Olivier Crouzet

Isolation and characterization of mesotrione-degrading Bacillus sp. from soil

Dissipation kinetics of mesotrione, a new triketone herbicide, sprayed on soil from Limagne (Puy-de-Dôme, France) showed that the soil microflora were able to biotransform it. Bacteria from this soil were cultured in mineral salt solution supplemented with mesotrione as sole source of carbon for the isolation of mesotrione-degrading bacteria. The bacterial community structure of the enrichment cultures was analyzed by temporal temperature gradient gel electrophoresis (TTGE). The TTGE fingerprints revealed that mesotrione had an impact on bacterial community structure only at its highest concentrations and showed mesotrione-sensitive and mesotrione-adapted strains. Two adapted strains, identified as Bacillus sp. and Arthrobacter sp., were isolated by colony hybridization methods. Biodegradation assays showed that only the Bacillus sp. strain was able to completely and rapidly biotransform mesotrione. Among several metabolites formed, 2-amino-4-methylsulfonylbenzoic acid (AMBA) accumulated in the medium. Although sulcotrione has a chemical structure closely resembling that of mesotrione, the isolates were unable to degrade it.

Stratification of Archaea in the Deep Sediments of a Freshwater Meromictic Lake: Vertical Shift from Methanogenic to Uncultured Archaeal Lineages

As for lineages of known methanogens, several lineages of uncultured archaea were recurrently retrieved in freshwater sediments. However, knowledge is missing about how these lineages might be affected and structured according to depth. In the present study, the vertical changes of archaeal communities were characterized in the deep sediment of the freshwater meromictic Lake Pavin. For that purpose, an integrated molecular approach was performed to gain information on the structure, composition, abundance and vertical stratification of archaeal communities thriving in anoxic freshwater sediments along a gradient of sediments encompassing 130 years of sedimentation. Huge changes occurred in the structure and composition of archaeal assemblages along the sediment core. Methanogenic taxa (i.e. Methanosaeta and Methanomicrobiales) were progressively replaced by uncultured archaeal lineages (i.e. Marine Benthic Group-D (MBG-D) and Miscellaneous Crenarchaeal Group (MCG)) which are suspected to be involved in the methane cycle.

New Design Strategy for Development of Specific Primer Sets for PCR-Based Detection of Chlorophyceae and Bacillariophyceae in Environmental Samples

ABSTRACT Studying aquatic microalgae is essential for monitoring biodiversity and water quality. We designed new sets of 18S rRNA PCR primers for Chlorophyceae and Bacillariophyceae by using the ARB software and implementing a virtual PCR program. The results of specificity analysis showed that most of the targeted algal families were identified and nontargeted organisms, such as fungi or ciliates, were excluded. These newly developed PCR primer sets were also able to amplify microalgal rRNA genes from environmental samples with accurate specificity. These tools could be of great interest for studying freshwater microalgal ecology and for developing bioindicators of the health status of aquatic environments.

Consonant recognition in noise with temporal cues: II. Effects of temporal envelope enhancement on response times

In an effort to evaluate the importance of envelope cues in speech recognition, response times and percentages of correct responses were measured simultaneously in normal‐hearing and hearing‐impaired listeners, using a forced‐choice identification paradigm. Naturally produced /aCa/ disyllables presented in a white noise background (+6 dB signal‐to‐noise ratio) were used to create temporal‐only stimuli having instantaneous amplitudes identical to the natural speech stimuli, but flat spectra. The temporal envelope of the /aCa/ disyllables was either left intact or enhanced by raising it to the power 2. In the first experiment, 13 young normal‐hearing listeners (24–27 years) were tested. The results show that envelope enhancement yields a general improvement in both percent correct identification (4.75%) and response times (63 ms). In the second experiment, nine hearing‐impaired listeners (53–71 years) were tested at a comfortable listening level. Overall, temporal expansion fails to show better consonant identification in terms of percentage of correct responses, but yields a significant improvement (66 ms) in terms of response time. These results suggest that: (1) the perceptual effects of speech‐envelope enhancement cannot be completely accounted for by percent correct‐responses measurements, and (2) response times seem to be more sensitive to the effects of envelope enhancement.