J. Kazmierczak

Bacterial diversity and carbonate precipitation in the giant microbialites from the highly alkaline Lake Van, Turkey

Lake Van harbors the largest known microbialites on Earth. The surface of these huge carbonate pinnacles is covered by coccoid cyanobacteria whereas their central axis is occupied by a channel through which neutral, relatively Ca-enriched, groundwater flows into highly alkaline (pH ~9.7) Ca-poor lake water. Previous microscopy observations showed the presence of aragonite globules composed by rounded nanostructures of uncertain origin that resemble similar bodies found in some meteorites. Here, we have carried out fine-scale mineralogical and microbial diversity analyses from surface and internal microbialite samples. Electron transmission microscopy revealed that the nanostructures correspond to rounded aragonite nanoprecipitates. A progressive mineralization of cells by the deposition of nanoprecipitates on their surface was observed from external towards internal microbialite areas. Molecular diversity studies based on 16S rDNA amplification revealed the presence of bacterial lineages affiliated to the Alpha-, Beta- and Gammaproteobacteria, the Cyanobacteria, the Cytophaga-Flexibacter-Bacteroides (CFB) group, the Actinobacteria and the Firmicutes. Cyanobacteria and CFB members were only detected in surface layers. The most abundant and diverse lineages were the Firmicutes (low GC Gram positives). To the exclusion of cyanobacteria, the closest cultivated members to the Lake Van phylotypes were most frequently alkaliphilic and/or heterotrophic bacteria able to degrade complex organics. These heterotrophic bacteria may play a crucial role in the formation of Lake Van microbialites by locally promoting carbonate precipitation.

Genuine modern analogues of Precambrian stromatolites from caldera lakes of Niuafoʻou Island, Tonga

Calcareous or dolomitic, often secondarily silicified, laminated microbial structures known as stromatolites are important keys to reconstruct the chemical and biotic evolution of the early ocean. Most authors assume that cyanobacteria-associated microbialitic structures described from Shark Bay, Western Australia, and Exuma Sound, Bahamas, represent modern marine analogues for Precambrian stromatolites. Although they resemble the Precambrian forms macroscopically, their microstructure and mineralogical composition differ from those characterizing their purported ancient counterparts. Most Precambrian stromatolites are composed of presumably in situ precipitated carbonates, while their assumed modern marine analogues are predominantly products of accretion of grains trapped and bound by microbial, predominantly cyanobacterial, benthic mats and biofilms and only occasionally by their physicochemical activity. It has therefore been suggested that the carbonate chemistry of early Precambrian seawater differed significantly from modern seawater, and that some present-day quasi-marine or non-marine environments supporting growth of calcareous microbialites reflect the hydrochemical conditions controlling the calcification potential of Precambrian microbes better than modern seawater. Here we report the discovery of a non-marine environment sustaining growth of calcareous cyanobacterial microbialites showing macroscopic and microscopic features resembling closely those described from many Precambrian stromatolites.

Growth, Structure and Calcification Potential of an Artificial Cyanobacterial Mat

Microbial mats growing on and within light-exposed surfaces harbor complex structured microbial communities of both aerobic, microaerophilic and anaerobic microbes, which in their concerted action exhibit almost closed cycles of carbon, sulfur and other essential elements for biological growth and development (Canfield and Des Marais 1993; van Gemerden 1993; Stal 2000). Diatoms and, primarily, cyanobacteria constitute the major primary producers in most microbial mats. Anoxygenic photosynthetic bacteria (both photoautotrophs and photoheterotrophs) are also abundant, but their contribution to the primary production of mats is regarded minor (Canfield and Des Marais 1993), with the exception of certain hot spring mats (Jorgensen and Nelson 1988) and coastal mats of purple bacteria (van Gemerden et al. 1989). Due to the absence or very minor presence of higher organisms (macrophytes and animals), microbial mats represent well developed microbially driven ecosystems. In extreme environments, like in hypersaline or geothermal waters, microbial mat communities are relatively stable over time periods >1 year and they can develop into cm to m thick cohesive layers consisting of >90% exopolymer and cells (e.g. Krumbein et al. 1977; Jorgensen et al. 1983; DesMarais 1995). Coastal mats in temperate environments are thinner and have a more ephemeral occurrence (Stal et al. 1985; van Gemerden et al. 1989). Intertidal microbial mats play an important role for coastal morphology due to their sediment binding and stabilization properties (Krumbein et al. 1994). In special aquatic environments, like alkaline lakes and tropical intertidal and subtidal zones, sediment trapping by microbial mats in combination with calcification leads to formation of conspicuous solid structures like beachrock lining the intertidal of tropical lagoons (Krumbein 1979b), and laminated cushion (Logan 1961; Dravis 1983; Riding et al.1991; Reid et al. 2000) and dome shaped (Kempe et al. 1991) structures interpreted as living stromatolites.

Recent cyanobacterial counterparts of Paleozoic Wetheredella and related problematic fossils

Recent and subfossil calcareous structures similar to Paleozoic marine problematic fossils known as Wetheredella Wood, 1948 have been found in a sea-linked, midly alkaline crater lake on Satonda Island, Indonesia. They are generated by calcifying mats of coccoid cyanobacteria (Pleurocapsa group) growing in crypts and crevices between the foliaceous thalli of calcareous red algae and agglomerations of nubecullinid foraminifers which form small reefs along the lake shore. The Wetheredella-like structures occur at depths ranging from near the water surface down to about 8 m

A TERRESTRIAL MODEL FOR AN ALKALINE MARTIAN HYDROSPHERE

Abstract The chemical evolution of the early hydrospheres on Earth and Mars could have been similar. It may have been characterized by long-lasting highly alkaline conditions. By analogy with sediments produced in terrestrial highly alkaline environments (soda lakes), traces of the martian alkaline hydrosphere could be found by remote sensing and/or landing missions in form of (i) CaMg carbonate precipitates, (ii) silicified deposits, (iii) volcanogenic natrocarbonatites, and (iv) efflorescenses. The potential significance of the highly alkaline Mars hydrosphere for the origin, sustenance, and subsequent evolution of living systems on that planet is discussed.

