Protocells: Bridging Nonliving and Living Matter (review)

Protocells are hypothetical lifelike entities, capable of growing and dividing, thus giving rise to offspring that are similar to their parents but, due to the noise inherent in the process, not identical to them. Protocells therefore possess all the ingredients necessary for Darwinian evolution, and it is possible to imagine that a population of initially very simple protocells change in time, acquiring more sophisticated properties.

Protocells might be at the heart of an entirely new biotechnology, if subject to specific selective pressure (for example, for removing toxic compounds or synthesizing useful ones). But besides potential applications, of course, they also carry an intrinsic interest: their relationship to the problem of the origins of life. Most researchers in protocells do not aim at precisely reproducing the process of the emergence of life on earth, a goal which might even turn out to be unachievable due to lack of recorded information. But it is apparent that succeeding in creating a viable population of protocells would provide at least a proof-of-principle of abiogenesis, and also a set of indications for choosing among various alternative scenarios. (Moreover, such an achievement would have the side effect of cutting short meaningless creationist or intelligent design talks.)

Protocells by Steen Rasmussen, Mark Bedeau, and Norman Packard provides a wide overview of current research on protocells in 28 papers written by different research leaders in the field. The coverage of the experimental and theoretical aspects is impressive. Many of the authors have been part of a large research project on protocells funded by the European Union (Programmable Artificial CElls, PACE for short) that provided a new impetus to the research on this topic, an impetus that was later increased by the U.S. Protocell Assembly project. PACE also provided the funding necessary to give rise in Venice to the ECLT, a new research centre devoted to "Living Technology" (this being the name proposed by the chief editors as an umbrella to cover the activities in this area). A new EU project on this subject is in the final negotiation phase, and it is expected to start very soon. So the field is fertile and active, and a book like this can provide a much-needed reference for all the practitioners.

The content is wide, and overall well-balanced between theory and experiments. Adequate room is given to the main scenarios to protocells, including: the various models where it is supposed that the action takes place inside a vesicle—in other words, that both gene duplication and the formation of new container molecules happen in the aqueous internal volume; the Los Alamos Protocell (sometimes called the "LA Bug"), where the key processes of gene duplication and metabolism take place in the nonpolar membrane of a vesicle (which contains a nucleic acid with a suitable lipophilic backbone); the Lipid World, where there are no genes in the classical sense, but the "genetic" memory is carried by the vesicle lipid composition

A few critical comments are the following. First, it seems that the various papers have been collected at different times, and some of them are not very up-to-date. The editors state that the process of writing the book started in 2003, and one can see that some of the papers have not undergone significant revisions in recent times: two-thirds of the papers do not have any reference more recent than 2005, and in most of the other papers they are just a few. While the effort of the editors to collect the contributions of so many first-class scientists has to be praised, a more up-to-date set of papers, for a book which appeared in 2009, would have been welcome.

In addition, there are two main scenarios for the spontaneous emergence of sets of self-replicating molecules, one of which is based on the idea of templatematching (typically, Watson-Crick type base pairing), the other on that of a network of reactions that collectively replicates the...