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An Overview of Biocement Production from Microalgae

Authors:
Dessy Ariyanti at Diponegoro University
Dessy Ariyanti
Noer Abyor Handayani at Diponegoro University
Noer Abyor Handayani
H. Hadiyanto at Diponegoro University
H. Hadiyanto
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The invention of microorganism's involvement in carbonate precipitation, has lead the exploration of this process in the field of construction engineering. Biocement is a product innovation from developing bioprocess technology called biocementation. Biocement refers to CaCO 3 deposit that formed due to microorganism activity in the system rich of calcium ion. The primary role of microorganism in carbonate precipitation is mainly due to their ability to create an alkaline environment (high pH and DIC increase) through their various physiological activities. Three main groups of microorganism that can induce the carbonate precipitation: (i) photosynthetic microorganism such as cyanobacteria and microalgae; (ii) sulphate reducing bacteria; and (iii) some species of microorganism involved in nitrogen cycle. Microalgae are photosynthetic microorganism and utilize urea using urease or urea amidolyase enzyme, based on that it is possible to use microalgae as media to produce biocement through biocementation. This paper overviews biocement in general, biocementation, type of microorganism and their pathways in inducing carbonate precipitation and the prospect of microalgae to be used in biocement production.
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... Out of the 28 strains, 5 strains ( Fig. 2: Group A) were positive for the urease test and capable to make Christensen's agar plate totally pink in 24 h at 5% and 10% of urea concentrations. This isolate was designated as numbers (4,5,10,13,28) and used for biocement production. The other ineffective strains ( Fig. 2: Group B) were excluded. ...
... The other ineffective strains ( Fig. 2: Group B) were excluded. 1,2,3,4,5,6,7,14,21, and 28, respectively. Accordingly, an increase in the value of electrical conductivity was observed over the period of 28 days, which indicates the growth and activity of bacteria and the breakdown of urea, and thus CaCO 3 precipitation. ...
Effects of Al2O3, SiO2 nanoparticles, and g-C3N4 nanosheets on biocement production from agricultural wastes
Article
Full-text available
  • Feb 2023
Environmental issues are brought up concerning the production of Portland cement. As a result, biocement serves as a reliable substitute for Portland cement in green construction projects. This study created a brand-new technique to create high-quality biocement from agricultural wastes. The technique is based on nanomaterials that improve and accelerate the "Microbially Induced Calcite Precipitation (MICP)" process, which improves the quality of the biocement produced. The mixture was further mixed with the addition of 5 mg/l of graphitic carbon nitride nanosheets (g-C3N4 NSs), alumina nanoparticles (Al2O3 NPs), or silica nanoparticles (SiO2 NPs). The cement: sand ratio was 1:3, the ash: cement ratio was 1:9, and water: cement ratio was 1:2. Cubes molds were prepared, and then cast and compacted. Subsequent de-molding, all specimens were cured in nutrient broth-urea (NBU) media until testing at 28 days. The medium was replenished at an interval of 7 days. The results show that the addition of 5 mg/l of g-C3N4 NSs with corncob ash delivered the highest “Compressive Strength” and the highest “Flexural Strength” of biocement mortar cubes of 18 and 7.6 megapascal (MPa), respectively; and an acceptable “Water Absorption” (5.42%) compared to all other treatments. This treatment delivered a “Compressive Strength”, “Flexural Strength”, and “Water Absorption” reduction of 1.67, 1.26, and 1.21 times the control (standard Portland cement). It was concluded that adding 5 mg/l of g-C3N4 NSs to the cementitious mixture enhances its properties, where the resulting biocement is a promising substitute for conventional Portland cement. Adding nanomaterials to cement reduces its permeability to ions, increasing its strength and durability. The use of these nanomaterials can enhance the performance of concrete infrastructures. The use of nanoparticles is an effective solution to reduce the environmental impact associated with concrete production.
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... It was found that incorporating microalgae biomass into concrete during the mixing phase provides enhanced durability and strength (Ariyanti, 2012;Jebamalar and Iyer, 2016;Luhar et al., 2022;Yu et al., 2022). Species that show potential for Bioconcrete/Biocement production are Porphyridium cruentum, Spirulina, Arthrospira sp, Chlorella vulgaris, Dunaliella salina, Muriellopsis sp. and Haematococcus pluvialis (Ariyanti and Abyor Handayani, 2011;Srinivas et al., 2021). ...
