Biodegradation of phenolic compounds by sulfate-reducing bacteria from contaminated sediments

The biodegradation of phenolic compounds under sulfate-reducing conditions was studied in sediments from northern Indiana. Phenol, p-cresol and 4-chlorophenol were selected as test substrates and added to sediment suspensions from four sites at an initial concentration of 10 mg/liter. Degradative abilities of the sediment microorganisms from the four sites could be related to previous exposure to phenolic pollution. Time to onset of biodegradation of p-cresol and phenol in sediment suspensions from a nonindustrialized site was approximately 70 and 100 days, respectively, in unacclimated cultures. In sediment slurries from three sites with a history of wastewater discharges containing phenolics, time to onset of biodegradation was 50–70 days for p-cresol and 50–70 days for phenol in unacclimated cultures. In acclimated cultures from all four sites, the length of the lag phase was reduced to 14–35 days for p-cresol and 25–60 days for phenol. Length of the biodegradative phase varied from 25 to 40 days for phenol and 10 to 50 days for p-cresol and was not markedly affected by acclimation. Substrate mineralization by sulfate-reducing bacteria was confirmed with radiotracer techniques using an acclimated sediment culture from one site. Addition of molybdate, a specific inhibitor of sulfate reduction, and bacterial cell inactivation inhibited sulfate reduction and substrate utilization. None of the sites exhibited the ability to degrade 4-chlorophenol, nor were acclimated phenol and p-cresol degrading cultures from a particular site able to cometabolize 4-chlorophenol.Correspondence to: D. Dean-Ross     

Biodegradation and detoxification of phenolic compounds by pure and mixed indigenous cultures in aerobic reactors

Degradation and detoxification of a mixture of persistent compounds (2-chlorophenol, phenol and m-cresol) were studied by using pure and mixed indigenous cultures in aerobic reactors. Biodegradation assays were performed in batch and continuous flow reactors. Biodegradation was evaluated by determining total phenols, ultraviolet spectrophotometry and chemical oxygen demand (COD). Microbial growth was measured by the plate count method. Scanning electronic microscopy was employed to observe the microbial community in the reactor. Detoxification was evaluated by using Daphnia magna toxicity tests. Individual compounds were degraded by pure bacteria cultures within 27 h. The mixture of 2-clorophenol (100 mgl⁻¹), phenol (50 mgl⁻¹) and m-cresol (50 mgl⁻¹) was degraded by mixed bacteria cultures under batch conditions within 36 h: 99.8% of total phenols and 92.5% of COD were removed; under continuous flow conditions 99.8% of total phenols and 94.9% of COD were removed. Mineralization of phenolic compounds was assessed by gas chromatography performed at the end of the batch assays and in the effluent of the continuous-flow reactor. Toxicity was not detected in the effluent of the continuous-flow reactor.     

Improvement of the kirromycin fermentation by resin addition

The kirromycin yield ofActinoplanes sp A8924 was improved from 30–50 mg L^–1 to 350 mg L^–1 by mutant selection and medium optimization. The incorporation of polystyrenic resins into the fermentations promoted a further fourfold enhancement of kirromycin productivity to 1500 mg L^–1. The positive effect of resin addition appears to be due to removal of kirromycin from the fermentation broth because kirromycin's minimal inhibitory concentration against the producing strain remained atca 350 mg L^–1.     

Anaerobic degradation of p-cresol in batch and continuous cultures by a denitrifying bacterial consortium

Summary The anaerobic degradation of p-cresol under denitrifying conditions by a bacterial consortium was studied in batch and continuous cultures. Concentrations up to 3 mm were degraded within 5–6 days with 4-hydroxybenzyl alcohol, 4-hydroxybenzaldehyde and 4-hydroxybenzoate as intermediates. Steady states could be maintained at only one dilution rate, D=0.04 h^–1. A further increase in the dilution rate to 0.0 8 h^–1 resulted in culture wash-out. An estimation of the Saturation constant was made (<1 mg/l), taking the maximum specific growth rate as 0.045 h^–1, thus yielding a value of 0.125 mg p-cresol/l. Correspondence to: N. Khoury     

