Trace elements in fruiting bodies of ectomycorrhizal fungi growing in Scots pine (Pinus sylvestris L.) stands in Poland

The trace metal contents in fruiting bodies of ectomycorrhizal (ECM) fungi, symbiotic partners of Scots pine, were studied on three sites situated in west-central Poland. Elements were determined by atomic absorption spectrometry in 123 samples of 16 species. The study explored the differences in metal accumulation in relation to site, fungal species, age and part of the fruiting body and results were related to metal content in soil and plant material (roots and needles). Soil analysis revealed that results were obtained under environmental conditions not subject to strong anthropogenic pressure. Median metal concentrations did not differ disparately between sites, although the concentrations of each of the tested metals in the individual species varied to a large extent. Extremely high levels of Al with a large bioconcentration factor (BCF) were found in sporocarps of Thelephora terrestris. The spread between the highest and the lowest concentration (max/min) was very wide in Al, Cd and Pb and these elements may be considered to be absorbed preferentially by fruiting bodies of some species whereas Fe, Mn and Zn, with relatively low values of max/min, are normally absorbed by the majority of fungi. There was no clear relationship between caps and stipes in metal content. However, a tendency to higher metal concentration in the caps was observed. The metal content in young and older fruiting bodies of five different fungi was species dependent. In order to estimate the degree of accumulation of each element by plant and mushrooms, bioconcentration factors (BCFs) were calculated. In plant material (roots and needles), highest values of BCFs were noted for essential metals, like Zn and Mn. Lead showed a definite exclusion pattern (BCF below 1). In fruiting bodies of tested fungi, especially in Amanita muscaria, cadmium was the most intensively accumulated metal. Lead was excluded by plants but was accumulated or excluded by fungi depending on the species. The significance of mycological observation and quantification of the metal content in monitoring of the forest ecosystem is discussed.     

Uptake and release of zinc by aquatic bryophytes (Fontinalis antipyretica L. ex. Hedw.)

The zinc uptake and posterior release by an aquatic bryophyte—Fontinalis antipyretica L. Ex Hedw.—was experimentally studied in laboratory exposing the plants to different zinc concentrations in the range, 1.0–5.0 mg l⁻¹, for a 144 h contamination period, and then exposed to metal-free water for a 120 h decontamination period. The experiments were carried out in perfectly mixed contactors at controlled illumination, using mosses picked out in February 1997, with a background initial zinc concentration of 263 mg g⁻¹ (dry wt.). A first-order mass transfer kinetic model was fitted to the experimental data to determine the uptake and release constants, k₁ and k₂, the zinc concentration in mosses at the end of the uptake period, C_mu, and at the equilibrium, for the contamination and decontamination stages, C_me and C_mr, respectively. A bioconcentration factor, BCF=k₁/k₂ (zinc concentration in the plant, dry wt./zinc concentration in the water) was determined. A biological elimination factor defined as BEF=1−C_mr/C_mu was also calculated. BCF decreases from about 4500 to 2950 as Zn concentration in water increases from 1.05 to 3.80 mg l⁻¹. BEF is approximately constant and equal to 0.80. Comparing Zn and Cu accumulation by Fontinalis antipyretica, it was concluded that the uptake rate for Zn (145 h⁻¹) is much lower than for Cu (628 h⁻¹) and the amount retained by the plant decreased by a factor of about seven.     

Cadmium and lead in selected tissues of two commercially important fish species from the Adriatic Sea

Baseline levels of cadmium and lead were determined in muscle tissue and liver of hake (Merluccius merluccius) and red mullet (Mullus barbatus), two commercially important fish species from the eastern Adriatic. Concentrations of trace metals in liver (Cd: 6–183 μg kg⁻¹ w. wt. ; Pb: 39–970 μg kg⁻¹ w. wt.) were within the range of recently published data for the Mediterranean. In the muscle tissue, cadmium concentrations (4.1–29 μg kg⁻¹ w. wt.) were among the lowest reported values for the Mediterranean, whereas lead levels (49–158 μg kg⁻¹ w. wt.) were within the range of values reported for various coastal areas of the Mediterranean. Presented data on cadmium and lead content in the studied fish species provide no proof of the general pollution of the Adriatic. Obtained data were tested in relation to fish length. Metal concentrations in liver decreased with the increase in fish size, whereas no significant correlation was found between trace metal levels in the muscle tissue and the length of both species. Relationships between metal concentrations and sex were also tested, but they gave no significant results. A comparison of contaminant concentrations in the edible tissue of hake and red mullet with the Croatian legislation shows that the consumption of their meat is not harmful for humans, not even for the most endangered population from the coastal region.     