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... In the literature, most studies on calcium carbonate formation utilized the bacterium Bacillus pasteurii (Sporosarcina pasteurii) [9][10][11][12][13][14][15][16]. There are also studies which were conducted by using different microorganisms other than this species [17][18][19][20][21][22][23][24][25][26]. ...
THE EFFECTS OF DIFFERENT SOURCES OF CALCIUM IN IMPROVEMENT OF SOILS BY MICROBIALLY INDUCED CALCITE PRECIPITATION (MICP)
Article
Full-text available
  • Jan 2019
Several soil improvement techniques are successfully implemented today. Studies are increasingly becoming popular on microbially induced calcite precipitation (MICP) as an environment-friendly and sustainable method that is an alternative to other soil improvement techniques. Our study examined the effects of different sources of calcium on an improvement that was carried out on a sand soil with a 35% relative density by using the MICP method. The results were analyzed by using unconfined compression, permeability, calcite formation percentage, pH, SEM (scanning electron microscopy) and XRD (x-ray diffraction) experiments. As a result of the unconfined compression test, the strength values were obtained as 2406 kPa in the specimens where calcium chloride was used as a calcium source, 2435 kPa in the specimens where calcium nitrate was used and 64 kPa in the specimens where calcium acetate was used. The permeability experiment revealed a decrease in permeability of 80.8% for calcium chloride, 23% for calcium nitrate and 90.4% for calcium acetate. According to the results of the SEM analyses, the structures that formed in all specimens bound the grains to each other and coated the surfaces of the grains. In the XRD analyses, calcite formation was observed in the specimens where calcium chloride and calcium nitrate were used as the source, while, in contrast, vaterite formations were also observed in the specimens where calcium acetate was used as the source. It was determined that different sources of calcium had different effects on improvement of sand soils by microbially induced calcite precipitation (MICP).
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... In MICP, four different and diverse microorganisms are involved: 1. Photosynthetic organisms like algae (different groups of algae listed in table 2); 2. Sulphate reducing bacteria involved in dissimilation reduction of sulphate; 3. Organic acid utilizing organisms; and 4. Organisms are involved in the nitrogen cycle, especially in the ammonification of amino acids, nitrate reduction, and hydrolysis of urea [15]. Among the four groups listed, Sporosarcina pastuerii have been widely exploited for the production of bio-cement on different substrates such as sandy soil, calcareous soil, calcium chloride, urea, acetic acid (obtained through pyrolysis of lignocellulose biomass) and limestone powder [5,[16][17][18][19]. The fungus has been reported to produce bio-cement (Penicillium chrysogenum CS1), a urease-producing strain. ...
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... Thus, the use of Ureaplasma urealyticum and other such pathogenic bacteria is restricted. The recommended bacterial species for biocementation are ureolytic bacteria of the genera Bacillus, Sporosarcina, Spoloactobacilus, Clostridium and Desulfotomaculum [40,58]. Biocementation by urea hydrolysis involves growing the bacteria in suitable growth medium containing all essential nutrients (such as nutrient broth), and then providing them with the environment rich in urea and calcium ions. ...
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... Later research has provided evidence of at least 200 different bacterial strains capable of precipitating CaCO3 [24,25]. These microorganisms include cyanobacteria, microalgae, sulfate-reducing bacteria, and organisms involving the nitrogen cycle [26]. The metabolic pathways followed by these microorganisms for the CaCO3 precipitation include photosynthesis, urea hydrolysis, and denitrification. ...
Applications of microbial calcium carbonate precipitation in concrete through denitrification - a review
Article
  • Mar 2023
This study aims to review the potential for microbial calcium carbonate precipitation (MCP) as an effective method for environmental remediation and its application in construction restoration. This review aims to provide in-depth knowledge of microbial calcium carbonate precipitation through the concrete denitrification process. One of the critical parameters reviewed in this study is the choice of denitrifying bacteria that can be used for inclusions in concrete. There are limited reports on denitrifying bacteria used in concrete for enhancing its mechanical and durability characteristics. Hence, this study reviews the different types of denitrifying bacteria that can be used in concrete. Diaphorobacter nitroreducens and Pseudomonas aeruginosa with cell concentration in the range of 105–109 CFU/ml along with calcium formate and calcium nitrate as nutrients are found to be effective. For these bacterial inclusions, the crack healing efficiency is found to range from 350 to 590 µm for 28 days depending on the protective carrier used. Another critical parameter reviewed in this study is the suitable technique for microbial inclusions into concrete. To determine the effectiveness of self-healing, the concentration of bacterial cells required and nutrients required are also reviewed. Additionally, the capacity of denitrifying bacteria as an instrument of self-healing against crack formation is evaluated. Finally, the broad applications of microbial calcium carbonate precipitation through denitrification are discussed in various fields, and the drawbacks of application in concrete are discussed. Overall, it is discovered that the denitrification pathway is more environmentally friendly while still being as successful as current techniques in enhancing the mechanical characteristics of concrete.
