Screening of Fungi for Potential Application of Self-Healing Concrete

Investigating the potential of delignified rice husk as a carbon-rich resource for extracting glucose and its utilization in biocement production through fungal isolates

Burning rice straw is now a significant issue faced by different regions in India, as its burning releases harmful gases, mainly carbon dioxide. Various techniques are now in trend to utilize the rice straw, e.g., producing compressed natural gas using rice straw, bioethanol, etc., as a substrate for various microorganisms. A high quantity of non-utilized rice husk generates more ideas for its proper utilization. The cellulose, hemicellulose, and lignin found in rice straws can be a fungi growth medium. In this research, the delignification of rice husk is done by acid (2% and 4% H2SO4) and alkali (2% and 4% NaOH) at 121 °C at 103 kPa for 1 h to obtain crude carbon source which is further utilized for biomineralization. The glucose is subjected to qualitative and quantitative analysis using Molisch's and Dinitro salicylic tests. The delignification process showed a positive outcome when 2% H2SO4 is utilized maximum yield of 5.9 ug/ml free sugar concentration. Representing the highest glucose yield compared to the experiment's other acid and base substances used. Various techniques such as field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier transformed infra-red (FTIR) spectroscopy are employed to examine surface and chemical alterations. The 2% H2SO4 pretreated rice husk is utilized for microbial-induced calcite precipitation using fungal isolates S1 (3), S1 (18), and S4 (1). The calcite and vaterite produced by biomineralization are confirmed using XRD for fungal isolates namely, S1 (3), S1 (18), and S4 (1) having percentage crystallinity of 59%, 46.428%, and 62.69% percentage crystallinity respectively.

Advances in microbial self-healing concrete: A critical review of mechanisms, developments, and future directions

The self-healing bioconcrete, or bioconcrete as concrete containing microorganisms with self-healing capacities, presents a transformative strategy to extend the service life of concrete structures. This technology harnesses the biological capabilities of specific microorganisms, such as bacteria and fungi, which are integral to the material's capacity to autonomously mend cracks, thereby maintaining structural integrity. This review highlights the complex biochemical pathways these organisms utilize to produce healing compounds like calcium carbonate, and how environmental parameters, such as pH, temperature, oxygen, and moisture critically affect the repair efficacy. A comprehensive analysis of recently published peer-reviewed literature, and contemporary experimental research forms the backbone of this review with a focus on microbiological aspects of the self-healing process. The review assesses the challenges facing self-healing bioconcrete, including the longevity of microbial spores and the cost implications for large-scale implementation. Further, attention is given to potential research directions, such as investigating alternative biological agents and optimizing the concrete environment to support microbial activity. The culmination of this investigation is a call to action for integrating self-healing bioconcrete in construction on a broader scale, thereby realizing its potential to fortify infrastructure resilience and sustainability.

Analysis of the Current State of Research on Bio-Healing Concrete (Bioconcrete)

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.

Fungal colonization and penetration of mortar as a suitable simulant for concrete: Implications for fungal biodeterioration in the built environment

A range of fungal species showed variable abilities to colonize and penetrate a mortar substrate. Calcium biomineralization was a common feature with calcium-containing crystals deposited in the microenvironment or encrusting hyphae, regardless of the specific mortar composition. Several species caused significant damage to the mortar surface, exhibiting burrowing and penetration, surface etching, and biomineralization. In some cases, extensive biomineralization of hyphae, probably by carbonatization, resulted in the formation of crystalline tubes after hyphal degradation on mortar blocks, including those amended with Co or Sr carbonate. Ca was the only metal detected in the biomineralized formations with Co or Sr undetectable. Aspergillus niger, Stemphylium sp. and Paecilomyces sp. could penetrate mortar with differential responses depending on the porosity. Fluorescent staining of thin sections recorded penetration depths of ∼530 um for A. niger and ∼620 um for Stemphylium sp. Penetration depth varied inversely with porosity and greater penetration depths were achieved in mortar with a lower porosity (lower water/cement ratio). These results have provided further understanding of biodeteriorative fungal interactions with cementitious substrates that can clearly affect structural integrity. The potential significance of fungal colonization and such biodeteriorative phenomena should not be overlooked in built environment contexts, including radionuclide storage and surface decontamination.

Harnessing Fungi Signaling in Living Composites

Signaling pathways in fungi offer a profound avenue for harnessing cellular communication and have garnered considerable interest in biomaterial engineering. Fungi respond to environmental stimuli through intricate signaling networks involving biochemical and electrical pathways, yet deciphering these mechanisms remains a challenge. In this review, an overview of fungal biology and their signaling pathways is provided, which can be activated in response to external stimuli and direct fungal growth and orientation. By examining the hyphal structure and the pathways involved in fungal signaling, the current state of recording fungal electrophysiological signals as well as the landscape of fungal biomaterials is explored. Innovative applications are highlighted, from sustainable materials to biomonitoring systems, and an outlook on the future of harnessing fungi signaling in living composites is provided.

Investigation of the interface of fungal mycelium composite building materials by means of low-vacuum scanning electron microscopy

