Amplification of the rbcL gene from dissolved and particulate DNA from aquatic environments

The carboxylation of ribulose biphosphate by the enzyme ribulosebisphosphate carboxylase/oxygenase is the mechanism for CO2 fixation and primary production in nearly all ecosystems on this planet. Although certain algal isolates and higher plants contain conserved nucleotide sequences in the large subunit of the gene (rbcL) for this enzyme, such genes from natural microbial assemblages have not been heretofore examined. Using oligonucleotide primers designed for conserved regions of the rbcL gene of a Synechococcus sp. (Anacystis nidulans), we have amplified rbcL from DNA preparations from planktonic samples from a Florida reservoir and from algal isolates by the polymerase chain reaction. We have also detected rbcL by gene amplification in the extracellular DNA fraction of this reservoir, indicating that phytoplankton can be a source of dissolved DNA. These results suggest that gene amplification can be applied for the detection of conserved genes encoding enzymes involved in important ecological functions in aquatic environments.