Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

Effect of ammonia on the anaerobic degradation of protein by a mesophilic and thermophilic biowaste population

The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was investigated. For peptone concentrations from 5 g l⁻¹ to 20 g l⁻¹ the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l⁻¹ day⁻¹ compared to 320 mg l⁻¹ day⁻¹ at 10 g l⁻¹ peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH₃/g peptone in the mesophilic cultures. If 0.5–6.5 g l⁻¹ ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand (COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures were most active if around 1 g ammonia l⁻¹ was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and methane formation revealed a K _i (50%) for NH₃ of 92, 95 and 88 mg l⁻¹ at 37 °C and 251, 274 and 297 mg l⁻¹ at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH₃ than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 10⁸ peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only 5.6 × 10⁷ cfu/ml was observed. Received: 24 April 1998 / Received revision: 26 June 1998 / Accepted: 27 June 1998     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

Enhanced degradation of phenol by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. CP4 entrapped in agar and calcium alginate beads in batch and continuous processes

Phenol is one of the major toxic pollutants in the wastes generated by a number of industries and needs to be eliminated before their discharge. Although microbial degradation is a preferred method of waste treatment for phenol removal, the general inability of the degrading strains to tolerate higher substrate concentrations has been a bottleneck. Immobilization of the microorganism in suitable matrices has been shown to circumvent this problem to some extent. In this study, cells of Pseudomonas sp. CP4, a laboratory isolate that degrades phenol, cresols, and other aromatics, were immobilized by entrapment in Ca-alginate and agar gel beads, separately and their performance in a fluidized bed bioreactor was compared. In batch runs, with an aeration rate of 1 vol⁻¹ vol⁻¹ min⁻¹, at 30°C and pH 7.0 ± 0.2, agar-encapsulated cells degraded up to 3000 mg l⁻¹ of phenol as compared to 1500 mg l⁻¹ by Ca-alginate-entrapped cells whereas free cells could tolerate only 1000 mg l⁻¹. In a continuous process with Ca-alginate entrapped cells a degradation rate of 200 mg phenol l⁻¹ h⁻¹ was obtained while agar-entrapped cells were far superior and could withstand and degrade up to 4000 mg phenol l⁻¹ in the feed with a maximum degradation rate of 400 mg phenol l⁻¹ h⁻¹. The results indicate a clear possibility of development of an efficient treatment technology for phenol containing waste waters with the agar-entrapped bacterial strain, Pseudomonas sp. CP4.     

Effects of plant growth regulators and sucrose on post harvest physiology,membrane stability and vase life of cut spikes of gladiolus

Effects of post-harvest application of two plant growth regulators viz., gibberellic acid (GA₃) and benzyl adenine (BA) with sucrose in the vase solution on cell membrane stability and vase life of gladiolus were investigated. The vase solution treatment combinations of GA₃ and BA with sucrose significantly increased the membrane stability index and enhanced the vase life as compared to the sucrose alone treatments or the controls. Vase solution treatment of GA₃ (50 mg l⁻¹), followed by BA (50 mg l⁻¹) with sucrose (50 g l⁻¹) significantly increased solution uptake, fresh weight and dry weight of cut spikes. The same treatments also enhanced the concentration of reducing and non-reducing sugars in gladioli petals 4 days after treatment (DAT). Cut spikes in vase solution enriched with 50 mg l⁻¹ GA₃ + 50 g l⁻¹ sucrose showed higher antioxidative enzyme activities of superoxide dismutase (SOD) and glutathione reductase (GR), lower lipoxygenase (LOX) activity and lipid peroxidation (measured as TBARS). Petal membrane stability index was also highest in cut spikes 6 DAT with 50 mg l⁻¹ GA₃ + 50 g l⁻¹ sucrose vase solution. Treatment of gladiolus cut spikes with 50 mg l⁻¹ GA₃ + 50 g l⁻¹ sucrose vase solution showed two fold increase in vase life and improved flower quality with a higher number of open flower per spike at any one time. These results suggest that post-harvest application of GA₃ (50 mg l⁻¹) with sucrose (50 g l⁻¹) maintains higher spike fresh and dry weight, improves anti-oxidative defence, stabilizes membrane integrity leading to a delay in petal cell death.     

