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All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Filamentous Trichomic Prokaryotes in Carbonaceous Meteorites: Indigenous Microfossils, Minerals, or Modern Bio-Contaminants?

Large complex filaments have been detected in freshly fractured interior surfaces of a variety of carbonaceous meteorites. Many exhibit the detailed morphological and morphometric characteristics of known filamentous trichomic prokaryotic microorganisms. In this paper we review prior studies of filamentous microstructures encountered in the meteorites along with the elemental compositions and characteristics of the, fibrous evaporite minerals and filamentous cyanobacteria and homologous trichomic sulfur bacteria. The meteorite images and elemental compositions will compared with data obtained with the same instruments for abiotic microstructures and living and fossil microorganisms in order to evaluate the relative merits of the alternate hypotheses that have been advanced to explain the nature and characteristics of the meteorite filaments. The possibiility that the filaments found in the meteorites may be comprise modern bio-contaminants will be evaluated in light of their observed elemental compositions and data by other researchers on the detection of indigenous complex organic biosignatures, and extraterrestrial amino acids and nucleobases found in the Murchison CM2 and the Orgueil CI1 carbonaceous meteorites.

Hoover, Richard B.↗
NASA NTRS2011

Filaments in Carbonaceous Meteorites: Mineral Crystals, Modern Bio-Contaminants or Indigenous Microfossils of Trichomic Prokaryotes?

Environmental (ESEM) and Field Emission Scanning Electron Microscopy (FESEM) investigations have resulted in the detection of a large number of complex filaments in a variety of carbonaceous meteorites. Many of the filaments were observed to be clearly embedded the rock matrix of freshly fractured interior surfaces of the meteorites. The high resolution images obtained combined with tilt and rotation of the stage provide 3-dimensional morphological and morphometric data for the filaments. Calibrated Energy Dispersive X-ray Spectroscopy (EDS) and 2-D elemental X-ray maps have provided information on the chemical compositions of the filaments and the minerals of the associated meteorite rock matrix. These observations are used to evaluate diverse hypotheses regarding the possible abiotic or biogenic nature of the filaments found embedded in these meteorites.

Hoover, Richard B.↗
NASA NTRS2005

Mineralized Remains of Morphotypes of Filamentous Cyanobacteria in Carbonaceous Meteorites

The quest for conclusive evidence of microfossils in meteorites has been elusive. One difficulty arises from the fact than many abiotic or inorganic microstructures, mineral grains, and coating artifacts can mimic the smaller representatives of the microbial world that possess very simple morphologies (unicellular cocci or bacilli). However, there exist a wide variety of large, filamentous trichomic prokaryotic microorganisms (cyanobacteria and sulfur bacteria) with sufficiently well known and complex morphologies that they can be recognized and are known to be of unquestionable biogenic origin. The taphonomic modes of fossilization and their of their life habits and processes frequently result in distinctive chemical biosignatures associated with carbonization, silicification, calcification, phosphatization and metal-binding properties of their cell-walls, trichomes, sheaths and extracellular polymeric substances (EPS). Strong differences of mineral concentrations in closely associated and visibly differentiated cellular microstructures provide strong evidence of biogenicity. This evidence is further enhanced by the detection of recognizable and distinct microstructures (e.g., uniseriate or multiseriate filaments, trichomes, sheaths, cells of proper sizes and size distributions) and growth characteristics (e.g., basal or apical cells, true or false branching of trichomes, tapered or uniform filaments, robust or thin sheaths) and reproductive and nitrogen fixation habits (e.g., baeocytes, hormogonia, akinetes and heterocysts), Microfossils of cyanobacteria and cyanobacterial mats and stromatolites have been recognized a described from many of the most ancient rocks on Earth. The crucial problem lies in developing valid protocols and methodologies for establishing that the putative microfossils are truly indigenous and not merely recent microbial contaminants. During the past several years, we have conducted Field Emission Scanning Electron Microscopy (FESEM) investigations of freshly fractured interior surfaces of carbonaceous meteorites, terrestrial rocks, and recent microbial extremophiles and filamentous cyanobacteria. These studies have resulted in the detection in a several carbonaceous meteorites of the mineralized remains of a wide variety of complex filamentous trichomic microorganisms. These embedded forms are consistent in size and microstructure with well-preserved morphotypes of mat- forming filamentous trichomic cyanobacteria and the degraded remains of microfibrils of cyanobacterial sheaths. We present the results of comparative imaging studies and EDAX elemental analyses of recent cyanobacteria (e.g. Calothrix, Oscillatoria, and Lyngbya) that are similar in size, morphology and microstructure to morphotypes found embedded in meteorites. EDAX elemental studies reveal that forms found in carbonaceous meteorites often have highly carbonized sheaths in close association with permineralized filaments, trichomes and microbial cells. Ratios of critical bioelements (C:O, C:N, C:P, and C:S) reveal dramatic differences between microfossils in Earth rocks and meteorites and in filaments, trichomes, hormogonia, and cells of recent cyanobacteria.

