Science risks retracing its own tracks if early research is forgotten

Howard Gest

Howard Gest is Distinguished Professor Emeritus of Microbiology and Adjunct Professor of History & Philosophy of Science I at Indiana University, Bloomington.

Those who are ignorant of history are condemned to repeat it." This is one of the many variations of George Santayana's famous quotation of 1905. It is particularly apt in describing some current and recent research efforts in microbial ecology. Thus, NASA's publicity machine has seized on "extremophiles," giving the impression that such microbes have been discovered recently, just in time to bolster faltering hopes that evidence for past or present microbial life on Mars will be forthcoming. The ubiquity of bacteria, well known for over a century, was rediscovered by NASA in 2007 in disconcerting circumstances . . . reported under a New York Times headline (October 9, 2007): "In NASA's Sterile Areas, Plenty of Robust Bacteria. . . . Researchers have found a surprising diversity of hardy bacteria in a seemingly unlikely place-the so-called sterile clean rooms where NASA assembles its spacecraft and prepares them for launching." The leader of the study (C. Moissi et al., FEMS Microbiol. Ecol. 61:509-521, 2007) is quoted as saying that their findings will advance the search for life on Mars and other worlds "by sparking improved cleaning and sterilization methods." Thanks, but we already have excellent methods!

Presently, we see articles rediscovering the complexity of microbial ecology in milieus such as soils, waters, and the animal intestine (e.g., see "Gut Reactions," Science 324:1136-1137, 2009). Since current texts have become heavy, encyclopedic tomes with scant coverage of the history of microbiological research, it is evidently time for guiding "molecular ecologists" and multidisciplinary research teams to important basic literature. A wag once said that sometimes six months in the lab can save an hour in the library. Research during the early decades of the 20th century established the fundamental facts that microbes of great physiological diversity occur in huge numbers in natural circumstances. I recommend H. G. Schlegel's General Microbiology 7th ed., 1986 (Cambridge Univ. Press) for a succinct description of basic ecological facts. Schlegel points out that "the number of symbiotic associations between animals and microorganisms is immense." The latter and other major aspects of microbial ecology are comprehensively described by Klein (2005), who has also advanced the field with a "postgenomic perspective" (2007). He emphasizes that "DNA-based analyses of natural microbial assemblages using bulk extraction-based approaches do not provide specific information on the active microbes functioning in particular locations and conditions."

Winogradsky and Beijerinck. Roger Stanier (1951) noted that Sergei Winogradsky and Martinus Beijerinck share the honors for revealing two great concepts of microbiology: "the physiological specificity of different microbial types, and the essential role of microorganisms in maintaining the cycle of matter." This required the development of special methodologies in discovery of the chemosyntheic autotrophs and major bacterial catalysts of the earth's nitrogen cycle (Winogradsky), and the technique of "selective enrichment culture." Analysis of the microbial ecology of soil by such methods led to a cornucopia of knowledge in general microbiology and identification of important species whose properties are grist for the mill of "molecular ecological" studies.

Winogradsky, in particular, had deep insights into the complexities of microbial ecology, and introduced novel methods of study which are probably largely unknown to present day researchers. For example, the technique of "separative enrichment," in which a solid medium of silica gel is impregnated with suitable nutrients and inoculated at spaced intervals with small particles of soil. Such enrichments closely simulated the physical conditions in soil and permitted isolation of the more slowly growing types in a given physiological group. In 1925, Winogradsky proposed that microorganisms found in an ecosystem can be classified in either of two categories-autochthonous: those indigenous and always present in a given ecosystem (soil, intestine, etc.), and allochthonous: organisms dependent on an occasional increase in concentration of certain nutrients or in the presence of specific nutrients.

Beijerinck had insatiable curiosity and was a prodigious worker. Among the numerous bacteria he discovered and characterized between 1888 and 1904 were: Rhizobium leguminosarum, Azotobacter chroococcum, Thiobacillus thioparus, and Desulfovibrio desulfuricans. Beijerinck published a large number of important researches dealing with fundamental problems in the physiology of bacteria, the bacteria of soil, and infectious diseases of plants. From his intermittent research on "tobacco mosaic disease," he concluded that the pathogen was a "contagium vivum fluidum." The latter was later understood as the concept of a virus. For the complete lengthy reference to Beijerinck's collected works see Gest 2009.