Aerobic cometabolic degradation of trichloroethene by methane and ammonia oxidizing microorganisms naturally associated with <Emphasis Type="Italic">Carex comosa</Emphasis> roots

The degradation potential of trichloroethene by the aerobic methane- and ammonia-oxidizing microorganisms naturally associated with wetland plant (Carex comosa) roots was examined in this study. In bench-scale microcosm experiments with washed (soil free) Carex comosa roots, the activity of root-associated methane- and ammonia-oxidizing microorganisms, which were naturally present on the root surface and/or embedded within the roots, was investigated. Significant methane and ammonia oxidation were observed reproducibly in batch reactors with washed roots incubated in growth media, where methane oxidation developed faster (2 weeks) compared to ammonia oxidation (4 weeks) in live microcosms. After enrichment, the methane oxidizers demonstrated their ability to degrade 150 μg l⁻¹ TCE effectively at 1.9 mg l⁻¹ of aqueous CH₄. In contrast, ammonia oxidizers showed a rapid and complete inhibition of ammonia oxidation with 150 μg l⁻¹ TCE at 20 mg l⁻¹ of NH₄ ⁺-N, which may be attributed to greater sensitivity of ammonia oxidizers to TCE or its degradation product. No such inhibitory effect of TCE degradation was detected on methane oxidation at the above experimental conditions. The results presented here suggest that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments.     

Resorcinol degradation by a <Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> strain under osmotic stress: mono and binary substrate matrices with phenol

A phenol-degrading Penicillium chrysogenum strain previously isolated from a salt mine was able to grow at 1,000 mg l⁻¹ of resorcinol on solid medium. The aerobic degradation of resorcinol by P. chrysogenum CLONA2 was studied in batch cultures in minimal mineral medium with 58.5 g l⁻¹ of sodium chloride using resorcinol as the sole carbon source. The fungal strain showed the ability to degrade up to 250 mg l⁻¹ of resorcinol. Resorcinol and phenol efficiency degradation by P. chrysogenum CLONA2 was compared. This strain removes phenol faster than resorcinol. When phenol and resorcinol were in binary substrate matrices, phenol enhanced resorcinol degradation, and organic load decreased with respect to the mono substrate matrices. The acute toxicity of phenol and resorcinol, individually and in combination, to Artemia franciscana larvae has been verified before and after the bioremediation process with P. chrysogenum CLONA2. The remediation process was effective in mono and binary substrate systems.     

Enhanced regeneration of haploid plantlets from microspores of <Emphasis Type="Italic">Brassica napus</Emphasis> L. using bleomycin,PCIB, and phytohormones

The effects of three periods of incubation (10, 20 and 30 min) at different levels of bleomycin (0, 0.1, 0.2, 0.3, 0.4 and 0.5 μg ml⁻¹), as well as three periods of exposure (12, 24 and 48 h) to different levels of the anti-auxin p-chlorophenoxyisobutyric acid (PCIB), including 1, 2, 3, 4 and 5 mg l⁻¹, on microspore embryogenesis of rapeseed cv. ‘Amica’ were investigated. Microspore embryogenesis was significantly enhanced following 20 min treatment with 0.2 μg ml⁻¹ bleomycin compared with untreated cultures. Highest embryo yield (163 embryos Petri dish⁻¹) was observed with 24 h treatment of 4 mg l⁻¹ PCIB. The highest percentage of secondary embryogenesis was observed on B₅ medium containing 0.15 mg l⁻¹ of gibberellic acid (GA₃) and 0.2 mg l⁻¹ 6-benzyladenine (BA) in 4–6 mm microspore-derived embryos (MDEs). Most callus formed on B₅ medium containing 0.15 mg l⁻¹ GA₃, 0.1 mg l⁻¹ BA and 0.1 mg l⁻¹ indole-3-acetic acid (IAA) when 4–6 mm embryos were used. Regeneration was highest on B₅ medium containing 0.05 mg l⁻¹ GA₃ or 0.1 mg l⁻¹ BA and 0.2 mg l⁻¹ IAA with 2–4 mm embryos. Microspore embryogenesis and plant regeneration could be improved by both bleomycin and PCIB when the appropriate MDE length and phytohormone level were selected.     