Hoover, Richard B.↗
NASA NTRS1995

Paleobiology of the Mesoproterozoic Billyakh Group, Anabar Uplift, northern Siberia

Silicified peritidal carbonates of the Mesoproterozoic Kotuikan and Yusmastakh Formations, Anabar Uplift, northeastern Siberia, contain exceptionally well-preserved microfossils. The assemblage is dominated by ellipsoidal akinetes of nostocalean cyanobacteria (Archaeoellipsoides) and problematic spheroidal unicells (Myxococcoides); both are allochthonous and presumably planktonic. The assemblage also includes distinctive mat-forming scytonematacean and entophysalidacean cyanobacteria, diverse short trichomes interpreted as cyanobacterial hormogonia or germinated akinetes, rare longer trichomes, and several types of colonial unicells. Although many taxa in the Kotuikan-Yusmastakh assemblage are long-ranging prokaryotes, the overall character of the assemblage is distinctly Mesoproterozoic, with its major features shared by broadly coeval floras from Canada, China, India, and elsewhere in Siberia. Microfossils also occur in middle to inner shelf shales of the Ust'-Il'ya and lower Kotuikan Formations. Leiosphaerid acritarchs (up to several hundred microns in diameter) characterize this facies. As in other Mesoproterozoic acritarch assemblages, acanthomorphic and other complex forms that typify Neoproterozoic assemblages are absent. The combination in Billyakh assemblages of exceptional preservation and low eukaryotic diversity supports the hypothesis that nucleated organisms diversified markedly near the Mesoproterozoic-Neoproterozoic boundary. The assemblages also demonstrate the antiquity of cyanobacteria capable of cell differentiation and suggest the importance of both changing peritidal substrates and evolving eukaryotes in determining stratigraphic patterns of Proterozoic prokaryotes. The permineralized assemblage contains 33 species belonging to 17 genera. Ten new species or new combinations are proposed: Archaeoellipsoides costatus n. sp., A. elongatus n. comb., A. dolichos n. comb., A. minor n. nom., A. crassus n. comb., A. major n. comb., A. bactroformis n. sp., Veteronostocale medium n. sp., Filiconstrictosus cephalon n. sp., and Partitiofilum yakschinii n. sp.

Non-NASA Center↗
NASA NTRS2005

Morphology and Elemental Composition of Recent and Fossil Cyanobacteria

Cyanobacteria (cyanophyta, cyanoprokaryota, and blue-green algae) are an ancient, diverse and abundant group of photosynthetic oxygenic microorganisms. Together with other bacteria and archaea, the cyanobacteria have been the dominant life forms on Earth for over 3.5 billion years. Cyanobacteria occur in some of our planets most extreme environments - hot springs and geysers, hypersaline and alkaline lakes, hot and cold deserts, and the polar ice caps. They occur in a wide variety of morphologies. Unlike archaea and other bacteria, which are typically classified in pure culture by their physiological, biochemical and phylogenetic properties, the cyanobacteria have historically been classified based upon their size and morphological characteristics. These include the presence or absence of heterocysts, sheath, uniseriate or multiseriate trichomes, true or false branching, arrangement of thylakoids, reproduction by akinetes, binary fission, hormogonia, fragmentation, presence/absence of motility etc. Their antiquity, distribution, structural and chemical differentiation, diversity, morphological complexity and large size compared to most other bacteria, makes the cyanobacteria ideal candidates for morphological biomarkers in returned Astromaterials. We have obtained optical (nomarski and phase contrast)/fluorescent (blue and green excitation) microscopy images using an Olympus BX60 compound microscope and Field Emission Scanning Electron Microscopy images and EDAX elemental compositions of living and fossil cyanobacteria. The S-4000 Hitachi Field Emission Scanning Electron Microscope (FESEM) has been used to investigate microfossils in freshly fractured interior surfaces of terrestrial rocks and the cells, hormogonia, sheaths and trichomes of recent filamentous cyanobacteria. We present Fluorescent and FESEM Secondary and Backscattered Electron images and associated EDAX elemental analyses of recent and fossil cyanobacteria, concentrating on representatives of the genera Calothnx, Leptolyngbya, Lyngbya, Planktolyngbya and Oscillatoria.

