Biogeochemistry of organic matter in Lake Geneva: I — particulate hydrocarbons as biogenic and anthropogenic molecular markers

A study of the biogeochemistry of organic matter in Lake Geneva at a central station (SHL2), was carried out at key periods of the biological cycles from November 1985 to September 1986. The seasonal variability of particulate hydrocarbons was studied in the epilimnion and the hypolimnion, focusing on specific periods such as high phytoplankton productivity and rising herbivorous zooplankton activity (May 1986), clearness of waters (June 1986) and intense mixing of waters (February 1986).Analysis of non-aromatic hydrocarbons (NAH) indicated that their major source is the autochtonous phytoplankton. Year 1986 was characterized by a spring bloom of nanoplankton (chlorophyceae and cryptophyceae) which remained predominant during summer and fall. These biological events were correlated with an increase of biogenic NAH, particulary n-alkane and alkene concentrations; the latter increased by one order of magnitude in May. n-Alkane distributions maximized at n-C₁₇ or n-C₂₉, and the n-C₁₇/n-C₂₉ ratio varied in surface water from 2.8 in May to 0.06 in November of the preceding year, reflecting phytoplankton dominant species. Values of NAH/POC, n-alkanes/POC, alkenes/POC and pristane/phytane ratios underwent seasonal and vertical variations which could be related to grazing and/or settling of particles. NAH, n-alkane and alkene enrichment in hypolimnion particles was interpreted to be a result of zooplankton migrations.A series of 37 monoenes and polyenes having from 15 to 31 carbon atoms, originating from planktonic sources, were recognized in the particulate matter by gas chromatography/mass spectrometry (GC/MS). Their distribution was described in 3 sized particles (> 200 µm, 200-60 µm and < 60 µm, identified as adult zooplankton, young zooplankton and nanoplankton respectively) at two different periods of the biological cycle, May and June 1986. Low level inputs originating from terrestrial higher plants were evident in particles; the value of the Carbon Preference Index (CPI) in the carbon range 23–35 was less than 2.8.In all samples analyzed by GC, an unresolved complex mixture of hydrocarbons (UCM) was present and was interpreted, at least in May, as partly originating from the degradation of organic matter by microorganisms. Typical anthropogenic PAH, such as benzofluoranthene and dibenzo (a) anthracene, were found at a low level (9 and 3 ng l^–1 respectively). The absence of hopane-type hydrocarbons, except in November 1985 and in September 1986, and typical combustion PAH associated with particles indicated high temperature pyrolytic contaminants rather than petroleum-derived compounds.     

Bioremediation of experimental petroleum spills on mineral soils in the Vestfold Hills,Antarctica

The effect of nutrient and water enhancement on the biodegradation of petroleum was tested in Antarctic mineral soils. Nitrogen, phosphorus and potassium were applied in solution, with or without gum xanthan or plastic covers, to sites artificially contaminated with distillate. The effectiveness of these procedures was assessed by measuring changes in total petroleum hydrocarbons; heptadecane/pristane and octadecane/phytane ratios; in concentrations of major hydrocarbon components and in microbial numbers and activity.Significantly lower hydrocarbon concentrations were recorded after one year in soils treated with fertilizer solutions, but only in the surface 3 cm. These soils also showed lowered heptadecane/pristane and octadecane/ phytane ratios and had the highest levels of microbial activity relative to other plots. Soils treated with gum xanthan. or covered with plastic had the highest residual hydrocarbon levels. Both treatments inhibited evaporative loss of hydrocarbon, and there were indications that gum xanthan was utilized by the microbiota as an alternative carbon source to distillate. Higher temperatures were recordecd under the plastic but no stimulation of biodegradation was detected.Estimated numbers of metabolically active bacteria were in the range 10⁷ to 10⁸ g^–1 dry weight of soil, with an estimated biomass of 0.03 to 0.26 mg g^–1 soil. Estimated numbers of amoebae were in the range 10⁶ to 10⁷ g^–1 soil (biomass of 2 to 4 mgg^–1). The highest populations were recorded in fertilized, contaminated soils, the only soils where petroleum degradation was demonstrated.     

