Chemostat and in‐situ colonization kinetics of thermothrix thiopara on calcite and pyrite surfaces

Growth and attachment rates of Thermothrix thiopara on calcite and pyrite were quantitated in a thiosulfate‐limited chemostat and in the thermal spring where the organism is found in nature. Surface growth rates were quantitated by using the surface colonization and exponential growth equations. These two models were compared as means of determining surface growth rates. In the chemostat, T. thiopara cells colonizing calcite and pyrite surfaces grew at approximately one‐third the rate of suspended cells. However, T. thiopara attached to pyrite faster than to calcite. In the thermal spring, growth and attachment rates were equal on calcite and pyrite. It was concluded that the exponential growth equation overestimates in‐situ surface growth rates and that T. thiopara grows more slowly when colonizing mineral surfaces than when growing in suspension. Lower growth rates on surfaces may be due to a reduced cell surface area for nutrient uptake or an increased specific maintenance rate.     

Colonization of sulfide‐oxygen interfaces on hot spring tufa by Thermothrix thiopara

Cream‐colored streamers of Thermothrix thiopara were found at the sulfide‐oxygen interfaces of active tufa mounds where reducing geothermal groundwaters mixed with the oxidizing atmosphere. In the Jemez hot springs, the molar ratio of sulfide to oxygen was 0.3 to 0.8 at streamer locations within the interface. This corresponded to the optimum stoichiometric proportion (0.5) necessary for sulfur metabolism. The mechanism of cell positioning at the interface was studied by shifting the interface location with a plastic cover to extend reducing conditions from the mouth of the spring to the edge of the plastic. Macroscopically visible streamers of filamentous cells became established at the new interface within a period of eight days. They could then be reestablished at the original interface by removing the cover.

Calcite crystals, pyrite crystals, and membrane enrichment vials were incubated on both sides of the interface and the kinetics of colonization determined. The preferential attachment of rod‐shaped cells to pyrite appeared to be the mechanism by which cells located themselves where pyrite occurred in situ, upstream from the interface. The formation of filamentous cells from rod‐shaped cells was induced by oxygen‐limited growth conditions. This moved the cells slightly downstream and directly within the interface.     

Growth Kinetics and Yield Coefficients of the Extreme Thermophile Thermothrix thiopara in Continuous Culture

Thermothrix thiopara did not appear to be stressed at high temperature (72°C). Both the actual and theoretical yields were higher than those of analogous mesophilic sulfur bacteria, and the specific growth rate (μ_max) was more rapid than that of most autotrophs. The specific growth rate (0.58 h⁻¹), specific maintenance rate (0.11 h⁻¹), actual molar growth yield at μ_max (Y_max = 16 g mol⁻¹), and theoretical molar growth yield (Y_G = 24 g mol⁻¹) were all higher for T. thiopara (72°C) than for mesophilic (25 to 30°C) Thiobacillus spp. The growth efficiencies for T. thiopara at 70 and 75°C (0.84 and 0.78) were significantly higher than at 65°C (0.47). Corresponding specific maintenance rates were highest at 65°C (0.41 h⁻¹) and lowest at 70 and 75°C (0.11 and 0.15 h⁻¹, respectively). Growth efficiencies of metabolically similar mesophiles were generally higher than for T. thiopara. However, the actual yields at μ_max were higher for T. thiopara because its theoretical yield was higher. Thus, at 70°C, T. thiopara was capable of deriving more metabolically useful energy from thiosulfate than were mesophilic sulfur bacteria at 25 and 30°C. The low growth efficiency of T. thiopara reflected higher maintenance expenditures. T. thiopara had higher maintenance rates than Thiobacillus ferroxidans or Thiobacillus denitrificans, but also attained higher molar growth yields. It is concluded that sulfur metabolism may be more efficient overall at extremely high temperatures due to increased theoretical yields despite increased maintenance requirements.     

