Biodegradation study by Pseudomonas sp. of flexible polyurethane foams derived from castor oil

The synthesis and biodegradation of polyurethane foams obtained from environmentally benign processes were studied.Flexible polyurethane foams based on castor oil modified with maleic anhydride (MACO) were synthesized. The synthesis involved a single-stage process by mixing castor oil/MACO (weight ratios 75:25 and 25:75) and 2-4 toluene diisocyanate (TDI) in stoichiometric amount of OH:NCO. The biodegradability studies with cultures of a Pseudomonas sp. strain (DBFIQ-P36) involved incubation periods of 2 months at 37 °C. Polymers were characterized before and after biodegradation by Fourier Transform Infrared Spectroscopy (FT-IR), INSTRON mechanical tester, and Scanning Electron Microscopy (SEM). The results showed that the addition of MACO produces a considerable increase in the rate of degradation and an important change in the chemical and morphological structures. This is due to the presence of ester groups that are vulnerable to chemical hydrolysis and enzymatic attack. The eco-toxicity after the biodegradation was evaluated. Toxic compounds such as primary amines were identified by Gas Chromatography–Mass Spectrometry (GC–MS) in combination with Nuclear Magnetic Resonance (NMR) as degradation products.     

Biodegradation of phenanthrene by Pseudomonas sp. BZ-3, isolated from crude oil contaminated soil

A phenanthrene (PHE) degrading bacterium strain BZ-3 was isolated from the crude oil contaminated soil in Binzhou, China. The isolate was identified as Pseudomonas sp. BZ-3 on the basis of 16S rRNA gene sequence. Various experiments were conducted to investigate the effect of pH, salinity and PHE concentration on the degradation efficiency of PHE. The degradation efficiency and degradation metabolites of PHE were detected by using GC–MS and HPLC-MS analyses. The strain BZ-3 could degrade 75% of PHE at an initial concentration of 50 mg/L under 20 g/L salinity in 7 days. PHE degradation kinetics was estimated in a first-order degradation rate model and the rate coefficient was calculated as 0.108 d⁻¹. On the basis of the identified degradation metabolites, the strain BZ-3 could degrade PHE in the salicylate metabolic pathway. In a mixture system consisting of PHE and other PAHs including naphthalene (NA), anthracene (ANTH), and pyrene (PYR), the strain BZ-3 showed an efficiently degradation capability. Further study showed that the strain BZ-3 could also use NA, ANTH, PYR, xylene, 1-hydroxy-2-naphthoic acid, and hexane as the sole carbon and energy source, but did not grow on nitrobenzene-containing medium.     

Oxidation and reduction of plastoquinone by photosynthetic and respiratory electron transport in a cyanobacterium Synechococcus sp.

The I-D dip, an early transient of the fluorescence induction, was examined as a means to monitor redox changes of plastoquinone in cells of a cyanobacterium, Synechococcus sp. That the occurrence of the dip depends upon the reduced state of the plastoquinone pool was indicated by observations that 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not affect the initial rise to I but abolished the subsequent decline from I to D and that illumination of the cells with light 1, prior to fluorescence measurements, eliminated the transient. The I-D dip was prominent in freshly harvested cells containing abundant endogenous substrates, disappeared slowly as the cells were starved by aeration but reappeared on addition of fructose to the starved cells in the dark. The dip that had been induced by a brief illumination of the starved cells with light 2 was rapidly diminished in the dark and KCN inhibited the dark decay of the transient. The results indicate that plastoquinone is reduced with endogenous as well as exogenous substrates and oxidized by a KCN-sensitive oxidase in the dark, thus providing strong support for the view that plastoquinone of photosynthetic electron transport also functions in respiration. In addition, the occurrence of a cyclic pathway of electrons from Photosystem I to plastoquinone, possibly via ferredoxin or NADP, was suggested. Several lines of evidence indicate that, under a strong light 2, Photosystem I-dependent oxidation of plastoquinone predominates over Photosystem II-dependent reduction of the quinone in the cyanobacterium which contains Photosystem I more abundantly than Photosystem II.     

