Microbe Magazine (American Society of Microbiology, May 2005)

Power, Sex, Suicide: Mitochondria and the Meaning of Life

Reviewed by Franklin M. Harold, University of Washington, Seattle

Don’t let the titillating title deter you from reading this stimulating book! If you are under the impression, as I was, that mitochondria are yesterday’s organelles, let Nick Lane show you how much they have taught us that is new, interesting, and quite possibly true. The book is serious and scholarly, yet written in an easy-going, nontechnical style; it makes an enjoyable read. You may wish to reserve judgment on some points (I do, even though I had the privilege of advising the author on several chapters), but the thesis as a whole is persuasive and guaranteed to animate the little gray cells.

Mitochondria, as everyone knows, serve as the powerhouse of eukaryotic cells. They generate useful energy in the bacterial manner, by coupling the transport of electrons along the respiratory chain to a current of protons across the mitochondrial inner membrane, which in turn drives ATP synthesis. Their involvement in other aspects of cell biology grows out of this bizarre mechanism. Internalizing energy generation in cytoplasmic organelles relieved a constraint on cell size, and made eukaryotic cells possible. Dissipation of the proton current by the controlled leakage of protons is one basis of metabolic heat production, and helps to underpin the warm-blooded way of life. Any blockage of electron transport promotes leakage of electrons from the respiratory chain, which pass on to oxygen with the formation of free radicals. Chemically reactive radicals damage mitochondrial membranes, initiate certain diseases, serve as the signal for cell suicide (apoptosis), and may even be involved in the invention of sex. Free radicals, and the damage they do, is very likely what makes us age. We live by our mitochondria, and in the end we die by them.

For microbiologists, the most thought-provoking part of the book may well be the first half, which centers on the role of mitochondria in the origin of the eukaryotic cell. One of the few solid facts in cell evolution is that mitochondria ( and chloroplasts as well) are the descendants of bacterial endosymbionts. The mystery is, what sort of cell hosted those endosymbionts? Lane accepts the thesis, championed by William Martin and others, that it all began with a syntrophic association between a methanogenic archaeon and a versatile proteobacterium capable of both respiration and fermentative hydrogen production. As the partnership became ever more intimate, the eubacterium turned into an endosymbiont and eventually into an organelle. And Lane carries the argument further, to claim that the evolution of eukaryotic cells could only have occurred by an endosymbiotic pathway, which is therefore the indispensable prerequisite for the rise of life forms larger and more complex than bacteria. It follows that “the acquisition of mitochondria was the pivotal moment in the history of life” ( p. 17). Lane argues with verve that “the secret of complex life lies in the chimeric nature of the eukaryotic cell, a hopeful monster born in an improbable merger 2,000 million years ago, an event still frozen in our innermost constitution” (p. 29).

Lane’s presentation ties together “the whole trajectory of evolution, from the origin of life itself, through the genesis of complex cells and multicellular organisms, to the attainment of larger sizes, sexes, warm-bloodedness and into the decline of old age and death” (p. 6). It is surely not the whole truth, nor is it likely to be nothing but the truth. But it is a brave attempt to accomplish a feat that is becoming all too rare in contemporary science: to grasp the tangle of data from many disparate fields, and to weave them into a unifying pattern that makes sense of the way things are.