SaintAmand, Ann↗
NASA NTRS2009

Microfossils in Carbonaceous Meteorites

Microfossils of large filamentous trichomic prokaryotes have been detected during in-situ investigations of carbonaceous meteorites. This research has been carried out using the Field Emission Scanning Electron Microscope (FESEM) to examine freshly fractured interior surfaces of the meteorites. The images obtained reveal that many of these remains are embedded in the meteorite rock matrix. Energy Dispersive X-Ray Spectroscopy (EDS) studies establish that the filamentous microstructures have elemental compositions consistent with the meteorite matrix, but are often encased within carbon-rich electron transparent sheath-like structures infilled with magnesium sulfate. This is consistent with the taphonomic modes of fossilization of cyanobacteria and sulphur bacteria, since the life habits and processes of these microorganisms frequently result in distinctive chemical biosignatures associated with the properties of their cell-walls, trichomes, and the extracellular polymeric substances (EPS) of the sheath. In this paper the evidence for biogenicity presented includes detailed morphological and morphometric data consistent with known characteristics of uniseriate and multiseriate cyanobacteria. Evidence for indigeneity includes the embedded nature of the fossils and elemental compositions inconsistent with modern biocontaminants.

Hoover, Richard B.↗
NASA NTRS1993

Microfossils of the Early Archean Apex chert - New evidence of the antiquity of life

Eleven taxa (including eight heretofore undescribed species) of cellularly preserved filamentous microbes, among the oldest fossils known, have been discovered in a bedded chert unit of the Early Archean Apex Basalt of northwestern Western Australia. This prokaryotic assemblage establishes that trichomic cyanobacteriumlike microorganisms were extant and morphologically diverse at least as early as about 3465 million years ago and suggests that oxygen-producing photoautotrophy may have already evolved by this early stage in biotic history.

Schopf, J. W.↗
NASA NTRS1987

Association of a new type of gliding, filamentous, purple phototrophic bacterium inside bundles of Microcoleus chthonoplastes in hypersaline cyanobacterial mats

An unidentified filamentous purple bacterium, probably belonging to a new genus or even a new family, is found in close association with the filamentous, mat-forming cyanobacterium Microcoleus chthonoplastes in a hypersaline pond at Guerrero Negro, Baja California Sur, Mexico, and in Solar Lake, Sinai, Egypt. This organism is a gliding, segmented trichome, 0.8-0.9 micrometer wide. It contains intracytoplasmic stacked lamellae which are perpendicular and obliquely oriented to the cell wall, similar to those described for the purple sulfur bacteria Ectothiorhodospira. These bacteria are found inside the cyanobacterial bundle, enclosed by the cyanobacterial sheath. Detailed transmission electron microscopical analyses carried out in horizontal sections of the upper 1.5 mm of the cyanobacterial mat show this cyanobacterial-purple bacterial association at depths of 300-1200 micrometers, corresponding to the zone below that of maximal oxygenic photosynthesis. Sharp gradients of oxygen and sulfide are established during the day at this microzone in the two cyanobacterial mats studied. The close association, the distribution pattern of this association and preliminary physiological experiments suggest a co-metabolism of sulfur by the two-membered community. This probable new genus of purple bacteria may also grow photoheterotrophically using organic carbon excreted by the cyanobacterium. Since the chemical gradients in the entire photic zone fluctuate widely in a diurnal cycle, both types of metabolism probably take place. During the morning and afternoon, sulfide migrates up to the photic zone allowing photoautotrophic metabolism with sulfide as the electron donor. During the day the photic zone is highly oxygenated and the purple bacteria may either use oxidized species of sulfur such as elemental sulfur and thiosulfate in the photoautotrophic mode or grow photoheterotrophically using organic carbon excreted by M. chthonoplastes. The new type of filamentous purple sulfur bacteria is not available yet in pure culture, and its taxonomical position cannot be fully established. This organism is suggested to be a new type of gliding, filamentous, purple phototroph.

NASA Discipline Exobiology↗
NASA NTRS1990

Endospore-forming filamentous bacteria symbiotic in termites: ultrastructure and growth in culture of Arthromitus

Many morphologically distinguishable filamentous spore-forming bacteria symbiotic in the paunch (hypertrophied hindguts) of wood-eating insects have been seen since Arthromitus was first described and named as a plant by Leidy in 1850. Previous descriptions were inadequate for acceptance of the group in modern bacteriological literature. Twenty-two distinguishable arthromitids in nine different arthropod hosts are recorded on the basis of microscopic studies. Five are named, including two whose ultrastructure are detailed: Arthromitus chasei sp. nov. that lives in the damp wood-eating termite Zootermopsis angusticollis (from the west coast of North America) and Arthromitus reticulitermitidis sp. nov. from the subterranean west coast termite Reticulitermes tibialis. A pterotermiditis from the desert termite Pterotermitidis occidentis; A. zootermopsidis, also from Z. angusticollis; and A. cristatus (Leidy, 1881) from Reticulitermes flavipes of eastern North America are also named here. Characterized by trichomes that show a morphogenetic sequence from no spores through immature spores to mature spores with spore filaments, Arthromitus symbionts can be identified as members of the genus by light microscopy and habitat. Electron microscopy reveals their remarkable complexity. They attach by spore filaments to various objects including the host gut wall; their maturation extends distally toward the termite lumen. By surface sterilization of the termite, maceration of the paunch, exposure to boiling temperatures and plating on soft acetate agar, the heat resistant nature of the spores and facultatively aerobic nature of Arthromitus sp. (from Zootermopsis) was demonstrated.