Denitrification of a landfill leachate with high nitrate concentration in an anoxic rotating biological contactor

The denitrification performance of a lab-scale anoxic rotating biological contactor (RBC) using landfill leachate with high nitrate concentration was evaluated. Under a carbon to nitrogen ratio (C/N) of 2, the reactor achieved N-NO₃ ⁻ removal efficiencies above 95% for concentrations up to 100 mg N-NO₃ ⁻ l⁻¹. The highest observed denitrification rate was 55 mg N-NO₃ ⁻ l⁻¹ h⁻¹ (15 g N-NO₃ ⁻ m⁻² d⁻¹) at a nitrate concentration of 560 mg N-NO₃ ⁻ l⁻¹. Although the reactor has revealed a very good performance in terms of denitrification, effluent chemical oxygen demand (COD) concentrations were still high for direct discharge. The results obtained in a subsequent experiment at constant nitrate concentration (220 mg N-NO₃ ⁻ l⁻¹) and lower C/N ratios (1.2 and 1.5) evidenced that the organic matter present in the leachate was non-biodegradable. A phosphorus concentration of 10 mg P-PO₄ ³⁻ l⁻¹ promoted autotrophic denitrification, revealing the importance of phosphorus concentration on biological denitrification processes.     

Aerobic biodegradation of nitrobenzene by a defined microbial consortium immobilized in polyurethane foam

An aerobic microbial consortium constructed by the combination of Rhodotorula mucilaginosa Z1, Streptomyces albidoflavus Z2 and Micrococcus luteus Z3 was immobilized in polyurethane foam and its ability to degrade nitrobenzene was investigated. Batch experimental results showed that polyurethane-foam-immobilized cells (PFIC) more efficiently degrade 200–400 mg l⁻¹ nitrobenzene than freely suspended cells (FSC). Kinetics of nitrobenzene degradation by PFIC was well described by the Andrews equation. Compared with FSC, PFIC exhibited better reusability (over 100 times) and tolerated higher shock-loadings of nitrobenzene (1,000 mg l⁻¹). Moreover, In the presence of salinity (≤5% NaCl, w/v), phenol (≤150 mg l⁻¹) and aniline (≤50 mg l⁻¹), respectively, degradation efficiency of nitrobenzene by PFIC reached over 95%. Even in the presence of both 100 mg l⁻¹ phenol and 50 mg l⁻¹ aniline, over 75% nitrobenzene was removed by PFIC in 36 h. Therefore, the immobilization of the defined consortium in polyurethane foam has application potential for removing nitrobenzene in industrial wastewater treatment system.     

Comparison of saccharification process by acid and microwave-assisted acid pretreated swine manure

The saccharification process of swine manure by conventional and microwave-assisted acid pretreated were investigated using cellulose enzymes, respectively. The optima for microwave-assisted acid pretreated swine manure is achieved when swine manure of 50 g l⁻¹ of substrate concentration and water amount 40 ml was pretreated by 4% H₂SO₄ concentration with 445 W microwave powers for 30 min at pretreatment period, and temperature 50 °C, enzyme loading 2 mg g⁻¹ substrate, substrate concentration 5 g l⁻¹ and initial medium pH 4.8 at enzymes hydrolysis period by microwave-assisted acid pretreated, respectively. The optimal conditions by conventional acid pretreated is obtained when 50 g l⁻¹ swine manure was submerged in 40 ml, 4% H₂SO₄ maintained at 130 °C for 3 h at pretreatment period, and temperature 45 °C, enzyme loading 2 mg g⁻¹ substrate, substrate concentration 15 g l⁻¹ and initial medium pH 5.2 at enzymes hydrolysis period, respectively. Under the optimum conditions microwave-assisted acid pretreatment could achieve higher yield of reducing sugar, short reaction time, and lower energy consumption than from the conventional acid pretreatment, which indicates that microwave-assisted acid pretreatment is more suitable for swine manure pretreatment than by acid alone.     

