Biomedical subjects
L Margulis
Publications and source records attributed to L Margulis.
Heliobacterium and the origin of chrysoplasts.
Chrysoplasts, golden-yellow and brown photosynthetic membrane-bounded plastids, photosynthetic organelles of algae such as phaeophytes (brown seaweeds), bacillariophytes (diatoms) and chrysophytes (golden-yellow algae including silicoflagellates), are hypothesized to have originated from brownish photoheterotrophic bacteria such as the newly discovered anaerobic nitrogen-fixing Heliobacterium. The consequences of this hypothesis as well as the data required to verify or disprove it are presented.
Desiccation resistance and contamination as mechanisms of gaia.
The gaia hypothesis, formulated by J.E. Lovelock, asserts the composition of the reactive gases, the oxidation-reduction state and the temperature of the lower atmosphere of the planet Earth are actively regulated by the biota. Lovelock and Watson, using highly simplified mathematical models, have shown that the modulation of atmospheric temperature can be achieved by exponentially growing populations of differently colored organisms ("dark and light daisies"). It is more likely that the modulation of atmospheric gas composition is based on the colligative properties of exponentially growing mixed populations of microorganisms rather than on "daisies". Exponential growth of one population of microorganisms leads to gaseous and other metabolic products released to the environment, which favor the exponential growth of different populations, each with their own unique emissions. Extremely high densities of mixed populations of microorganisms ensue. These populations form structured microbial communities composed of members in varying states of activity. Growth potential of metabolically diverse populations most likely provides the basis for the responsiveness of the biota to changing environments. We have attempted to measure an aspect of the growth potential and diversity of one microbial community, that from a flat laminated microbial mat dominated by the cyanobacterium, Microcoleus. Microbial mat samples collected at yearly intervals between 1977 and 1982 were allowed to dry. Subsamples were revived under laboratory conditions by rewetting, and the resulting complex microbial populations were analyzed. Greater than 10(4) viable organisms per ml were estimated to be present in the desiccated samples. Only a portion of the diverse community could be characterized. There were at least 115 different types of desiccation resistant microorganisms present in these samples, primarily bacteria. However, more than a dozen types of rather uncommon fungi and protoctists were removed from naturally desiccated material. Several did not fit descriptions of previously known species or strains. Neither animals nor plants were recovered from these tiny samples. We present minimal diversity estimates for microorganisms in both the desiccated samples and the corresponding fresh laminated microbial mat community from which they were taken. We found that many organisms in laboratory samples capable of immediate growth from a desiccated state were not common components of growing mats in the field.(ABSTRACT TRUNCATED AT 400 WORDS)
Order amidst animalcules: the Protoctista kingdom and its undulipodiated cells.
The eukaryotic microorganisms have always been studied and described in the context of Zoology (as tiny animals), Botany (as tiny plants), Mycology (as water molds) or Microbiology (as disease agents). Because their extent (as a group of about 200,000 species) and differences from the rest of life (worthy of Protoctista kingdom status) only recently has been recognized, their classification within the Plant and Animal kingdoms remains in scandalous disarray. Admitting this problem, this paper represents a step toward achieving nomenclatural order based on ultrastructural, biochemical and evolutionary considerations.
Symbiosis as a mechanism of evolution: status of cell symbiosis theory.
Several theories for the origin of eukaryotic (nucleated) cells from prokaryotic (bacterial) ancestors have been published: the progenote, the direct filiation and the serial endosymbiotic theory (SET). Compelling evidence for two aspects of the SET is now available suggesting that both mitochondria and plastids originated by symbioses with a third type of microbe, probably a Thermoplasma-like archaebacterium ancestral to the nucleocytoplasm. We conclude that not enough information is available to negate or substantiate another SET hypothesis: that the undulipodia (cilia, eukaryotic flagella) evolved from spirochetes. Recognizing the power of symbiosis to recombine in single individual semes from widely differing partners, we develop the idea that symbiosis has been important in the origin of species and higher taxa. The abrupt origin of novel life forms through the formation of stable symbioses is consistent with certain patterns of evolution (e.g punctuated equilibria) described by some paleontologists.
The stratified microbial community at Laguna Figueroa, Baja California, Mexico: a possible model for prephanerozoic laminated microbial communities preserved in cherts.