Phenol degradation in a three-phase biofilm fluidized sand bed reactor

A previous three phase fluidized sand bed reactor design was improved by adding a draft tube to improve fluidization and submerged effluent tubes for sand separation. The changes had little influence on the oxygen transfer coefficients(K _L a), but greatly reduced the aeration rate required for sand suspension. The resulting 12.5 dm³ reactor was operated with 1 h liquid residence time, 10.2dm³/min aeration rate, and 1.7–2.3 kg sand (0.25–0.35 mm diameter) for the degradation of phenol as sole carbon source. The K _La of 0.015 s^–1 gave more than adequate oxygen transfer to support rates of 180g phenol/h · m³ and 216 g oxygen/h · m³. The biomass-sand ratios of 20–35 mg volatiles/g gave estimated biomass concentrations of 3–6 g volatiles/dm³. Offline kinetic measurements showed weak inhibition kinetics with constants ofK _s=0.2 mg phenol/dm³, K _o2=0.5 mg oxygen/dm³ and KinI= 122.5 mg phenol/dm³. Very small biofilm diffusion effects were observed. Dynamic experiments demonstrated rapid response of dissolved oxygen to phenol changes below the inhibition level. Experimentally simulated continuous stagewise operation required three stages, each with 1 h residence time, for complete degradation of 300 mg phenol/dm³ · h.     

Tolerance of nitrifying sludge to p-cresol

p-Cresol at 17 mg l^–1 in a nitrifying culture inhibited by 70% nitrate formation whereas at 10 mg l^–1 there was no effect. p-Cresol at 220, 470, and 910 mg l^–1 was converted to intermediates after adaptation times of 8 h, 24 h, and 40 h, respectively. The sludge recovered 44% of its activity after transformation of p-cresol.     

d-Glucose does not catabolite repress a transketolase-deficientd-ribose-producingBacillus subtilis mutant strain

WhenBacillus subtilis strain ATCC 21951, a transketolase-deficientd-ribose-producing mutant, was grown ond-glucose plus a second substrate which is metabolized via the oxidative pentose phosphate cycle (d-gluconic acid,d-xylose,l-arabinose ord-xylitol),d-glucose did not catabolite repress metabolism of the second carbon source. Thed-ribose yield obtained with the simultaneously converted carbon substrates, significantly exceeded that when onlyd-glucose was used. In addition, the concentration of glycolytic by-products and the fermentation time significantly decreased. Based on these findings, a fermentation process was developed withB. subtilis strain ATCC 21951 in whichd-glucose (100 g L^–1) andd-gluconic acid (50 g L^–1) were converted into 45 g L^–1 ofd-ribose and 7.5 g L^–1 of acetoin. A second process, based ond-glucose andd-xylose (100 g L^–1 each), yielded 60 g L^–1 ofd-ribose and 4 g L^–1 of acetoin plus 2,3-butanediol. Both mixed carbon source fermentations provide excellent alternatives to the less efficientd-glucose-based processes used so far.     

Cresols utilization by <Emphasis Type="Italic">Trametes versicolor</Emphasis> and substrate interactions in the mixture with phenol

The ability of the white rot fungus Trametes versicolor strain 1 to degrade and utilize methylated phenols (cresols) was established for the first time in a medium not containing any other carbon components. The data obtained demonstrated the better potential of the strain to assimilate p-cresol instead of o- or m- cresol. The 0.5 g/l p-cresol provided was degraded in full after 96 h. The effect of a dual substrate mixture (0.3 g/l phenol + 0.2 g/l p-cresol) on the growth behavior and degradation capacity of the investigated strain was examined. The cell-free supernatants were analyzed by HPLC. It was established that the presence of p-cresol had not prevented complete phenol degradation but had a significant delaying effect on the phenol degradation dynamics. Phenol hydroxylase, catechol 1.2-dioxygenase and cis,cis-muconate cyclase activities were obtained in conditions of single and mixed substrates cultivation. The influence of different phenolic substrates on phenol hydroxylase activity in Trametes versicolor 1 was established. The mathematical models describing the dynamics of single substrates’ utilization as well as the mutual influence of phenol and p-cresol in the mixture were developed on the bases of Haldane kinetics. The estimated interaction coefficients (I _ph/cr = 4.72, I _cr/ph = 7.46) demonstrated the significant inhibition of p-cresol on phenol biodegradation and comparatively low level of influence of phenol presence on the p-cresol degradation. Molecular 18S RNA gene taxonomy of the investigated strain was performed.     

