Genetic structure of natural populations of Nitrobacter in an aquatic environment
Nitrification has been essentially studied as a chemical process and the studies of the microbial population have been slightly worked out. This work constitutes a first attempt to study the diversity of Nitrobacter strains with the aim of working out the genetic structure of natural populations. The Nitrobacter population structure was compared between freshwater and sediments of the same lake. Nitrobacter isolates were identified and characterized by DNA/DNA hybridization, restriction pattern of rRNA genes, PCR/RFLP analysis of the ribosomal intergenic spacer and plasmid patterns. It was shown that this lake population was split into 3 subpopulations: a specific freshwater subpopulation, a specific sediment subpopulation and a nonspecific one. A 60 MDa plasmid was detected in 3,3% of freshwater isolates. A 37 MDa plasmid was detected in 59% of sediments isolates. This 37 MDa plasmid was not associated with a genomic group, but associated with a localization: the sediments. These results suggest that this 37 MDa plasmid could be implicated in the adaptation to sediment environment.
Key wordsNitrobacter natural population diversity plasmids freshwater sediments
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