The microbial mat community of the evaporite flat at North Pond, Laguna Figueroa (Baja California, Mexico) was actively involved in the production of laminated sediments prior to 1978. Heavy rains in 1979 and 1980 flooded the mat with 1 and 3 meters of meteoric water respectively. The flooding deposited up to 10 cm of silicoclastic sediment over the Microcoleus-dominated mat and resulted in the cessation of laminated sediment deposition. In 1982, the surface had been recolonized by species of cyanobacteria (Spirulina, Oscillatoria) and purple photosynthetic bacteria (Chromatium, Thiocapsa). The silicoclastic sediments and residual evaporites, which overlaid the laminated sediment, had been reworked into an anaerobic, sulfide-rich mud and contained well preserved sheaths of filamentous and coccoid bacteria. The Swaziland Sequence in the Barberton mountain land (which includes the Onverwacht and Fig Tree Group as well as the Swartkoppie zone between them) contains laminated sediments and carbon-rich chert. Structurally preserved microfossils have been found in the smooth black chert but not in the laminae. We concur with others who suggested that the laminated sediments from the Swaziland Sequence were deposited by an active stratified microbial community. However, we propose that these organisms which were preserved were originally buried in the associated sulfide-rich muds and were subsequently silicified.
Cell symbiosis [correction of symbioisis] theory: status and implications for the fossil record.
Recent geological treatises have presented three alternative models of the origins of eukaryotes as if they merited equal treatment. However, modern biological techniques, especially nucleic acid and protein sequencing, have clearly established the validity of the symbiotic theory of the origin of eukaryotic organelles. The serial endosymbiotic theory in its most extreme form states that three classes of eukaryotic cell organelles (mitochondria, plastids and undulipodia) originated as free-living bacteria (aerobic respirers, phototrophic bacteria and spirochetes respectively) in association with hosts that become the nucleocytoplasm (Thermoplasma-like archaebacterial hosts). Molecular biological information, primarily derived from ribosomal RNA nucleotide sequencing studies leads to the conclusion that the symbiotic origin theory for both mitochondria and plastids has been proven. The probability of an ancestral archaebacterial-Thermoplasma-like host for the nucleocytoplasm has been rendered more likely by discoveries by Dennis Searcy and his colleagues and Carl Woese and his colleagues. The most equivocal postulate of the symbiotic theory, the origin of undulipodia (cilia and other organelles of motility that develop from kinetosomes is under investigation now. The status of these postulates, as well as their implications for the fossil record, is briefly summarized here.
Karyotypic fission theory and the evolution of old world monkeys and apes.
The karyotypes of living catarrhines are correlated with the current concepts of their fossil record and systematic classification. A phylogeny, beginning at the base of the Oligocene, for those animals and their chromosome numbers is presented. Todd's (1970) theory of karyotypic fissioning is applied to this case - three fissioning events are hypothesized. A late Eocene event (the primary catarrhine fissioning) is hypothesized to underlie the diversification of the infraorder Catarrhini into its extant families, the second fissioning underlies the radiation of the pongidae/Hominidae in the Miocene and the third accounts for the high chromosome numbers (54 - 72) and the Neogene(Miocene-Pliocene-Pleistocene) radiation of members of the genus Cercopithecus. Published catarrhine chromosome data, including that for "marked" chromosomes (those with a large achromatic region that is the site for ribosomal RNA genes) are tabulated and analysed. The ancestral X chromosome is always retained in the unfissioned metacentric state. The Pongidae/Hominidae have 15 pairs of mediocentric chromosomes that survived the second fissioning whereas the other chromosomes (besides the X) are thought to be fission-derived acrocentrics. Both the detailed karyology and the trend from low to high numbers is best interpreted to support Todd's concept of adaptive radiations correlated with karyotypic fissioning in ancestral populations.
Microtubules, undulipodia and Pillotina spirochetes.
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Hydra viridis: transfer of metabolites between Hydra and symbiotic algae.
