Archaeal microbial communities present in municipal solid waste landfill leachates were characterized using a 16S rDNA approach. Phylogenetic affiliations of 239 partial length 16S rDNA sequences were determined. Sequences belonging to the order Methanosarcinales were dominant in the clone library and 65% of the clones belonged to the strictly acetoclastic methanogenic family Methanosaetaceae. Sequences affiliated to the metabolically versatile family Methanosarcinaceae represented 18% of the retrieved sequences. Members of the hydrogenotrophic order Methanomicrobiales were also recovered in limited numbers, especially sequences affiliated to the genera Methanoculleus and Methanofollis. Eleven euryarchaeal and thirteen crenarchaeal sequences (i.e. 10%) were distantly related to any hitherto cultivated microorganisms, showing that archaeal diversity within the investigated samples was limited. Lab-scale incubations were performed with leachates mixed with several methanogenic precursors (acetate, hydrogen, formate, methanol, methylamine). Microbial populations were followed using group specific 16S rRNA targeted fluorescent oligonucleotidic probes. During the incubations with acetate, acetoclastic methanogenesis was rapidly induced and led to the dominance of archaea hybridizing with probe MS1414 which indicates their affiliation to the family Methanosarcinaceae. Hydrogen and formate addition induced an important acetate synthesis resulting from the onset of homoacetogenic metabolism. In these incubations, species belonging to the family Methanosarcinaceae (hybridizing with probe MS1414) and the order Methanomicrobiales (hybridizing with probe EURY496) were dominant. Homoacetogenesis was also recorded for incubations with methanol and methylamines. In the methanol experiment, acetoclastic methanogenesis took place and archaea hybridizing with probe MS821 (specific for Methanosarcina spp.) were observed to be the dominant population. These results confirm that acetoclastic methanogenesis performed by the members of the order Methanosarcinales is predominant over the hydrogenotrophic and methylotrophic pathways in landfill leachates.

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Since 1991, herpesvirus infections have been reported among larvae and juveniles of various bivalves. Most of the studies focused on detection of viral infections of economically important species. However, the persistence of bivalve herpesviruses in the marine environment is poorly documented. The present study concerns the role of seawater parameters in Ostreid Herpesvirus 1 (OsHV-1) detection by polymerase chain reaction (PCR). Viral DNA extracted from purified particles or virions present in infected oyster larvae were detected by PCR after storage in different media at different temperatures. The lowest detection threshold was found using distilled water or Tris EDTA buffer. In seawater, the threshold was higher. The use of sterile media permitted detection of viral DNA stored over a longer period. Storage temperature also had a significant influence on detection, with lower temperatures promoting DNA detection over a longer period. In summary, water parameters such as temperature influenced detection of OsHV-1 DNA by PCR. However, the PCR technique may also be successfully applied to samples in natural seawater. Indeed, the PCR technique permitted detection of naked viral DNA at 100 ng l -1 in seawater in bioassays.KEY WORDS: Oyster Herpesvirus 1 · Viral DNA · Seawater · Detection · PCR · Temperature Resale or republication not permitted without written consent of the publisherDis Aquat Org 62: [35][36][37][38][39][40][41][42][43][44] 2004 outbreaks of mortality reported among Ostrea edulis and C. gigas spat were associated with detection of a herpes-like virus in France (Comps & Cochennec 1993, Renault et al. 1994a,b, 2000a. Herpes-like virus replication has also been observed in O. angasi adults in Australia (Hine & Thorne 1997) and in larval Triostrea chilensis in New Zealand (Hine 1997, Hine et al. 1998). Herpes-like viruses thus appear ubiquitous in bivalves. They are detected in different parts of the world, at different stages of development in different species. Moreover, herpes-like virus infections in bivalves are often associated with substantial mortalities. These observations highlight the importance of using a range of efficient diagnostic methods in order to assess the causative role of these viruses in bivalve mortalities. Using viral DNA extracted from infected C. gigas larvae (Le Deuff & Renault 1999), different molecular techniques, such as the polymerase chain reaction (PCR), have been developed (Renault & Lipart 1998, Renault et al. 2000b. PCR is used successfully to detect viral DNA during productive infections in oyster larvae and spat (Renault et al. 2000b). An in situ hybridisation technique has also been described (Lipart & Renault 2002). This technique may confirm the presence of herpes-like viruses in histological sections and localise viral DNA in different tissues and organs of infected individuals. Although these molecular techniques are now used to detect herpes-like viruses in marine bivalves when abnormal mortalities occur, no data are available about the dete...

Nitrified leachate recirculation represents a promising strategy for a more sustainable landfill management. Our objective was to determine the reactions involved in nitrate reduction in municipal solid waste batch biodegradation tests. Anaerobic digestion of waste in the three control reactors showed a good reproducibility. In two test reactors, nitrate was added at various moments of the waste degradation process. We observed that: (1) H2S concentration controlled the nitrate reduction pathway: above a certain threshold of H2S, dissimilatory nitrate reduction to ammonium (DNRA) replaced denitrification. (2) N2O/N2 ratio varied with the organic carbon concentration: the lower the easily biodegradable carbon concentration, the higher the N2O/N2 ratio. (3) N2 was consumed after denitrification. The possibility of a nitrogen fixation reaction in the presence of NH4 is discussed. Nitrified leachate recirculation during acidogenesis should be avoided because of higher H2S production which could induce DNRA.

Leachate recirculation allows an increase of moisture content and the enhancement of the anaerobic digestion of wastes in landfill. Since there is no ammonia elimination process in landfill when leachate is recirculated, NH R 4 may accumulate. One strategy for NH R 4 removal is to treat aerobically the leachate outside the landfill to convert NH R 4 into NO S 3 . When nitrified leachate is recirculated, denitrification should occur in the waste. We have previously shown that wastes have a large capacity to convert nitrate into N 2 . Nevertheless, in some cases we observed nitrate reduction without gaseous nitrogen production. Using a stepwise multiple regression models, H 2 S concentration was the unique parameter found to have a negative effect on N 2 production. We then suspected that dissimilatory nitrate reduction to ammonium (DNRA) occurred in the presence of H 2 S. In order to verify this hypothesis, 15 N nitrate injections were performed into microcosms containing different H 2 S concentrations. The ammonium 15 N enrichment was measured using an elemental analyser coupled to an isotope ratio mass spectrometer. In the two microcosms containing the highest H 2 S concentrations, the ammonium was 15 N enriched and at the end of the experiment all the added nitrate was converted into ammonium. For the two microcosms containing the lowest H 2 S concentrations, no 15 N enrichment of ammonium was observed. This isotopic approach has allowed us to demonstrate that, in the presence of significant concentrations of H 2 S, denitrification is replaced by DNRA.