A new study from the University of Virginia contrasts current theories of how mitochondria began. The study used next-generation DNA sequencing technologies to decode genomes of 18 bacteria that are closely related to mitochondria. The study indicates that parasitic bacteria were the first cousins of the mitochondria that help power cells in animals and plants, and first behaved as energy parasites in those cells before turning beneficial.

The study appears in last week’s issue in the online journal PLOS One, published by the Public Library of Science. The study provides an alternate theory to two current theories of how simple bacterial cells were consumed by host cells and eventually became mitochondria, the “powerhouse” organelles within almost all eukaryotic cells — animal and plant cells with a nucleus and other features. Mitochondria use adenosine triphosphate, or ATP, to power the cells, and are considered to be the energy currency of life by biologists.

The origin of mitochondria can be traced back to 2 billion years ago and is one of the most crucial events in the evolutionary history of life. However, little is known about the circumstances surrounding the origin of mitochondria, and the question is considered an enigma in modern biology.

The study’s lead author, U.Va. biologist Martin Wu, said in a statement, “We believe this study has the potential to change the way we think about the event that led to mitochondria.” He continued, “We are saying that the current theories – all claiming that the relationship between the bacteria and the host cell at the very beginning of the symbiosis was mutually beneficial – are likely wrong.”

According to the United Mitochondrial Disease Foundation, mitochondria are responsible for creating over 90 percent of the energy needed by the body to sustain life and support growth.