Thermothrix thiopara: Growth and Metabolism of a Newly Isolated Thermophile Capable of Oxidizing Sulfur and Sulfur Compounds

Thermothrix thiopara is isolated from hot sulfur springs. It occurs in situ at a temperature of 72°C, a pH of 7.0, and an HS^- concentration of 17.4 μmol/liter (0.8 ppm). The organism was capable of autotrophic growth. Sulfite, sulfur, and polythionates were formed and subsequently degraded to sulfate during growth with thiosulfate as the sole energy source. Thiosulfate was oxidized by the polythionate pathway, and the stoichiometry of growth on thiosulfate was determined. The organism was also capable of heterotrophic growth in amino acids and simple sugars. A source of reduced sulfur (methionine, glutathione) was required for heterotrophic growth. Growth occurred aerobically or anaerobically with nitrate as a terminal oxidant. Both nitrous oxide and dinitrogen were produced. At 73°C the maximum autotrophic growth rate in batch culture using thiosulfate was 0.56 generation per h. Under the same conditions in continuous culture, washout occurred at a dilution rate of 0.3 to 0.4 per h, corresponding to a cellular growth rate of 0.43 to 0.58 generation per h. This was nearly three times the growth rate for Thiobacillus denitrificans. T. thiopara is gram negative. It was also found to be both lysozyme and penicillin susceptible. As a result, this organism cannot be considered an archaebacterium.     

Exopolymeric substances of sulfate-reducing bacteria: Interactions with calcium at alkaline pH and implication for formation of carbonate minerals

Sulfate‐reducing bacteria (SRB) have been recognized as key players in the precipitation of calcium carbonate in lithifying microbial communities. These bacteria increase the alkalinity by reducing sulfate ions, and consuming organic acids. SRB also produce copious amounts of exopolymeric substances (EPS). All of these processes influence the morphology and mineralogy of the carbonate minerals. Interactions of EPS with metals, calcium in particular, are believed to be the main processes through which the extracellular matrix controls the precipitation of the carbonate minerals. SRB exopolymers were purified from lithifying mat and type cultures, and their potential role in CaCO₃ precipitation was determined from acid‐base titrations and calcium‐binding experiments. Major EPS characteristics were established using infrared spectroscopy and gas chromatography to characterize the chemical functional groups and the sugar monomers composition. Our results demonstrate that all of the three SRB strains tested were able to produce large amounts of EPS. This EPS exhibited three main buffering capacities, which correspond to carboxylic acids (pK_a = 3.0), sulfur‐containing groups (thiols, sulfonic and sulfinic acids – pK_a = 7.0–7.1) and amino groups (pK_a = 8.4–9.2). The calcium‐binding capacity of these exopolymers in solution at pH 9.0 ranged from 0.12g_Ca g_EPS^?1–0.15 g_Ca g_EPS^?1. These results suggest that SRB could play a critical role in the formation of CaCO₃ in lithifying microbial mats. The unusually high sulfur content, which has not been reported for EPS before, indicates a possible strong interaction with iron. In addition to changing the saturation index through metabolic activity, our results imply that SRB affect the rock record through EPS production and its effect on the CaCO₃ precipitation. Furthermore, EPS produced by SRB may account for the incorporation of metals (e.g. Sr, Fe, Mg) associated with carbonate minerals in the rock record.     

Mineralogical transformation and neoformation in granite caused by the lichens Tephromela atra and Ochrolechia parella

Tephromela atra and Ochrolechia parella are among the most abundant lichens colonizing granitic monuments in the region of Galicia (northwest Spain). In this work, their interaction with a two-mica granite used in the construction of the Toxosoutos Monastery (Noia, Galicia) was studied, using optical microscopy, scanning electron microscopy (with back-scattered-electron and energy-dispersive X-ray detection), X-ray diffractometry and atomic absorption spectroscopy to evaluate their physical, mineralogical and chemical effects. Both lichens contributed to physical weathering by penetrating intermineral voids and mineral cleavage planes, disaggregating the rock and entrapping the loosened mineral grains in their thalli. Significant chemical and mineralogical weathering also occurred, including depletion of potassium from biotite, transformation of this mica into hydroxyaluminium-vermiculite, and neoformation of whewellite and calcite in the lichen thalli. Neoformation of these calcium minerals on a calcium-poor rock such as granite is noteworthy, and this is the first time calcium carbonate has been detected within a lichen colonizing a granitic rock. Precipitation of the calcium carbonate was attributed to the local pH in the thalli having been raised due to release of sodium from nearby plagioclase during weathering.     

