Effect of growth temperature and pH on the aminopeptidase activity of Pseudomonas putida, P. fluorescens and Flavobacterium odoratum; the 4-nitroaniline test is reliable

No significant difference (p > 0.05) was observed in the specific aminopeptidase activity (SAA) developed by Pseudomonas fluorescens, P. putida and Flavobacterium odoratum either growing at pH 5.0–6.5 or at 7 and 12 °C. Nevertheless, a significant difference was found when comparing the SAA of these organisms. The SAA of F. odoratum was lower than those of pseudomonads. The 4-nitroaniline test is reliable to estimate the G⁻ load of fresh food products.     

PARTIAL PURIFICATION AND CHARACTERIZATION OF THE ORGANIC SOLVENT-TOLERANT LIPASE PRODUCED BY Pseudomonas fluorescens RB02-3 ISOLATED FROM MILK

Eighty-five putative Pseudomonas isolates were obtained from various raw milk and pasteurized milk samples using Pseudomonas CFC agar. Among them, 36 isolates were identified as Pseudomonas fluorescens, and one isolate was identified as Pseudomonas putida. Lipase activity of the strains was quantitatively measured by the spectrophotometric method using p-nitrophenyl palmitate (p-NPP) as substrate. Detected lipase activity of the strains was between 10.03 U/mL and 22.16 U/mL. Pseudomonas fluorescens RB02-3 possessed the highest lipase activity. The extracellular lipase of P. fluorescens RB02-3 strain was homogeneously purified using a combination of ammonium sulfate precipitation, dialysis, and gel filtration column chromatography. This purification procedure resulted in 2.97-fold purification with 20.3% recovery. The enzyme was characterized, and exhibited maximum activity at pH 7.0 and 50°C; after it was incubated for 1 h it was activated in the presence of hexane, ethyl acetate, isopropanol, and ethanol and remained stable after the incubation was extended for 2 hr. The lipase was slightly inhibited in the presence of Zn²⁺, Co²⁺, Cu²⁺, Ni²⁺ salts, and ethylenediamine tetraacetic acid (EDTA), whereas Cd²⁺, sodium dodecyl sulfate (SDS), and Tween-80 had no effect on its activity.     

19F NMR study on the biological Baeyer-Villiger oxidation of acetophenones

The biological Baeyer–Villiger oxidation of acetophenones was studied by ¹⁹F nuclear magnetic resonance (NMR). The ¹⁹F NMR method was used to characterise the time-dependent conversion of various fluorinated acetophenones in either whole cells of Pseudomonas fluorescens ACB or in incubations with purified 4′-hydroxyacetophenone monooxygenase (HAPMO). Whole cells of P. fluorescens ACB converted 4′-fluoroacetophenone to 4-fluorophenol and 4′-fluoro-2′-hydroxyacetophenone to 4-fluorocatechol without the accumulation of 4′-fluorophenyl acetates. In contrast to 4-fluorophenol, 4-fluorocatechol was further degraded as evidenced by the formation of stoichiometric amounts of fluoride anion. Purified HAPMO catalysed the strictly NADPH-dependent conversion of fluorinated acetophenones to fluorophenyl acetates. Incubations with HAPMO at pH 6 and 8 showed that the enzymatic Baeyer–Villiger oxidation occurred faster at pH 8 but that the phenyl acetates produced were better stabilised at pH 6. Quantum mechanical characteristics explained why 4′-fluoro-2′-hydroxyphenyl acetate was more sensitive to base-catalysed hydrolysis than 4′-fluorophenyl acetate. All together, ¹⁹F NMR proved to be a valid method to evaluate the biological conversion of ring-substituted acetophenones to the corresponding phenyl acetates, which can serve as valuable synthons for further production of industrially relevant chemicals. Journal of Industrial Microbiology & Biotechnology (2001) 26, 35–42. Received 20 April 2000/ Accepted in revised form 16 September 2000     

An integrated approach for the evaluation of biological control of the complex Polymyxa betae/Beet Necrotic Yellow Vein Virus,by means of seed inoculants

