Synthetic oligonucleotide probes for detection of mercury-resistance genes in environmental freshwater microbial communities in response to pollutants.

Mercury-resistance genes were detected byin situ hybridization using new synthetic oligonucleotide probes specific formerA andmerB genes according to the published sequences of the corresponding enzymes. These DNA probes were used for the detection of specific mercury-resistant microorganisms isolated from the Rhine River which had been polluted 3 years previously in 1986. Mercuric reductase and organomercurial lyase genes persist in the bacterial genome even after the disappearance of the pollutant but are absent in axenic amoebae. A total of 49 bacterial isolates showed DNA homologies with the(32)P-labelled DNA probes and 15 free-living amoebae were selected due to their harboured symbiotic mercury-resistant bacteria.

Phenylmercuric acetate biodegradation by environmental strains of Pseudomonas species.

Organomercurial pollution occurring in the Rhine river in 1986 led us to study the possibility of depollution by mercury-resistant environmental aquatic strains. Four species of Pseudomonas were investigated for their ability to biotransform phenylmercuric acetate (PMA). Such biological depollution was demonstrated to be due to an enzymatic activity in whole cells and in cell-free extracts from Pseudomonas fluorescens and other Pseudomonas species. PMA biotransformation was followed by high-performance liquid chromatography. Some of those bacteria growing between 4 and 41 degrees C probably represent a natural means of organomercurial depollution, which acts slowly in interaction with other organisms and non-organic porous surfaces.