"Back transfer" of metabolites from food to endosymbiotic algae in the digestive cells of Hydra viridis was demonstrated. Brine shrimp nauplii labeled with tritiated precursors of protein and nucleic acids (DNA and RNA) were fed to light and dark grown hydras. The fate of the label after a single feeding with radioactive material in hydra and algal fractions was followed by scintillation counting and autoradiographic techniques. Labeled thymidine was incorporated into DNA in both light- and dark-grown hydras. Although the symbiosis persists indefinitely in hydras in darkness (7-10 days) the number of algae per cell is reduced. Tritiated orotic acid and tritiated uridine, RNA precursors, were incorporated into peptides and proteins, and to a lesser extent into simple sugars, oligosaccharides, and oligonucleotides in hydra and algal fractions. Thus the metabolites of the brine shrimp food are available to both partners. A decrease over time in label introduced as 3H-orotic acid and 3H-uridine and incorporated into hydra RNA is compensated for by an increase in label in the algae, implying competition for constant quantities of metabolites from the single feeding. Although food availability, light, number of algae per cell, and other factors influence the quantity and rate of nutrient transfer between the partners, in both light and dark grown hydras the amount of "back transfer" of metabolites to the symbiotic algae is impressive.
A red Beneckea from Laguna Figueroa, Baja California.
A new bacterium (nitrate-respiring, prodigiosin-producing, marine curved rod with a sheathed flagellum) has been isolated from anaerobic mud underlying a microbial meat. This brightly pigmented red bacterium, referred to as strain BV1 (Baja California vibrio, isolate 1) was taken from a closed, hypersaline basin at Laguna Figueroa (or Laguna Mormona), Baja California de Norte, Mexico. It is closely related to the recently described Beneckea gazogenes (Harwood, 1978), which was isolated from an estuarine habitat, the Sippewissett salt marsh at Woods Hole, Massachusetts, U.S.A. Strain BV1 and B-gazogenes are both oxidase positive facultative anaerobic curved rods which bear a single polar flagellum, and synthesize the red-orange tri-pyrrole pigment prodigiosin. The bacterium, which fluoresces green when excited with UV light (lambda = 455 nm), deposits pigment extracellularly in copious quantities. The extracellular pigment deposits fluoresce red-yellow. Both BV1 and B. gazogenes are able to grow utilizing xylose, cellobiose or arabinose, products of plant biosynthesis, as sole carbon sources. BV1 differs from B. gazogenes in cell size, pattern of pigment production, nutritional characteristics, the ability to perform anaerobic respiration using nitrate as a terminal electron acceptor, sensitivity to a newly discovered lytic phage and to the antibiotic vibriostat O/129.
Bacterial resistance to ultraviolet irradiation under anaerobiosis: implications for pre-phanerozoic evolution.
The concept that low concentrations of atmospheric oxygen and consequent unattenuated ultraviolet irradiation limited the emergence of Phanerozoic life, the Berkner-Marshall hypothesis, is no longer tenable. Anaerobic bacteria, which probably evolved far earlier than Metazoa, were irradiated in a special chamber under strictly anaerobic conditions. Both intrinsic resistance and photoreactivation by visible light were discovered in obligately and facultatively anaeroboc microbes. Atmospheric scientists have shown that small amounts of oxygen would have limied pre-Phanerozoic surface ultraviolet irradiation to fluxes well below those used in the anaerobic experiments described. Since adequate ultraviolet protection mechanisms evolved early, the late Proterozoic appearance of Metazoa probably was not related to high fluxes of solar ultraviolet radiation.
The symbiotic microbial community of the Sonoran Desert termite: Pterotermes occidentis.
Pterotermes occidentis is a large, obscure, very primitive dry wood termite limited to the Sonoran desert of North America. Its development, caste system and behavior are discussed in relation to aspects of its ecology. What appear to be single wood-digesting individual termites are in fact insect hosts which harbor extensive microbial communities estimated to contain more than 40 interacting species. All healthy, wood-eating Pterotermes contain these densely populated communities of highly motile symbionts suggesting that species diversity is necessary for termite survival. A morphological catalogue of the major hindgut microbes is presented here. From 10(7) to 10(11) bacteria and from 10(3) to 10(6) protists/ml of hindgut fluid are found in an average nymph or larva. The species of four wood-ingesting mastigotes (genera Trichonympha, Metadevescovina, Tricercomitus and Microrhopalodina) and nearly 30 morphologically distinct types of bacteria are described. The description of this morphological diversity observed with light, scanning and transmission electron microscopy is a prerequisite to functional analyses of the symbioses. Since Pterotermes is easily maintained in the laboratory and is so large it is hoped that it will provide a useful model for symbiosis research.