Low-vacuum scanning electron microscopy (low-vacuum SEM) is widely used for different applications, such as the investigation of noncoated specimen or the observation of biological materials, which are not stable to high vacuum. In this study, the combination of mineral building materials (concrete or clay plaster) with a biological composite (fungal mycelium composite) by using low-vacuum SEM was investigated. Fungal biotechnology is increasingly gaining prominence in addressing the challenges of sustainability transformation. The construction industry is one of the biggest contributors to the climate crises and, therefore, can highly profit from applications based on regenerative fungal materials. In this work, a fungal mycelium composite is used as alternative to conventional insulating materials like Styrofoam. However, to adapt bio-based products to the construction industry, investigations, optimisations and adaptations to existing solutions are needed. This paper examines the compatibility between fungal mycelium materials with mineral-based materials to demonstrate basic feasibility. For this purpose, fresh and hardened concrete specimens as well as clay plaster samples are combined with growing mycelium from the tinder fungus Fomes fomentarius. The contact zone between the mycelium composite and the mineral building materials is examined by scanning electron microscopy (SEM). The combination of these materials proves to be feasible in general. The use of hardened concrete or clay with living mycelium composite appears to be the favoured variant, as the hyphae can grow into the surface of the building material and thus a layered structure with a stable connection is formed. In order to work with the combination of low-density organic materials and higher-density inorganic materials simultaneously, low-vacuum SEM offers a suitable method to deliver results with reduced effort in preparation while maintaining high capture and magnification quality. Not only are image recordings possible with SE and BSE, but EDX measurements can also be carried out quickly without the influence of a coating. Depending on the signal used, as well as the magnification, image-recording strategies must be adapted. Especially when using SE, an image-integration method was used to reduce the build-up of point charges from the electron beam, which damages the mycelial hyphae. Additionally using different signals during image capture is recommended to confirm acquired information, avoiding misinterpretations.

Fungal biodeterioration and preservation of cultural heritage, artwork, and historical artifacts: extremophily and adaptation

SUMMARYFungi are ubiquitous and important biosphere inhabitants, and their abilities to decompose, degrade, and otherwise transform a massive range of organic and inorganic substances, including plant organic matter, rocks, and minerals, underpin their major significance as biodeteriogens in the built environment and of cultural heritage. Fungi are often the most obvious agents of cultural heritage biodeterioration with effects ranging from discoloration, staining, and biofouling to destruction of building components, historical artifacts, and artwork. Sporulation, morphological adaptations, and the explorative penetrative lifestyle of filamentous fungi enable efficient dispersal and colonization of solid substrates, while many species are able to withstand environmental stress factors such as desiccation, ultra-violet radiation, salinity, and potentially toxic organic and inorganic substances. Many can grow under nutrient-limited conditions, and many produce resistant cell forms that can survive through long periods of adverse conditions. The fungal lifestyle and chemoorganotrophic metabolism therefore enable adaptation and success in the frequently encountered extremophilic conditions that are associated with indoor and outdoor cultural heritage. Apart from free-living fungi, lichens are a fungal growth form and ubiquitous pioneer colonizers and biodeteriogens of outdoor materials, especially stone- and mineral-based building components. This article surveys the roles and significance of fungi in the biodeterioration of cultural heritage, with reference to the mechanisms involved and in relation to the range of substances encountered, as well as the methods by which fungal biodeterioration can be assessed and combated, and how certain fungal processes may be utilized in bioprotection.

Composite biomediated engineering approaches for improving problematic soils: Potentials and opportunities

Several conventional chemical stabilizers are used for soil stabilization, among which cement is widely adopted. However, the high energy consumption and environmental challenges associated with these stabilizers have necessitated the transition toward the adoption/deployment of eco-friendly approaches for soil stabilization. Biomediated techniques are sustainable soil improvement methods adopting less toxic microorganisms, enzymes, or polymers for cementing soil. However, these processes also have several drawbacks, such as slow hardening, environmental impact, high cost, and lack of compatibility with different types of soils. It is hypothesized that these limitations may be overcome by exploring the prospects and opportunities offered by hybrid technological approaches involving the integration of nontraditional stabilizers and microbial-induced biomineralization processes for improving problematic soils. This paper discusses selected previous studies integrating different technologies and their benefits and challenges. The emerging fungi-based bio-mediation techniques and the possibility of forming sustainable fungal-based biocomposites to improve problematic soils are also highlighted.

Conditions for CaCO3 Biomineralization by Trichoderma Reesei with the Perspective of Developing Fungi-Mediated Self-Healing Concrete

Concrete, a widely used building material, often suffers from cracks that lead to corrosion and degradation. A promising solution to enhance its durability is the use of fungi as self-healing agents, specifically by harnessing their ability to promote calcium carbonate (CaCO3) precipitation on their cell walls. However, the ideal conditions for CaCO3 precipitation by the filamentous fungal species Trichoderma reesei are still unclear. In this study, the biomineralization properties of T. reesei in liquid media are investigated. Two different calcium sources, calcium chloride (CaCl2) and calcium lactate are tested, at varying concentrations and in the presence of different nutritional sources that support growth of T. reesei. This study also explores the effects on fungal growth upon adding cement to the medium. Calcium lactate promotes greater fungal biomass production, although less crystals are formed as compared to samples with CaCl2. An increasing calcium concentration positively influences fungal growth and precipitation, but this effect is hindered upon the addition of cement. The highest amounts of biomass and calcium carbonate precipitation are achieved with potato dextrose broth as a nutritional source. By identifying the optimal conditions for CaCO3 precipitation by T. reesei, this study highlights its potential as a self-healing agent in concrete.

The Evaluation of the Effectiveness of Biomineralization Technology in Improving the Strength of Damaged Fiber-Reinforced LWAC

Concrete cracks and local damage can affect the bond performance between concrete and steel bars, thereby reducing the durability of reinforced concrete structures. Compared with general concrete crack repair methods, biomineralization repair not only has effective bonding capabilities but is also particularly environmentally friendly. Therefore, this study aimed to apply biomineralization technology to repair damaged fiber-reinforced lightweight aggregate concrete (LWAC). Two groups of LWAC specimens were prepared. The experimental group used lightweight aggregates (LWAs) containing bacterial spores and nutrient sources, while the control group used LWAs without bacterial spores and nutrient sources. These specimens were first subjected to compression tests and pull-out tests, respectively, and thus were damaged. After the damaged specimen healed itself in different ways for 28 days, secondary compression and pull-out tests were conducted. The self-healing method of the control group involved placing the specimens in an incubator. The experimental group was divided into experimental group I and experimental group II according to the self-healing method. The self-healing method of experimental group I was the same as that of the control group. The self-healing method of experimental group II involved soaking the specimen in a mixed solution of urea and calcium acetate for two days, and then taking it out and placing it in an incubator for two days, with a cycle of four days. The test results show that in terms of the relative bond strength ratio, the experimental group II increased by 17.9% compared with the control group. Moreover, the precipitate formed at the cracks in the sample was confirmed to be calcium carbonate with the EDS and XRD analysis results, which improved the compressive strength and bond strength after self-healing. This indicates that the biomineralization self-healing method used in experimental group II is more effective.

