naturalSCIENCE Home BOOK REVIEW Your Comment

DARK LIFE: Martian Nanobacteria, Rock-Eating Cave Bugs, and Other Extreme Organisms of Inner Earth and Outer Space

Michael Ray Taylor

Simon & Schuster/Scribner, New York, 1999, Hardcover, 288 pages, $23 list, ISBN: 0684841916. Available from Amazon.com at 30% off the cover price

Reviewed for naturalSCIENCE by

Edward E. Ishiguro Note 1

Professor and Chair, Department of Biochemistry and Microbiology, University of Victoria, Victoria, B.C., Canada


Microbes are now recognized as the most diverse group of living organisms. Although an accurate count of microbial species is currently unavailable, it is generally agreed that they outnumber the half-million or so described species of insects which have long been thought to represent the quintessence of biodiversity. Microorganisms inhabit every corner of our Earth, including niches that our conventional wisdom would deem uninhabitable. In recent years, for example, viable microbes have been recovered from Antarctic ice cores, deep-sea volcanic vents, and deep cores taken from the Earth's subsurface. These microbes are the "dark life" of Michael Ray Taylor's book. Taylor suggests that such microbial forms may even reside extraterrestrially. Life in Taylor's ecosystems occurs in the absence of sunlight, hence the reference to "dark."

This book is Taylor's personal account of his 10-year odyssey, covering the period from 1988 to 1998, in search of dark life. Taylor is a journalist and not a scientist by trade, but he provides an excellent list of references that includes most of the relevant literature in the field, indicating that he is well read on the topic of dark life. The book is a good introduction to dark life, but it is not flawless.

There were two obvious errors that I found. On page 48, Taylor describes the polymerase chain reaction (PCR). He states that Taq polymerase keeps "DNA from breaking down when exposed to heat." This is not correct. Taq polymerase is a heat-resistant enzyme that is responsible for making the many copies of a desired gene in the PCR reaction and has no role in stabilizing DNA. Its key property is its thermostability, which permits it to tolerate the high temperature cycles in the PCR procedure. Incidentally, I was disappointed that Taylor did not expound further the impact that PCR has had, and continues to have, in dark life research. The second error is on page 110. "Bernard Postgate" is really John Postgate, unless he has a nickname that I am not aware of.

Taylor highlights the work of David McKay and his coworkers on a Mars meteorite called ALH 84001 that suggested the presence of life on Mars (1). McKay observed what was interpreted as fossilized microbes embedded in this meteorite. In my opinion, Taylor gave far too much coverage to these results since the current consensus is that the report is incorrect. However, McKay's work certainly renewed an interest in the possibility of life on Mars, particularly dark or subterranean life. Despite the questionability of the Mars rock studies, life on Mars is still a popular subject, but that interest is now being fueled by advances in other areas of dark microbiology.

Taylor also spends far too much time describing the work of Robert Folk, a retired geologist from the University of Texas, on the formation of travertine in the hot springs around Viterbo, Italy. Folk has proposed that tiny bacteria, that he calls "nannobacteria" or "nanobacteria" (I will use the latter spelling), are directly responsible for the formation of travertines and, in fact, in the precipitation of all minerals and crystals associated with hot springs. His studies have been published in geochemical journals (e.g., see 2) and, to my knowledge, have never been peer-reviewed by microbiologists. I personally find his hypothesis a weak one based largely on electron microscopic evidence of fossilized nanobacteria in travertines. There is no solid evidence that the observed structures are derived from viable microbes. I would view this work in the same light as the Mars rock studies. I am sure, on the other hand, that interesting microbes could be isolated from these hot springs; unusual microbes have been recovered from every hot spring examined to date. Whether these microbes are involved in geochemical activities, such as those proposed by Folk, is an interesting question that deserves further investigation. In this connection, Taylor describes the work of E. Olavi Kajander who is head of a medical research group in Finland. Kajander has reported the direct involvement of nanobacteria in the formation of human kidney stones. He proposes that these nanobacteria could serve as crystallization centers for the formation of renal calculi. He has also claimed that nanobacteria can be isolated from a variety of mammalian body fluids. These studies have been published in the prestigious journal, The Proceedings of the National Academy of Sciences of the United States of America (3). I have personally read this report and was fairly convinced by it. However, Kajander's work has recently been challenged by his colleagues (4). Moreover, a recent review reports that all trials designed to confirm the presence of microbes in human kidney stones have yielded negative results (5).