Biomass relationship to growth and phosphate uptake ofPseudomonas fluorescens,Escherichia coli andAcinetobacter radioresistens in mixed liquor medium

The ability ofPseudomonas fluorescens, Escherichia coli andAcinetobacter radioresistenns to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (10²–10⁵ cells ml^–1) were used. At a high initial biomass concentration (10⁸ cells ml^–1), phosphate was removed during the lag phase and during logarthmic growth byP. fluorescens. Escherichia coli. at high initial biomass concentrations (10⁷ cells ml^–1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantily of phosphate during the stationary growth phase.Acinetobacter radioresistens, at high initial cell densities (10⁶, 10⁷ cells ml^–1) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase.Pseudomonas fluorescens removed phosphate more thanA. radioresistens andE. coli with specific average ranges from 3.00–28.50 mg L^–1 compared to average ranges of 4.92–17.14 mg L^–1 forA. radioresistens and to average ranges of 0.50–8.50 mg L^–1 forE. coli.     

Biodegradation of phenol and <Emphasis Type="Italic">m</Emphasis>-cresol by <Emphasis Type="Italic">Candida albicans</Emphasis> PDY-07 under anaerobic condition

Strain Candida albicans PDY-07 was used to study the anaerobic biodegradation of phenol and m-cresol as single and dual substrates in batch cultures. The strain had a higher potential to degrade phenol than m-cresol. The cell growth kinetics of batch cultures with various initial m-cresol concentrations was investigated, and the Haldane kinetic model adequately described the dynamic behavior of cell growth on m-cresol. When cells grew on the mixture of phenol and m-cresol, substrate interactions were observed. Phenol inhibited the utilization of m-cresol; on the other hand, m-cresol also inhibited the degradation of phenol. However, the presence of low-concentration phenol enhanced m-cresol biodegradation; 100 mg/l m-cresol could be completely degraded within a shorter period of time than m-cresol alone in the presence of 150–300 mg/l phenol. The maximum m-cresol biodegradation rate was obtained at the existence of 200 mg/l phenol. Phenol was preferably utilized by the strain as a carbon and energy source. In addition, a sum kinetics model was used to describe the cell growth behavior in binary mixture of phenol and m-cresol, and the interaction parameters were determined. The model adequately predicted the growth kinetics and the interaction between the substrates.     

Kinetics of bio-oxidation of a medium comprising phenol and a mixture of organic contaminants

The kinetics of bio-oxidation by a microbial ensemble of a model mixture of contaminants that mimicked the ground-water pollution plume at an existing contaminated site was investigated. Phenol at 50 mg/l and a mixture of ten organic contaminants (MOC) (benzene, tetrachloromethane, trichloroethylene, toluene, o-xylene, 1,4-dichlorobenzene, o-cresol, nitrobenzene, naphthalene and 2,6-dichlorophenol) at individual concentrations ranging from 150 g/l to 600 g/l were the components of the model mixture. The microbial ensemble consisted of at least three Pseudomonas spp. isolated from the polluted site. Patterns of oxygen uptake rate (OUR) for the oxidation of phenol alone and with added MOC were treated mathematically. The values for kinetic parameters that gave the best fit to the data were respectively 11.29 and 15.03 ml O₂ h^–1 (mg protein)^–1 for the OUR maximum (OUR_max), 75.89 mg/l and 33.66 mg/l for the saturation constant (K _s), 105.92 mg/l and 36.44 mg/l for the inhibitor constant (K _i), and 89.66 mg/l and 35.02 mg/l the substrate minimum inhibitory concentration (S _mic). This study also scrutinised interference between the two components of the model mixture of contaminants (phenol and MOC) on the basis of variations in kinetic patterns. MOC was shown to be toxic at milligram per litre levels. The microbial ensemble increased phenol oxidation in response to MOC, possibly to obtain the energy to overcome this toxic effect. This was indicated by an acceleration of phenol oxidation in response to increasing concentrations of MOC and higher OUR_max for oxidation of phenol in the presence of MOC. The toxicity of MOC also resulted in enhanced vulnerability of the microbial ensemble to a phenol inhibitory effect, indicated by the diminution of K _i and S _mic. The microbial ensemble showed high resistance to inhibition by the sole presence of phenol possibly because of adaptation to toxic features of MOC during the processes of enrichment and cultivation.     

