Yousef Abu Kwaik of the University of Louisville and his team said their work could help lead to development of new antibiotics and vaccines for the disease.
"It is possible that the process we have identified presents a great target for new research in antibiotic and vaccine candidates, not only for Legionnaires' disease but in other bacteria that cause illness," Abu Kwaik said in a statement.
For two years, the researchers examined Legionella, which is an intercellular bacterium that exists in amoebae in the water systems; it is transmitted to humans through inhalation of water droplets. Cooling towers and whirlpools are the major sources of transmission.
The study, published in the journal Science, said the bacterium uses the amoeba's cellular process to "tag" proteins, causing them to degrade into their basic elements of amino acids, which are used by the bacteria as the main source of energy to grow and cause disease.
"The bacteria live on an 'Atkins diet' of low carbs and high protein and they trick the host cell to provide that specialized diet," Abu Kwaik said.