Fluorescent whitening agents: Acute fish toxicity and accumulation studies

Four fluorescent whitening agents (FWA), three of which are currently marketed in the United States for use as ingredients in household laundry detergents, were tested to determine their acute toxicity to the bluegill (Lepomis macrochirus), as well as their potential for significant accumulation in the flesh of the bluegill and channel catfish (Ictalurus punctatus), two species of fish common to U.S. waters. Results of the acute toxicity bioassays showed that no acutely toxic effects on fish, caused by these materials, would be expected at concentrations well above their projected environmental levels. Rates of accumulation and maximum levels accumulated were evaluated in the laboratory for a period of 90–105 days, followed by an examination of the rate of elimination of these materials from the fish over a 28-day period. Under these conditions, neither species accumulated any of three anionic fluorescent whitening agents (sulfonated stilbene derivatives) when exposed to nominal concentrations of 0.125, 1.25, or 12.5 μg 1⁻¹ in water. A nonionic FWA not currently used in the U.S. detergent formulations was significantly accumulated at the two highest concentrations tested. The nonionic FWA accumulated was rapidly eliminated by fish upon their transfer to water devoid of this chemical. Elimination of FWA was essentially complete by 14 days. No significant accumulation by fish was detected with any FWA when exposure was conducted at levels approximating projected environmental concentrations. Details of the acute toxicity tests, and the patterns of accumulation and elimination seen in this study, as well as their significance, are discussed.     

Chlorinated hydrocarbons in fish from the river PO (Italy)

Pesticides and PCBs levels have been determined in two species of fish from the river Po during 1979--1980 at five sampling stations in different seasons. Significant higher levels have been observed in most industrial areas. When expressed on the basis of fat content, river fish levels are higher than those reported for fish from the Adriatic sea. Using experimental BCF (bioconcentration factors), pesticides and PCB concentrations in water have been calculated from fish values, and compared with measured concentrations.     

Sublethal toxicity and biotransformation of pyrene in Lumbriculus variegatus (Oligochaeta)

The aim of this work was to study the toxicity and biotransformation of polyaromatic hydrocarbon (PAH) pyrene in the oligochaete aquatic worm, Lumbriculus variegatus. PAHs are ubiquitous environmental pollutants that pose a hazard to aquatic organisms, and metabolizing capability is poorly known in the case of many invertebrate species. To study the toxicity and biotransformation of pyrene, the worm was exposed for 15 days to various concentrations of water-borne pyrene. The dorsal blood vessel pulse rate was used as a sublethal endpoint. Pyrene biotransformation by L. variegatus was studied and the critical body residues (CBR) were estimated for pyrene toxicity. The toxicokinetics of pyrene uptake was evaluated. A combination of radiolabeled (¹⁴C) and nonlabeled pyrene was used in the exposures, and liquid scintillation counting (LSC) and high-pressure liquid chromatography were employed in both water and tissue residue analyses. The results showed that L. variegatus was moderately able to metabolize pyrene to 1-hydroxypyrene (1-HP), thus demonstrating that the phase-I-like oxidizing enzyme system metabolizes pyrene in L. variegatus. The amount of the 1-HP was 1-2% of the amount of pyrene in the worm tissues. The exposure to pyrene reduced the blood vessel pulse rate significantly (p < 0.05), showing that pyrene had a narcotic effect. The estimated CBRs remained constant during the exposure time, varying from 0.120 to 0.174 mmol pyrene/kg worm wet weight. The bioconcentration factors (BCF) decreased as exposure concentration increased. It was suggested that the increased toxicity of pyrene accounted for the decrease in BCFs by lowering the activity of the organism.     

Variation of ATP content in Scenedesmus dimorphus cells grown in a chemostat culture and its comparison with chlorophyll-A content

The variations of ATP and chl-a contents in Scenedesmus dimorphus cells grown in a chemostat culture under nutrient limitation were investigated. ATP and chl-a contents per algal dry weight varied in the ranges of 0.15–1.64 μg mg⁻¹ (0.33–3.82 μg mg⁻¹ as ATP/C ratio) and 0.32–1.32% (7.8–30.8 μg mg⁻¹ as chl-a/C ratio), respectively, under the conditions of T-N/T-P ratio of 2–50 by weight and dilution rate of 1–4 per day. At every T-N/T-P ratio, both ATP and chl-a contents increased as dilution rate increased. At a given dilution rate, ATP content decreased systematically as T-N/T-P ratio increased, with the only exception at dilution rate of 4 per day. It was considered based on the result that ATP or chl-a can hardly be used successfully as an indicator of algal biomass.     