Thiosulfate and tetrathionate degradation as well as biofilm generation by Thiobacillus intermedius and Thiobacillus versutus studied by microcalorimetry,HPLC, and ion-pair chromatography

The growth of Thiobacillus (T.) intermedius strain K12 and Thiobacillus versutus strain DSM 582 on thiosulfate and tetrathionate was studied combining on-line measurements of metabolic activity and sulfur compound analysis. Most results indicate that T. intermedius oxidized thiosulfate via tetrathionate to sulfate. Concomittantly, sulfur compound intermediates like triand pentathionate were detectable. The formation is probably the result of highly reactive sulfane monosulfonic acids. The formation of tetrathionate allows the cells to buffer temporarily the proton excretion from sulfuric acid production. With T. versutus intermediate sulfur compounds were not detectable, however, sulfur was detectable. The possibility of a thiosulfate oxidation via dithionate, S₂O _inf6 ^sup2- , is discussed. The on-line measurement of metabolic activity by microcalorimetry enabled us to detect that cells of T. intermedius adhere to surfaces and produce a biofilm by a metabolic process whereas those of T. versutus fail to do so. The importance of the finding is discussed.     

Paenibacillus sp. Strain SB-6 Induces Weathering of Ca-montmorillonite: Illitization and Formation of Calcite

Investigation of the weathering of silicate minerals is helpful to understand the process of soil development, cycling of nutrient elements, and potential applications in fixation of carbon dioxide from the atmosphere through carbonate precipitation. In this study, weathering experiments of calcium-montmorillonite were conducted using Paenibacillus sp. strain SB-6 for 70 days. The results indicated that the Si⁴⁺, Al³⁺, Ca²⁺ and Na⁺ concentrations in the medium of the biotic experiments were evidently higher than those of the abiotic experiments, and that Paenibacillus sp. could help the transformation of partial montmorillonite into an illite–montmorillonite mixed-layer. In the process of illitization, K⁺ went into the interlayer of montmorillonite and hydrated Ca²⁺ and Na⁺ released from it. In the late stage of the experiments, the Ca²⁺ released from montmorillonite combined with carbonate ions generated by the bacterial metabolism, forming calcite.     

Transformation of galena to pyromorphite produces bioavailable sulfur for neutrophilic chemoautotrophy

The aqueous concentration of lead [Pb(II)] in geochemical environments is controlled by the solubility of Pb‐bearing minerals and their weathering products. In contaminated soils, a common method for in situ stabilization of Pb(II) is the addition of phosphate to convert more redox sensitive sulfide minerals into sparingly soluble pyromorphite [Pb₅(PO₄)₃X]. In this study, we conducted experimental studies to investigate the fate of reduced sulfur during the conversion of galena [PbS] to chloropyromorphite [Pb₅(PO₄)₃Cl]. Powder X‐ray diffraction analysis indicated that the reaction of phosphate with galena under oxic conditions resulted in the oxidation of sulfide and formation of elemental sulfur [S₈]. Under oxic abiotic conditions, the S₈ was retained in the solid phase, and negligible concentrations of sulfur as sulfide and thiosulfate were detected in the aqueous phase and only a small amount of sulfate. When PbS reacted in the presence of the chemoautotrophic organism Bosea sp. WAO, the S₈ in the secondary mineral was oxidized to sulfate. Strain WAO produced significantly more sulfate from the secondary S₈ than from the primary galena. Microscopic analysis of mineral–microbe aggregates on mineral‐embedded slide cultures showed that the organism was colocalized and increased in biomass over time on the secondary mineral surface supporting a microbial role. The results of this study indicate that stimulation of sulfur‐oxidizing activity may be a direct consequence of phosphate amendments to Pb(II)‐contaminated soils.     

