Testing of the universal cld gene primer sets on environmental DNAs. Top of gel, touchdown PCR using the DCD-F/DCD-R primer set, corresponding to a 484-bp internal region of the cld gene. Bottom of gel, nested PCR on the above reactions, using the UCD-238F/UCD-646R primer set, corresponding to a 408-bp internal region of the cld gene. Lane 1, Pseudomonas sp. strain PK (positive control); lane 2, Los Alamos well 2; lane 3, Los Alamos well 3; lane 4, Los Alamos well 4; lane 5, Los Alamos well 5; lane 6, Los Alamos well 7; lane 7, campus library pond; lane 8, campus library soil; lane 9, campus lake; lane 10, Lake Fryxell sediment; lane 11, Lake Fryxell 7-m water column; lane 12, Lake Fryxell 12-m water column; lane 13, Lake Hoare 12-m water column; lane 14, Lake Hoare mat; lane 15, Vida; lane 16, negative control (no DNA); lane 17, 100-bp ladder.