Influence of inter-annual variations in climatic factors on fecal coliform levels in Mississippi Sound

Information on the effects of inter-annual variations in climatic factors on fecal coliform levels in coastal waters is scarce. We used 11 years (1990–2001) of rainfall, water temperature, Pearl River stage and salinity data to assess the effects of the 1991–1992 and 1997–1998 El Niño events on fecal coliform levels in Mississippi Sound. El Niño-Southern Oscillation had major effects on Pearl River stage and water quality in the Sound. The geometric mean fecal coliform number differed among years (P=0.0001), being highest during 1991–1992 El Niño years (14.22 MPN per 100 ml) and lowest during 1999–2000 La Niña years (<1.8 MPN per 100 ml). Mean salinity varied among years (P=0.0001) from 9 ppt (1991–1992) to 21 ppt (1999–2000). Mean water temperature was lowest in 1997–1998 (14.5 °C) and highest in 1998–2000 (19.4 °C). Pearl River stage differed among years (P=0.0001), ranging from 1.96 m (1999–2000) to 3.57 m (1997–1998). Inverse relationships were observed between fecal coliform levels and salinity (r²=0.74; P=0.001) and water temperature (r²=0.69; P=0.001), whereas positive relationships were obtained with total rainfall (r²=0.52; P=0.013) and Pearl River stage (r²=0.90; P=0.0001). These relationships are useful for evaluating the potential effects of climate change on water quality and classification of shellfish growing waters in order to protect humans from consuming contaminated shellfish in shallow river-influenced estuaries.     

Bacteriological, virological and chemical evaluation of a wastewater-aquaculture system

Levels of fecal coliforms (FC), fecal streptococci (FS), Salmonella spp and enteric viruses were monitored in the water, sediment and fish in experimental wastewater-fish ponds near Benton, Arkansas, U.S.A. Concentrations of five heavy metals were also monitored in the fish and wastewater. Concentrations of indicator bacteria were reduced by as much as 99.7% through the series of six ponds which had a calculated total retention time of 72 days. Two filter-feeding species of Chinese carp, Hypophthalmichthys molitrix (silver carp) and Aristichthys nobilis (bighead carp), grown in the last three ponds accumulated FC and FS in their digestive tracts and skin at levels as great or greater than in the surrounding water and sediment. Only low levels of FC and FS were found in the fish muscle tissue (maximum of 25 FS per 100 g) even when concentrations of bacteria in the gut exceeded 10⁵ per 100 g. Concentrations of bacteria in the water and sediment were not good predictors of concentrations in the fish. No Salmonella and no enteric viruses were isolated from the fish, but this lack of isolates was attributed to the extremely low levels which were present in the influent wastewater. Higher levels of copper and mercury were found in the fish flesh than in the surrounding water, with three of eleven fish samples containing higher than acceptable levels of mercury in the edible portion. Based on the efficiency of wastewater treatment, an aquaculture system using silver and bighead carp was judged to be a viable treatment system for domestic sewage resulting in a product suitable for animal or human consumption if proper precautions are taken in harvesting and processing the fish.     

The bioavailability of copper in wastewater to Lemna minor with biological and electrochemical measures of complexation

Lemna minor (duckweed) was grown in treated domestic wastewater containing added Cu to study the relationship between complexation and bioavailability. Growth was not inhibited until total Cu exceeded 0.079–0.119 mg/l or internal Cu exceeded 81 to 235 μ/g. Cu²⁺ was detectable in the wastewater when total Cu measured ≥ 0.378 mg/l. There was a significant (P < 0.05) relationship between Cu bioconcentration and total Cu in wastewater that was attributed, in part, to heterotrophy of duckweed. Results indicated that, in addition to the bioavailable Cu²⁺ species, some complexes of Cu formed with ligands in wastewater may also be bioavailable. Measurement of the Cu Complexing Capacity (CC) of the wastewater by Ion-Selective Electrode (ISE) gave values of 0.26 to 0.29 mg/l and indicated the presence of ligands with a continuum of binding strengths which eliminated two of three commonly used methods for calculating CC. The biologically-measured CuCC based on growth was 0.077–0.125 mg/l when calculated by two out of three measures of Effective Concentration (EC) and was two to three times more sensitive than the ISE method for measurement of CC. ECs based on tissue concentration of Cu rather than solution concentration were 81–471 μ/g and have been proposed as an alternative for work in complex solutions like wastewater.     