Preservation of overmature,ancient, sedimentary organic matter in carbonate concretions during outcrop weathering

Concretions are preferentially cemented zones within sediments and sedimentary rocks. Cementation can result from relatively early diagenetic processes that include degradation of sedimentary organic compounds or methane as indicated by significantly ¹³C‐depleted or enriched carbon isotope compositions. As minerals fill pore space, reduced permeability may promote preservation of sediment components from degradation during subsequent diagenesis, burial heating and outcrop weathering. Discrete and macroscopic organic remains, macro and microfossils, magnetic grains, and sedimentary structures can be preferentially preserved within concretions. Here, Cretaceous carbonate concretions of the Holz Shale are shown to contain relatively high carbonate‐free total organic carbon (TOC) contents (up to ~18.5 wt%) compared to the surrounding host rock (with <2.1 wt%). TOC increases with total inorganic carbon (TIC) content, a metric of the degree of cementation. Pyrite contents within concretions generally correlate with organic carbon contents. Concretion carbonate carbon isotope compositions (δ¹³C_carb) range from ?22.5 to ?3.4‰ (VPDB) and do not correlate strongly with TOC. Organic carbon isotope compositions (δ¹³C_org) of concretions and host rock are similar. Thermal maturity data indicate that both host and concretion organic matter are overmature and have evolved beyond the oil window maturity stage. Although the organic matter in general has experienced significant oxidative weathering, concretion interiors exhibit lower oxygen indices relative to the host. These results suggest that carbonate concretions can preferentially preserve overmature, ancient, sedimentary organic matter during outcrop weathering, despite evidence for organic matter degradation genetic mechanisms. As a result, concretions may provide an optimal proxy target for characterization of more primary organic carbon concentrations and chemical compositions. In addition, these findings indicate that concretions can promote delayed oxidative weathering of organic carbon in outcrop and therefore impact local chemical cycling.     

Microbial degradation of formaldehyde in white mineral dispersions preserved with formaldehyde-releasing biocides

Two different formaldehyde-degrading microorganisms, Pseudomonas putida and Methylobacterium extorquens, were isolated from calcium carbonate slurry containing the formaldehyde-releasing biocide (ethylenedioxy) dimethanol. Their relative formaldehyde biodegradation and formic acid production kinetics were studied in broth and in calcium carbonate slurry for each microorganism individually, as well as in mixed cultures. Furthermore, the minimal inhibition concentration (MIC) was determined. The results indicated that in slurry, M. extorquens is more tolerant of formaldehyde than P. putida. In slurry, microbial-induced oxidation of formaldehyde caused a temporary accumulation of formic acid, which is presumed to be responsible for pH drop and destabilisation of the calcium carbonate slurry suspension systems. In addition, the residual formaldehyde concentration was observed to drive dominance and recovery of individual formaldehyde-resistant microorganisms in the slurry. Overall, this investigation indicated that biodegradation of formaldehyde in calcium carbonate slurry is brought about by alternating dominance of bacterial genera of mixed formaldehyde-resistant microbial populations.     

Linking sedimentary sulfur and iron biogeochemistry to growth patterns of a cold‐water coral mound in the Porcupine Basin,S.W. Ireland (IODP Expedition 307)