Effect of temperature and additional carbon sources on phenol degradation by an indigenous soil <Emphasis Type="Italic">Pseudomonad</Emphasis>

A new indigenous soil bacterium Pseudomonas sp. growing on phenol and on a mixture of phenol, toluene, o-cresol, naphthalene and 1,2,3-trimethylbenzene (1,2,3-TMB) was isolated and characterized. Phylogenetic analysis suggested its classification to Pseudomonadaceae family and showed 99.8% DNA sequence identity to Pseudomonas pseudoalcaligenes species. The isolate was psychrotroph, with growth temperatures ranging from ca. 0 to 40 °C. The GC–MS structural analysis of metabolic products of phenol degradation by this microorganism indicated a possible ortho cleavage pathway for high concentrations (over 200 mg L^–1) of phenol. Biodegradation rates by this species were found to be three times more effective than those previously reported by other Pseudomonas strains. The effect of temperature on phenol degradation was studied in batch cultures at temperatures ranging from 10 to 40°C and different initial phenol concentrations (up to 500mgL^–1). Above 300mgL^–1 of initial phenol concentration no considerable depletion was recorded at both 10 and 40°C. Maximum degradation rates for phenol were recorded at 30°C. The biodegradation rate of phenol was studied also in the presence of additional carbon sources (o-cresol, toluene, naphthalene, 1,2,3-TMB) at the optimum growth temperature and was found significantly lower by a factor of eight in respect to the strong competitive inhibition between the substrates and the more available sources of carbon and energy. The Haldane equation =_m S/(K_S+S+S²/K_I) was found to best fit the experimental data at the optimum temperature of 30°C than the Monod equation with kinetic constants _m=0.27h^–1, K_S=56.70mgL^–1, K_I=249.08mgL^–1.     

Biological treatment of phenolic wastes: Comparison between free and immobilized cell systems

Summary Phenol degradation by free and immobilized cells ofFusarium flocciferum was studied in a chemostat at steady-state conditions. For the free cell system the dilution rates varied from 0.02 to 0.13h^–1, with a total phenol removal up to 0.08h^–1. Wash-out seemed to set in at 0.11h^–1. The immobilized cells showed virtually complete phenol utilization at 1g/l, over a period of four months. At D=0.2h^–1 and above 1g/l phenol, the complete phenol removal is not achieved: a progressive increase in the outlet concentration was observed attaining a value of 284mg/l at 1.5g/l.     

Bioreactor seaweed cell culture for production of bioactive oxylipins

Liquid cell suspension cultures derived from marine plants have the potential to biosynthesize novel biomedicinal compounds in a controlled environment. Of particular interest are the eicosanoids and related oxylipins emanating from the 15-lipoxygenase manifold of the arachidonic acid cascade, which is active in the brown algaLaminaria saccharina. Filamentous cell clumps ofL. saccharina isolated from female gametophytes were cultured in an illuminated bubble-column bioreactor in GP2 artificial seawater nutrient medium at 13 °C and air flow rate of 0.35 L air min^–1 L^–1 culture (vvm). Growth kinetics and biomass productivity data were obtained as a function of incident light intensity (2.4 to 98mol photon m^–2 s^–1) and initial cell density (27 to 149 mg DCW L^–1). Maximum cell densities exceeded 1200 mg DCW L^–1 after a 20 day cultivation time at optimal conditions of 98mol photon m^–2 s^–1 and 118 mg DCW L^–1 initial cell density. Qualitative analysis of chloroform/methanol extracts of the cell culture biomass by GC-MS confirmed the presence of the hydroxy fatty acids 13-HODTA and 13-HOTE, the likely products of 15-lipoxygenase catalyzed oxidation of linoleic or linolenic acids.     

Environmental effects on growth and biochemical composition ofNitzschia inconspicua Grunow

The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition ofNitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8–176 M), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64–66 mg ash-free dry weight (AFDW) L^–1, and specific growth rate () based on chlorophylla (0.41–0.50 d^–1) of the cultures grown within 0.3–3.0 mM NaNO₃ were not significantly different. Cultures supplemented with glucose (0.1 % w/v), acetate (0.1 % w/v) or 5% CO₂ attained higher biomass (85, 85, 97 mg AFDW L^–1) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO₃ contained higher carbohydrate contents (14.8–21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO₂. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7–45.0% and 36.4–45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7–5.4% and 3.4–5.9% TFA respectively. Cultures aerated with 5% CO₂ attained the highest biomass (97 mg AFDW L^–1) and yield of 20:5 (n-3) (0.34 mg L^–1).     