Rhizomania is an extremely severe sugarbeet disease caused by the complex Polymyxa betae/Beet Necrotic Yellow Vein Virus (BNYVV). A relatively small number of recently introduced sugarbeet cultivars characterized by a high tolerance to rhizomania are available on the market. An integrated approach was therefore developed using Pseudomonas fluorescens biological control agents (BCAs) in order to improve yield performance of cultivars characterized by a medium tolerance to the disease. A genetically modified biological control agent, Pseudomonas fluorescens F113Rif (pCUGP), was developed for enhanced production of the antimicrobial metabolite 2,4-diacetylphloroglucinol (Phl) and lacking an antibiotic resistance marker gene, making the strain suitable for field release. The ability of synthetic Phl and P. fluorescens F113Rif (pCUGP) to antagonize the fungal vector, P. betae, was assessed in microcosm trials. Results encouraged the preparation of multiple field trials in a soil naturally infested with P. betae/BNYVV, to determine the biocontrol efficacy of P. fluorescens F113Rif (pCUGP) and to assess its impact on sugarbeet yield and quality and on the indigenous microbial population. While the colonization ability of P. fluorescens F113Rif (pCUGP) was satisfactory at sugarbeet emergence (2.5×10⁶ CFU g^–1 root), control of rhizomania was not achieved. Inoculation of sugarbeet with Pseudomonas fluorescens F113Rif (pCUGP) did not affect crop yield and quality nor affect the numbers of selected microbial populations.     

Barrier function of the cell wall during uptake of nickel ions

Cell walls were isolated from roots of six plant species to study their ion-exchange capacity for nickel ions (S _Ni) at Ni²⁺ concentration of 10⁻³ M. The S _Ni values varied depending on the plant species from 50 to 150 μmol Ni²⁺ per gram dry wt; the sorption capacity increased in a row: Poaceae < Chenopodiaceae < Fabaceae. At pH 5 the sorption capacity of cell walls for nickel ions was determined by the presence of carboxyl groups of polygalacturonic acid in the polymeric cell-wall matrix. In all cases the ion-exchange capacity of cell walls was higher at pH 8 than at pH 5, indicating that Ni²⁺ binds also to a carboxyl group different from that of polygalacturonic acid. Irrespective of plant species, the presence of EDTA in the solution diminished drastically the absorption capacity of cell walls for Ni²⁺. It is concluded that the presence of 10⁻³ M EDTA weakens the defense properties of cell walls. The sequestration of Ni²⁺ in the cell wall can be considered as an effective means of plant cell defense against elevated concentrations of nickel ions in the external medium.     

Effects of Pseudomonas fluorescens F113 on Ecological Functions in the Pea Rhizosphere Are Dependent on pH

Abstract The aim of this microcosm study was to determine influence of the antibiotic 2,4-diacetylphloroglucinol (DAPG) on the effect of wild-type and functionally modified Pseudomonas fluorescens F113 strains in a sandy loam soil of pH 5.4 planted with pea (Pisum sativum var Montana). The functional modification of strain F113 was a repressed production of DAPG, useful in plant disease control, creating the DAPG negative strain F113 G22; both were marked with a lacZY gene cassette. Lowering the soil pH to 4.4 significantly reduced the plant shoot and root weights and the root length, whereas the bacterial inocula had no significant effect. Both inocula significantly reduced the shoot/root ratio at pH 5.4, but this effect was not evident at the lowered or elevated (6.4) pH levels. The decrease in pH significantly increased the fungal and yeast colony-forming units from the rhizosphere (root extract), but did not affect the total bacterial c.f.u.'s. Inoculatioin with strain F113 in the pH 4.4 soil resulted in a significantly greater total bacterial population. The fungal and yeast c.f.u.'s were not significantly affected by the inocula at any pH studied. Increasing the pH significantly increased the indigenous Pseudomonas population in comparison to the reduced pH treatment and significantly increased both the introduced and total Pseudomonas populations. The antibiotic producing strain significantly reduced the total bacterial population and the NAGase activity (related to fungal activity) at pH 6.4 where the inocula population was the greatest. Alkaline phosphatase, phosphodiesterase, aryl sulfatase, β-glucosidase, alkaline β-galactosidase, and NAGase activities significantly increased with increasing in pH. The F113 inocula reduced the acid phosphatase activity at pH 5.4 and increased the acid β-galactosidase activity over all the pH treatments. The results presented illustrate the variation in impact with soil pH, with implications for variability in efficacy of Pseudomonas fluorescens biocontrol agents with soil pH. Received: 26 June 1998; Accepted: 1 February 1999     