Challenger Mound, a 150‐m‐high cold‐water coral mound on the eastern flank of the Porcupine Seabight off SW Ireland, was drilled during Expedition 307 of the Integrated Ocean Drilling Program (IODP). Retrieved cores offer unique insight into an archive of Quaternary paleo‐environmental change, long‐term coral mound development, and the diagenetic alteration of these carbonate fabrics over time. To characterize biogeochemical carbon–iron–sulfur transformations in the mound sediments, the contents of dithionite‐ and HCl‐extractable iron phases, iron monosulfide and pyrite, and acid‐extractable calcium, magnesium, manganese, and strontium were determined. Additionally, the stable isotopic compositions of pore‐water sulfate and solid‐phase reduced sulfur compounds were analyzed. Sulfate penetrated through the mound sequence and into the underlying Miocene sediments, where a sulfate–methane transition zone was identified. Small sulfate concentration decreases (<7 mm ) within the top 40 m of the mound suggested slow net rates of present‐day organoclastic sulfate reduction. Increasing δ³⁴S‐sulfate values due to microbial sulfate reduction mirrored the decrease in sulfate concentrations. This process was accompanied by oxygen isotope exchange with water that was indicated by increasing δ¹⁸O‐sulfate values, reaching equilibrium with pore‐water at depth. Below 50 mbsf, sediment intervals with strong ³⁴S‐enriched imprints on chromium‐reducible sulfur (pyrite S), high degree‐of‐pyritization values, and semi‐lithified diagenetic carbonate‐rich layers characterized by poor coral preservation, were observed. These layers provided evidence for the occurrence of enhanced microbial sulfate‐reducing activity in the mound in the past during periods of rapid mound aggradation and subsequent intervals of non‐deposition or erosion when geochemical fronts remained stationary. During these periods, especially during the Early Pleistocene, elevated sulfate reduction rates facilitated the consumption of reducible iron oxide phases, coral dissolution, and the subsequent formation of carbonate cements.     

Evaluation of a proposed surface colonization equation usingThermothrix thiopara as a model organism

The colonization equation shown below was evaluated usingThermothrix thiopara as a model organism. $$N = (A/\mu )e^{\mu t} - A/\mu $$ where: N=number of cells on surface (cells field^?1); A = attachment rate (cells field^?1 h^?1); M=specific growth rate (h^?1); t=incubation period (h). Previous studies of microbial surface colonization consider attachment and growth independently. However, the proposed colonization equation integrates the effects of simultaneous attachment and growth. Using this equation, the specific growth rate ofT. thiopara was found to be 0.38±0.3 h^?1 during in situ colonization. Estimates ofμ were independent of incubation period after 4 h (2 generations). Shorter incubations were inadequate to produce sufficient microcolonies for accurate determination of specific growth rate. Empirical data for the time course of colonization fell within the 95% confidence interval of predicted values. The attachment rate, although assumed to be constant, was found to continuously increase with time. This increase may have been an artifact due to the continuous deposition of travertine on the surface, or may indicate the need for a function to replace A in the colonization equation. Using the exponential growth equation, the progeny of cells that attach during incubation are considered to be progeny of cells that attach initially. This erroneously inflated the growth rate by 55%.     

Stromatolitic knobs in Storr's Lake (San Salvador,Bahamas): a model system for formation and alteration of laminae

The initial lamination in young, metabolically active Scytonema knobs developing in Storr's Lake (Bahamas) results from the iterative succession of two different stages of microbial growth at the top of this microbialite. Stage 1 is dominated by vertically oriented cyanobacterial filaments and is characterized by a high porosity of the fabric. Stage 2 shows a higher microbial density with the filaments oriented horizontally and with higher carbonate content. The more developed, dense microbial community associated with Stage 2 of the Scytonema knobs rapidly degrades extracellular organic matter (EOM) and coupled to this, precipitates carbonate. The initial nucleation forms high‐Mg calcite nanospheroids that progressively replace the EOM. No precipitation is observed within the thick sheath of the Scytonema filaments, possibly because of strong cross‐linking of calcium and EOM (forming EOM‐Ca‐EOM complexes), which renders Ca unavailable for carbonate nucleation (inhibition process). Eventually, organominerals precipitate and form an initial lamina through physicochemical and microbial processes, including high rates of photosynthetic activity that lead to ¹³C‐enriched DIC available for initial nucleation. As this lamina moves downward by the iterative production of new laminae at the top of the microbialite, increased heterotrophic activity further alters the initial mineral product at depth. Although some rare relic preservation of ‘Stage 1–Stage 2’ laminae in subfossil knobs exists, the very fine primary lamination is considerably altered and almost completely lost when the knobs develop into larger and more complex morphologies due to the increased accommodation space and related physicochemical and/or biological alteration. Despite considerable differences in microstructure, the emerging ecological model of community succession leading to laminae formation described here for the Scytonema knobs can be applied to the formation of coarse‐grained, open marine stromatolites. Therefore, both fine‐ and coarse‐grained extant stromatolites can be used as model systems to understand the formation of microbialites in the fossil record.     