Toward Self-Healing Concrete Infrastructure: Review of Experiments and Simulations across Scales

Cement and concrete are vital materials used to construct durable habitats and infrastructure that withstand natural and human-caused disasters. Still, concrete cracking imposes enormous repair costs on societies, and excessive cement consumption for repairs contributes to climate change. Therefore, the need for more durable cementitious materials, such as those with self-healing capabilities, has become more urgent. In this review, we present the functioning mechanisms of five different strategies for implementing self-healing capability into cement based materials: (1) autogenous self-healing from ordinary portland cement and supplementary cementitious materials and geopolymers in which defects and cracks are repaired through intrinsic carbonation and crystallization; (2) autonomous self-healing by (a) biomineralization wherein bacteria within the cement produce carbonates, silicates, or phosphates to heal damage, (b) polymer-cement composites in which autonomous self-healing occurs both within the polymer and at the polymer-cement interface, and (c) fibers that inhibit crack propagation, thus allowing autogenous healing mechanisms to be more effective. In all cases, we discuss the self-healing agent and synthesize the state of knowledge on the self-healing mechanism(s). In this review article, the state of computational modeling across nano- to macroscales developed based on experimental data is presented for each self-healing approach. We conclude the review by noting that, although autogenous reactions help repair small cracks, the most fruitful opportunities lay within design strategies for additional components that can migrate into cracks and initiate chemistries that retard crack propagation and generate repair of the cement matrix.

Screening fungal strains isolated from a limestone cave on their ability to grow and precipitate CaCO 3 in an environment relevant to concrete

Fungi-mediated self-healing concrete is a novel approach that promotes the precipitation of calcium carbonate (CaCO ₃ ) on fungal hyphae to heal the cracks in concrete. In this study, we set out to explore the potential of fungal species isolated from a limestone cave by investigating their ability to precipitate CaCO ₃ and to survive and grow in conditions relevant to concrete. Isolated strains belonging to the genera Botryotrichum sp. , Trichoderma sp. and Mortierella sp. proved to be promising candidates for fungi-mediated self-healing concrete attributed to their growth properties and CaCO ₃ precipitation capabilities in the presence of cement.

Unlocking the magic in mycelium: Using synthetic biology to optimize filamentous fungi for biomanufacturing and sustainability

Filamentous fungi drive carbon and nutrient cycling across our global ecosystems, through its interactions with growing and decaying flora and their constituent microbiomes. The remarkable metabolic diversity, secretion ability, and fiber-like mycelial structure that have evolved in filamentous fungi have been increasingly exploited in commercial operations. The industrial potential of mycelial fermentation ranges from the discovery and bioproduction of enzymes and bioactive compounds, the decarbonization of food and material production, to environmental remediation and enhanced agricultural production. Despite its fundamental impact in ecology and biotechnology, molds and mushrooms have not, to-date, significantly intersected with synthetic biology in ways comparable to other industrial cell factories (e.g. Escherichia coli,Saccharomyces cerevisiae, and Komagataella phaffii). In this review, we summarize a suite of synthetic biology and computational tools for the mining, engineering and optimization of filamentous fungi as a bioproduction chassis. A combination of methods across genetic engineering, mutagenesis, experimental evolution, and computational modeling can be used to address strain development bottlenecks in established and emerging industries. These include slow mycelium growth rate, low production yields, non-optimal growth in alternative feedstocks, and difficulties in downstream purification. In the scope of biomanufacturing, we then detail previous efforts in improving key bottlenecks by targeting protein processing and secretion pathways, hyphae morphogenesis, and transcriptional control. Bringing synthetic biology practices into the hidden world of molds and mushrooms will serve to expand the limited panel of host organisms that allow for commercially-feasible and environmentally-sustainable bioproduction of enzymes, chemicals, therapeutics, foods, and materials of the future.

Microbial-induced calcium carbonate precipitation: Influencing factors, nucleation pathways, and application in waste water remediation

Microbial-induced calcium carbonate precipitation (MICP) is a technique that uses the metabolic action of microorganisms to produce CO₃^2- which combines with free Ca²⁺ to form CaCO₃ precipitation. It has gained widespread attention in water treatment, aimed with the advantages of simultaneous removal of multiple pollutants, environmental protection, and ecological sustainability. This article reviewed the mechanism of MICP at both intra- and extra-cellular levels. It summarized the parameters affecting the MICP process in terms of bacterial concentration, ambient temperature, etc. The current status of MICP application in practical engineering is discussed. Based on this, the current technical difficulties faced in the use of MICP technology were outlined, and future research directions for MICP technology were highlighted. This review helps to improve the design of existing water treatment facilities for the simultaneous removal of multiple pollutants using the MICP and provides theoretical reference and innovative thinking for related research.