Effects of a plume front on the distribution of inorganic and organic matter off the Rhône River

Hydrological and chemical structures off the Rhône River estuary resulting from the introduction of the river flow into the Mediterranean Sea are described. The effect of the fresh-water/sea-water interface on the distribution of inorganic and organic matter off the Rhône river is investigated. Strong vertical gradients of inorganic and dissolved organic matter such as lipids characterized the first few meters in this area (from 83.7 to 0.6 N-NO₃ µgat l^–1, from 6.39 to 0.92 N-NH₄ µgat l^–1 and from 299 to 73 µg l^–1 of total dissolved lipids). At the interface, substantial increases of particulate organic (PON: from 45 µg l^–1 at surface to 118 µg l^–1 at the interface, POC: from 462 to 876 µg l^–1, total particulate lipids: from 33 to 648 µg l^–1) and suspended matter in general (from 18 to 22.2 mg l^–1) were observed. High phytoplanktonic production may account for some of this enrichment, although passive accumulation might also be involved.     

Total organochlorine and organobromine in Finnish water courses

Methods were developed for analyzing total organochlorine (TOCl) and total organobromine (TOBr) in different kinds of water, sediment and biological samples. Sediment samples were extracted with alkaline propanone and biological samples with a neutral propanone + water solution. Neutron activation analysis (NAA) was used for the halogen determination. The detection limits for TOCl and TOBr are respectively 5 and 0.5 µg l^–1 for water (sample size 100 ml) and 0.3 and 0.1 µg g^–1 dw (sample size 1 g) for sediment and biological samples. Recoveries for common organochlorine compounds were usually over 90%.TOCl concentrations measured in waters in a natural condition were below 15 µg l^–1; and in polluted waters, from 100 to 500 µg l^–1, and occasionally to 2000 µg l^–1. TOBr concentrations were generally well below 10 µg 1^–1.     

Limitations in substrate utilization efficiency by Zymomonas mobilis

Summary Optimal growth conditions for Zymomonas mobilis have been established using continuous cultivation methods. Optimal substrate utilization efficiency occurs with 2.5 g l^–1 yeast extract, 2.0 g l^–1 ammonium sulfate and 6.0 g l^–1 magnesium sulfate in the media. Catabolic activity is at its maximum with glucose uptake rates of 16–18 g l^–1 h^–1 and ethanol production rates of 8–9 g l^–1 h^–1, Q_g values of 22–26 and Q_p values between 11 and 13, which results in 40 g l^–1 h^–1 ethanol yields using a 100 g l^–1 substrate feed. Any increase in these parameters goes on cost of substrate utilization efficiency. Calcium pantothenate can not substitute yeast extract.Abbreviations G Glucose (%) - Pant Calcium pantothenate (mg l^–1) - D Dilution rate (h^–1) - NH₄ Ammonium sulfate (%) - M_g Magnesium sulfate (%) - S₁ Residual glucose in the fermenter (g l^–1) - S₀ Glucose feed (g l^–1) - Eth Ethanol concentration (g l^–1) - GUR Glucose uptake rate (g l^–1 h^–1) - Q_g Specific glucose uptake rate (g g^–1 h^–1) - Q_p Specific ethanol production rate (g g^–1 h^–1) - EPR Ethanol production rate (g l^–1 h^–1) - Y_g Yield coefficient for glucose (g g^–1) - Y_p Conversion efficiency (%) - C Biomass concentration (g l^–1) Present address: (Until June 1982) Institut für Mikrobiologie, TH Darmstadt, 6100 Darmstdt, Federal Republic of Germany     

The Shatt al-Arab River: A nutrient salt and organic matter source to the Arabian Gulf

The distribution of dissolved reactive phosphate, nitrate and nitrite in the waters as well as total organic carbon, total phosphorus and Kjeldahl nitrogen in the sediments of the Shatt al-Arab Estuary and the NW Arabian Gulf were studied from November 1979 to April 1980. The Shatt al-Arab waters contain 0.18 to 0.70 µg-at P-PO _inf4 ^sup3– l^–1, 26.12 to 52.39 µg-at N-N0 _inf3 ^sup– l^–1 and 0.53 to 0.70 µg-at N-NO _inf2 ^sup– l^–1, indicating that this river should be considered a source of nutrients to the Arabian Gulf. It is concluded that most of the nitrate is supplied in dissolved form, while an appreciable amount of phosphate is absorbed to fine suspended particles and released at higher salinities. Total organic carbon in surficial sediments was found to vary between 0.14% and 0.96%. These rather low values are attributed to dilution by dust fallout, which is a major cource of sediments in this area.     