Improvement of a mammalian cell culture process by adaptive,model-based dialysis fed-batch cultivation and suppression of apoptosis

Both conventional and genetic engineering techniques can significantly improve the performance of animal cell cultures for the large-scale production of pharmaceutical products. In this paper, the effect of such techniques on cell yield and antibody production of two NS0 cell lines is presented. On the one hand, the effect of fed-batch cultivation using dialysis is compared to cultivation without dialysis. Maximum cell density could be increased by a factor of ~5–7 by dialysis fed-batch cultivation. On the other hand, suppression of apoptosis in the NS0 cell line 6A1 bcl-2 resulted in a prolonged growth phase and a higher viability and maximum cell density in fed-batch cultivation in contrast to the control cell line 6A1 (100)3. These factors resulted in more product formation (by a factor ~2). Finally, the adaptive model-based OLFO controller, developed as a general tool for cell culture fed-batch processes, was able to control the fed-batch and dialysis fed-batch cultivations of both cell lines.Abbreviations A membrane area (dm²) - c _Glc,F glucose concentration in nutrient feed (mmol L^–1) - c _Glc,FD glucose concentration in dialysis feed (mmol L^–1) - c _Glc,i glucose concentration in inner reactor chamber (mmol L^–1) - c _Glc,o glucose concentration in outer reactor chamber (dialysis chamber) (mmol L^–1) - c _Lac,FD lactate concentration in dialysis feed (mmol L^–1) - c _Lac,i lactate concentration in inner reactor chamber (mmol L^–1) - c _Lac,o lactate concentration in outer reactor chamber (dialysis chamber) (mmol L^–1) - c _LS,FD limiting substrate concentration in dialysis feed (mmol L^–1) - c _LS,i limiting substrate concentration in inner reactor chamber (mmol L^–1) - c _LS,o limiting substrate concentration in outer reactor chamber (dialysis chamber) (mmol L^–1) - c _Mab monoclonal antibody concentration (mg L^–1) - F _D feed rate of dialysis feed (L h^–1) - F _Glc feed rate of nutrient concentrate feed (L h^–1) - K _d maximum death constant (h^–1) - k _d,LS death rate constant for limiting substrate (mmol L^–1) - k _Glc monod kinetic constant for glucose uptake (mmol L^–1) - k _Lac monod kinetic constant for lactate uptake (mmol L^–1) - k _LS monod kinetic constant for limiting substrate uptake (mmol L^–1) - K _Lys cell lysis constant (h^–1) - K _S,Glc monod kinetic constant for glucose (mmol L^–1) - K _S,LS monod kinetic constant for limiting substrate (mmol L^–1) - µ cell-specific growth rate (h^–1) - µ _d cell-specific death rate (h^–1) - µ _d,min minimum cell-specific death rate (h^–1) - µ _max maximum cell-specific growth rate (h^–1) - P _Glc membrane permeation coefficient for glucose (dm h^–1) - P _Lac membrane permeation coefficient for lactate (dm h^–1) - P _LS membrane permeation coefficient for limiting substrate (dm h^–1) - q _Glc cell-specific glucose uptake rate (mmol cell^–1 h^–1) - q _Glc,max maximum cell-specific glucose uptake rate (mmol cell^–1 h^–1) - q _Lac cell-specific lactate uptake/production rate (mmol cell^–1 h^–1) - q _Lac,max maximum cell-specific lactate uptake rate (mmol cell^–1 h^–1) - q _LS cell-specific limiting substrate uptake rate (mmol cell^–1 h^–1) - q _LS,max maximum cell-specific limiting substrate uptake rate (mmol cell ^–1 h^–1) - q _Mab cell-specific antibody production rate (mg cell^–1 h^–1) - q _MAb,max maximum cell-specific antibody production rate (mg cell^–1 h^–1) - t time (h) - V _i volume of inner reactor chamber (culture chamber) (L) - V _o volume of outer reactor chamber (dialysis chamber) (L) - X _t total cell concentration (cells L^–1) - X viable cell concentration (cells L^–1) - Y _Lac/Glc kinetic production constant (stoichiometric ratio of lactate production and glucose uptake) (–)     

Effect of pH,aeration and sucrose feeding on the invertase activity of intactS. cerevisiae cells grown in sugarcane blackstrap molasses

S. cerevisiae was grown in a blackstrap molasses containing medium in batch and fed-batch cultures. The following parameters were varied: pH (from 4.0 to 6.5), dissolved oxygen (DO) (from 0 to 5.0 mg O₂L^–1) and sucrose feeding rate. When glucose concentration (S) was higher than 0.5 g L^–1 a reduction in the specific invertase activity of intact cells (v) and an oscillatory behavior of v values during fermentation were observed. Both the invertase reduction and the oscillatory behavior of v values could be related to the glucose inhibitory effect on invertase biosynthesis. The best culture conditions for attainingS. cerevisiae cells suitable for invertase production were: temperature=30°C; pH=5.0; DO=3.3 mg O₂L^–1; (S)=0.5 g L^–1 and sucrose added into the fermenter according to the equations: (V–V_o)=t²/16 or (V–V_o)=(V_f–V_o)·(e^0.6t–1)/10.This work was supported by FAPESP     