Application of Biomineralization Technology to Self-Healing of Fiber-Reinforced Lightweight Concrete after Exposure to High Temperatures

In the field of civil engineering, concrete self-healing technology plays an important role. Concrete self-healing should be able to effectively heal cracks, not only improving the internal structure, but also improving the mechanical properties and durability of the concrete structure. The biomineralization-repair method is characterized by its potential for long-lasting, rapid, and active crack repair potential. Biomineralization repair has an effective bond ability, is compatible with concrete components, and is also environmentally friendly. This study used biomineralization to explore the self-healing of fiber-reinforced lightweight concrete after its exposure to high temperatures. Concrete specimens of a control group (using lightweight aggregate without bacterial spores and a nutrient source) and an experimental group (using lightweight aggregate containing bacterial spores and a nutrient source) were prepared. The repair effect of the microbial self-healing concrete after the exposure to high temperature was observed by a crack-width gauge, field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). According to the EDS and XRD analyses, the precipitate formed at the crack was calcium carbonate. After 28 days of self-healing, the water absorption rate of the experimental group was lower than that of the control group. This is because the specimens of the penetration test were taken from the middle of the concrete cylinder after high temperature, and their bacterial survival rate was higher, which made the mineralization more significant. However, the mechanical test results of the control and experimental groups after the self-healing in the water were not substantially different, which indicated that the bacterial mineralization in the experimental group was slow in the absence of an adequate source of nutrients.

Effects of Capsule Type on the Characteristics of Cement Mortars Containing Powder Compacted Capsules

Several studies have been reported on self-healing concrete using bacteria, admixtures, and microcapsules. Among these self-healing techniques, encapsulating cement-based materials is advantageous in that large amounts of self-healing material can be contained in a capsule and released at the cracked site for a targeted reaction. This study produced a powder compacted capsule (PCC) using the droplet and blended manufacturing methods to encapsulate cementitious materials. This study refers to the PCCs as droplet-PCC (D-PCC) and blended-PCC (B-PCC) according to the manufacturing method used. The fluidity, compressive strength, carbonation, drying shrinkage, and water permeability of cement mortar with PCCs were evaluated. The test results show that the flow of the mortar sample using D-PCC was slightly higher than that of the mortar using B-PCC. The compressive strength of the mortar sample with B-PCC was generally higher than that of the mortar sample with D-PCC. The compressive strength of the B-PCC2 sample (with 0.2% of B-PCC) was the highest at all curing ages. This may be because the B-PCC fracture load was higher than that of the D-PCC. In addition, more hydrates were observed in the B-PCC sample than in the D-PCC sample. A crack healing effect was observed in the samples with PCC, regardless of the PCC type. The effect was the greatest in the B-PCC6 sample (with 0.6% of B-PCC). The results of this study provide a reference for the PCC type and mix ratio that would yield the best mechanical properties and crack healing effect.

Bacterial Carbonate Precipitation Using Active Metabolic Pathway to Repair Mortar Cracks

A study was conducted to check the efficacy of microbial pathways for calcite precipitation to heal pre-existing cracks in mortar. In this experiment, realistic cracks of varying widths were induced on a mortar sample. Different repair methods were applied to a total of 22 mortar samples. Twelve cracked mortar samples with average crack widths ranging from 0.29 to 1.08 mm were subjected to biodeposition treatment using calcium lactate as a food source. The remaining ten samples were split into two groups: five cracked mortar samples were exclusively exposed to the bacterial solution, while the remaining five samples were immersed in distilled water. Digital image processing was used to extract the crack characteristics before and after the repair application. During several repair cycles, image processing was used to track healing. Further, these repaired mortar samples underwent examination for water permeability, ultra-sonic examination, and examination for recovered compressive strength. A forensic examination of the healing product in terms of morphology and elemental composition was conducted using RAMAN, XRD, SEM-EDS, and TGA. The water permeability of the repaired mortar sample using biodeposition with Ca-lactate was dramatically reduced, but samples treated with bacterial solution and distilled water did not exhibit any significant reduction. Complete crack healing was observed when using Ca-lactate as a food source for microbial repair. The forensic analysis confirmed the presence of calcite in healing precipitates.

Bacterial Performance in Crack Healing and its Role in Creating Sustainable Construction

Building practices began with human civilization. Cement is the most commonly used building construction material throughout the world. These traditional building materials have their own environmental impact during production, transportation, and construction, but also have limitations on building quality and cost. Biological construction materials are currently emerging technology to combat emissions from the construction sector. Different civil and biotechnology researchers have turned to microorganisms for the production of bio construction materials that are environmentally friendly, socially acceptable, and economically feasible but can also produce high strength. Scanning electron microscope (SEM) and X-Ray diffraction (XRD) are the most characterization methods used to observe and ensure the production of calcite precipitate as bacterial concrete. As compared to conventional concrete, bacterial concrete was greater by 35.15% in compressive strength, 24.32% in average tensile strength, and 17.24% in average flexural strength, and it was 4 times lower in water absorption and 8 times lower in acid resistivity than conventional concrete. Genetic engineering has great potential to further enhance the mechanical strength of bacterial concrete for use in crack repairs in existing buildings.

A Experimental Study on Engineered Cementitious Composites (ECC) Incorporated with Sporosarcina pasteurii

Microbial-induced calcium carbonate precipitation (MICP) has been successfully applied to self-healing concrete with improved mechanical properties, while the performance of engineered cementitious composites (ECC) incorporated with bacteria is still lacking. In this study, Sporosarcina pasteurii, which has a strong ability to produce calcium carbonate, was introduced into engineered cementitious composites (ECC) with mechanical properties analyzed in detail. A multiscale study including compression, tension and fiber pullout tests was carried out to explore the Sporosarcina pasteurii incorporation effect on ECC mechanical properties. Compared with the control group, the compressive strength of S.p.-ECC specimens cured for 7 days was increased by almost 10% and the regained strength after self-healing was increased by 7.31%. Meanwhile, the initial crack strength and tensile strength of S.p.-ECC increased by 10.25% and 12.68%, respectively. Interestingly, the crack pattern of ECC was also improved to some extent, e.g., bacteria seemed to minimize crack width. The addition of bacteria failed to increase the ECC tensile strain, which remained at about 4%, in accordance with engineering practice. Finally, matrix/fiber interface properties were altered in S.p.-ECC with lower chemical bond and higher frictional bond strength. The results at the microscopic scale explain well the property improvements of ECC composites based on the fine-scale mechanical theory.