Protein production from whey usingPenicillium cyclopium; growth parameters and cellular composition

Summary The growth parameters ofPenicillium cyclopium have been evaluated in a continuous culture system for the production of fungal protein from whey. Dilution rates varied from 0.05 to 0.20 h^–1 under constant conditions of temperature (28°C) and pH (3.5). The saturation coefficients in the Monod equation were 0.74 g l^–1 for lactose and 0.14 mg l^–1 for oxygen, respectively. For a wide range of dilution rates, the yield was 0.68 g g^–1 biomass per lactose and the maintenance coefficient 0.005 g g^–1 h^–1 lactose per biomass, respectively. The maximum biomass productivity achieved was 2 g l^–1 h^–1 biomass at dilution rates of 0.16–0.17 h^–1 with a lactose concentration of 20 g l^–1 in the feed. The crude protein and total nucleic acid contents increased with a dilution rate, crude protein content varied from 43% to 54% and total nucleic acids from 6 to 9% in the range of dilution rates from 0.05 to 0.2 h^–1, while the Lowry protein content was almost constant at approximately 37.5% of dry matter.Nomenclature (mg l^–1) C_o initial concentration of dissolved oxygen - (h^–1) D dilution rate - (mg l^–1) K₀₂ saturation coefficient for oxygen - (g l^–1) K_s saturation coefficient for substrate - (g g^–1 h^–1) lactose per biomass) m maintenance energy coefficient - (mM g^–1 h^–1O₂ per biomass) Q₀₂ specific oxygen uptake rate - (g l^–1) S residual substrate concentration at steady state - (g l^–1) S_o initial substrate concentration in feed - (min) t_1/2 time when C_o is equal to C_o/2 - (g l^–1) X biomass concentration - (g l^–1) X biomass concentration at steady state - (g g^–1 biomass per lactose) Y_G yield coefficient for cell growth - (g g^–1 biomass per lactose) Y_x/s overall yield coefficient - (h^–1) specific growth rate     

Inorganic phosphate in exposed sediments of the River Garonne

Fractionation of inorganic phosphates in sediments of the River Garonne was carried out during a period of low water discharge. Sediments were collected under 5 cm of water (LS), in the dried river bank (MS) and in the riparian forest (RS). Sediments were sampled at two dates, during a period in which the water level fell gradually, causing sediment LS to be air exposed.Sediments were analysed for total phosphate, iron bound phosphate (Fe(OOH)P) using Ca-NTA and Ca bound phosphate (CaCO₃P) using Na-EDTA.Total-P varies from 552 (RS at date 1) to 2072 µg g^–1 (LS at date 2). There are significant differences between sediments and a significant increase from date 1 to date 2 in sediment LS only (1825 to 2072 µg g^–1). Fe(OOH)P varies from 186 (RS at date 1) to 874 µg g^–1 (LS at date 2). The highest values correspond to sediment LS. Moreover, Fe(OOH)P increased significantly between date 1 and 2 in LS (560 to 874 µg g^–1) as well as in sediment MS (248 to 432 µg g^–1). Ca bound P concentrations differed significantly between sediments (75, 112, 235 µg g^–1 for sediments RS, MS and LS respectively) but not between sampling dates.These differences are attributed to the conditions of deposition of the sediments (such as morphology and hydrology of the river) and to the changes in chemical composition during the drying out of the sediments.     

Acetone butanol ethanol (ABE) production from concentrated substrate: reduction in substrate inhibition by fed-batch technique and product inhibition by gas stripping

Acetone butanol ethanol (ABE) was produced in an integrated fed-batch fermentation-gas stripping product-recovery system using Clostridium beijerinckii BA101, with H₂ and CO₂ as the carrier gases. This technique was applied in order to eliminate the substrate and product inhibition that normally restricts ABE production and sugar utilization to less than 20 g l^–1 and 60 g l^–1, respectively. In the integrated fed-batch fermentation and product recovery system, solvent productivities were improved to 400% of the control batch fermentation productivities. In a control batch reactor, the culture used 45.4 g glucose l^–1 and produced 17.6 g total solvents l^–1 (yield 0.39 g g^–1, productivity 0.29 g l^–1 h^–1). Using the integrated fermentation-gas stripping product-recovery system with CO₂ and H₂ as carrier gases, we carried out fed-batch fermentation experiments and measured various characteristics of the fermentation, including ABE production, selectivity, yield and productivity. The fed-batch reactor was operated for 201 h. At the end of the fermentation, an unusually high concentration of total acids (8.5 g l^–1) was observed. A total of 500 g glucose was used to produce 232.8 g solvents (77.7 g acetone, 151.7 g butanol, 3.4 g ethanol) in 1 l culture broth. The average solvent yield and productivity were 0.47 g g^–1 and 1.16 g l^–1 h^–1, respectively.     