NASA Discipline Number 52-30↗
NASA NTRS2006

Fossils of Prokaryotic Microorganisms in the Orgueil Meteorite

The Orgueil CII meteorite, which fell in southern France on the evening of May 14, 1864, has been one of the most extensively studied of all known carbonaceous meteorites. Field Emission Scanning Electron Microscopy (FESEM) studies of freshly fractured interior surfaces of the Orgueil meteorite have resulted in the detection of the fossilized remains of a large and diverse population of filamentous prokaryotic microorganisms. The taphonomy and the diverse modes of the preservation of these remains ,are diverse. Some of the remains exhibit carbonization of a hollow sheath and in other cases the remains are permineralized with water-soluble evaporite minerals, such as magnesium sulfate or ammonium salts. After the sample is fractured and the interior surfaces are exposed to the atmospheric moisture, some of these friable remains have been observed to exhibit significant alterations in appearance with time. Images are presented to document the changes that have been observed in some forms within the past two years. Images and EDS spectral data will also be presented to document the studies carried out on abiotic forms to search for possible nonbiological interpretations of the indigenous filamentous microstructures that have been found in the Orgueil meteorite. Images and EDS data will be presented showing the size, size range, morphology and chemical compositions of abiotic microstructures found in native crystalline and fibrous Epsomites from Poison Lake, Washington, USA and Catalayud, Zaragoza, Aragon, Spain. Many of these embedded forms are consistent in size and microstructure with cyanobacteria morphotypes. Some of the forms are exhibit known characteristics differentiation of cells, and reproductive structures of filamentous trichomic prokaryotes (bacteria and cyanobacteria) and the degraded remains of microfibrils associated with sheaths of cyanobacteria. In this paper, recently obtained comparative images and EDS data will be presented for the mineralized remains found in the Orgueil meteorite and these forms will be compared with known cyanobacteria of the family Oscillatoriaceae. Many of the indigenous filamentous microstructures found in Orgueil filaments are dramatically different from the abiotic microstructures found in the fibrous epsomites and these forms are interpreted as the molds, casts and the well preserved permineralized remains (microfossils) of filamentous prokaryotes that are embedded in and indigenous to the matrix of the Orgueil CI1 carbonaceous meteorite.

Hoover, Richard B.↗
NASA NTRS2007

Microfossils of Cyanobacteria in Carbonaceous Meteorites

During the past decade, Environmental and Field Emission Scanning Electron Microscopes have been used at the NASA/Marshall Space Flight Center to investigate freshly fractured interior surfaces of a large number of different types of meteorites. Large, complex, microfossils with clearly recognizable biological affinities have been found embedded in several carbonaceous meteorites. Similar forms were notably absent in all stony and nickel-iron meteorites investigated. The forms encountered are consistent in size and morphology with morphotypes of known genera of Cyanobacteria and microorganisms that are typically encountered in associated benthic prokaryotic mats. Even though many coccoidal and isodiametric filamentous cyanobacteria have a strong morphological convergence with some other spherical and filamentous bacteria and algae, many genera of heteropolar cyanobacteria have distinctive apical and basal regions and cellular differentiation that makes it possible to unambiguously recognize the forms based entirely upon cellular dimensions, filament size and distinctive morphological characteristics. For almost two centuries, these morphological characteristics have historically provided the basis for the systematics and taxonomy of cyanobacteria. This paper presents ESEM and FESEM images of embedded filaments and thick mats found in-situ in the Murchison CM2 and Orgueil cn carbonaceous meteorites. Comparative images are also provided for known genera and species of cyanobacteria and other microbial extremophiles. Energy Dispersive X-ray Spectroscopy (EDS) studies indicate that the meteorite filaments typically exhibit dramatic chemical differentiation with distinctive difference between the possible microfossil and the meteorite matrix in the immediate proximity. Chemical differentiation is also observed within these microstructures with many of the permineralized filaments enveloped within electron transparent carbonaceous sheaths. Elemental distributions of these embedded filaments are not consistent with recent cyanobacteria or other living or preserved microbial extremophiles that have been investigated during this research. The meteorite filaments often have nitrogen content below the sensitivity level of the EDS detector. Carbon, Sulphur, Iron or Silicon are often highly enriched and hence anomalous C/N and CIS ratios when compared with modem cyanobacteria. The meteorite forms that are unambiguously recognizable as biological filaments are interpreted as indigenous microfossils analogous to several known genera of modem cyanobacteria and associated trichomic filamentous prokaryotes.

Hoover, Richard B.↗