Abstract: Compositions and methods are provided for the rapid and highly accurate identification of the entire essential genome of any organism under a given selection condition at a resolution of a few base pairs. An engineered transposon bearing an adapter sequence for ultra high throughput adaptor-based sequencing is employed for hyper-saturated transposon mutagenesis. Transposon junctions are subsequently isolated and collectively amplified through a shared parallel PCR strategy such that a second adaptor sequence is further incorporated into template DNA so that the first adaptor sequence and the second adaptor sequence flank the 5? and 3? regions of the sample DNA, respectively. Sample DNA is then sequenced in an ultra high-throughput adaptor-based DNA sequencer using adaptor primers. Transposon insertion sites are mapped onto the organism's genome, allowing for the algorithmic identification of essential genetic elements based on genomic transposition frequency.