Bioenergetics and RNA/DNA ratios in the common carp (Cyprinus carpio ) under hypoxia

Hypoxia caused by eutrophication occurs over large areas in aquatic systems worldwide. Common carp (Cyprinus carpio) exposed to hypoxia (1 mg · O₂ · l⁻¹ and 2 mg · O₂ · l⁻¹) for 1 week showed a significant reduction in feeding rate, respiration rate, faecal production and nitrogenous excretion compared to those maintained at normoxia (7 mg · O₂ · l⁻¹). Fish exposed to hypoxia showed negative scope for growth (SfG), but no significant difference in the specific growth rate was revealed after 1 week in both hypoxic groups. A significant reduction in RNA/DNA ratio was, however, clearly evident in the white muscle of the 1 mg · O₂ · l⁻¹ treatment group, but not in the 2 mg · O₂ · l⁻¹ treatment group. Both specific growth rate and RNA/DNA ratio were significantly reduced when fish were exposed to severe hypoxia (0.5 mg · O₂ · l⁻¹) for 4 weeks. At all levels of hypoxia, growth reduction was accompanied by a significant decrease in RNA/DNA ratio in white muscle. Covariance analysis showed no significant difference between the slope of RNA/DNA ratio and growth rate under normoxic conditions and 0.5 mg · O₂ · l⁻¹ for 4 weeks (F=1.036, P > 0.326), as well as 1.0 mg · O₂ · l⁻¹ and 2.0 mg · O₂ · l⁻¹ for 1 week (F = 0.457, P > 0.5), indicating that the RNA/DNA ratio serves as a biomarker of growth under all oxygen levels, at least under controlled experimental conditions. SfG also appears to be more sensitive than the RNA/DNA ratio in responding to hypoxia in fish. Accepted: 15 September 2000     

Asparagus racemosus cell cultures: a source for enhanced production of shatavarins and sarsapogenin

Asparagus racemosus is an important monocot medicinal plant that is in great demand for its steroidal saponins called shatavarins. This study was initiated to optimize the conditions for production of shatavarins in cell cultures of A. racemosus in a modified Murashige and Skoog (MS) medium supplemented with six different combinations of growth regulators. Biomass accumulation was correlated with saponin production over a 30-d culture cycle. Biomass and saponin accumulation patterns were dependent on combinations of growth regulators and the pH of the medium. Maximum levels of saponin and biomass accumulation were recorded on day 25 of the culture cycle within a pH range of 3.4 to 5.6. Total saponin produced by the in vitro cultures was 20-fold higher than amounts produced by cultivated plants. Saponin accumulation was not a biomass-associated phenomenon; cultures which showed the highest biomass accumulation were not the highest saponin accumulators. Maximum biomass (28.30 ± 0.29 g l⁻¹) and maximum levels of shatavarin IV(11.48 ± 0.61 mg g⁻¹) accumulation was found using a medium containing 2.0 mg l⁻¹ 2,4-D, 2 g l⁻¹ casein hydrolysate and 0.005% pectinase. The highest levels of sarsapogenin, secreted and intracellular (4.02 ± 0.09 mg g⁻¹), accumulated using a medium containing 1.0 mg l⁻¹ NAA, 1.0 mg l⁻¹ 2,4-D, 0.5 mg l⁻¹ BAP, 2 g l⁻¹ casein hydrolysate and 0.005% pectinase, after 25 d. Shatavarins were secreted into the medium and can be isolated easily for further purification.     

Evaluation of enrichments of sulfate reducing bacteria from pristine hydrothermal vents sediments as potential inoculum for reducing trichloroethylene

The evaluation of enrichments from pristine hydrothermal vents sediments on its capability of reducing trichloroethylene (TCE) under sulfate reducing conditions with lactate and volatile fatty acids (VFAs) as substrates was performed. Effect of the possible TCE biodegradation intermediates cis and trans 1,2 dichloroethenes on sulfate reduction (SR) was also evaluated. The influence of cyanocobalamin (CNB₁₂) and riboflavin (RF) on the SR and biodegradation of TCE was also determined. Sediments from the vents were incubated at 37°C and supplemented with 4 g l⁻¹ SO₄ ²⁻, lactate or VFAs and amended in the corresponding treatments with either CNB₁₂ or RF in separated experiments. A percentage of TCE removal of 86 (150 μmol l⁻¹ initial concentration) was attained coupled to 48% sulfate depletion with lactate as substrate. Up to 93% removal of TCE (300 μmol l⁻¹ initial concentration) and 40% of sulfate was reached for VFAs as electron donor. A combination of lactate and CNB₁₂ yielded the best SR. The overall results suggest a syntrophic association in this microbial community in which sulfate reducers, dehalogenating, and probably halorespiring bacteria may be interacting and taking advantage of the fermentation of substrates differently, but without interruption of SR in spite of the fact that TCE was always present. It was also clear that sulfate reduction must be established in the cultures before any degradation can occur. The microbial community present in these hydrothermal vents sediments could be a new source of inoculum for bioreactors designed for dechlorination purposes.     