Novel strategy for biodegradation of 4-nitrophenol by the immobilized cells of Pseudomonas sp. YPS3 with Acacia gum

The mass organic compound 4-nitrophenol with low molecular is involved in many chemicals processes and most common organic pollutants. 4-Nitrophenol (4-NP) existing in soils and water bodies, thereby causing severe environmental impact and health risk. Even low concentrations are harmful to health and potential mutagenic and carcinogenic. Though the existing methods of biodegradation though effective, their popularity is hindered due to high cost. Hence, in the present study a less expensive method involving the use of Pseudomonas sp. with gum arabic (PAA) was tested. The biodegradation of 4-NP was thoroughly investigated by progressive characterization methods. The promising Pseudomonas sp. YPS 3 was identified with biochemical and molecular identification process. The average particle sizes of stable crystalline PAA was 8–20 nm. The experiments were conducted with optimized parameters viz., pH (7.0), concentration (30 ppm), temperature (37 °C) and time (6 h). The study was tested as adsorbent particle size on 4-NP concurrent adsorption-biodegradation. In addition, these Pseudomonas sp. YPS3 and its PAA are used as an eco-friendly for removal of toxic organic 4-NP pollutant from the ecosystems.     

Adaptation of Pseudomonas sp. GJ1 to 2-bromoethanol caused by overexpression of an NAD-dependent aldehyde dehydrogenase with low affinity for halogenated aldehydes

Pseudomonas sp. GJ1 is able to grow with 2-chloroethanol as the sole carbon and energy source, but not with 2-bromoethanol, which is toxic at low concentrations (1 mM). A muatnt that could grow on 2-bromoethanol with a growth rate of 0.034 h^–1 at concentrations up to 5 mM was isolated and designated strain GJ1M9. Measurement of enzyme activities showed that mutant and wild-type strains contained a PMS-linked alcohol dehydrogenase that was active with halogenated alcohols and that was threefold overexpressed in the mutant when grown on 2-chloroethanol, but only slightly overproduced when grown on 2-bromoethanol. Both strains also contained an NAD-dependent alcohol dehydrogenase that had no activity with halogenated alcohols. Haloacetate dehalogenase levels were similar in the wild-type and the mutant. Activities of NAD-dependent aldehyde dehydrogenase were only slightly higher in extracts of the mutant grown with 2-bromoethanol than in those of the wild-type grown with 2-chloroethanol. SDS-PAGE, however, showed that this enzyme amounted to more than 50% of the total cellular protein in extracts of the mutant from 2-bromoethanol-grown cells, which was fourfold higher than in extracts of the wild-type strain grown on 2-chloroethanol. The enzyme was purified and shown to be a tetrameric protein consisting of subunits of 55 kDa. The enzyme had low K_m values for acetaldehyde and other non-halogenated aldehydes (0.8–4 μM), but much higher K_m values for chloroacetaldehyde (1.7 mM) and bromoacetaldehyde (10.5 mM), while V_max values were similar for halogenated and non-halogenated aldehydes. Cultures that were pregrown on 2-chloroethanol rapidly lost aldehyde dehydrogenase activity after addition of 2-bromoethanol and chloroamphenicol, which indicates that bromoacetaldehyde inactivates the enzyme. To achieve growth with 2-bromoethanol, the high expression of the enzyme thus appears to be necessary in order to compensate for the high K_m for bromoacetaldehyde and for inactivation of the enzyme by bromoacetaldehyde. Received: 31 August 1995 / Accepted: 4 December 1995     

Purification and characterization of two extracellular peroxidases from Streptomyces sp. strain AM2, a decolorizing actinomycetes responsible for the biodegradation of natural humic acids

Two extracellular humic acids peroxidases called HaP1 and HaP2 were isolated from the Streptomyces sp. strain AM2 and, based on MALDI-TOF MS analysis. The purified enzymes were determined as monomers with molecular masses of 40,351.11 and 25,175.19 Da, respectively. The N-terminal amino acid sequences of HaP1 and HaP2 were identified, and their optimum pH values were determined as 6 and 7.5, respectively. Standard 2,4-dichlorophenol (2,4-DCP) assays showed that both enzymes had maximal activity at 55 °C. HaP2 was stable at 55 °C for more than 24 h and had a half-life of 90 min at 65 °C. Although the catalytic properties of HaP1 and HaP2 were nearly identical, their stabilities and Reinheitzahl (RZ) values were substantially different. Both peroxidases were found to be heme proteins that catalyzed the oxidation of a wide range of substrates in the presence of hydrogen peroxide (H₂O₂), with HaP2 exhibiting a broader range of substrate specificity. The characterization of peroxidase activity revealed activity against humic acids, guiacol, 2,4-DCP, l-3,4-dihydroxyphenylalanine, and 2,4,5-trichlorophenol as well as other chlorophenols in the presence of H₂O₂. However, the inhibition of peroxidase activity by the addition of potassium cyanide and sodium azide also indicated the presence of heme components in the tertiary structure of these enzymes.     