A major role for nitrification in the weathering of minerals of brown acid forest soils

Experiments employing lysimeters and a comparison of soil leachates at >‐0.03 MPa and soil solutions extracted at ‐2.5 MPa showed the importance of nitrification in the weathering of minerals of brown acid forest soils (dys‐trochrept) which are formed over large areas in temperate climates.

Mineralization of litter from plants characteristic of such soils (in particular Festuca silvatica and Abies pectinata) produces large amounts of nitric acid. This bacterial nitrification is responsible for the solubilization of Ca²⁺, Mg²⁺, and K⁺ and must be involved in the slow weathering of minerals by acidolysis and in the biogeochemical cycling of Ca²⁺, Mg²⁺, and K⁺ in these soils. Soil solutions extracted at ‐2.5 MPa reflect much more the microbial activity than the leachates from soil and provide interesting information.     

Fungal degradation of calcium-, lead- and silicon-bearing minerals

The aim of this study was to examine nutritional influence on the ability of selected filamentous fungi to mediate biogenic weathering of the minerals, apatite, galena and obsidian in order to provide further understanding of the roles of fungi as biogeochemical agents, particularly in relation to the cycling of metals and associated elements found in minerals. The impact of three organic acid producing fungi (Aspergillus niger, Serpula himantioides and Trametes versicolor) on apatite, galena and obsidian was examined in the absence and presence of a carbon and energy source (glucose). Manifestation of fungal weathering included corrosion of mineral surfaces, modification of the mineral substrate through transformation into secondary minerals (i.e. crystal formation) and hyphal penetration of the mineral substrate. Physicochemical interactions of fungal metabolites, e.g. H⁺ and organic acids, with the minerals are thought to be the primary driving forces responsible. All experimental fungi were capable of mineral surface colonization in the absence and presence of glucose but corrosion of the mineral surface and secondary mineral formation were affected by glucose availability. Only S. himantioides and T. versicolor were able to corrode apatite in the absence of glucose but none of the fungi were capable of doing so with the other minerals. In addition, crystal formation with galena was entirely dependent on the availability of glucose. Penetration of the mineral substrates by fungal hyphae occurred but this did not follow any particular pattern. Although the presence of glucose in the media appeared to influence positively the mineral penetrating abilities of the fungi, the results obtained also showed that some geochemical change(s) might occur under nutrient-limited conditions. It was, however, unclear whether the hyphae actively penetrated the minerals or were growing into pre-existing pores or cracks.     

Litho‐diagenetic implications of the calcium oxalate‐carbonate biogeochemical cycle in semiarid Calcretes,Nazareth, Israel

Microscopic observations of calcrete soil samples in semiarid environments from Israel reveal a particular vesicular microfabric. The calcrete horizon is indurated but highly porous and all the pores are coated with a gray layer (quasi‐coating) of secondary calcium carbonate. Two kinds of needles are found inside the pores: thin and regular needles (calcite), and filaments with very sharp spikes that are of fungal origin. Analysis of the proportions of C, O, and Ca were made with an E.D.S. microprobe connected with a scanning electron microscope to distinguish calcite (CaCO₃) from calcium oxalate (CaC₂O₄) and to differentiate inorganic from organic influences. Under biological control, calcium oxalate coexists with calcium carbonate; both contribute to rock diagenesis. In the pores, biological activity promotes a complex cycling of calcium leading to recementation of the matrix and further lithification. Thus, this kind of calcrete is due to geological evolution as much as to biochemical control.     