Chemical limnology of two artificial lakes used for both stormwater management and recreation

The aims of this study were to document the mainly chemical behaviour of two linked artificial lakes used for both stormwater management and recreation in the new town of Craigavon. Further, the understanding of their behaviour should help in their management and the design of other similar lakes.The lake mean total phosphorus (73 µg P l^–1), nitrate (0.50 mg N l^–1) and chlorophyll a (25 µg l^–1) concentrations, Secchi depth (1.2 m) and the estimated total phosphorus loading (1.98 g m^–2 a^–1) all classify the main lake as eutrophic. An important source of the phosphorus load on the lakes is the urban area of Craigavon (52% of the total load). The interrelationships between total phosphorus, chlorophyll a and Secchi depth in the main lake are similar to those in natural ones. In addition, the lake follows the total phosphorus load — trophic state relationships (lake total phosphorus and chlorophyll a concentrations and Secchi depth) found to apply elsewhere. These two points indicate that the artificial lakes in Craigavon behave similarly to natural ones.     

Glucose repression of xylitol production in Candida tropicalis mixed-sugar fermentations

Glucose repressed xylose utilization inCandida tropicalis pre-grown on xylose until glucose reached approximately 0–5 g l^–1. In fermentations consisting of xylose (93 g l^–1) and glucose (47 g l^–1), xylitol was produced with a yield of 0.65 g g^–1 and a specific rate of 0.09 g g^–1 h^–1, and high concentrations of ethanol were also produced (25 g l^–1). If the initial glucose was decreased to 8 g l^–1, the xylitol yield (0.79 g g^–1) and specific rate (0.24 g g^–1 h^–1) increased with little ethanol formation (<5 g l^–1). To minimize glucose repression, batch fermentations were performed using an aerobic, glucose growth phase followed by xylitol production. Xylitol was produced under O₂ limited and anaerobic conditions, but the specific production rate was higher under O₂ limited conditions (0.1–0.4 vs. 0.03 g g^–1 h^–1). On-line analysis of the respiratory quotient defined the time of xylose reductase induction.     

An adaptive on-line control feed rate system in a laboratory scale bakers yeast process

Summary A new control policy for the on-line optimization of the nutrient supply in bakers yeast process is proposed. A feed rate corresponding to minimal substrate uptake time was shown to be optimal for cell yield and specific growth rate. Cultivation results of baker's yeast are presented.Nomenclature c glucose concentration in wort (mol.l^–1) - C total glucose used (mol) - c_e ethanol concentration in wort (mg.l^–1) - c_p glucose concentration in fresh medium (mol.l^–1) - dt/dc glucose consumption time (sec.mol^–1) - F substrate feed rate (litre.hr^–1) - q_c glucose uptake rate (mol.hr^–1) - Q_c specific glucose uptake rate (moll.g^–1.hr^–1) - qO₂ oxygen uptake rate (mol.hr^–1) - QO₂ specific oxygen uptake rate (mol.g^–1.hr^–1) - r_x productivity (g.l^–1.hr^–1) - t time (hr) - x biomass concentration (g.l^–1) - X total biomass (g) - Y_x/c cell yield (g.g^–1): (g.mol^–1) - Y_o/c consumed oxygen to glucose ratio (mol.mol^–1)     

Physiological background for using freshwater mussels in monitoring copper and lead pollution

In studying the effect of copper (10 ± 0.57 µg Cu l^–1 and 100 ± 3.01 µg Cu l^–1) and lead (50 ± 1.12 µg Pb l^–1 and 500 ± 12.5 µg Pb l^–1) on the filtration activity of Anodonta cygnea L. it was found that both heavy metals resulted in significant shortening of the active periods, but little change occurred in the length of the rest periods. The concentrations of copper and lead were measured in the gill, foot, mantle, adductor muscle and kidney for 840 hours of exposure to 10.9 ± 5 µg Cu l^–1 and 57.0 ± 19 µg Pb l^–1 as well as during subsequent depuration. Uptake was observed after 72 hours of exposure. The highest copper concentration (59.1 ± 16.2 µg Cu g^–1) was measured at 672 h in the mantle, and the highest lead value (143 ± 26.1 µg Pb^–1) was obtained in the kidney. Depuration of copper was fastest from the foot, and from the adductor muscle for lead. The gill had the longest half-depuration time (> 840 h for copper and > 672 h for lead).     