Statistical medium optimization for enhanced azadirachtin production in hairy root culture of Azadirachta indica

Azadirachtin, a well-known biopesticide, is a secondary metabolite extracted from the seeds of Azadirachta indica. In the present study, azadirachtin was produced in hairy roots of A. indica, generated by Agrobacterium rhizogenes-mediated transformation of leaf explants. Liquid cultures of A. indica hairy roots were developed with a liquid-to-flask volume ratio of 0.15. The kinetics of growth and azadirachtin production were established in a basal plant growth medium containing MS medium major and minor salts, Gamborg’s medium vitamins, and 30 g l⁻¹ sucrose. The highest azadirachtin accumulation in the hairy roots (up to 3.3 mg g⁻¹) and azadirachtin production (∼44 mg l⁻¹) was obtained on Day 25 of the growth cycle, with a biomass production of 13.3 g l⁻¹ dry weight. To enhance the production of azadirachtin, a Plackett–Burman experimental design protocol was used to identify key medium nutrients and concentrations to support high root biomass production and azadirachtin accumulation in hairy roots. The optimal nutrients and concentrations were as follows: 40 g l⁻¹ sucrose, 0.19 g l⁻¹ potassium dihydrogen phosphate, 3.1 g l⁻¹ potassium nitrate, and 0.41 g l⁻¹ magnesium sulfate. Concentrations were determined by a central composite design protocol and verified in shake-flask cultivation. The optimized medium composition yielded a root biomass production of 14.2 g l⁻¹ and azadirachtin accumulation of 5.2 mg g⁻¹, which was equivalent to an overall azadirachtin production of 73.84 mg l⁻¹, 68% more than that obtained under non-optimized conditions.     

Characterization of Candida sp. NY7122, a novel pentose-fermenting soil yeast

Yeasts that ferment both hexose and pentose are important for cost-effective ethanol production. We found that the soil yeast strain NY7122 isolated from a blueberry field in Tsukuba (East Japan) could ferment both hexose and pentose (d-xylose and l-arabinose). NY7122 was closely related to Candida subhashii on the basis of the results of molecular identification using the sequence in the D1/D2 domains of 26S rDNA and 5.8S-internal transcribed spacer region. NY7122 produced at least 7.40 and 3.86 g l⁻¹ ethanol from 20 g l⁻¹ d-xylose and l-arabinose within 24 h. NY7122 could produce ethanol from pentose and hexose sugars at 37°C. The highest ethanol productivity of NY7122 was achieved under a low pH condition (pH 3.5). Fermentation of mixed sugars (50 g l⁻¹ glucose, 20 g l⁻¹ d-xylose, and 10 g l⁻¹ l-arabinose) resulted in a maximum ethanol concentration of 27.3 g l⁻¹ for the NY7122 strain versus 25.1 g l⁻¹ for Scheffersomyces stipitis. This is the first study to report that Candida sp. NY7122 from a soil environment could produce ethanol from both d-xylose and l-arabinose.     

