Eric Trably

Acetate Oxidation Is the Dominant Methanogenic Pathway from Acetate in the Absence of Methanosaetaceae

ABSTRACT The oxidation of acetate to hydrogen, and the subsequent conversion of hydrogen and carbon dioxide to methane, has been regarded largely as a niche mechanism occurring at high temperatures or under inhibitory conditions. In this study, 13 anaerobic reactors and sediment from a temperate anaerobic lake were surveyed for their dominant methanogenic population by using fluorescent in situ hybridization and for the degree of acetate oxidation relative to aceticlastic conversion by using radiolabeled [2-14C]acetate in batch incubations. When Methanosaetaceae were not present, acetate oxidation was the dominant methanogenic pathway. Aceticlastic conversion was observed only in the presence of Methanosaetaceae.

Statistical tools for the optimization of a highly reproducible method for the analysis of polycyclic aromatic hydrocarbons in sludge samples

The aim of this study is to develop and optimize an analytical method for the determination of 14 priority PAHs in sludge samples based on Accelerated Solvent Extraction (ASE) coupled to RP-HPLC/fluorescence detection. Statistical tools were used to demonstrate the influence of the parameters during the optimization steps. The final parameters were selected to provide analytical errors statistically as low as possible. First, couples of excitation/emission detection wavelengths were tested, and some were finally selected to provide errors lower than 2%. It was then demonstrated that PAH extraction efficiencies are not statistically influenced by the ASE parameters. It was also found that the ASE extraction from sludge samples provides statistically similar results to those obtained with traditional Soxhlet extraction, but with a lower reproducibility error. After optimization, the accuracy of the method was validated with a certified sludge. In conclusion, an optimized analytical procedure has been proposed to monitor PAHs during lab-scale experiments requiring highly repeatable and accurate results from a low sample volume contaminated by PAHs at trace levels.

A strict anaerobic extreme thermophilic hydrogen-producing culture enriched from digested household waste.

Aims:  The aim of this study was to enrich, characterize and identify strict anaerobic extreme thermophilic hydrogen (H2) producers from digested household solid wastes.

Microbial dynamics in anaerobic enrichment cultures degrading di-n-butyl phthalic acid ester.

Although anaerobic biodegradation of di-n-butyl phthalic acid ester (DBP) has been studied over the past decade, only little is known about the microorganisms involved in the biological anaerobic degradation pathways. The aim of this work is to characterize the microbial community dynamics in enrichment cultures degrading phthalic acid esters under methanogenic conditions. A selection pressure was applied by adding DBP at 10 and 200 mg L(-1) in semi-continuous anaerobic reactors. The microbial dynamics were monitored using single strand conformation polymorphism (SSCP). While only limited abiotic losses were observed in the sterile controls (20-22%), substantial DBP biodegradation was found in the enrichment cultures (90-99%). In addition, significant population changes were observed. The dominant bacterial species in the DBP-degrading cultures was affiliated to Soehngenia saccharolytica, a microorganism described previously as an anaerobic benzaldehyde degrader. Within the archaeal community, there was a shift between two different species of the genus Methanosaeta sp., indicating a highly specific impact of DBP or degradation products on archaeal species. RNA-directed probes were designed from SSCP sequences, and FISH observations confirmed the dominance of S. saccharolytica, and indicated floccular microstructures, likely providing favourable conditions for DBP degradation.