Mixed inhibitions by methanol, furfural and acetic acid on xylitol production by Candida guilliermondii

Xylose production by Candida guilliermondii FTI 20037 was carried out in a synthetic medium in the presence of 0–100 g methanol l^–1, 0–0.7 g furfural l^–1 or 0–1.3 g acetic acid l^–1. Kinetic results show a mixed inhibition mechanism in all three cases. Maximum specific productivity and saturation constant for product formation were, in the absence of inhibition, 3.6 g_P g_X ^–1 h^–1 and 232 g_S l^–1, respectively, while the inhibition constants, K _i and K _i, were 17 and 50 g methanol l^–1, 0.62 and 7.0 g furfural l^–1, 0.69 and 3.5 g acetic acid l^–1, which suggests the following order of inhibition: furfural > acetic acid > methanol.     

Nutrients in pore waters from Dead Sea sediments

Pore waters were separated from 50 cm-long cores of Dead Sea sediments raised from waters depths of 25, 30 and 318 m. The salinity of the pore water is close to that of the overlying water at 225–230 g l^–1 chloride. The titration alkalinity of the pore water is about 60 % of the overlying water, and sulfate is also depleted. Ammonia and phosphate concentrations are higher than those of the water column with up to 50 mg l^–1 N-NH₃ (ten times increase) and 350 µg l^–1 P-PO _inf4 ^sup3– (four to eight times increase). Early diagenetic reactions are a result of decomposition of organic matter and of water-sediment interactions, resulting in aragonite precipitation, phosphate removal to the sediments, probably by absorption on iron-oxyhydroxides followed by remobilization, reduction of sulfate and formation of iron sulfides and accumulation of ammonia. Mass balance calculations show that pore water contribute about 80% of the ammonia and 30% of the phosphate input into the Dead Sea water column. On the other hand, the sediments act as a sink for carbonate and sulfate.     

Factors influencing fractional phosphorus composition in sediments of Spanish reservoirs

Total phosphorus in sediment (P_sed) and its fractional composition (reactive phosphate extracted with NaOH, NaOH-RP, reactive phosphate extracted with HCl, HCl-RP, and residual phosphate, residual-P) have been determined in superficial sediments of 43 Spanish reservoirs located in different limnological regions and with different trophic states. Data were evaluated by statistical analysis to examine the influence of regional distribution and trophic status. Relations with calcium, manganese, iron and aluminium contents have also been studied.In the western part of Spain, reservoirs presented the highest values on average of P_sed, NaOH-RP and residual-P (1296, 328 and 877 µg g^–1 dw., respectively) and the lowest values of HCl-RP (91.0 µg g^–1 dw.). The main phosphorus fractions were residual-P (> 50%) and NaOH-RP (>10%). In the eastern area, P_sed NaOH-RP and residual-P attained the lowest values on average (502, 4 and 330 µg g^–1 dw., respectively), whereas HCl-RP presented the highest values (167 µg g^–1 dw.). The main fractions were residual-P (> 50%) and HCl-RP (> 25%).Trophic status seemed to be a secondary factor controlling P_sed. The highest contents of P_sed were found in eutroohic reservoirs, but only when those of the same region were compared, and the statistical significance (ANOVA F test) of the observed differences was very small (p < 0.057).     

Distribution and release of sedimentary phosphorus in Lake Ladoga

Sedimentary phosphorus fractions and phosphorus release from the sediments were studied in Lake Ladoga at altogether 46 sampling sites, representing the full range of sediment types encountered in the lake. Determination of P fractions and physico-chemical analyses were made of surface sediment cores (10–20 cm long, each sampled at 3–4 levels) and in the overlying water. The range of total phosphorus per dry weight of sediment was 0.2–3.3 mg g^–1, and that of inorganic P 0.1–2.5 mg g^–1. The levels of interstitial soluble phosphorus, range 2–613 µg 1^–1 for total P and 1–315 µg 1^–1 for inorganic P, were higher than those of dissolved P concentrations in the overlying water. Diffusive fluxes of phosphate from sediment to the overlying water were estimated using three independent methods. The estimated range was 4–914 µg P m^–2 d^–1; the mean value for the whole bottom area, 0.1 mg P m^–2 d^–1, is lower than previously published estimates. The estimated annual contribution of sedimentary inorganic P flux to Lake Ladoga water is equal to 620 tons of P per year, which amounts to more than 10% of the estimated external P load into the lake. 68% of the total diffusive flux emanates from deep water sediments, which are not exposed to seasonal variation of conditions. In deep lakes, such as Lake Ladoga, phosphorus release from the sediments is controlled primarily by diffusive mechanisms. Wave action and currents as well as bioturbation are probably of importance mainly in shallow near-shore areas. Phosphorus release by gas ebullition and macrophytes is considered negligible.     

