Estimation of the abundance of the cadmium resistance gene cadA in microbial communities in polluted estuary water

We describe herein a molecular method for estimating the abundance of the c adA gene, which encodes a Cd2+/ATPase protein transporter, in bacterial DNA extracted from samples of environmental water. Competitive polymerase chai n reaction (cPCR) may be the most appropriate technique for assessing the p revalence of the cadA gene in microbial communities in highly heterogeneous and polluted environments, such as the Seine estuary (France). We describe the development of this method: (i) the choice of two specific primers, ba sed on the sequences encoding the cadmium binding site and the ion channel domains; (ii) the construction of a competitor sequence and assessment of i ts amplification efficiency; and (iii) the estimation of the copy number of the cadA gene. The cadA content in the bacterial community is expressed as the number of gene copies per ng of total DNA extracted, which is independ ent of the DNA extraction yield. This molecular procedure was improved to a nalyze cadA levels in bacterial DNA extracted from estuary water accidental ly contaminated with cadmium. Results revealed a subsequent increase in the copy number of the CadA gene in the microbial community. (C) 2001 Editions scientifiques et medicales Elsevier SAS.