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... For example, low levels of phosphorus induce the PHA production (Orejuela-Escobar et al., 2021). Due to the assimilation of CO 2 as a carbon source, photosynthetic organisms, especially microalgae and cyanobacteria, can induce carbonate precipitation to produce bio-cement (Dessy et al., 2011). Compared to the conventional cement, the microalgae-based bio-cement process avoids high temperature (1500 • C) used in the production process and significantly reduces greenhouse gas emissions. ...
Recent advances in CO2 fixation by microalgae and its potential contribution to carbon neutrality
Article
  • Jan 2023
  • CHEMOSPHERE
Many countries and regions have set their schedules to achieve the carbon neutrality between 2030 and 2070. Microalgae are capable of efficiently fixing CO2 and simultaneously producing biomass for multiple applications, which is considered one of the most promising pathways for carbon capture and utilization. This work reviews the current research on microalgae CO2 fixation technologies and the challenges faced by the related industries and government agencies. The technoeconomic analysis indicates that cultivation is the major cost factor. Use of waste resources such as wastewater and flue gas can significantly reduce the costs and carbon footprints. The life cycle assessment has identified fossil-based electricity use as the major contributor to the global warming potential of microalgae-based CO2 fixation approach. Substantial efforts and investments are needed to identify and bridge the gaps among the microalgae strain development, cultivation conditions and systems, and use of renewable resources and energy.
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... Biocementation, known as microbially induced carbonate precipitation (MICP), involves the use of microorganisms to precipitate calcium carbonate (CaCO 3 ) as a cementing agent [134][135][136][137]. This binder is generally used to repair damaged concrete structures, stabilize soil, and replace conventional Portland cement [138,139]. ...
Prioritization of habitat construction materials on Mars based on multi-criteria decision-making
Article
  • May 2023
Mars is the most accessible planet in the solar system for habitation and could serve as a base for exploring more distant planets. Space agencies and scientists worldwide continue exploring Mars to gain more geologic and atmospheric information in preparation for constructing space habitats. The harsh planetary conditions of Mars require the development of new or modified methods for building infrastructure and formulating binders. Each type of concrete has advantages and disadvantages, and we need to find the best binder for use in construction on Mars. In this study, eight construction materials, including Ordinary Portland cement (OPC), sulfur concrete, geopolymer, sintered material, polymer-bound regolith, products of geo-thermite reactions, regolith-based magnesium oxychloride, and microbial-induced calcite precipitation, are reviewed according to 14 criteria. The criteria are availability, shipping, water requirement, technical working conditions, curing time, temperature, total required energy, strength, durability, cosmic radiation shield (density and hydrogen content), additives needed, sustainability, safety, and recyclability. We applied the Fuzzy Analytic Hierarchy Process (AHP) approach to assign a weighting to each criterion. Finally, we used three multi-criteria decision-making (MCDM) methods to determine the most suitable mortar for construction under the harsh conditions on Mars. The results show that if the general conditions of Mars are considered uniform such as different temperatures and geologies dependent on location, geopolymer concrete is the best material for construction based on Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and Weighted Aggregates Sum Product Assessment (WASPAS) methods, and sintered material concrete and sulfur concrete are equally ranked second. Correspondingly, five concretes of Portland cement, products of geo-thermite reactions, regolith-based magnesium oxychloride, polymer-bound regolith, and microbial-induced calcite precipitation are the most efficient construction materials, respectively. In addition, using the Fuzzy AHP method, the criteria of shipping and sustainability have the highest and lowest weighting, respectively, in the decision-making process. The use of MCDM methods and inductive analysis provides a scientific approach that enables the comparison of the potential of several space concrete materials for better decision making in future research and construction within the next 10–20 years.