Analysis of some metabolites of organic solvents in urine by high-performance liquid chromatography with β-cyclodextrin

Chromatographic separation of the metabolites derived from toluene, ethylbenzene, styrene and xylene was carried out on untreated urine samples from factory workers. The elution sequence was as follows: phenylglyoxilic acid, 3-hydroxy-2-butanone, hippuric acid, o-methylhippuric acid, p-methylhippuric acid, m-methylhippuric acid, p-cresol, m-cresol and o-cresol. The stability constants (K_G) of cresol and methylhippuric acid derivatives were evaluated. The capacity factor (k′), selectivity factor (α) and resolution (R_s) are described with a variety of mobile phases containing β-cyclodextrin (β-CD). The optimum concentration ratio of ethanol–water–acetic acid–β-CD was determined to be 20:80:0.3:1.4%. Under these conditions, k′ values of the five metabolites were 2<k′<6, and all α values were greater than 1.5. Simultaneous determinations of the metabolites were carried out in real urine samples from factory workers using the standard addition method. Validation of the method and the detection limit are described under the optimum conditions attained in this experiment.     

Anaerobic degradation of phenol in batch and continuous cultures by a denitrifying bacterial consortium

Summary The anaerobic degradation of phenol under denitrifying conditions by a bacterial consortium was studied both in batch and continuous cultures. Anaerobic degradation was dependent on NO_f3 ^p– and concentrations up to 4 mm phenol were degraded within 2–5 days. During continuous growth in a fermenter, steady states could be maintained at eight dilution rates (D) corresponding to residence times between 12.5 and 50 h. Culture wash-out occurred at D=0.084 h^–1. The kinetic parameters obtained for anaerobic degradation of phenol under denitrifying conditions by the consortium were: maximam specific growth rate = 0.091 h^–1; saturation constant = 4.91 mg phenol/l; true growth yield = 0.57 mg dry wt/mg phenol; maintenance coefficient = 0.013 mg phenol/mg dry wt per hour. The Haldane model inhibition constant was estimated from batch culture data giving a value of 101 mg/l. The requirement of CO₂ for the anaerobic degradation of phenol with NO_f3 ^p– indicates that phenol carboxylation to 4-hydroxybenzoate was the first step of phenol degradation by this culture. 4-Hydroxybenzoate, proposed as an intermediate of phenol carboxylation under these conditions, was detected only in continuous cultures at very low growth rates (D=0.02 h^–1), but was never detected as a free intermediary metabolite either in batch or in continuous cultures. Correspondence to: N. Khoury     

Sources and sinks of dissolved organic carbon in a forested swamp catchment

Concentrations of dissolved organic carbon (DOC) were measured in precipitation, throughfall, stemflow, and soil, peat and stream water in a 50 ha catchment with a central 5 ha swamp at Mont St. Hilaire, Quebec. DOC concentrations in precipitation were low (2.0 mg L^–1), but increased in passage through the tree canopies as throughfall (9.1–14.6 mg L^–1) and stemflow (23.1–30.1 mg L^–1). For the period July 1–November 15, 1987, 0.5 g DOC m^–2 was imported as precipitation, and forest canopies contributed a further 1.4–1.7 g m^–2 2 to the soil surface. DOC concentrations were higher (46.0 and 67.6 mg L^–1) in upland soil organic horizons, but decreased with depth because subsoil mineral horizons acted as a major sink of DOC. A laboratory experiment using leaf leachate revealed that subsoil horizons were able to adsorb DOC, with equilibrium DOC concentrations ranging from 3 to 19 mg L^–1. Soil organic carbon appeared to be an important determinant of equilibrium DOC concentrations. The swamp was a major source of DOC, with an overall average DOC concentration of 58.6 mg L^–1 and showed strong spatial and temporal variations related to hydrologic and thermal regimes. During base flow periods, stream DOC concentrations were small (< 3 mg L^–1), dominated by water fed from springs draining upland soils. During high flows, stream DOC concentrations increased through the contribution of DOC-rich water originating in the swamp. Sources, sinks and transport of DOC are thus a function of a complex set of inter-related biotic and abiotic process.