Andrew Wier

Lynn Margulis

Wier, Andrew

Margulis, Lynn

Hemeroteca Cientifica Catalana

55Except in Philadelphia where his greater-than-lifesize statueadorns the entrance to the great Academy of Natural Sciences,and the University of Pennsylvania biology department ishoused in the building that bears his name, Joseph Leidy(1823–1891) is virtually unknown today. Yet his myriadcontributions to science are important and entirely trustworthy.Although Leidy was one of America’s greatest naturalists,his biographer, Leonard Warren [9], found it necessary todevote an entire chapter to Leidy’s lack of reputation (Chapter16, “The eclipse of Leidy”). In his fascinating new book ofgreat interest to microbiology Warren writes (p. 251):“In thecourse of his career, Leidy examined tens of thousands oforganic forms and described and named over a thousand newones —fossils, protozoa [sic], parasites of many forms, insects,molluscs, and helminths—a feat virtually without precedent.What did this busy investigator have in mind? ... Withoutquestion he gathered his knowledge because it gave himpleasure.” A precise tabulation of Leidy’s contributions waspublished more than 100 years after his death [2]. In 1923,more than 30 years after he died, Leidy was commemoratedby one of his many admirers: “Dr. Leidy’s vision covered allnature, from the mammals and gigantic reptiles of the past tothe world of small things which are revealed to the eye by thehighest powers of the microscope; and I never knew anyonewho carried on so varied a series of observations withoutconfusion.” Leidy is considered “the founder of Americanvertebrate paleontology, parasitology, and protozoology andAmerica’s foremost anatomist, the person who revealed thepower and versatility of the microscope...” (p. 252 [9]). Notonly was he the first in North America to discover the dinosaurbut he was the first in the world to discern what wood-dwelling “white ants” (termites) eat. His impatient curiosityled him to investigate the dwellers of a decaying log in NewJersey. He reported that a squeeze of intestinal fluid revealed(“like citizens leaving a crowded meeting hall”) a flurry oflive “parasites” [5]. When he documented the bacilli,trichomonads, prysonymphids and hypermastigotes thatexuded from the “termes” hindgut he named his 1850 paper,“On the existence of endophyta in healthy animals as a naturalcondition” [4].Leidy discovered benign, indeed requisite cellulolyticprotists responsible for the ingestion of wood by termites. Hewas also the first to recognize the Trichinella nematode as thecause of trichinosis caused by undercooked pork. He gavebinomial names in use today to hundreds of New Worldanimals, fungi, protists and bacteria. Leidy’s descriptions anddrawings of amoebae (rhizopods) are still without parallel. “Adriven man, he seemed possessed by a sustained frenzy,” or asone acquaintance put it, “absorbed in his new discoveries ofrhizopods in the cracks of the city pavements” (p. 251 [9]).“How can life be tiresome as long as there is still a new rhizopodundescribed?” (p. VI [9]) is the way Leidy himself stated hispassion in his sparse and appropriate style.Disdaining speculation, Leidy always remained closeto his original material. None of his observations has beenshown to be mistaken or exaggerated. He may also be claimedAndrew WierLynn MargulisDepartment of Geosciences, University of Massachusetts, Amherst, USACorrespondence to: Lynn Margulis. Department of Geosciences.University of Massachusetts. Amherst, MA 01003-5810. USATel.: +1-413-5452286 Fax: +1-413-5451200E-mail: pbi@bio.umass.eduPERSPECTIVESINTERNATL MICROBIOL (2000) 3:55–58© Springer-Verlag Ibérica 2000The wonderful lives of Joseph Leidy(1823–1891)to be the founder of the forensic use of the microscope: amurderer confessed that blood was really human, and notfrom a chicken as he had claimed, after Leidy noted thatits red cells lacked the requisite nuclei of avian red bloodcells. Leidy in 1851 transplanted human tumor tissue underthe skin of a frog, and determined, five months later, that thetumor had acquired a new blood supply and was thriving.His keen microscopy skills ended the current medical theorythat hay fever, asthma, colds and other respiratory disorderswere caused by an infusorian (an old name for ciliates),“Asmathos ciliaris ”. He showed “A. ciliaris” to be no morethan deformed ciliated epithelial cells in the mucus ofpatients! Trained as a physician, Leidy practiced