A (1) and tsangibeilin B (5) structures were confirmed by single-crystal X-ray diffraction analysis. Compounds 1-5 displayed moderate antibacterial activity against Escherichia coli 6r3, Acinetobacter calcoaceticus DSM 586, and Pseudonamas stutzeri A1501, with the minimum inhibitory concentrations ranging from 10 to 50 μM, respectively. In addition, the compounds exhibited antiplasmodial activity against erythrocytic stages of chloroquine-resistant Plasmodium falciparum strain NF54 and weak cytotoxicity against L6 cell lines.

Biodegradation of alkyl derivatives of aromatic hydrocarbons and cell surface properties of a strain of Pseudomonas stutzeri

Pseudomonas stutzeri strain 9 was isolated from petroleum-contaminated soil. The main purpose of this study was to investigate how the long-term contact of this strain with diesel oil influences its surface and biodegradation properties. The experiments showed that the tested strain was able to degrade aromatic alkyl derivatives (butylbenzene, sec-butylbenzene, tert-butylbenzene and isobutylbenzene) and that the storage conditions had an influence on the cell surface properties. Also greater agglomeration of the cells was observed in the scanning electron microscope (SEM) micrographs and confirmed in particle size distribution results. The results also indicated that the addition of rhamnolipids to the hydrocarbons led to modification of the surface properties of P. stutzeri strain 9, which could be observed in the zeta potential and hydrophobicity values.

Cellular and transcriptional response of Pseudomonas stutzeri to quantum dots under aerobic and denitrifying conditions

Pseudomonas stutzeri was exposed to quantum dots (QDs) with three different surface coatings (anionic polymaleic anhydride-alt-1-octadecene (PMAO), cationic polyethylenimine (PEI), and carboxyl QDs) under both aerobic and anaerobic (denitrifying) conditions. Under aerobic conditions, toxicity (assessed per growth inhibition) increased from PMAO to carboxyl to PEI QDs. The positive charge of PEI facilitated direct contact with negatively charged bacteria, which was verified by TEM analysis. Both PMAO and PEI QDs hindered energy transduction (indicated by a decrease in cell membrane potential), and this effect was most pronounced with PEI QDs under denitrifying conditions. Up-regulation of denitrification genes (i.e., nitrate reductase narG, periplasmic nitrate reductase napB, nitrite reductase nirH, and NO reductase norB) occurred upon exposure to subinhibitory PEI QD concentrations (1 nM). Accordingly, denitrification activity (assessed per respiratory nitrate consumption in the presence of ammonia) increased during sublethal PEI QD exposure. However, cell viability (including denitrification) was hindered at 10 nM or higher PEI QD concentrations. Efflux pump genes czcB and czcC were induced by PEI QDs under denitrifying conditions, even though Cd and Se dissolution from QDs did not reach toxic levels (exposure was at pH 7 to minimize hydrolysis of QD coatings and the associated release of metal constituents). Up-regulation of the superoxide dismutase (stress) gene sodB occurred only under aerobic conditions, likely due to intracellular production of reactive oxygen species (ROS). The absence of ROS under denitrifying conditions suggests that the antibacterial activity of QDs was not due to ROS production alone. Overall, this work forewarns about unintended potential impacts to denitrification as a result of disposal and incidental releases of QDs, especially those with positively charged coatings (e.g., PEI QDs).

Differential effects of dissolved organic carbon upon re-entrainment and surface properties of groundwater bacteria and bacteria-sized microspheres during transport through a contaminated, sandy aquifer