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Analysis of the Current State of Research on Bio-Healing Concrete (Bioconcrete)
Article
Full-text available
  • Sep 2024
The relatively small tensile strength of concrete makes this material particularly vulnerable to cracking. However, the reality is that it is not always possible and practically useful to conduct studies on high-quality sealing cracks due to their inaccessibility or small opening width. Despite the fact that currently there are many technologies for creating self-healing cement composites, one of the most popular is the technology for creating a biologically active self-healing mechanism for concrete. It is based on the process of carbonate ion production by cellular respiration or urease enzymes by bacteria, which results in the precipitation of calcium carbonate in concrete. This technology is environmentally friendly and promising from a scientific and practical point of view. This research focuses on the technology of creating autonomous self-healing concrete using a biological crack-healing mechanism. The research methodology consisted of four main stages, including an analysis of the already conducted global studies, ecological and economic analysis, the prospects and advantages of further studies, as well as a discussion and the conclusions. A total of 257 works from about 10 global databases were analyzed. An overview of the physical, mechanical and operational properties of bioconcrete and their changes is presented, depending on the type of active bacteria and the method of their introduction into the concrete mixture. An analysis of the influence of the automatic addition of various types of bacteria on various properties of self-healing bioconcrete is carried out, and an assessment of the influence of the method of adding bacteria to concrete on the process of crack healing is also given. A comparative analysis of various techniques for creating self-healing bioconcrete was performed from the point of view of technical progress, scientific potential, the methods of application of this technology, and their resulting advantages, considered as the factor impacting on strength and life cycle. The main conditions for a quantitative assessment of the sustainability and the possibility of the industrial implementation of the technology of self-healing bioconcrete are identified and presented. Various techniques aimed at improving the recovery process of such materials are considered. An assessment of the influence of the strength of cement mortar after adding bacteria to it is also given. Images obtained using electron microscopy methods are analyzed in relation to the life cycle of bacteria in mineral deposits of microbiological origin. Current gaps and future research prospects are discussed.
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A mini review of enzyme-induced calcite precipitation (EICP) technique for eco-friendly bio-cement production
Article
Full-text available
  • Feb 2024
  • ENVIRON SCI POLLUT R
This paper has presented a mini review of previously published articles dealing with bio-cement production using enzyme-induced calcite precipitation (EICP) technique. EICP is a biological, sustainable, and natural way of producing calcite without the direct involvement of microorganisms from urea and calcium chloride using urease enzyme in water-based solution with minimum energy consumption and eco-friendly. Calcite is a renewable bio-material that acts as a binder to improve the mechanical properties of soils like strength, stiffness, and water permeability. EICP has many real applications such as fugitive duct control with low cost comparing with water application or pouring, self-healing cracked concretes, and upgrade or change the low-volume road surfaces that are difficult for road constructions. The crystal structure of finally produced calcium carbonate (CaCO 3), calcite is affected by the source of calcium ion; the calcite produced from calcium chloride has a rhombohedral crystal structure. The urease enzyme used for EICP applications could be produced in a laboratory-scale from different plant species, bacteria, some yeasts, fungi, tissues of humans, and invertebrates. Nevertheless, urease enzyme produced from jack beans has showed urease enzyme activity around 2700-3500U/g, and the tendency to replace the urease enzyme found in the global market. All urease enzymes have 12-nm size, and this smaller size makes EICP preferable for all types of soil or sands including fine and silt sands.
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Remediation of Concrete Using Microorganisms
Article
  • Jan 2001
  • ACI MATER J
This paper describes an innovative biotechnology utilizing microbiologically-induced mineral precipitation for concrete remediation. Calcite precipitation induced by Bacillus pasteurii was studied in two types of portland cement mortar specimens: one prepared from mixing with micro-organisms, and the other with simulated cracks filled with microbial mixtures. The study showed that there was a significant increase in compressive strength of the portland cement mortar cubes containing lower concentrations of live cells. Compressive strengths of the cubes containing live or dead cell mass, however, decreased as cell concentrations and curing time increased, suggesting the interference of mortar integrity by biomass. Cracks filled with bacteria and sand demonstrated a significant increase in compressive strength and stiffness values when compared with those without cells. Scanning electron micro-graphs identified that microbiological calcite precipitation occurred mainly close to the surface areas of the crack, where a dense growth of calcite crystals embedded with cells was observed.
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Community and environmental influences on reef coral calcification
Article
  • Nov 2000
Reef corals calcify faster in the presence of non-calcareous algae. Ratios of calcification to photosynthesis appear to be affected by the ratio of alkalinity to acidity, which controls how efficiently the protons from calcification convert bicarbonate to carbon dioxide. By forcing calcifiers to calcify faster, algal proliferation on nutrient-enriched reefs may adversely affect the reef-builders.