Adsorption of flavobacterium breve and pseudomonas fluorescens p17 on different metals: Electrochemical polarization effect

The electrochemical polarization effect on early adsorption of Flavobacterium breve and Pseudomonas fluorescens P17 to platinum, titanium, stainless steel, copper, aluminum alloy and mild steel was studied. A well‐defined peak characterized the bacterial adsorption dependence on externally applied potential. Maximal adsorption occurred in the potential range of ‐0.5 to 0.5 V (SCE) for all tested metals. A shift of applied potential towards both a positive and a negative direction from the maximal adsorption potential (Emax,ad) was accompanied by a gradual decrease in bacterial adsorption. The extent of bacterial adsorption strongly depended on the nature of the metallic substratum and decreased accordingly as follows: platinum > titanium > stainless steel > aluminum alloy > carbon steel > copper. Adsorption on all tested metals was approximately two orders of magnitude higher with the relatively more hydrophobic F. breve compared to the less hydrophobic P. fluorescens P17. The effect of electrochemical polarization on the initial stages of bacterial adsorption onto metallic substrata is further discussed.     

Generation and initial characterization of Pseudomonas stutzeri KC mutants with impaired ability to degrade carbon tetrachloride

Under iron-limiting conditions, Pseudomonas stutzeri KC secretes a small but as yet unidentified factor that transforms carbon tetrachloride (CT) to CO₂ and nonvolatile products when activated by reduction at cell membranes. Pseudomonas fluorescens and other cell types activate the factor. Triparental mating was used to generate kanamycin-resistant lux::Tn5 recombinants of strain KC. Recombinants were streaked onto the surface of agar medium plugs in microtiter plates and were then screened for carbon tetrachloride degradation by exposing the plates to gaseous ¹⁴C-carbon tetrachloride. CT⁺ recombinants generated nonvolatile ¹⁴C-labeled products, but four CT^– recombinants did not generate significant nonvolatile ¹⁴C-labeled products and had lost the ability to degrade carbon tetrachloride. When colonies of P. fluorescens were grown next to colonies of CT⁺ recombinants and were exposed to gaseous ¹⁴C-carbon tetrachloride, ¹⁴C-labeled products accumulated around the P. fluorescens colonies, indicating that the factor secreted by CT⁺ colonies had diffused through the agar and become activated. When P. fluorescens was grown next to CT^– colonies, little carbon tetrachloride transformation was observed, indicating a lack of active factor. Expression of lux reporter genes in three of the CT^– mutants was regulated by added iron and was induced under the same iron-limiting conditions that induce carbon tetrachloride transformation in the wild-type. Received: 23 November 1998 / Accepted: 15 March 1999     

Characterization of a metal resistant Pseudomonas sp. isolated from uranium mine for its potential in heavy metal (Ni2+, Co2+, Cu2+, and Cd2+) sequestration

Heavy metal sequestration by a multimetal resistant Pseudomonas strain isolated from a uranium mine was characterized for its potential application in metal bioremediation. 16S rRNA gene analysis revealed phylogenetic relatedness of this isolate to Pseudomonas fluorescens. Metal uptake by this bacterium was monophasic, fast saturating, concentration and pH dependent with maximum loading of 1048 nmol Ni²⁺ followed by 845 nmol Co²⁺, 828 nmol Cu²⁺ and 700 nmol Cd²⁺ mg^?1 dry wt. Preferential metal deposition in cell envelope was confirmed by TEM and cell fractionation. FTIR spectroscopy and EDX analysis revealed a major role of carboxyl and phosphoryl groups along with a possible ion exchange mechanism in cation binding. Binary system demonstrated selective metal binding affinity in the order of Cu²⁺ > Ni²⁺ > Co²⁺ > Cd²⁺. A comparison with similar metal uptake reports considering live bacteria strongly indicated the superiority of this strain in metal sequestration, which could be useful for developing efficient metal removal system.     