Effect of Immobilizing Bacillus megaterium on the Compressive Strength and Water Absorption of Mortar

The world’s growing population and industrialization have led to increased construction activities. This has increased the amount of waste aggregates which can be recycled in construction and cut the cost of infrastructure development. This study, therefore, reports the experimental findings for the effect of immobilizing Bacillus megaterium on the compressive strength and water absorption of laboratory prepared test mortar. Bacterial solution used in this work had a concentration of 1.0 × 107 cells/mL. The impact of recycled mortar impregnated with bacteria was studied after curing the specimens in water, saturated lime water, and 1.5% sulfuric acid. Compressive strength for test specimens cured in the three media was determined at the 2nd, 7th, 28th, and 56th day of curing. SEM analysis was done for mortars cured in acidic media and saturated lime water after curing for 28 days. The test results indicated that curing in water and saturated water improved the compressive strength, while the acidic medium lowered it. Recycled mortar is, therefore, an ideal material for immobilizing Bacillus megaterium before introduction into fresh concrete/mortar. The use of recycled mortar is a good strategy to reduce wastes from construction activities, save on the cost of construction materials, and enhance environmental conservation.

Fungal-induced CaCO3 and SrCO3 precipitation: a potential strategy for bioprotection of concrete

Biomineralization of CaCO₃ by microorganisms is a well-documented process considered applicable to concrete self-healing and metal bioremediation. Urea hydrolysis is the most widely explored and efficient pathway regarding concrete bioprotection. However, the potential of fungi has received relatively little attention compared to bacteria. In this work, we show that Fusarium cerealis, Phoma herbarum and Mucor hiemalis, isolated from concrete, could produce 828.6-941.3 mg L^-1 ammonium‑nitrogen in liquid media through urea hydrolysis indicating significant urease activity, and could grow in moderate (pH 8.3) or even extremely alkaline (pH 10.6) conditions. After culture in media containing 50 mM CaCl₂, at least 48.8% Ca²⁺ was removed from solution by the selected fungi as calcite. The accumulation of Ca by the biomass was around 83.64-114.21 mg g^-1. In addition, all fungi could mediate strontium carbonate formation with F. cerealis processing the highest ability for Sr removal, with ~61% added Sr being removed from solution. Scanning electron microscopy showed carbonate biominerals were encrusted on hyphae or aggregated in fungal pellets. When equivalent concentrations of Ca²⁺ and Sr²⁺ were supplemented to the media, CaCO₃ with incorporated Sr formed with F. cerealis and M. hiemalis, and Sr(Sr, Ca)(CO₃)₂ with P. herbarum. Our results demonstrate the potential of fungi in providing carbonate coatings for concrete surfaces and simultaneous immobilization of Sr. We anticipate our work will promote further practical field research on porous cementitious materials protection by fungi and immobilization of potentially toxic metals from metal-laden ingredients, such as fly ash and granulated ground blast furnace slag.

Mycelium-Based Composite: The Future Sustainable Biomaterial

Because of the alarming rate of human population growth, technological improvement should be needed to save the environment from pollution. The practice of business as usual on material production is not creating a circular economy. The circular economy refers to an economic model whose objective is to produce goods and services sustainably, by limiting the consumption and waste of resources (raw materials, water, and energy). Fungal-based composites are the recently implemented technology that fulfills the concept of the circular economy. It is made with the complex of fungi mycelium and organic substrates by using fungal mycelium as natural adhesive materials. The quality of the composite depends on both types of fungi and substrate. To ensure the physicochemical property of the fabricated composite, mycelium morphology, bimolecular content, density, compressive strength, thermal stability, and hydrophobicity were determined. This composite is proven to be used for different applications such as packaging, architectural designs, walls, and insulation. It also has unique features in terms of low cost, low emission, and recyclable.

Critical Analysis for Life Cycle Assessment of Bio-Cementitious Materials Production and Sustainable Solutions

The purpose of this study is to study the life cycle assessment of biocementitious materials production in comparison to traditional cement materials production. The environmental impact of production processes over the life cycle was evaluated on the basis of global warming and ozone depletion, human health, land, freshwater, marine ecotoxicity, and natural water system eutrophication. LCA uses endpoint methods (ECO indicators) and SimaPro 8 software to assess the health and environmental impact of raw materials used in the production process, including cement, Ca(NO3)2·4H2O, urea, molasses, and electricity. The results showed that cement materials made 82.88% of the world’s warming in all raw materials used in production processes, 87.24% of the world’s health, 89.54% of the deforestation of freshwater, and 30.48% to marine eutrophication. Ca(NO3)2·4H2O contributes by 58.88% to ozone depletion, 15.37 to human carcinogenic toxicity, 3.19% to freshwater eutrophication, and 11.76% to marine eutrophication. In contrast, urea contributes 38.15% to marine eutrophication and 5.25% to freshwater eutrophication. Molasses contribute by 13.77% to marine eutrophication. Cement contributes 74.27% to human health damage, 79.36% to ecosystem damage; Ca(NO3)2·4H2O contributes 13.54% to human health damage and 9.99% to ecosystem damage; while urea contributes 6.5% to human health damage and 5.91% to ecosystem damage. Bio-cementitious wastewater should undergo a treatment process to remove urea and molasses residues, as well as nitrates, before final disposal into the environment.

Controlling pore-scale processes to tame subsurface biomineralization

Microorganisms capable of biomineralization can catalyze mineral precipitation by modifying local physical and chemical conditions. In porous media, such as soil and rock, these microorganisms live and function in highly heterogeneous physical, chemical and ecological microenvironments, with strong local gradients created by both microbial activity and the pore-scale structure of the subsurface. Here, we focus on extracellular bacterial biomineralization, which is sensitive to external heterogeneity, and review the pore-scale processes controlling microbial biomineralization in natural and engineered porous media. We discuss how individual physical, chemical and ecological factors integrate to affect the spatial and temporal control of biomineralization, and how each of these factors contributes to a quantitative understanding of biomineralization in porous media. We find that an improved understanding of microbial behavior in heterogeneous microenvironments would promote understanding of natural systems and output in diverse technological applications, including improved representation and control of fluid mixing from pore to field scales. We suggest a range of directions by which future work can build from existing tools to advance each of these areas to improve understanding and predictability of biomineralization science and technology.