Evolutionary prerequisites for early Phanerozoic calcareous skeletons.
This paper develops the concept that the dramatic appearance of calcareous skeletons in the Lower Cambrian is directly related to the origin of refined mechanisms of intracellular modulation of calcium ion concentration. An homologous family of calcium modulated proteins has recently been discovered. These proteins contain "EF hands", involved in the maintenance of low concentrations of intracellular calcium and the informational use of calcium ion flow (Kretsinger, 1977). The evolution of this specialized calcium physiology, especially in muscle systems, coupled with natural selection by predators are identified as some of the preadaptations for the impressive Tommotian diversification of calcified metazoans. The distribution of calcium biominerals in the phyla of the five kingdoms and the time of first appearance of calcareous mineralization in the fossil record are tabulated. Macroscopic calcified hard parts apparently required the prior evolution of certain cell, tissue and organ system physiologies which are briefly discussed here.
Undulipodia, flagella and cilia.
The term flagella is ambiguous. It refers to bacterial structures composed of flagellin protein and to eukaryotic structures composed of microtubule proteins and ATPase (tubulin and dynein). The fact that cilia are nearly identical to eukaryotic flagella and have nothing in common with prokaryotic flagella is not apparent from the terminology. It is proposed that the 30-year old suggestion of Smagina and reiterated by Kuznicki and others, be adopted: that cilia and eukaryotic flagella be called "undulipodia." The term flagella ought to be restricted to prokaryotic organelles, bacterial flagella and spirochaete axial filaments: solid structures composed of flagellin which protrude through the plasma membrane and lack intrinsic motility throughout their length. Undulipodia are defined as intrinsically motile intracellular structures showing a 9-fold symmetry in the pattern of arrangement of 24 nm diameter microtubules. They are limited to eukaryotes, members of the protoctist, animal and plant kingdoms.
Possible evolutionary significance of spirochaetes.
Large symbiotic spirochaetes of the family Pillotaceae (e.g. pillotinas) are found in dry wood and subterranean termites (Hollande & Garagozlou 1967). These morphologically distinctive spirochaetes comprise several genera. Some of them contain microtubules within their protoplasmic cylinders. They demonstrate a variety of relations with their termite and protist hosts. Some are free-living within the lumen of the intestine, some tend to be associated with filamentous and other bacteria, some are found regularly coursing between the numerous undulipodia ( = eukaryotic flagella, cilia, and other (9 + 2) organelles of motility) of hypermastigotes and polymastigotes. Still other smaller termite spirochaetes are regularly attached to protists via specialized attachment sites. Some even form motility symbiosis with their host protists. The analogy between the behaviour of host-associated spirochaetes and the possible steps in the origin of the undulipodia and mitotic system of eukaryotes is discussed briefly.
An ultraviolet light induced bacteriophage in Beneckea gazogenes.
An ultraviolet light induced prophage has been discovered in the red pigmented marine vibrio Beneckea gazogenes. Two spontaneously derived pigment mutants, one forming pink colonies and one lacking pigment and forming white colonies, were also irradiated. The presence of pigment was not related to phage induction; uv-induced cell lysis occurred in wildtype and mutant strains at the same dosages. Lysis was not prevented or retarded by exposure after irradiation to visible light indicating the phenomenon was not photoreactivable. Electron micrographs of the 'T-like' B. gazogenes phage are shown. A second beneckea was isolated form the anaerobic zone of cyanobacterial mats growing in the hypersaline environment of Laguna Mormona, Baja California. The Baja beneckea does not harbor a uv inducible prophage and is resistant to the B. gazogenes phage under all conditions tested.
The Viking Mission: implications for life on Mars.
The results of the Viking Biology experiments are best explained by non-biological phenomena: The interaction of the reagents with the materials comprising the regolith. Conditions of water activity, temperature, availability of carbon sources and others in most regions of the planet are too extreme for survival and growth of any known Earth microorganisms. Although the possibility persists that some very unusual form of life is somewhere on that planet the evidence is best interpreted as negative. Even though there is no evidence for current life on Mars, whether or not life ever originated there is not known.