Size selective continuous flow filtration method for detection of Cryptosporidium and Giardia

We describe a size selective continuous flow filtration method for detecting Cryptosporidium oocyst and Giardia cyst in finished water. Twenty liters of finished water spiked with Cryptosporidium oocysts (110) and Giardia cysts (60) were filtered through macro (5.0–10.0 μm) and micro (3.0 μm) pore-sized polycarbonate-track-etch (PCTE) membrane filters housed into two separate 47 mm diameter filter holders joined with a stainless steel nipple. The macro-pore-sized filters removed larger unwanted particles while allowing the Cryptosporidium oocysts and Giardia cysts to pass through, these being subsequently captured on the micro-pore-sized filter. The eluted oocysts and cysts were transferred onto the well-slide, stained by IFA and examined microscopically. The mean recovery efficiencies obtained for Cryptosporidium oocysts using the filter pairs of macro 5 μm and micro 3 μm, macro 8 μm and micro 3 μm, and macro 10 μm and micro 3 μm were 67.3%, 77.2–85.0% and 76.9–82.2%, respectively. Whereas the recovery rates for Giardia cysts using the same filter pairs were 0, 55 and 77.1%. The filter pair having the pore size of macro 10 μm and micro 3 μm was found to be most efficient in the simultaneous detection of Cryptosporidium and Giardia in the finished water. This method is simple, easy, rapid and economical.     

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus were investigated under aerobic and anaerobic conditions. The total phosphorus content of this bacterium varied from 0.3 to 1.7 mmol g⁻¹ dry cells or from 0.93 to 5.3% of dry cell weight under various culture conditions. The log-phase cells accumulated polyphosphates of 0.33−0.64 mmol P g⁻¹ dry cells. ³¹P NMR spectra suggested that a portion of polyphosphates was likely bonded to some sort of structural components of the cell. A. calcoaceticus release phosphate linearly with time when transferred from aerobic to anaerobic conditions. The release rate was in the range of 5.9–14.7 × 10⁻³ mmol P g⁻¹ dry cells h⁻¹ and about 4–8% of cellular phosphorus was released during the initial 6 h. During the process of phosphate release acetate was not taken up by this bacterium.     

Evaluation of kinetic parameters of a sulfur-limestone autotrophic denitrification biofilm process

In this study, four kinetic parameters of autotrophic denitrifiers in fixed-bed sulfur–limestone autotrophic denitrification (SLAD) columns were evaluated. The curve-matching method was used by conducting 22 non-steady-state tests for estimation of half-velocity constant, K_s and maximum specific substrate utilization rate, k. To estimate the bacteria yield coefficient, Y and the decay coefficient, k_d, two short term batch tests (before and after the starvation of the autotrophic denitrifiers) were conducted using a fixed-bed SLAD column where the biofilm was fully penetrated by nitrate-N. It was found that K_s=0.398 mg NO₃⁻–N/l, k=0.15 d⁻¹, k_d=0.09–0.12 d⁻¹, and Y=0.85–1.11 g VSS/g NO₃⁻–N. Our results are consistent with those obtained from SLAD biofilm processes, but different from those obtained from suspended-growth systems with thiosulfate or sulfur powders as the S source. The method developed in this study might be useful for estimation of four Monod-type kinetic parameters in other biofilm processes. However, cautions must be given when the estimated parameters are used because the measurements of the biomass and the biofilm thickness could be further improved, and the assumption of sulfur being a non-limiting substrate needs to be proved.     