The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol

A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam (PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR), packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation rate of phenol (q _s ^max) decreased in the order: PBRC (598 mg l⁻¹h⁻¹) > PBR (PU, 471 mg l⁻¹h⁻¹) > PBR (SG, 394 mg l⁻¹h⁻¹) > FBR (PU, 161 mg l⁻¹h⁻¹) > FBR (SG, 91 mg l⁻¹ h⁻¹). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized in colloidal SiO₂ enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic packing. Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000     

Enhanced phenol degradation by immobilized Acinetobacter sp. strain AQ5NOL 1

A locally isolated Acinetobacter sp. Strain AQ5NOL 1 was encapsulated in gellan gum and its ability to degrade phenol was compared with the free cells. Optimal phenol degradation was achieved at gellan gum concentration of 0.75% (w/v), bead size of 3 mm diameter (estimated surface area of 28.26 mm²) and bead number of 300 per 100 ml medium. At phenol concentration of 100 mg l⁻¹, both free and immobilized bacteria exhibited similar rates of phenol degradation but at higher phenol concentrations, the immobilized bacteria exhibited a higher rate of degradation of phenol. The immobilized cells completely degrade phenol within 108, 216 and 240 h at 1,100, 1,500 and 1,900 mg l⁻¹ phenol, respectively, whereas free cells took 240 h to completely degrade phenol at 1,100 mg l⁻¹. However, the free cells were unable to completely degrade phenol at higher concentrations. Overall, the rates of phenol degradation by both immobilized and free bacteria decreased gradually as the phenol concentration was increased. The immobilized cells showed no loss in phenol degrading activity after being used repeatedly for 45 cycles of 18 h cycle. However, phenol degrading activity of the immobilized bacteria experienced 10 and 38% losses after the 46 and 47th cycles, respectively. The study has shown an increased efficiency of phenol degradation when the cells are encapsulated in gellan gum.     

Substrate specificity of a recombinant ribose-5-phosphate isomerase from <Emphasis Type="Italic">Streptococcus pneumoniae</Emphasis> and its application in the production of <Emphasis Type="SmallCaps">l</Emphasis>-lyxose and <Emphasis Type="SmallCaps">l</Emphasis>-tagatose

A putative ribose-5-phosphate isomerase (RpiB) from Streptococcus pneumoniae was purified with a specific activity of 26.7 U mg⁻¹ by Hi-Trap Q HP anion exchange and Sephacryl S-300 HR 16/60 gel filtration chromatographies. The native enzyme existed as a 96-kDa tetramer with activity maxima at pH 7.5 and 35°C. The RpiB exhibited isomerization activity with l-lyxose, l-talose, d-gulose, d-ribose, l-mannose, d-allose, l-xylulose, l-tagatose, d-sorbose, d-ribulose, l-fructose, and d-psicose and exhibited particularly high activity with l-form monosaccharides such as l-lyxose, l-xylulose, l-talose, and l-tagatose. With l-xylulose (500 g l⁻¹) and l-talose (500 g l⁻¹) substrates, the optimum concentrations of RpiB were 300 and 600 U ml⁻¹, respectively. The enzyme converted 500 g l⁻¹ l-xylulose to 350 g l⁻¹ l-lyxose after 3 h, and yielded 450 g l⁻¹ l-tagatose from 500 g l⁻¹ l-talose after 5 h. These results suggest that RpiB from S. pneumoniae can be employed as a potential producer of l-form monosaccharides.     

The Green Microalga <Emphasis Type="Italic">Chlorella saccharophila</Emphasis> as a Suitable Source of Oil for Biodiesel Production

The aim of this study was to investigate the potential of the green microalga Chlorella saccharophila as a source of oil for biodiesel production. We evaluated for the first time, the effect of salinity and/or nitrogen depletion (ND) on cell growth, lipid accumulation and lipid profile in this microalga. The fatty acid methyl esters (FAME) identified for C. saccharophila in this study consisted of C-16:0, C-18:0, C-18:1 cis, and C-18:1 trans. Among these, C-18:1 (indicator of biodiesel quality) was the main FAME found, representing approximately 76 and 80% of total FAME under normal and ND growing conditions, respectively. Under a normal growing condition this microalga showed 154.63 mg l⁻¹ d⁻¹, 63.33 mg l⁻¹ d⁻¹, and 103.73 mg l⁻¹ of biomass productivity, lipid productivity, and FAME yield, respectively. The higher biomass productivity (159.58 mg l⁻¹ d⁻¹), lipid productivity (99.33 mg l⁻¹ d⁻¹), and FAME yield (315.53 mg l⁻¹) were obtained under the ND treatment. In comparison to other related studies, our results suggest that C. saccharophila can be considered as a suitable source of oil for biodiesel production.