Injection-and-recovery studies involving a contaminated, sandy aquifer (Cape Cod, Massachusetts) were conducted to assess the relative susceptibility for in situ re-entrainment of attached groundwater bacteria (Pseudomonas stuzeri ML2, and uncultured, native bacteria) and carboxylate-modified microspheres (0.2 and 1.0 μm diameters). Different patterns of re-entrainment were evident for the two colloids in response to subsequent injections of groundwater (hydrodynamic perturbation), deionized water (ionic strength alteration), 77 μM linear alkylbenzene sulfonates (LAS, anionic surfactant), and 76 μM Tween 80 (polyoxyethylene sorbitan monooleate, a very hydrophobic nonionic surfactant). An injection of deionized water was more effective in causing detachment of micrsopheres than were either of the surfactants, consistent with the more electrostatic nature of microsphere's attachment, their extreme hydrophilicity (hydrophilicity index, HI, of 0.99), and negative charge (zeta potentials, ζ, of -44 to -49 mv). In contrast, Tween 80 was considerably more effective in re-entraining the more-hydrophobic native bacteria. Both the hydrophilicities and zeta potentials of the native bacteria were highly sensitive to and linearly correlated with levels of groundwater dissolved organic carbon (DOC), which varied modestly from 0.6 to 1.3 mg L(-1). The most hydrophilic (0.52 HI) and negatively charged (ζ -38.1 mv) indigenous bacteria were associated with the lowest DOC. FTIR spectra indicated the latter community had the highest average density of surface carboxyl groups. In contrast, differences in groundwater (DOC) had no measurable effect on hydrophilicity of the bacteria-sized microspheres and only a minor effect on their ζ. These findings suggest that microspheres may not be very good surrogates for bacteria in field-scale transport studies and that adaptive (biological) changes in bacterial surface characteristics may need to be considered where there is longer-term exposure to contaminant DOC.

Antioxidative and antibacterial effects of seeds and fruit rind of nutraceutical plants belonging to the Fabaceae family

In the present study, the seeds and fruit rind of six plants of the Fabaceae family were selected to evaluate their potential as antioxidant and antibacterial agents. The dried powders were individually extracted with various organic solvents by the cold percolation method, were evaluated for antibacterial activity and methanol extracts used for antioxidant activities. Total phenol, protein and sugar contents were also measured. Antioxidant activities were measured by DPPH free radical scavenging activity, superoxide anion radical scavenging activity and reducing capacity assessment. Antibacterial activity was measured by the agar well diffusion method against four Gram positive and four Gram negative bacteria. The methanol extract of the fruit rind of C. indica showed the maximum DPPH free radical scavenging activity, superoxide anion radical scavenging activity, a high reducing capacity assessment and also had the highest total phenol content. There was a direct correlation between the phenol content and the antioxidant activity. The antibacterial activity of all the extracts was more pronounced on Gram positive bacteria than on Gram negative bacteria. Thus, the fruit rind of C. indica showed the best antioxidant and antibacterial activities.

[Community-acquired Pseudomonas stutzeri meningitis in an immunocompetent patient]

Pseudomonas stutzeri which is an aerobic, non-fermentative gram-negative bacillus frequently found in soil, water and hospital environment, rarely leads to serious community-acquired infections. In this report a case of community-acquired meningitis due to P. stutzeri was presented. A 73-years-old male patient was admitted to the emergency department with the complaints of nausea, vomiting, headache, dizziness, difficulties in walking and speaking and loss of consciousness. There was no history of an underlying disease or immunosuppression. Physical examination revealed nuchal rigidity, however, Kernig and Brudzinski signs were negative. The cerebrospinal fluid (CSF) analysis revealed 0.4 mg/dl glucose (simultaneous blood glucose 145 mg/dl), and 618 mg/dl protein and 640 leucocyte/mm3 (90% PMNL). No bacteria were detected in Gram stained and Ehrlich-Ziehl-Neelsen stained CSF smears. Upon the diagnosis of acute bacterial meningitis, treatment with ceftriaxone and ampicillin was initiated, however, the patient died after 16 hours of hospitalization. CSF culture yielded the growth of gram-negative oxidase-positive bacteria and the isolate was identified as P. stutzeri by Vitek-2 Compact system (bioMerieux, France). The isolate was found to be sensitive to piperacillin/tazobactam, amikacin, gentamycin, ceftazidime, cefepime, ciprofloxacin, imipenem and meropenem. Since the patient was lost due to acute respiratory and cardiac failure, it was not possible to change the therapy to agent specific therapy. In conclusion, it should always be kept in mind that uncommon agents could lead to community-acquired meningitis in elderly patients and empirical treatment protocols might fail in such cases resulting in high morbidity and mortality.