Effects of pH on the bioconcentration of pyrene in the larval midge, Chironomus riparius

Bioconcentration, depuration and biotransformation of the polycyclic aromatic hydrocarbon, pyrene, were studied at pH 4, 6 and 8 with larval stages of the chironomid midge, Chironomus riparius. ¹⁴C-labelled pyrene was applied. The results revealed pH-dependant bioconcentration and depuration-kinetics as well as biotransformation of pyrene. At higher pH the bioconcentration rate (k₁) was greater than at lower pH. Hereby the bioconcentration rate correlated with the accumulation potential of pyrene. That means at pH 8 the larvae accumulated pyrene strongest, at pH 4 the bioconcentration of the larvae was lowest. Due to biotransformation of pyrene the calculated bioconcentration factor (BCF) based on total ¹⁴C found in the larvae. Depuration revealed a biphasic kinetic. Data were fit with a two compartment model to calculate the volume of each of the two compartments. To calculate for the depuration rate (k₂), data were additionally fit with a one compartment model. The larvae displayed an intriguing pH-dependent behaviour: At pH 4 the Chironomus larvae started to increase mucus-production of the salivary glands and accelerated the built up of their tubes. The latter were of “cocoon”-like structure. At pH 8 the composition of the tubes was more loose. It is hypothezised that this response to an acidified environment caused the reduced bioconcentration rate as well as the reduced biconcentration.     

Significance of attached cyanobacteria relevant to the occurrence of musty odor in Lake Kasumigaura

The microorganisms and compounds causing musty odor in the second largest lake in Japan, Lake Kasumigaura, where the water is used for drinking, fisheries and agricultural purposes, were examined during the severe occurrence of musty odor in 1989 and 1990. This study was undertaken to determine the microorganisms and their metabolites responsible for the musty odor. Phormidium tenue, which has been reported to be the main contributor of the odor in Lake Kasumigaura, was isolated. Furthermore, four monoxenic strains of the odor producing attached cyanobacteria, Phormidium viscosum, Lyngbya allorgei, Oscillatoria splendida and Phormidium uncinatum, were isolated from submerged rocks and sediments in the lake. All of the four attached strains produced only geosmin, which was confirmed by gas chromatograph/mass spectrometer analysis, in the monoxenic cultures. In particular, we confirmed for the first time that P. viscosum, L. allorgei and P. uncinatum produced geosmin. Both the planktonic Phormidium tenue, a well known 2-methylisoborneol (MIB) producer and geosmin-producing attached cyanobacteria were closely associated with the occurrence of musty odor in Lake Kasumigaura.     

Disappearance of aromatic hydrocarbons and organic sulfur compounds from fish flesh reared in crude oil suspension

Eels (Anguilla japonica Temminck and Schlegel) were reared in sea water containing a crude oil suspension (50 ppm for 10 days for aromatic hydrocarbons, 2500 ppm for 3 days for organic sulfur compounds), then transferred to clean sea water. The disappearance of aromatic hydrocarbons and organic sulfur compounds from eel flesh was examined.

Concentration ratio (concentration of eel flesh/concentration of water) of benzene, toluene, m- or p-xylene and o-xylene on 10 days is 3.5, 13.2, 23.6 and 21.4 respectively.

Benzene, toluene, m- or p-xylene and o-xylene, disappeared after the transfer to clean sea water, and half life period is 0.5, 1.4, 2.6 and 2.0 days respectively in first phase which lasted 0–5 days.

Organic sulfur compounds in eel flesh decreased as the time spent in clean sea water increased, but were still present after 30 days.

The results suggest that aromatic hydrocarbons and organic sulfur compounds could serve as markers of oil pollution in fish.     

Bioconcentration of linear alkylbenzene sulfonate (LAS) in bluegill (Lepomis macrochirus)

The potential of the surfactant linear alkylbenzene sulfonate (LAS) to be bioconcentrated in various tissues and organs of bluegill (Lepomis macrochirus) was determined during a 35 day continuous exposure to a mean measured water concentration of 0.5 (±0.05) mg l^{−1 14}C-ring labelled LAS and during a 14 day depuration study. Based on the assumption that all of the ¹⁴C-radioactivity was present as intact LAS, which represents the maximum amount of LAS that could be present, the steady state whole body bioconcentration factor (BCF) was 104 and the muscle BCF was 36. The site of greatest concentration was the gall bladder with a BCF of approx. 5000. The BCF for liver, gills and viscera, remaining carcass, and blood ranged from 64 to 283. Clearance of ¹⁴C-activity from the organs and tissues was rapid with half-lives of 2–5 days. These results on LAS were obtained by both the plateau and kinetic methods of data analysis and are similar to other published data on surfactant bioconcentration.     

