Life in Ancient Ice. John D. Castello and Scott O. Rogers, eds. Princeton University Press, New Haven, CT, 2005. 336 pp. $69.50 (ISBN 0691074755 cloth).
Life in Ancient Ice, edited by John Castello and Scott Rogers, arose from an international workshop of the same title in 2001. Despite the time that has passed since the original workshop, the issues and content discussed in the book are still current. Nineteen chapters follow the introduction, with subjects that range from the types and sources of microbes in polar environments (including permafrost, glacier, and lake ice) to the types of organisms found within ice cores. The authors discuss issues such as the contamination, preservation, and viability of microbes, including viral pathogens, and the use of icy ecosystems on Earth as analogues for those potentially on other extraplanetary bodies.
A reader new to the topic will be impressed by the myriad of microbial life forms that exist in present-day icy environments, such as the ice cover of the lakes of the Antarctic Dry Valleys, the sea ice around Antarctica, and permafrost around the globe. A more au fait reader will be impressed that cryopreservation of viable organisms can approach timescales of hundreds of thousands or millions of years. For example, fungi may stay viable for 400 thousand years in Antarctic ice, and yeasts in Siberian permafrost may be viable after 3 million years. These assertions are likely to stimulate the imagination of new researchers, who could perhaps think laterally about the potential of ice cores in the study of evolutionary biology and the extraction of commercially exploitable chemicals, such as antifreeze proteins, anticancer drugs, and antibiotics. The fact that some of these long-stored yet viable organisms are not true psychrophiles, or cold-adapted organisms, further sparks the imagination and curiosity. Finally, those with a keen research interest in this area will eagerly scour the book for information on protocol (e.g., obtaining ice core samples without drilling fluids to minimize contamination), new literature, new methodologies, and the easy proximity of comparative data on a variety of microbes to give them an edge with new grant applications.
It is the nature of a book with chapters by a number of authors that some of the text is more polished than other parts, and that different chapters will resonate with different readers. My personal favorites are the chapters on cyanobacteria in lake ice cover by Priscu and colleagues and on fungi in glacier ice by Ma and colleagues, and the chapters on yeasts, fungi, and phototrophs in permafrost by Faizutdinova and colleagues, Ivanushkina and colleagues, and Vishnivetskaya and colleagues, respectively. These make the reader think outside the box. The new norm is to expect ice to act as an ecosystem as long as liquid water, whether at freezing point or supercooled, is present. The new norm is also to expect cold ice masses to act as a repository for potentially viable ancient organisms. The jury seems to be out at present about the longevity of preservation. The chapters on yeasts (by Sarmer and colleagues) and viruses (by Castello and colleagues) in ice cores in Greenland confirm this new norm, and the potential preservation of viral pathogens of humans in ice sheets (by Shoham) is a logical progression. It is one that requires careful consideration. Christner and colleagues document the characteristics of bacteria found in a range of ancient ice cores, showing how their properties help them to remain viable in what would otherwise be thought to be an inhospitable environment.
The material is this book is both stimulating and challenging. The concluding chapter by Castello and Rogers cautions that many, but not all, of the microbes found in ice cores may be contaminants. The challenge for the next generation of ice core microbiologists is to convince their own community that the coring methodology and ice sample treatments are rigorous, and that the very low numbers of microbes found are indeed representative of those in uncontaminated ice. My hunch, as an interested geochemist, is that viable organisms are preserved in ancient ice, and that the coming decade will see a proliferation of new work to corroborate the view of Castello and Rogers.