Scanning transmission X-ray microscopy study of microbial calcification

Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in microbial fossilization. Characterization of both the organic and mineral components in biomineralized samples is, however, usually difficult at the appropriate spatial resolution (i.e. at the submicrometer scale). Scanning transmission X‐ray microscopy (STXM) was used to measure C K‐edge, P L‐edge, and Ca L‐edge near‐edge X‐ray absorption fine structure (NEXAFS) spectra of some calcium‐containing minerals common in biomineralization processes and to study the experimental biomineralization by the model microorganism, Caulobacter crescentus. We show that the Ca L_2,3‐edges for hydroxyapatite, calcite, vaterite, and aragonite are unique and can be used as probes to detect these different mineral phases. Using these results, we showed that C. crescentus cells, when cultured in the presence of high calcium concentration, precipitated carbonate hydroxyapatite. In parallel, we detected proteins, polysaccharides, and nucleic acids in the mineralizing bacteria at the single‐cell scale. Finally, we discussed the utility of STXM for the study of natural fossilized microbial systems.     

Studies in the Liagoraceae (Nemaliales, Rhodophyta) I. The genus Trichogloea

The calcified, though strongly mucosoid gametophytes of Trichogloea (Nemaliales, Liagoraceae) usually appear seasonally for a short period in tropical and subtropical regions. Vegetative and reproductive characteristics of the presently recognized species, Trichogloea requienii (Mont.) Kützing (the generitype), Trichogloea lubrica J. Agardh, and Trichogloea herveyi W. R. Taylor, are described and compared. In addition, the identities of two previously synonymized species, Trichogloea jadinii Børgesen and Trichogloea javensis B0rgesen are clarified. Species of the genus display considerable variation in habit and branching patterns, necessitating an assessment of reproductive structures for accurate identification. Reliable features of Trichogloea include the structure of the medulla and the cortical (assimilatory) filaments, location and structure of carpogonial branches and spermatangia, and the nature of sterile filaments in the vicinity of the cystocarp. Secondary features include both external and internal branching pattern, and the proportion of calcium carbonate to lubricous material, the latter having to be assessed from fresh collections. The present study provides a comparative morphological account of the species of Trichogloea. As a result, T. requienii, T. lubrica, T. herveyi are confirmed as independent species; T. jadinii is removed from synonymy with T. lubrica and placed in that of T. requienii, and T. javensis is confirmed as a synonym of Izziella orientalis (J. Agardh) Huisman et Schils.     

Bio-precipitation of Calcite with Preferential Orientation Induced by Synechocystis sp. PCC6803

This article presents a research study on the deposition process of Ca²⁺ induced by Synechocystis sp. PCC6803 in BG11 liquid medium with different Ca²⁺ concentrations and different pH. The changes of Ca²⁺ concentrations were measured by using atomic absorption method and the corresponding dynamical models were studied. Minerals and cells were analyzed by high resolution transmission electron microscope, selected area electron diffraction, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction. The selected area electron diffraction patterns were analyzed by Digital Micrograph 3.7 software. The result showed that Ca²⁺ concentrations decreased faster in the experimental group. The changes of calcium carbonate precipitation were fitting to an exponential model. PH 7 and Ca²⁺ concentration of 1.5 g/L were most conducive to calcium carbonate precipitation in the corresponding gradient range. The result of high-resolution transmission electron microscopy showed that minerals in the experimental group differed obviously from that of the control group in the surface morphology, but both of them were calcites. It also showed that a certain number of minute calcites adhesion to the outer surfaces of S. PCC6803 cells. The result of scanning electron microscopy displayed that many sunken holes emerged on the surfaces of the prismatic calcium carbonate minerals. The results of X-ray diffraction proved that minerals induced by S. PCC6803 were calcites with preferential orientation. This article discusses the process of carbonate formation and the possible role played by S. PCC6803. It may be useful to further study the mechanism of microbial carbonates deposition in the field of geology.