Hydrolysis of lignocellulosic feedstock by novel cellulases originating from Pseudomonas sp. CL3 for fermentative hydrogen production

A newly isolated indigenous bacterium Pseudomonas sp. CL3 was able to produce novel cellulases consisting of endo-β-1,4-d-glucanase (80 and 100 kDa), exo-β-1,4-d-glucanase (55 kDa) and β-1,4-d-glucosidase (65 kDa) characterized by enzyme assay and zymography analysis. In addition, the CL3 strain also produced xylanase with a molecular weight of 20 kDa. The optimal temperature for enzyme activity was 50, 45, 45 and 55 °C for endo-β-1,4-d-glucanase, exo-β-1,4-d-glucanase, β-1,4-d-glucosidase and xylanase, respectively. All the enzymes displayed optimal activity at pH 6.0. The cellulases/xylanase could hydrolyze cellulosic materials very effectively and were thus used to hydrolyze natural agricultural waste (i.e., bagasse) for clean energy (H₂) production by Clostridiumpasteurianum CH4 using separate hydrolysis and fermentation process. The maximum hydrogen production rate and cumulative hydrogen production were 35 ml/L/h and 1420 ml/L, respectively, with a hydrogen yield of around 0.96 mol H₂/mol glucose.     

One-step process for debromination and aerobic mineralization of tetrabromobisphenol-A by a novel Ochrobactrum sp. T isolated from an e-waste recycling site

A novel bacterium, Ochrobactrum sp. T, capable of simultaneous debromination and aerobic mineralization of tetrabromobisphenol-A (TBBPA), was isolated from a sludge sample collected from an electronic-waste recycling site. The bacterium exhibited maximal debrominase activity at pH 6.5, 35 °C, and 200 rpm in Luria-Bertani culture medium. Initial TBBPA concentration and pH had more significant effects on degradation efficiency than those of temperature and inoculum size. Degradation and debromination efficiencies of 91.8% and 86.7%, respectively, were achieved within 72 h under optimized conditions of 35 °C, pH 7.0, inoculum volume of 25 mL, and TBBPA concentration of 3 mg L⁻¹. In addition, a 35.6% decrease in total organic carbon was observed after the degradation of 5 mg L⁻¹ TBBPA for 120 h. Eight metabolic intermediates were identified during the biodegradation of TBBPA. This study is the first report to propose a one-step process for TBBPA debromination and mineralization by a single bacterial strain.     

Cr(VI) reduction by Enterobacter sp. DU17 isolated from the tannery waste dump site and characterization of the bacterium and the Cr(VI) reductase

Out of nineteen bacteria screened from the tannery waste dump site, the most effective isolate, strain DU17 was selected for Cr(VI) reduction process among the non-pathogenic once. Based on 16S rRNA gene sequence analysis, the bacterium was identified as Enterobacter sp. DU17. Its amplified Cr(VI) reductase gene showed maximum homology with flavoprotein of Enterobacter cloacae. Enterobacter sp. DU17 reduced Cr(VI) maximally at 37 °C and pH 7.0. Various co-metals, electron (e⁻) donors and inhibitors were tested to study their effect on Cr(VI) reduction. In presence (0.2% each) of glucose and fructose, Enterobacter sp. DU17 reduced Cr(VI) completely after 16 and 20 h, respectively. Since the concentration of total Cr was invariable after remediation as detected through AAS analysis, this experiment disclosed that responsible operation was associated with extracellular Cr(VI) reduction process rather than uptake mechanism. Multiple antibiotic resistance index of 0.08 for this bacterium was very low as compared to standard risk assessment value of 0.20. With high Cr(VI) reducing capability, non-pathogenicity and antibiotic sensitivity, Enterobacter sp. DU17 is found to be very efficient in removing Cr(VI) toxicity from the environment.