The nanobacteria of Folk and Kajander are unusually small, with diameters of 0.2 micrometers or less. There is no doubt that this is a hot topic. Philippa Uwins, Richard Webb and Anthony Taylor have recently reported a new form of nanoorganism that they call a nanobe (6). Their work is again based mostly on microscopic observations and like the work of Folk, fails to show conclusively that these structures represent living organisms. Such studies on nanorganisms have sparked numerous recent discussions on how small cells can really be (e.g., see (7)). The issue of size is interesting but not as important to me as showing that such organisms truly exist.

The above examples aside, the story of dark life is deeply fascinating. Taylor is a caver, and the book would certainly not be complete without his description of an expedition into Lechuguilla Cave in New Mexico, to recover samples of dark life. In this regard, I was surprised to find that Taylor mentions in only a single sentence the work of Tullis Onstott on rock-eating thermophiles that he recovered from a hot chamber more than two miles below the surface in a South African gold mine. Onstott believes that the rock samples that yielded these microbes may have been sealed off from the surface about 2 billion years ago. Furthermore, in view of the fact that Taylor cites a key review by Frederickson and Onstott that was published in Scientific American (8) in his reference list, I was also disappointed to find that he did not provide broader coverage on deep subsurface microbiology. Frederickson and Onstott describe finding viable microbes in core samples taken from subsurface formations almost 2 miles below the surface, at temperatures as high as 75°C. These are very significant findings. Interestingly, it is believed that these forms of dark life, like the South African gold mine specimens, have been separated from the Earth's surface for many millions of years. Taylor does describe microbial life from undersea volcanic vents. He sporadically mentions Lake Vostok, a vast body of liquid water beneath about 4 kilometers of glacial ice in Antarctica. Recent reports indicate the presence of viable microoranisms in Vostok deep ice cores (9), and the existence of life in the waters of Lake Vostok is anticipated. The Lake Vostok project promises to be a fascinating one. As noted, studies on such usual ecosysytems are the current driving forces for the renewed interest in the possibility of extraterrestrial life.

In summary, Dark Life is well written and entertaining reading. It will provide an excellent introduction to the microbiology of extreme environments.

References

(1) McKay, D., E.K. Gibson Jr., K.L. Thomas-Keprta et al. 1996. Search for past life on Mars: possible relic biogenic activity in Martian meteorite ALH84001. Science 273:924–930. Online article

(2) Folk, R.L., 1993. SEM imaging of bacteria and nannobacteria in carbonates in rocks. J. Sediment. Petrol. 63:990-999.

(3) Kajander, E.O. and N. Çiftçioglu. 1998. Nanobacteria: An alternative mechanism for pathogenic intra- and extracellular calcification and stone formation. Proc. Nat. Acad. Sci. 95:8274-8279. Online article

(4) Abbott, A. 1996. Battle lines drawn between 'nanobacteria' researchers. Nature 401:105.

(5) Kramer, G. et al. 2000. Role of bacteria in the development of kidney stones. Curr. Opin. Urol. 10:35-38. PubMed abstract

(6) Unwins, P.J.R., R.I. Webb and A.P. Taylor. 1998. Novel nano-organisms from Australian sandstones. Am. Mineral. 83:1541–1550. Online abstract, Full text PDF file

(7) Moore, P.B. 1999. A biophysical chemist's thoughts on cell size. In Size Limits of Very Small Microorganisms: Proceedings of a Workshop. National Academy Press, Washington, DC, 164 p. Online article

(8) Fredrickson, J.K. and T.C. Onstott. Microbes deep inside the earth. Sci. Am. October 1996, p. 42. Online article

(9) Karl, D.M., D.F. Bird, K. Björkman, T. Houlihan, R. Shackelford and L. Tupas. 1999. Microorganisms in the Accreted Ice of Lake Vostok, Antarctica. Science 286:2144–2147.

Other links

(1) Thomas Gold of Cornell University discusses indications that the crust of the Earth may support an immense microbial biomass in "The Deep Hot Biosphere"

(2) naturalSCIENCE's nanobiology page.


Notes

1 Dr. Edward Ishiguro is the chair of the Biochemistry and Microbiology department of the University of Victoria, in British Columbia, Canada. He can be reached by email at eishuv@uvvm.uvic.ca. His research interests are detailed on his web page.

Copyright © 2000, naturalSCIENCE Journals

Your comment on this or any item in naturalSCIENCE is invited and should be addressed to: publisher@naturalscience.com. For further information on submitting a contribution to naturalSCIENCE, please see the Author Guide


naturalSCIENCE Contents Top of Page