A Review on the Performance Evaluation of Autonomous Self-Healing Bacterial Concrete: Mechanisms, Strength, Durability, and Microstructural Properties

The development of cracks, owing to a relatively lower tensile strength of concrete, diverse loading, and environmental factors driving the deterioration of structures, is an inescapable key concern for engineers. Reparation and maintenance operations are thus extremely important to prevent cracks from spreading and mitigating the lifetime of structures. However, ease of access to the cracked zone may be challenging, and it also needs funds and manual power. Hence, autonomous sealing of cracks employing microorganisms into the concrete sans manual intervention is a promising solution to the dilemma of the sustainable improvement of concrete. ‘Ureolytic bacteria’, key organism species in rumen-producing ‘urease’ enzymes such as Bacillus pasteurii or subtilis—when induced—are capable of producing calcium carbonate precipitations into the concrete. As their cell wall is anionic, CaCO3 accumulation on their surface is extensive, and the whole cell, therefore, becomes crystalline and ultimately plugs pores and cracks. This natural induction technique is an environmentally friendly method that researchers are studying intensively. This manuscript reviews the application process of bacterial healing to manufacture autonomous self-healing bacterial concrete. Additionally, it provides a brief review of diverse attributes of this novel concrete which demonstrate the variations with the auto-addition of different bacteria, along with an evaluation of crack healing as a result of the addition of these bacteria directly into concrete or after encapsulation in a protective shell. Comparative assessment techniques for autonomous, bio-based self-healing are also discussed, accompanied by progress, potential, modes of application of this technique, and its resultant benefits in the context of strength and durability. Imperatives for quantitative sustainability assessment and industrial adoption are identified, along with the sealing of artificially cracked cement mortar with sand as a filling material in given spaces, as well as urea and CaCl2 medium treatment with Bacillus pasteurii and Sporosarcina bacteria. The assessment of the impact on the compressive strength and rigidity of cement mortar cubes after the addition of bacteria into the mix is also considered. Scanning electron microscope (SEM) images on the function of bacteria in mineral precipitation that is microbiologically induced are also reviewed. Lastly, future research scope and present gaps are recognised and discussed.

A review on the potential of filamentous fungi for microbial self-healing of concrete

Concrete is the most used construction material worldwide due to its abundant availability and inherent ease of manufacturing and application. However, the material bears several drawbacks such as the high susceptibility for crack formation, leading to reinforcement corrosion and structural degradation. Extensive research has therefore been performed on the use of microorganisms for biologically mediated self-healing of concrete by means of CaCO₃ precipitation. Recently, filamentous fungi have been recognized as high-potential microorganisms for this application as their hyphae grow in an interwoven three-dimensional network which serves as nucleation site for CaCO₃ precipitation to heal the crack. This potential is corroborated by the current state of the art on fungi-mediated self-healing concrete, which is not yet extensive but valuable to direct further research. In this review, we aim to broaden the perspectives on the use of fungi for concrete self-healing applications by first summarizing the major progress made in the field of microbial self-healing of concrete and then discussing pioneering work that has been done with fungi. Starting from insights and hypotheses on the types and principles of biomineralization that occur during microbial self-healing, novel potentially promising candidate species are proposed based on their abilities to promote CaCO₃ formation or to survive in extreme conditions that are relevant for concrete. Additionally, an overview will be provided on the challenges, knowledge gaps and future perspectives in the field of fungi-mediated self-healing concrete.