Winogradsky had a very long career, and his collected works were published as Microbiologie du Sol in 1949 (861 pp). This remarkable epic, covering 50 years of research, consists of 10 parts, the last one entitled The Principles of Ecological Microbiology. Stanier's 1951 perceptive analysis of Winogradsky's great contributions ended with the statement "His elaboration of the concept of an ecologically defined microbial species may well prove one of the cornerstones of future bacterial taxonomy."

Tidbits on Extreme Ecology. The great diversity of physiological/metabolic patterns among microorganisms accounts for the fact that a number of species can thrive in "extreme" environments. The absence of visible life forms gave the highly saline Dead Sea its name. Aristotle (384-322 B.C.) wrote that the sea was so "salty bitter" that fish could not live in it. An expedition in 1863 reported that despite all efforts, "no living creatures were found in the waters of the Dead Sea." But in 1936, Benjamin Volcani demonstrated the presence of viable osmophilic bacteria as well as many species of algae in "Dead" sea water. His studies also focused on organisms present on the sea bottom sediment, overlain by water containing salt concentrations of 25 to 32%. Two of Volcani's reports in Nature (145:975, 1940; 152:274-275, 1943) on Dead Sea organisms described Scenedesmus quadricauda, diatoms, and positive enrichment cultures for various kinds of aerobic and anaerobic bacteria.

Volcani received the first doctoral degree in microbiology awarded by the Hebrew University. His dissertation on Dead Sea halophiles was written in Hebrew, and Haloferax volcanii was named in his honor. For many years, Volcani was a professor of microbiology at the Scripps Institution of Oceanography (University of California, San Diego), where he did notable research on diatoms. Although silicon was believed to be biologically inert, Volcani discovered that in diatoms it was required for many biochemical pathways.

As early as 1881, bacteria that could grow at 60-70°C were isolated from the Seine River. During the past 40 years, considerable attention has been given to thermophilic extremophiles. The microbiology of hot environments, however, was not investigated systematically until Thomas Brock undertook a major study. From 1965 through 1971, the laboratory work of Brock and his students, associated with extensive field work, was conducted at Indiana University in Bloomington, and subsequently at the University of Wisconsin-Madison. Their research on thermophiles in hot pools of Yellowstone National Park and other thermal areas yielded a comprehensive body of basic ecological information and pure type cultures of novel thermophiles of importance. The latter included Thermus aquaticus, which contains thermostable Taq polymerase, a major tool in molecular biology research; Thermoplasma, which can grow at 55°C and pH 2; and the hyperthermophile Sulfolobus, capable of growing at temperatures as high as 90°C and pH of 1-2. The work of the Brock group is described in detail in Brock's 1978 classic book on thermophiles (see also Brock's chapter "The origins of research on thermophiles" in Reysenbach et al. 2001).

The Outlook. There is little doubt that the further development of powerful Web-based research engines will eventually make the detailed history of microbiological research more readily available than it is at present (for an update, see "The Unseen Scholars," in Los Alamos Science and Technology Magazine, December 2008, p. 20-23). However, scientists now doing research on microbial ecology are well advised to make special efforts to learn of past accomplishments to avoid falling into the trap that Santayana warned against. At present, there is no substitute for browsing in a well-developed physical library of books.

SUGGESTED READING

Brock, T. D. 1978. Thermophilic microorganisms and life at high temperatures. Springer, New York, Heidelberg, Berlin.

Gest, H. 2009. Historical adventures in scientific discovery: Microbiology/biochemistry. https:scholarworks.iu.edu/dspace/handle/2022/3358  

Klein, D. A. 2005. Microorganism interactions and microbial ecology, p. 577-613. In L. Prescott, J. P. Harley, and D. A. Klein, Microbiology, 6th ed. W. C. Brown-McGraw Hill, Dubuque.

Klein, D. A. 2007. Seeking microbial communities in nature: a postgenomic perspective. Microbe 2:591-595.

Reysenbach, A-L., M. Voytek, and R. Mancinelli (ed.). 2001. Thermophiles/Biodiversity, ecology and evolution. Kluwer Academic/Plenum Publishing, New York.

Stanier, R. Y. 1951. The life-work of a founder of bacteriology. A review of Microbiologie du Sol (Winogradsky). Quart. Rev. Biol. 26:35-37.