medicinefor only a few years until returning to his interest in scienceand teaching. Warren’s saga explains clearly how Leidyalways preferred his curiosity-driven self-determinedresearch. His collections, teaching charts and museumspecimens ranged from mineral collections to large mammalsto drawings of microbial communities.Although he never lacked national and internationalcolleagues, as well as correspondents, Leidy had not a singlescientific co-author in his entire career. In their quantitativeanalysis of Leidy’s immense contribution to the identificationand classification of extant and extinct organisms new toscience, Glassman et al. [2], provide us with a dichotomoustable. Two kinds of organisms are listed: “Animals” (and,by name, the many new genera and species names Leidyconferred) and “Plants”. Remarkably, especially as we recallthat this paper was published in 1993, under the heading of“Plants” Leidy’s contribution is listed: “Many plants,including fungi”. Unfortunately, most members of the publicstill today recognize only these two great kingdoms oforganisms. In the public eye, of course, all “microbes” aregerms, enemies of people that do not count as life even enoughto be classified as either animal or plant. This animal-plantdichotomy, a gross misconception that obviously persists evenamong today’s scholars, aggravates the continuedundervaluation of Leidy’s contribution. Here we consideronly one, but one of special interest to microbiologists: Leidy’sdiscovery of the natural habitat of Bacillus cereus. Thisaccount is derived from the splendid archives of the Academyof Natural Science in downtown Philadelphia, Leidy’spublications [4, 5] and our own work [6].Hundreds of Leidy’s original drawings reside in theAcademy’s cabinets —among them his exquisite microscopicanalyses. As the “last man who knew everything” and a superbteacher, Leidy always generously shared his time and energywith motivated acquaintances, friends, colleagues and students.For the benefit of his admiring students he arranged hispainstaking and accurate drawings for us as gorgeous wallcharts, one of which is highly reduced here (Fig. 1). Themicrobial community of the intestine of the millipede Julusmarginatus is revealed. Both the Trichomyces and the thinnerArthromitus are “rooted” in the chitinous intestinal epitheliumof this arthropod. Of course by Leidy’s and subsequentreckoning these attached gut microbes are “non-photosyntheticplants”.The detail and accuracy of Leidy’s drawings of theepibionts permits us to recognize without a doubtmicroorganisms we know from our own long experience withtermites, millipedes, roaches and sowbugs. The attachedfilamentous spore formers have also been found by manyother microscopists in the intestines of other animals: ducks,rodents, humans and many other kinds of arthropods. Ourwork has mostly involved those in the intestines ofsubterranean and dry wood-eating termites [7] and Porcelliascaber , the sowbug [3]. Recently we found Leidy’s “non-photosynthetic plant”, this filamentous spore former, in thegreat tropical Caribbean cockroach Blaberus giganteus [1].In these publications we prove that these intestines are thenatural habitat of an organism that, in culture, is familiar toall microbiologists as Bacillus cereus. Leidy would probablybe delighted to know that it was he who discovered B. cereusin its “natural condition”. His careful work permits us tounderstand why, in culture, this bacillus retains a greatpredilection for high concentrations of food, a sensitivity tolight, a tendency to form spores on exposure to dryness orair, and to be motile in young cultures. We now understandwhy these bacteria form filaments and settle down to attachor at least, when the cultures are mature, to make stickyexudates. Most of all, we have a context for their incredibleresistance to environmental insults of desiccation, acidity andanoxia.Here magnificent unpublished photomicrographs by thesuperb electron microscopist, the late David G. Chase (inaddition to the others in our papers referenced below [6, 8])verify how observant was Leidy; they display at high powerthe attachment of the spore formers to the gut and thedifferentiation of the spores within the filaments. These bacilliare not, as widely touted, “soil organisms”, since, in the soilthey are dormant as spores. Rather they are normal inhabitantsof animals. The filamentous spore-forming “non-photosynthetic plants” of Leidy are cyclical symbionts whosedefecated spores persist in the soil. They grow as motile bacilliand short filaments when contingencies provide them with56 INTERNATL MICROBIOL Vol. 3, 2000 Wier, MargulisFig. 