Fouling communities of microscopic fungi on various substrates of the Black Sea

Fungi are the most active biodeteriorators of natural and man-made materials. The article presents generalizations of the studies (2001–2019) of communities of microscopic fungi within biofilms on various substrates: shells of live Mytilus (Mytilus galloprovincialis, 670 specimens) and Ostreidae (Crassostrea gigas, 90 specimens), fragments of driftwood (over 7,000), stones (40), concrete of hydrotechnical constructions along the shoreline (80) and wood between concrete blocks in constructions on the shores (80). The studies were carried out in Odessa Oblast, the coastal zone of Sevastopol and open area of the Black Sea. There were identified 123 species of micromycetes, belonging to 65 genera, 33 families, 21 orders, 10 classes, 4 divisions, 2 kingdoms: Fungi and Chromista (fungi-like organisms). The Chromista kingdom was represented by 1 species – Ostracoblabe implexa, on shells of C. gigas. The number of species of micromycetes on various substrates varied 23 (wood between concrete blocks of hydrotechnical constructions) to 74 (shells of M. galloprovincialis at the depths of 3 and 6 m). On all the substrates, the following species were found; Alternaria alternata, Botryotrichum murorum. The communities were found to contain pathogenic fungi Aspergillus fumigatus (shells of mollusks, stones, concrete), A. terreus (concrete), Fusarium oxysporum, Pseudallescheria boydii (shells of mollusks). The best representation was seen for the Pleosporales order – from 12.9% (shells of M. galloprovincialis, 0.3 m depth) to 33.3% (shells of C. gigas) of the species composition. Toxin-producing species of Microascales in mycological communities accounted for 1.6% (driftwood) to 40.0% (concrete), and were also observed on shells of Bivalvia – 11.1–32.3%. Similarity of species composition of mycological communities according to Bray-Curtis coefficient varied 21.1% (driftwood and concrete, 10 shared species) to 72.7% (shells of M. galloprovincialis, the depths of 3 and 7 m and shells of C. gigas, 45 shared species). Using graphs of indices of mean taxonomic distinctness (AvTD, Δ+) and variation (Variation in Taxonomic Distinctness index, VarTD, Λ+), we determined deviations of taxonomic structure of the studied mycological communities from the level of mean expected values, calculated based on the list of species, taking into account their systematic positions. The lowest values of index Δ+ were determined for communities on shells of M. galloprovincialis, 0.3 m depth, driftwood, stones and concrete. These communities had uneven distribution of species according to higher taxonomic ranks and minimum number of the highest taxa: 4–6 classes, 1–2 divisions, Fungi kingdom. Disproportion in species composition with decrease in the number of the highest taxa occurred in extreme environmental conditions. Using index Λ+, we found that the most complex taxonomic structure of fungi communities has developed on concrete and shells of C. gigas. In mycological communities on those substrates, the number of species was low (25 and 46), but they belonged to 4–7 classes, 2–3 divisions, 1–2 kingdoms. To compare the structures of mycological communities that have developed in such substrates in biotopes sea, sea-land-air, land-air, we compiled a list of fungi based on the literature data, which, taking into account our data, comprised 445 species of 240 genera, 103 families, 51 orders, 15 classes, 5 divisions, 2 kingdoms. The analysis revealed that on substrates with similar chemical composition, in all the biotopes, the species of the same divisions dominated (genus and family may vary). Therefore, in the biotope land-air – Hypocreales, Pleosporales, Eurotiales (genera Acremonium, Fusarium, Alternaria, Aspergillus, Penicillium); sea – Pleosporales, Eurotiales, Microascales (Alternaria, Aspergillus, Penicillium, Corollospora); sea-land-air – Pleosporales, Microascales (Alternaria, Leptosphaeria, Aspergillus, Penicillium, Corollospora, Halosarpheia). Monitoring of species composition of myxomycetes is needed in farms that cultivate industrial objects, recreation sites, various buildings for prevention of mycotoxin intoxication and infestation by mycodermatoses and other diseases caused by opportunistic and pathogenic fungi.

Fouling communities of microscopic fungi on various substrates of the Black Sea

Fungi are the most active biodeteriorators of natural and man-made materials. The article presents generalizations of the studies (2001–2019) of communities of microscopic fungi within biofilms on various substrates: shells of live Mytilus (Mytilus galloprovincialis, 670 specimens) and Ostreidae (Crassostrea gigas, 90 specimens), fragments of driftwood (over 7,000), stones (40), concrete of hydrotechnical constructions along the shoreline (80) and wood between concrete blocks in constructions on the shores (80). The studies were carried out in Odessa Oblast, the coastal zone of Sevastopol and open area of the Black Sea. There were identified 123 species of micromycetes, belonging to 65 genera, 33 families, 21 orders, 10 classes, 4 divisions, 2 kingdoms: Fungi and Chromista (fungi-like organisms). The Chromista kingdom was represented by 1 species – Ostracoblabe implexa, on shells of C. gigas. The number of species of micromycetes on various substrates varied 23 (wood between concrete blocks of hydrotechnical constructions) to 74 (shells of M. galloprovincialis at the depths of 3 and 6 m). On all the substrates, the following species were found; Alternaria alternata, Botryotrichum murorum. The communities were found to contain pathogenic fungi Aspergillus fumigatus (shells of mollusks, stones, concrete), A. terreus (concrete), Fusarium oxysporum, Pseudallescheria boydii (shells of mollusks). The best representation was seen for the Pleosporales order – from 12.9% (shells of M. galloprovincialis, 0.3 m depth) to 33.3% (shells of C. gigas) of the species composition. Toxin-producing species of Microascales in mycological communities accounted for 1.6% (driftwood) to 40.0% (concrete), and were also observed on shells of Bivalvia – 11.1–32.3%. Similarity of species composition of mycological communities according to Bray-Curtis coefficient varied 21.1% (driftwood and concrete, 10 shared species) to 72.7% (shells of M. galloprovincialis, the depths of 3 and 7 m and shells of C. gigas, 45 shared species). Using graphs of indices of mean taxonomic distinctness (AvTD, Δ+) and variation (Variation in Taxonomic Distinctness index, VarTD, Λ+), we determined deviations of taxonomic structure of the studied mycological communities from the level of mean expected values, calculated based on the list of species, taking into account their systematic positions. The lowest values of index Δ+ were determined for communities on shells of M. galloprovincialis, 0.3 m depth, driftwood, stones and concrete. These communities had uneven distribution of species according to higher taxonomic ranks and minimum number of the highest taxa: 4–6 classes, 1–2 divisions, Fungi kingdom. Disproportion in species composition with decrease in the number of the highest taxa occurred in extreme environmental conditions. Using index Λ+, we found that the most complex taxonomic structure of fungi communities has developed on concrete and shells of C. gigas. In mycological communities on those substrates, the number of species was low (25 and 46), but they belonged to 4–7 classes, 2–3 divisions, 1–2 kingdoms. To compare the structures of mycological communities that have developed in such substrates in biotopes sea, sea-land-air, land-air, we compiled a list of fungi based on the literature data, which, taking into account our data, comprised 445 species of 240 genera, 103 families, 51 orders, 15 classes, 5 divisions, 2 kingdoms. The analysis revealed that on substrates with similar chemical composition, in all the biotopes, the species of the same divisions dominated (genus and family may vary). Therefore, in the biotope land-air – Hypocreales, Pleosporales, Eurotiales (genera Acremonium, Fusarium, Alternaria, Aspergillus, Penicillium); sea – Pleosporales, Eurotiales, Microascales (Alternaria, Aspergillus, Penicillium, Corollospora); sea-land-air – Pleosporales, Microascales (Alternaria, Leptosphaeria, Aspergillus, Penicillium, Corollospora, Halosarpheia). Monitoring of species composition of myxomycetes is needed in farms that cultivate industrial objects, recreation sites, various buildings for prevention of mycotoxin intoxication and infestation by mycodermatoses and other diseases caused by opportunistic and pathogenic fungi.