Phylogenetic analysis of alkaline proteinase producing fluorescent pseudomonads associated with green gram (<Emphasis Type="Italic">Vigna radiata</Emphasis> L.) rhizosphere

Fifty fluorescent pseudomonads were isolated from rhizospheric soil of green gram from nearby area of Kaziranga, Assam, India and assayed for their extracellular proteinase production. Out of these isolates, 20 were found to be prominent in proteinase production. Genetic diversity of the 20 isolates were analyzed through BOX-PCR fingerprinting and 16S rDNA-RFLP along with three reference strains, viz., Pseudomonas fluorescens (NCIM2099^T), Pseudomonas aureofaciens (NCIM2026^T), and Pseudomonas aeruginosa (MTCC2582^T). BOX-PCR produced two distinct clusters at 56% similarity coefficient and seven distinct BOX profiles. 16S rDNA-RFLP with three tetra-cutters restriction enzymes (HaeIII, AluI, and MspI) revealed two major clusters A and B; cluster A contained only single isolate FPS9 while the rest of 22 isolates belonged to the cluster B. Based on phenotypic characters and 16S rDNA sequence similarity, all the eight highly proteinase-producing strains were affiliated with P. aeruginosa. The proteinase was extracted from two most prominent strains (KFP1 and KFP2), purified by a three-step process involving (NH₄)₂SO₄ precipitation, gel filtration, and ion exchange chromatography. The enzyme had an optimal pH of 8.0 and exhibit highest activity at 60°C and 37°C by KFP1 and KFP2 respectively. The specific activities were recorded as 75,050 (for KFP1) and 81,320 U/mg (for KFP2). The purified enzyme was migrated as a single band on native and SDS-PAGE with a molecular mass of 32 kDa. Zn²⁺, Cu²⁺, and Ni²⁺ ion inhibited the enzyme activity. Enzyme activity was also inhibited by EDTA established as their metallo-proteinase nature.     

Partial purification and some properties of urease from the alkaliphilic cyanobacteriumNostoc calcicola

Urease extracted from an alkaliphilic diazotrophic cyanobacteriumNostoc calcicola was partially purified and some of its properties were studied. Urease purified 39-fold from the crude enzyme extract showed its optimum activity at pH 7.5 and at 40°C with aK _m value of 120 μmol/L. The enzyme was found to be sensitive to metal cations, particularly Hg²⁺, Ag⁺ and Cu²⁺. 4-Hydroxymercuribenzoate (a mercapto-group inhibitor) and acetohydroxamic acid (a chelating agent of nickel) inhibited, the enzyme activity completely. These results suggest the involvement of an SH-group and Ni²⁺ in the activity of urease fromN. calcicola.     

Phytoremediation and absorption isotherms of heavy metal ions by Convolvulus tricolor (CTC)

In recent years, use of plants for remediation of contaminated soils, especially removal of heavy metals, is considered. The current study tends to investigate the removal of lead and nickel ions by the Convolvulus tricolor (CTC), was grown for 30 days in different concentrations of lead and nickel ions. Then concentration of them in soil and different organs of the plant was measured by atomic absorption spectrometry.

The highest absorbed of them occurred in concentration 0.001N, which highest Pb²⁺ accumulation is in the aerial parts of the plant: leaf > stem > root and for Ni²+: root > stem > leaf. No ion was observed into the flowers and nickel ion absorption is more of lead ion in different plant organs of CTC.

The experimental isotherm data were investigated using isotherms of Langmuir, Freundlich, BET, Temkin and Dubinin–Radushkevich (DRK). The correlation coefficient for all of them is calculated that show the best correlation coefficient for Ni²⁺ adsorption is obtained BET model, whereas for Pb²⁺ adsorption in root is Freundlich model but for its leaf and stem is BET model. The results show, CTC is suitable for Pb²⁺ and Ni²⁺ and this technique is in-situ method, simple, and low cost.     

Purification and properties of fluoroacetate dehalogenase from <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> DSM 8341

The degradation of fluoroacetate by microorganisms has been established for some time, although only a handful of dehalogenases capable of hydrolyzing the stable C–F bond have been studied. Pseudomonas fluorescens DSM 8341 was originally isolated from soil and readily degrades fluoroacetate, thus it was thought that its dehalogenase might have some desirable properties. The enzyme was purified from cell-free extracts and characterised: it is a monomer of 32,500 Da, with a pH optimum of 8 and is stable between pH 4 and 10; its activity is stimulated by some metal ions (Mg²⁺, Mn²⁺ and Fe³⁺), but inhibited by others (Hg²⁺, Ag²⁺). The enzyme is specific for fluoroacetate, and the K _m for this substrate (0.68 mM) is the lowest determined for enzymes of this type that have been investigated to date.     