1 One of Leidy’s many beautiful wall charts archived at the Academyof Natural Science of Philadelphia. This one depicts the intestinal epithelialcells of the millipede Julus marginatus at the bottom. Besides the threeswimming ciliates and the unidentified mastigotes, one recognizes an attachednematode replete with eggs and six trichomes of Trichomyces sp., the obligatesymbiotrophic fungus. We added arrows to Arthromitus sp., with and withoutspores, attached to the Trichomyces sp. or directly to the epithelium. Thebranched Arthromitussp. at the bottom right was seen in termite preparationsby Harold Kirby (1900–1952) and by us [6]. The branched Gram-positivebacterium is clearly a bacillus. It resembles the Arthromitussp. observed inthe sowbug, Porcellia scaber [3], which in culture is Bacillus cereus . Notaxonomic description of it has ever been made in either the botanical or themicrobiological literature. The actual size of the wall chart is approximately2 ´ 3 m57Joseph Leidy (1823–1891) INTERNATL MICROBIOL Vol. 3, 2000of moisture and food. The short flagellated filaments coursethrough the intestines looking for “docking sites”. They findthem, usually at the surface of the chitinous epithelium, asdocumented by electron microscopy (Fig. 2). They attach,differentiate, and some even form “spore attachmentfilaments”. Then they release spores, usually from their distalfree ends. By peristaltic action the spores are expelled fromthe anus to reside, until further opportunities for sustenancearise, in the soil. Modern microbiologists, especially thosewho work with genes involved in differentiation of B. cereusstill have much to learn from the legacy of the Philadelphiandoctor. As wise naturalist and superb artist his major lessonfor microbiologists is that they, like him, should be studentsof life in nature, life under “natural conditions”, before theyincubate their objects of study in the artificial environmentof the research laboratory.References1. Feinberg L, Jorgensen J, Haselton A, Pitt A, Rudner R, Margulis L (1999)Arthromitus (intestinal filamentous spore-forming symbionts) in thecockroach Blaberus giganteus : dietary influences on bacterialdevelopment and population density. Symbiosis. (In press)2. Glassman S, Bolt EA Jr, Spammer EE (1993) Joseph Leidy and the ‘GreatInventory of Nature’. J Acad Nat Sci Philadelphia 144:1–193. Jorgensen J, Dolan S, Haselton A, Kolchinsky R (1997) Isolation andcultivation of spore-forming filamentous bacteria from Porcellia scaber.Can J Microbiol 43:129–1354. Leidy J (1850) On the existence of endophyta in healthy animals as anatural condition. Proc Acad Nat Sci Philadelphia 4:225–2295. Leidy J (1881) The parasites of termites. J Acad Nat Sci Philadelphia8:425–4476. Margulis L, Jorgensen JZ, Rainey FA, Lo S-C (1990) The Arthromitusstage of Bacillus cereus: Intestinal symbionts of animals. Proc Nat AcadSci USA 95:1236–12417. Margulis L, Olendzenski L, Afzelius BA (1990) Endospore-formingfilamentous bacteria symbiotic in termites: Ultrastructure and growth inculture of Arthromitus. Symbiosis 8:95–1168. To LP, Margulis L, Nutting WL, Chase D (1980) The symbiotic microbialcommunity of the Sonoran desert termite: Pterotermes occidentis(Walker). BioSystems 13:109–1379. Warren L (1998) Joseph Leidy: the last man who knew everything. YaleUniversity Press, New Haven and London58 INTERNATL MICROBIOL Vol. 3, 2000 Wier, MargulisFig. 2 “Arthromitus” attached to the chitinous gut wall of the California termite,Reticulitermes tibialis. Portions of the termite epithelial cells are seen at thebottom and right side of the transmission electron micrograph. The attachmentstructure seems to be composed of exudate from the bacterium and localthickening of the insect chitin at the region of attachment. The dark bodiesjust inside the chitinous layer are termite mitochondria. This protograph, takenby David G. Chase in about 1984, reveals in detail the “Arthromitus” intestinalattachment first described by Joseph Leidy. (Magnification, ca. 50,000´ )

The wonderful lives of Joseph Leidy (1823–1891)

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The wonderful lives of Joseph Leidy (1823–1891)

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Hemeroteca Cientifica Catalana