No abstract

Microorganisms degrading phenolic compounds play an important role in soil carbon cycling as well as in pesticide degradation. The pcaH gene encoding a key ring-cleaving enzyme of the beta-ketoadipate pathway was selected as a functional marker. Using a degenerate primer pair, pcaH fragments were cloned from two agricultural soils. Restriction fragment length polymorphism (RFLP) screening of 150 pcaH clones yielded 68 RFLP families. Comparison of 86 deduced amino acid sequences displayed 70% identity to known PcaH sequences. Phylogenetic analysis results in two major groups mainly related to PcaH sequences from Actinobacteria and Proteobacteria phyla. This confirms that the developed primer pair targets a wide diversity of pcaH sequences, thereby constituting a suitable molecular marker to estimate the response of the pca community to agricultural practices.

Numerous biological, physical and chemical parameters are involved in retention and removal of chemical pollutant and bacteria in wastewater treatment systems. Biofilm presence was often cited for its influence in these mechanisms. Sandy soil is the most used packing material in wastewater treatment study and little information is available for the other soil. The objectives of this study were to compare purification efficiency of packing materials (soil) and to allow a better understanding in purification mechanisms in one-site wastewater treatment. Our work focused on water pollution removal and biofilm development. For this purpose, four experimental reactors were packed with sand and silt suitable for on-site wastewater treatment plant. They were dosed with septic effluent at loads of 5 and 12 cm/j for sand and 2 and 5 cm/j for silt. The purification performances and biofilm development were monitored on 245 for sand filters and 65 days for silt filters. Dissolve oxygen concentration from the treated effluents showed better values for the low loads and for the silt reactors. Also, organic pollutant remove by oxidation (COD and DOC) were better eliminated in the following reactors: Silt (2 cm/j) > Silt (5 cm/j) > Sand (5 cm/j) > Sand (12 cm/j). Adsorption was the mechanism of ammonium removal in silt although nitrification took part in sand. Biofilm development was observed in the first 2.5 cm and 10 cm in the sand reactors loaded at 5 and 12 cm/j respectively.

Biofilm development in wastewater treatment system by soil infiltration is often mentioned for its participation to purification efficiency and clogging zone formation. It appears necessary to understand its evolution in order to better control the operation of these systems. The objective of this study was to improve knowledge about the temporal evolution of the biofilm structure in the first centimetres of infiltration system. For this purpose, metabolic fingerprints by Biolog EcoPlate™ and molecular fingerprints by Ribosomal Intergenic Spacer Analysis (RISA) were carried out on sand, septic effluent and treated effluent samples from two experimental reactors supplied with different hydraulic loads collected at different times. The metabolic capabilities of sand microflora decreased in time.In the same way, molecular structure of the biofilm community changed and converged to similar structure in time. Principal components analysis on RISA gel revealed a "buffering effect" of the sand filter on the genetic structure of the bacterial community from treated effluent. The kinetics of evolution of the both metabolic and genetic fingerprints showed a reduction of the metabolic and genetic potentials of septic and treated effluents for the same times. The population dynamic within the biofilms appears interesting evidence in the comprehension of the operation of the treatment systems.