Metal Sorption to Pseudomonas fluorescens: Influence of pH,Ionic Strength and Metal Concentrations

Migration behavior of radionuclides should be understood in order to estimate the impact of high-level radioactive waste (HLW) disposal on the environment. Bacteria, one of the major organic sorbents in solid and aquatic environments, can affect the fate of actinides and lanthanides by sorption onto their cell surfaces. In this study, the sorption of the radionuclide Americium (Am(III)) and several metal ions (Eu(III), Cu(II) and Ca(II)) to Pseudomonas fluorescens were measured under various conditions. It was revealed that as pH decreased, the sorption of Eu(III) and Am(III) increased when the metals were at relatively low concentrations but decreased at higher metal concentrations. On the other hand, sorption of Cu(II) followed the opposite trend. In the case of calcium, an increase in calcium ions was observed due to release from the cells. These findings suggest that the sorption mechanisms for low levels of Eu(III) and Am(III) on the cells of Pseudomonas fluorescens are different from those of Cu(II), Ca(II), and high concentrations of Eu(III) (> 10 ^{? 5} M).     

Effect of Pseudomonas fluorescens RB4 and Bacillus subtilis 189 on the phytoremediation potential of Catharanthus roseus (L.) in Cu and Pb-contaminated soils

The remediation of heavy metal-contaminated soils has become a critical issue due to toxic effects of these metals on living organisms. The current research was conducted to study the effect of Pseudomonas fluorescens RB4 and Bacillus subtilis 189 on the growth and phytoremediation potential of Catharanthus roseus in Cu- and Pb-contaminated soils. The bacterial strains exhibited significantly higher level of water-extractable Pb and Cu in Pb, Cu, and Cu+Pb-contaminated. The P. fluorescens RB4 inoculated plants, produced 102%, 48%, and 45% higher fresh weight (FW) in soils contaminated with Cu, Pb, and both elements, respectively, as compared to un-inoculated control plants. Similarly, B. subtilis 189 inoculated plants produced 108%, 43%, and 114% more FW in the presence of Cu, Pb, and both elements. The plants co-cultivated with both bacteria exhibited 121%, 102%, and 177% higher FW, in Cu, Pb, and both elements contaminated soils, as compared to respective un-inoculated control. Co-cultivation of P. fluorescens RB4, B. subtilis 189, and P. fluorescens RB4 + B. subtilis 189 resulted in higher accumulation of Cu and Pb in shoots of the C. roseus grown in contaminated soils as compared to un-inoculated control. Bacterial treatments also improved the translocation and metal bioconcentration factors. The growth and phytoextraction capability of C. roseus was improved by inoculation of P. fluorescens RB4 and B. subtilis 189.     

The Effect of Pseudomonas fluorescens and Fusarium oxysporum f.sp. cubense on Induction of Defense Enzymes and Phenolics in Banana

The effect of Pseudomonas fluorescens treatment and Fusarium oxysporum f. sp. cubense inoculation on induction of phenylalanine ammonia-lyase (PAL), peroxidase (POX), chitinase, -1,3-glucanase and accumulation of phenolics in banana (Musa sp.) was studied. When banana roots were treated with P. fluorescens strain Pf10, a two-fold increase in phenolic content in leaf tissues was recorded 3 – 6 d after treatment. Challenge inoculation with F. oxysporum, the wilt pathogen, steeply increased the phenolic content in P. fluorescens-treated banana plants. Significant increase in POX activity was detected 6 – 9 d after P. fluorescens treatment. PAL, chitinase and -1,3-glucanase activities increased significantly from 3 d after P. fluorescens treatment and reached the maximum 6 d after treatment. Challenge inoculation with F. oxysporum further increased the enzyme activities. These results suggest that the enhanced activities of defense enzymes and elevated content of phenolics may contribute to bioprotection of banana plants against F. oxysporum.     