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The Role of Autotrophic Picocyanobacteria in Calcite Precipitation in an Oligotrophic Lake
Article
  • Aug 2010
A 1-year field study monitoring depth profiles of picoplankton and physicochemical data in the oligotrophic Lake Lucerne (Switzerland) showed that picocyanobacteria play an important role in the CaCO3 precipitation process. Laboratory experiments with Mychonastes and Chlorella, isolated from Lake Lucerne and Synechococcus using ion selective electrodes, scanning electron microscopy and X-ray powder diffraction clearly demonstrated the potential of picoplankton for fast and effective CaCO3 precipitation. The combination of a field study with laboratory experiments confirmed the previous reports of picocyanobacteria triggering the CaCO3 precipitation in hardwater oligotrophic lakes. Electron micrographs of particles from the water column often reveal the size and shape of picoplankton cells covered by calcite. In addition the results from the laboratory approach indicated that algae and bacteria induced different precipitation mechanisms. Experiments with Mychonastes and Chlorella produced crystalline calcite completely covering the cells. Experiments with the cyanobacteria Synechococcus, however, yielded amorphous, micritic CaCO3, indicating a different precipitation process.
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Urea-degrading enzymes in algae
Article
  • Jun 1977
Extracts prepared from 10 bacteria-free algal cultures and 4 naturally occurring seaweeds were examined for urease and ATP-urea amidolyase (UAL-ase) activities. UAL-ase activity is confined to members of the classes Volvocales, Chlorococcales and Chaetophorales in the Chlorophyceae. Members of the Ulotrichales may possess either urease or UAL-ase. Ulva contains urease. All other algae, so far examined, which can grow with urea as nitrogen source contain urease but not UAL-ase.
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Mineral Formation by Bacteria in Natural Microbial Communities
Article
  • Jun 1998
  • FEMS MICROBIOL ECOL
This review focuses on bacteria and their role in mineral formation. As a consequence of their small size and diverse metabolic capabilities bacteria, more than any other type of living organism, are able to interact intimately with metal ions present in their environment. Some metals are required for metabolism and are taken into the cell through various mechanisms, then incorporated into the necessary physiological pathways and biosynthetic structures. This physiological aspect of metal-bacterial interaction will not be discussed but, rather, the ability of bacteria to accumulate metal ions and incorporate them into mineral phases will be described. This activity has widespread importance for the shaping of our planet and the recycling of mineral elements. Since bacteria are most frequently found as part of microbial communities it is within this context that their mineral-forming ability will be discussed.
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Microorganisms versus stony materials: A love-hate relationship
Article
  • Nov 2010
Micro-organisms can have a devastating effect on building materials. They produce a range of organic and inorganic acids and enzymes, inducing solution and alteration of mineral phases. Biofilms alter the water exchange of the material and also mechanical effects add to the biodeterioration. One especially deleterious process in which bacteria are involved, is biogenic sulphuric acid corrosion in sewer systems. On the other hand, some types of bacteria can be used in engineering applications, for example for biological cleaning and bioconsolidation. Bacterially induced carbonate precipitation has been proposed as an environmentally friendly method to consolidate and protect decayed limestone or cementitious materials. The method relies on the bacterially induced formation of a compatible and highly coherent carbonate precipitate. Furthermore, the same principle can be applied for manual or autonomous remediation of cracks in concrete and the bacteria are in this case used as self healing agents. KeywordsBiodeterioration-Biodegradation-Bioconsolidation-Microorganisms-Concrete-Stone
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Microbial carbonate precipitation in construction materials: A review
Article
  • Mar 2013
  • ECOL ENG
Evidence of microbial involvement in carbonate precipitation has led to the exploration of this process in the field of construction materials. One of the first patented applications concerned the protection of ornamental stone by means of a microbially deposited carbonate layer, i.e. biodeposition. The promising results of this technique encouraged different research groups to evaluate alternative approaches, each group commenting on the original patent and promoting its bacterial strain or method as the best performing. The goal of this review is to provide an in-depth comparison of these different approaches. Special attention was paid to the research background that could account for the choice of the microorganism and the metabolic pathway proposed. In addition, evaluation of the various methodologies allowed for a clear interpretation of the differences observed in effectiveness. Furthermore, recommendations to improve the in situ feasibility of the biodeposition method are postulated. In the second part of this paper, the use of microbially induced carbonates as a binder material, i.e. biocementation, is discussed. Bacteria have been added to concrete for the improvement of compressive strength and the remediation of cracks. Current studies are evaluating the potential of bacteria as self-healing agents for the autonomous decrease of permeability of concrete upon crack formation.