Rates of experimental microbiological contamination of fish exposed to polluted water

Fish inhabiting fecally polluted bodies of water are often used for human consumption. Such fish can be contaminated by enteric human pathogens and may pose a potential risk to public health. Controlled experiments with 132 fish of 100 g average weight were conducted to evaluate the rate of contamination of various tissues of fish (tilapia hybrids). The fish were exposed to E. coli introduced into the ambient water at concentrations of up to 10⁶ cfu/ml. Additional experiments were conducted with diluted wastewater containing Aeromonas, enterococci, fecal coliform and F+ coliphages. In another experiment poliovirus I was also added. The highest bacterial concentrations were recovered from the digestive tract (DT), some 5–24 h following exposure, with DT levels essentially similar to those in the inoculated water. In the E. coli experiments, geometric mean levels of about 10² cfu/cm² were recovered from the skin, 26 cfu/g in the spleen and 10² cfu/g in the liver. Most of the muscle samples were not contaminated. Greater contamination was not found under conditions of stress such as high organic load, a water temperature of 37°C or low levels of dissolved oxygen.     

A planktonic Oscillatoria species from Mississippi catfish ponds that produces the off-flavor compound 2-methylisoborneol

A planktonic, gas-vacuolate Oscillatoria species was isolated from catfish ponds in Mississippi during an episode of off-flavor and high 2-methylisoborneol (MIB) levels. Volatile compounds from unialgal cultures were isolated using closed-loop stripping, liquid-liquid extraction, and analyzed by gas chromatography and mass spectroscopy. The organism produced MIB at 75–87 μg 1⁻¹ after 2–3 wk of incubation at 25°C. The alga was found in moderate to high numbers in three pond water samples with high MIB levels, and low numbers in two other samples with low MIB levels. The organism was not present (less than one organism/10 ml) in nine other samples characterized by a “woody” or “swampy” odor and no detectable MIB. This Oscillatoria strain is believed to be the first blue-green alga that produces MIB ever isolated from Mississippi catfish ponds, and may be a cause of the off-flavor problem associated with MIB in those systems.     

Nitrobacter and Nitrospira genera as representatives of nitrite-oxidizing bacteria: detection, quantification and growth along the lower Seine River (France)

Pollution from agriculture and urban effluents influences the ecology and biochemical functioning of the Seine River. Nitrification dominates nitrogen transformations downstream of the effluents of the Paris wastewater treatment plant (WWTP) at Achères, treating, by activated sludge the wastewater of 6.5 million inhabitant equivalents from Paris and its suburbs, without nitrification and denitrification treatment. It discharges effluents containing large amounts of nitrogen, ammonium mostly (30 mg L⁻¹ N-NH₄⁺ L⁻¹), on average 45 mg L⁻¹ of suspended particulate matter, high quantities of total organic carbon (30 mg C L⁻¹) largely biodegradable (40%), and high concentration in total phosphorus (3 mg Tot P L⁻¹), as well as microorganisms. Ammonium, brought into the river system, is slowly nitrified in the lower Seine River and especially in the freshwater estuary. The nitrifying activities can be observed by measuring inorganic nitrogen compound concentrations and potential activities. To understand the contributions of the WWTP effluents, the upstream agricultural runoff water and the Seine tributaries, it is useful to investigate the bacterial community. Whereas ammonia oxidation has been widely studied, the second step, i.e. nitrite oxidation, is less well understood. We have previously analysed the ammonium-oxidizing bacterial (AOB) community in the Seine (Cébron, A., Berthe, T., Garnier, J., 2003. Nitrification and nitrifying bacteria in the lower Seine River and estuary (France). Appl. Environ. Microbiol. 69, 7091–7100; Cébron, A., Coci, M., Garnier, J., Laanbroek, H.J., 2004. DGGE analysis of the ammonia oxidizing bacterial community structure in the lower Seine River: impact of the Paris wastewater effluents. Appl. Environ. Microbiol. 70, 6726–6737), and focus here on the composition of the nitrite-oxidizing bacterial (NOB) community. As no general molecular probe targeting all known NOBs is currently available, we chose to target and quantify (by competitive PCR) the two genera Nitrobacter and Nitrospira assumed to be the major players in nitrite oxidation in freshwater environments. Nitrobacter species were dominant in the upstream Seine River basin but Nitrospira was the dominant NOB downstream of the WWTP. These two genera were equally represented in WWTP effluents. In the Seine River estuary, especially in the salinity gradient, the Nitrobacter proportion increases and that of Nitrospira disappears, possibly due dilution by seawater.