A comparison of enzyme-aided bleaching of softwood paper pulp using combinations of xylanase, mannanase and α-galactosidase

Enzymatic pretreatment of softwood kraft pulp was investigated using xylanase A (XylA) from Neocallimastix patriciarum in combination with mannanase and α-galactosidase. Mannanase A (ManA) from Pseudomonas fluorescens subsp. cellulosa and ManA from Clostridium thermocellum, both family 26 glycosyl hydrolases, are structurally diverse and exhibit different pH and temperature optima. Although neither mannanase was effective in pretreating softwood pulp alone, both enzymes were able to enhance the production of reducing sugar and the reduction of single-stage bleached κ number when used with the xylanase. Sequential incubations with XylA and P. fluorescens ManA produced the largest final κ number reduction in comparison to control pretreated pulp. The release of galactose from softwood pulp by α-galactosidase A (AgaA) from P. fluorescens was enhanced by the presence of ManA from the same microorganism, and a single pretreatment with these enzymes, in combination with XylA, gave the most effective κ number reduction using a single incubation. Results indicated that mixtures of hemicellulase activities can be chosen to enhance pulp bleachability. Received: 16 August 1999 / Received revision: 13 December 1999 / Accepted: 15 December 1999     

Effect of Ni2+ on Early Stages of Chlorophyll Biosynthesis and Pheophytinization in Euglena gracilis

The effect of Ni²⁺ on the early stages of chlorophyll biosynthesis and pheophytinization in Euglena gracilis cells was studied. Incubation of the cells with 10^–4 M Ni²⁺ for 7 days resulted in a higher chlorophyll content, enhanced production of 5-aminolevulinic acid (ALA), and in increased activity of 5-aminolevuluinic acid dehydratase (EC 4.2.1.24, ALAD), as compared to the control cells incubated without Ni²⁺. At a higher concentration (10^–3 M), Ni²⁺ markedly inhibited chlorophyll accumulation and ALAD activity, as compared to the control cells. At this concentration, Ni²⁺ also inhibited heme biosynthesis and strongly stimulated ALA production. It seems likely that, by affecting heme synthesis, Ni²⁺ increases the activity of the ALA production system. However, the suppression of subsequent stages of ALA conversion to chlorophyll, in particular ALAD inhibition, ultimately resulted in almost complete inhibition of chlorophyll biosynthesis. In addition to cessation of de novo chlorophyll synthesis in the presence of Ni²⁺ (10^–3 M) in Euglena cells, the existing chlorophyll was converted into pheophytin and almost completely degraded. We suppose that the Ni²⁺-induced pheophytinization is caused by an acidic shift of intracellular pH related to an impairment of cell membrane permeability by Ni²⁺ cations.     

Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp. lycopersici

Pseudomonas fluorescens isolate Pf1 was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici. Induction of defense proteins and chemicals by P. fluorescens isolate Pf1 against challenge inoculation with F. oxysporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F. oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5^th day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2^nd day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4^th day while activity of PPO reached maximum at the 5^th day after challenge inoculation. Isoform analysis revealed that a unique PPO1 isoform was induced and PO1 and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, -1,3 glucanase, chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to P. fluorescens isolate Pf1 treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pf1-treated root tissues challenged with the pathogen but also in roots treated with P. fluorescens isolate Pf1 alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F. oxysporum f. sp. lycopersici in tomato roots.     

Enhancement of Glutaraldehyde Biocidal Efficacy by the Application of an Electric Field. Effect on Sessile Cells and on Cells Released by the Biofilm

Summary The aim of this paper was to evaluate the possible enhancement of the biocidal efficacy of glutaraldehyde against Pseudomonas fluorescens biofilms by the application of an electric field. The behaviour of sessile cells and cells released by the biofilms was assed. Biofilms were formed on thin stainless steel coupons immersed in culture media inoculated with Pseudomonas fluorescens. Treatments using glutaraldehyde (TGA) and both glutaraldehyde and electric field application (TGAEF) were carried out with the samples with biofilms. TGA: samples with biofilms were immersed in glass cells containing a buffer solution with different glutaraldehyde concentrations in the 25–500 ppm range. TGAEF: samples with biofilms were immersed in an electrochemical cell containing glutaraldehyde solution where a direct electric current (4 × 10⁻⁴ A cm⁻²) was delivered to the chamber. The evolution of biofilms was observed through optical microscopy at real time. Results show that the electric field enhanced glutaraldehyde efficacy reducing the number of surviving cells in the range of one to four orders with respect to those with TGA treatment. The sensitivity of the cells to the treatments decreased in the following order: planktonic cells > cells released by the biofilm > sessile cells.