Evaluation of the meiobenthic copepod Bryocamptus zschokkei (Schmeil) as an ecologically-relevant test organism for lotic freshwaters

Despite proven utility as ecotoxicological testorganisms in marine systems, harpacticoidcopepods have not been used in freshwaterbiomonitoring. Here we assess the value ofBryocamptus zschokkei, a common member ofmeiofaunal stream communities, as a testorganism for lotic systems by measuring theeffects of copper on acute (survival ofovigerous females) and sub-lethal (offspringproduction, juvenile [i.e. naupliar andcopepodite] development times) end points. Allovigerous females survived exposure atconcentrations <180 µg Cu l^–1, butat >180 µg Cu l^–1, mortalityincreased with exposure times up to 72 h;seventy-two and ninety-six hour LC50s wereidentical (290 µg Cu l^–1). After sixtydays, total offspring production per femaledeclined with increasing copperconcentration; no offspring were producedat 150 µg Cu l^–1 and significantlyfewer offspring were produced at 100 µg Cul^–1 compared with the control. In thejuvenile development tests, nauplii andcopepodites did not survive at 150 µg Cul^–1, but there was no significant effecton development times at lower Cu concentrations(0–100 µg Cu l^–1). Comparison oflaboratory-derived, toxicity end points withdata for B. zschokkei populations incopper-contaminated streams in south-westEngland, demonstrated that significant declinesin the number of surviving offspring closelymatched concentrations of copper across whichdeclines in field populations occurred. Theseresults indicate that B. zschokkei haspotential as an ecologically-relevant testorganism for lotic systems.     

Chlorophyll differences in Mono Lake (California) observable on Landsat imagery

In Mono Lake (California), a large saline lake, chlorophyll concentrations in the euphotic zone increased from 4 to 45 µg l^–1 between July and October 1979. These seasonal changes in chlorophyll are detectable on imagery obtained with the multispectral scanner on Landsat. Computer-compatible tapes of Landsat images were normalized for solar zenith and corrected for atmospheric scatter and absorption to obtain Landsat band 4 emittances (W m^–2 str^–1) of 13.4 ± 0.5 when chlorophyll was 4 µg l^–1 and 4.6 ± 0.3 when chlorophyll was 45 µg l^–1. Lake wide, spatial heterogeneity of chlorophyll of 2 µg l^–1 in July and 8 µg l^–1 in October was not detectable on the Landsat imagery.     

Design of bacterial defined mixed cultures for biodegradation of specific crude oil fractions, using population dynamics analysis by DGGE

Hydrocarbon-degrading bacteria isolated from oil-polluted soils, were used to design three defined mixed cultures (DMC) for biodegradation of Maya crude oil fractions. The first degrading culture, DMC A was made up with 10 strains. Design of DMC B (six strains) and DMC C (three strains) was based on DGGE profiles obtained throughout biodegradation assays of different petroleum fractions. Biodegradation of the aliphatic fraction (10 000 mg l⁻¹) and an aromatic–polar mixture (5000 mg l⁻¹) was evaluated for the DMC B. Biodegradation of total hydrocarbons (10 000 mg l⁻¹) and its fractions was evaluated for DMC B and DMC C. During biodegradation assays, O₂ consumption and CO₂ production were assessed by respirometry, while population dynamics of predominant strains was based on PCR-DGGE profiles of partial 16S rDNA. Aliphatic fraction was completely biodegraded by DMC B, while degradation of the aromatic–polar mixture was 12.5% and for total hydrocarbons 40.5%. DMC B was able to degrade the aromatic fraction (31%) and even the polar fraction (19.6%) present in total hydrocarbons. DMC C degraded the aromatic and polar fractions (5.6% and 2%, respectively) present in total hydrocarbons. DGGE profiles of the DMCs indicated that Pseudomonas sp., Gordonia rubripertincta and a non-identified strain were predominant and probably responsible of the hydrocarbons biodegradation. The use of DGGE-fingerprinting to track microbial populations, allowed selecting strains to design efficient oil-degrading defined mixed cultures.