A single residue mutation of 5-enoylpyruvylshikimate-3-phosphate synthase in Pseudomonas stutzeri enhances resistance to the herbicide glyphosate

A novel class II 5-enoylpyruvylshikimate-3-phosphate synthase (EPSPS) was identified from Pseudomonas stutzeri A1501 by complementation of an Escherichia coli auxotrophic aroA mutant. The single amino acid substitution of serine (Ser) for asparagine (Asn)-130 of the A1501 EPSPS enhanced resistance to 200 mM glyphosate. The mutated EPSPS had a 2.5-fold increase for IC(50) [glyphosate] value, a 2-fold increase for K (i) [glyphosate] value, but a K (m) [PEP] value similar to that of wild type. The effect of the single residue mutation on glyphosate resistance was also analyzed using a computer-based three-dimensional model.

Membrane-bound L- and D-lactate dehydrogenase activities of a newly isolated Pseudomonas stutzeri strain

Pseudomonas stutzeri SDM was newly isolated from soil, and two stereospecific NAD-independent lactate dehydrogenase (iLDH) activities were detected in membrane of the cells cultured in a medium containing DL-lactate as the sole carbon source. Neither enzyme activities was constitutive, but both of them might be induced by either enantiomer of lactate. P. stutzeri SDM preferred to utilize lactate to growth, when both L-lactate and glucose were available, and the consumption of glucose was observed only after lactate had been exhausted. The Michaelis-Menten constant for L-lactate was higher than that for D-lactate. The L-iLDH activity was more stable at 55 degrees C, while the D-iLDH activity was lost. Both enzymes exhibited different solubilization with different detergents and different oxidation rates with different electron acceptors. Combining activity staining and previous proteomic analysis, the results suggest that there are two separate enzymes in P. stutzeri SDM, which play an important role in converting lactate to pyruvate.

[Meningitis due to Pseudomonas stutzeri: a case report]

Pseudomonas stutzeri is a saprophytic microorganism that rarely causes severe infections. In this report, a 28 days old male patient with meningomyelocele at birth was presented. The patient was admitted to the hospital with fever, and diagnosed as meningitis on the basis of physical examination and leukocytosis (blood: 16.380/mm3, cerebrospinal fluid (CSF): 130/mm3; 90% PMNL). Following diagnosis ceftriaxone therapy was started led to improvement in clinical and laboratory findings. However on the 20th day, the clinical signs and symptoms became worse, and the patient was diagnosed to develop a second meningitis attack by laboratory examination of CSF. P. stutzeri was isolated from the CSF culture, and the isolate was found to be resistant to ceftriaxone. Upon this result the therapy has changed to meropenem. On the 5th day of the therapy, the patient has slightly improved and he was discharged due to the wishes of his parents, however he died two days after discharge. This first case of P. stutzeri meningitis in neonates was presented to withdraw attention to this clinical entity.

Community-acquired pneumonia and empyema caused by Pseudomonas stutzeri: a case report

Pseudomonas stutzeri is an aerobic, nonfermentative, gram-negative rod with polar monotrichous flagella. We report the case of a four-year-old boy who developed community-acquired pneumonia and empyema caused by P. stutzeri. To our knowledge, this is the first report on community-acquired pneumonia and empyema caused by this organism in childhood.

TbtABM, a multidrug efflux pump associated with tributyltin resistance inPseudomonas stutzeri

Tributyltin (TBT) is a toxic agent used in marine antifouling paints. Among the bacterial flora of a polluted harbor, TBT-resistant strains of Pseudomonas stutzeri have been isolated. In the strain 5MP1 (TBT minimum inhibitory concentration (MIC) > or =1000 mg l(-1)), TBT resistance was found to be associated with the presence of the operon tbtABM, homologous to the resistance-nodulation-cell division (RND) efflux pump family, as demonstrated by cloning in Escherichia coli. TbtABM exhibited the greatest homology (60.9-84.9%) with the TtgDEF and SrpABC systems, both involved in aromatic compound tolerance in P. putida. TbtABM conferred multidrug resistance (MDR) including to n-hexane, nalidixic acid, chloramphenicol, and sulfamethoxazole (antibiotic MICsx4 for the E. coli host strain carrying the operon). By polymerase chain reaction amplification and hybridization experiments, the presence of tbtABM was detected in the TBT-sensitive P. stutzeri 3MP1 (TBT MIC 25 mg l(-1)). However, the latter strain did not seem to express TbtABM. This is the first description of a MDR efflux pump in P. stutzeri, and of a new kind of substrate, TBT, for the RND family of transporters.