 At the time, four known species of oil-metabolizing bacteria were known to exist, but when introduced into an oil spill, they competed with each other, limiting the amount of crude oil that they degraded.The genes necessary to degrade oil were carried on plasmids, which could be transferred among species.By irradiating the transformed organism with UV light after plasmid transfer, Prof. Chakrabarty discovered a method for genetic cross-linking that fixed all four plasmid genes in place and produced a new, stable, bacterial species (now called "Pseudomonas putida") capable of consuming oil one or two orders of magnitude faster than the previous four strains of oil-eating microbes.