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Ca-Carbonates Precipitation and Limestone Genesis – the Microbiogeologist Point of View
Article
  • Jul 1999
  • SEDIMENT GEOL
Experiments show that the production of carbonate particles by heterotrophic bacteria follows different ways. In heterotrophy, the passive carbonatogenesis is generated by modifications of the medium that lead to the accumulation of carbonate and bicarbonate ions and to the precipitation of solid particles. It is induced by several metabolic pathways of the nitrogen cycle (ammonification of amino-acids, degradation of urea and uric acid, dissimilatory reduction of nitrates) and of the sulphur cycle (dissimilatory reduction of sulphates). The active carbonatogenesis is independent of the mentioned metabolic pathways. The carbonate particles are produced by ionic exchanges through the cell membrane following still poorly known mechanisms. In autotrophy, non-methylotrophic methanogenesis and cyanobacterial photosynthesis also may contribute to the precipitation of carbonates (autotrophic carbonates). As carbonatogenesis is neither restricted to particular taxonomic groups of bacteria nor to specific environments, it has been an ubiquitous phenomenon since Precambrian times. Carbonatogenesis is the response of heterotrophic bacterial communities to an enrichment of the milieu in organic matter. After a phase of latency, there is an exponential increase of bacterial numbers together with the accumulation of metabolic end-products. These induce a pH increase and an accumulation of carbonate and hydrogenocarbonate ions in the medium. This phase ends into a steady state when most part of the initial enrichment is consumed and there is a balance between death and growth in bacterial populations. Particulate carbonatogenesis occurs during the exponential phase and ends more or less after the beginning of the steady state. The active carbonatogenesis seems to start first and to be followed by the passive one which induces the growth of initially produced particles. In eutrophic conditions, the first solid products are patches that appear on the surface of the bacterial bodies and coalesce until forming a rigid coating and/or particles excreted from the cell. All these tiny particles assemble into biomineral aggregates which often display `precrystalline' structures. These aggregates grow and form biocrystalline build-ups which progressively display more crystalline structures with growth. In oligotrophic conditions, the primary solid products are rapidly smoothed in the crystalline structure and leave no trace. In present aqueous environments, apart from deep ocean, the potential efficiency of heterotrophic bacterial carbonatogenesis in Ca-carbonate sedimentation is much higher than autotrophic or abiotic processes. It much more likely accounts for extensive apparently abiotic limestone formation than any of the latter. As far as biodetrital particles are concerned, it may be observed that the shells and tests of organisms are built from the activity of cellular organites which are nowadays considered by a number of biologists as endosymbiotic bacteria. Thus, apart from (probably mythical) purely evaporitic and autotrophic ones, most limestones must be considered as principally of heterotrophic bacterial origin. As the carbon of limestones is issued from organic matter, bacterial heterotrophic carbonatogenesis appears as a fundamental phenomenon in the relationships between atmosphere and lithosphere during the biogeological evolution of the Earth.
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Microbiological Precipitation of CaCO3
Article
  • Oct 1999
  • SOIL BIOL BIOCHEM
The process of microbial mineral plugging in porous media is common in nature. We examined physical and biochemical properties of CaCO3 precipitation induced by Bacillus pasteurii, an alkalophilic soil microorganism. X-ray diffraction analysis quantified the composition of the mineral deposited in sand and identified the CaCO3 crystal as calcite. Examination by scanning electron microscopy identified bacteria in the middle of calcite crystals, which acted as nucleation sites. The rate of microbiological CaCO3 precipitation correlated with cell growth and was significantly faster than that of chemical precipitation. Biochemical properties of urease (urea amidohydrolase, E.C. 3.5.1.5) from B. pasteurii that was indirectly involved in CaCO3 precipitation were examined to understand the kinetics of the microbiological process. Urease from B. pasteurii exhibited a relatively low affinity for urea at pH 7.0 with a Km of 41.6 mM and Vmax of 3.55 mM min−1 mg−1 protein and increased affinity at pH 7.7 with a Km of 26.2 mM and Vmax of 1.72 mM min−1 mg−1 protein. Results of kinetic studies indicate that urease activity and its affinity to urea are significantly high at the pH where calcite precipitation is favorable. Our findings further suggest a potential use of the microbial calcite precipitation process in remediation of the surface and subsurface of porous media.
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