Late Devonian marine anoxia challenged by benthic cyanobacterial mats

Mass occurrence of benthic cyanobacterial mats in a sequence of Late Devonian black shales and bituminous limestones of the Holy Cross Mts. (central Poland), enclosing the famous Kellwasser and Hangenberg extinction horizons, is reported. The microbiota forming the mats is compared with some modern benthic chroococcalean cyanobacteria. Similarly to their extant counterparts, the Devonian cyanobacteria must had been phototrophic and oxygenic aerobes which could, however, tolerate slightly sulfidic conditions characterizing the near-bottom waters of the Late Devonian epicontinental sea. The cyanobacterial mats successfully colonized the oxygen-deficient and H(2)S-enriched seabed otherwise unfavorable for most other benthic biota. The redox state of this sluggish Late Devonian sea, ascribed previously mostly to anoxic or euxinic conditions, is reassessed as probably pulsating between anoxic, dysoxic, and weakly oxic conditions. The redox state was dependent on the rate of oxygen production by the cyanobacterial mats, the intensity of H(2)S emissions from the decaying mat biomass, and the rate of planktonic production.

Microbialite Formation in Seawater of Increased Alkalinity, Satonda Crater Lake, Indonesia: Discussion

Arp et al. (2003) present data which confirm and refine the results of our long-time studies (field campaigns of 1986, 1993, 1996) on Satonda Crater Lake (summarized in Kempe and Kazmierczak 1993). They reiterate the importance of marine stratified water bodies in generating, through sulfate reduction, excess alkalinity, which in turns causes very high CaCO3 supersaturation levels. This geochemical process, called the alkalinity pump (Kempe 1990), was conceptually refined using the quasi-marine Satonda Lake as a geochemical model for some epicratonic marine basins from the geological past (Kempe and Kazmierczak 1994). The concept of an alkalinity pump is important for understanding the abundance of calcified benthic cyanobacterial mats in ancient shallow seas leading to the formation of a variety of marine calcareous microbialitic structures and fine-grained calcareous sediments accumulated on the seafloor (Kempe and Kazmierczak 1990; Kazmierczak et al. 1996). While principally agreeing with Arp et al.s results, we strongly disagree with two of their major conclusions. The first major objection concerns Arp et al.s scepticism with respect to the calcification potential of benthic cyanobacterial mats presently living in the lake. On the basis of samples gathered in 1993 and 1996, Arp et al. conclude that these mats calcify very weakly or, in some cases, do not calcify at all. This sharply contradicts our observations showing strong permineralization of the mats both with CaCO3 and silica (e.g., Kempe and Kazmierczak 1993, Pl. 6, figs. 3-6). Mat samples we took at the end of dry season 1986 demonstrate that calcification of the cyanobacteria occurred in vivo. Masses of minute grains of CaCO3 (predominantly Mg-calcite) were observed not only on the mat surface but also within the common mucilage sheaths (glycocalyx) surrounding aggregates of living cyanobacterial coccoid cells (classified as representatives of Pleurocapsales). Minute CaCO3 grains …

The Soda Ocean Concept and Its Bearing on Biotic Evolution

The soda ocean hypothesis (Kempe & Degens, 1985) suggests an early alkaline ocean of high pH and low calcium and magnesium concentrations. The dissolved carbonates were gradually lost during the Precambrian, leaving the present sodium chloride ocean. The Precambrian paleontological record and the calcium physiology of living cells implicate that the stepwisebuildup of calcium in the ancient ocean was of primary importance for the generation of multicellular life and the onset of biocalcification.

Palaeontology (Communication arising): Thermal alteration of the Earth's oldest fossils

Microscopic carbonaceous structures found in ancient rocks could provide clues to early life on Earth if they turn out to be genuine fossil microorganisms. Here we show that thermal alteration of microbial remains embedded in a mineral matrix may significantly change their original morphology and produce structures that resemble those of what are claimed to be the Earths oldest fossils. These observations may shed light on the controversy that surrounds these microfossils from the 3,465-Myr-old Apex Chert of the early Archaean Warrawoona Group in northwestern Australia.

Nanoparticle size effect on the magnetic and transport properties of (La0.7Sr0.3)0.9Mn1.1O3 manganites

Magnetic and transport thermal measurements of nanosize (La0.7Sr0.3)0.9Mn1.1O3 manganite are reported. The nanoparticles are synthesized with use of the co-precipitation method at different (800, 900, and 950°C) temperatures. Their crystal structure is determined to be perovskite-like with a rhombohedral distortion (the space group R3¯c). The phase composition and specific surface nanopowders are determined. The average size of synthesized nanoparticles (from 40to100nm) is estimated by both the method of low-temperature adsorption of argon and x-ray diffraction measurements. All the nanosize samples show ferromagnetic-like ordering with close phase transition temperatures. Their magnetization decreases with decreasing particle size. Comparison of experimental and calculated temperature dependences of the spontaneous magnetic moment shows that the spontaneous magnetization both in magnetic field and without field is well described in the framework of the double exchange model. The decrease of the magnetiza...