Isolation of alkaliphilic calcifying bacteria and their feasibility for enhanced CaCO3 precipitation in bio-based cementitious composites

Microbially induced calcite precipitation (MICP), secreted through biological metabolic activity, secured an imperative position in remedial measures within the construction industry subsequent to ecological, environmental and economical returns. However, this contemporary recurrent healing system is susceptible to microbial depletion in the highly alkaline cementitious environment. Therefore, researchers are probing for alkali resistant calcifying microbes. In the present study, alkaliphilic microbes were isolated from different soil sources and screened for probable CaCO3 precipitation. Non-ureolytic pathway (oxidation of organic carbon) was adopted for calcite precipitation to eliminate the production of toxic ammonia. For this purpose, calcium lactate Ca(C3 H5 O3 )2 and calcium acetate Ca(CH3 COO)2 were used as CaCO3 precipitation precursors. The quantification protocol for precipitated CaCO3 was established to select potent microbial species for implementation in the alkaline cementitious systems as more than 50% of isolates were able to precipitate CaCO3 . Results suggested 80% of potent calcifying strains isolated in this study, portrayed higher calcite precipitation at pH 10 when compared to pH 7. Ten superlative morphologically distinct isolates capable of CaCO3 production were identified by 16SrRNA sequencing. Sequenced microbes were identified as species of Bacillus, Arthrobacter, Planococcus, Chryseomicrobium and Corynebacterium. Further, microstructure of precipitated CaCO3 was inspected through scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal gravimetric (TG) analysis. Then, the selected microbes were investigated in the cementitious mortar to rule out any detrimental effects on mechanical properties. These strains showed maximum of 36% increase in compressive strength and 96% increase in flexural strength. Bacillus, Arthrobacter, Corynebacterium and Planococcus genera have been reported as CaCO3 producers but isolated strains have not yet been investigated in conjunction with cementitious mortar. Moreover, species of Chryseomicrobium and Glutamicibacter were reported first time as calcifying strains.

Ureolytic MICP-Based Self-Healing Mortar under Artificial Seawater Incubation

Ureolytic microbial-induced calcium carbonate precipitation (MICP) is a promising green technique for addressing sustainable building concerns by promoting self-healing mortar development. This paper deals with bacteria-based self-healing mortar under artificial seawater incubation for the sake of fast crack sealing with sufficient calcium resource supply. The ureolytic MICP mechanism was explored by morphology characterization and compositional analysis. With polyvinyl alcohol fiber reinforcement, self-healing mortar beams were produced and bent to generate 0.4 mm width cracks at the bottom. The crack-sealing capacity was evaluated at an age of 7 days, 14 days, and 28 days, suggesting a 1-week and 2-week healing time for 7-day- and 14-day-old samples. However, the 28-day-old ones failed to heal the cracks completely. The precipitation crystals filling the crack gap were identified as mainly vaterite with cell imprints. Moreover, fiber surface was found to be adhered by bacterial precipitates indicating fiber–matrix interfacial bond repair.

Bio-Cementation in Construction Materials: A Review

The rapid development of the construction sector has led to massive use of raw construction materials, which are at risk of exhaustion. The problem is aggravated by the high demand for cement as binding powder and the mass production of clay bricks for construction purposes. This scenario has led to high energy consumption and carbon emissions in their production. In this regard, bio-cementation is considered a green solution to building construction, because this technology is environmentally friendly and capable of reducing carbon emissions, thus slowing the global warming rate. Most of the previously published articles have focused on microbiologically induced calcium carbonate precipitation (MICP), with the mechanism of bio-cementation related to the occurrence of urea hydrolysis as a result of the urease enzymatic activity by the microbes that yielded ammonium and carbonate ions. These ions would then react with calcium ions under favorable conditions to precipitate calcium carbonate. MICP was investigated for crack repair and the surface treatment of various types of construction materials. Research on MICP for the production of binders in construction materials has become a recent trend in construction engineering. With the development of cutting edge MICP research, it is beneficial for this article to review the recent trend of MICP in construction engineering, so that a comprehensive understanding on microbial utilization for bio-cementation can be achieved.

Water-Transmitted Fungi are Involved in Degradation of Concrete Drinking Water Storage Tanks

Global warming, globalization, industrialization, and the rapidly growing population at present increasingly affect the production of safe drinking water. In combination with sustainable bio-based or recycled materials, used for water distribution systems, these factors promote emerging pathogens, including fungi. They can proliferate in oligotrophic water systems, affect the disinfection process, degrade building materials, and cause diseases in humans. In this study, we explored fungal-based degradation of modern concrete water storage tanks and the presence of fungi in chlorinated drinking water at the entrance and exit of the tanks. The degradation potential of isolated 52 fungal strains and their growth at different oligotrophic conditions was tested in vitro. Forty percent of strains grew at extremely oligotrophic conditions, and 50% classified as aerophilic. Two-thirds of tested strains produced acids, with Penicillium strains as the best producers. Only 29.7% of the strains were able to grow at 37 °C, and none of them was isolated from drinking water at consumers' taps. Although not yet part of the guidelines for building materials in contact with drinking water, fungi should be taken into consideration in case of visible degradation. Their number of consumers' endpoints should be checked to exclude possible health risks for consumers.

Calcifying Bacteria Flexibility in Induction of CaCO3 Mineralization

Microbially induced CaCO₃ precipitation (MICP) is considered as an alternative green technology for cement self-healing and a basis for the development of new biomaterials. However, some issues about the role of bacteria in the induction of biogenic CaCO₃ crystal nucleation, growth and aggregation are still debatable. Our aims were to screen for ureolytic calcifying microorganisms and analyze their MICP abilities during their growth in urea-supplemented and urea-deficient media. Nine candidates showed a high level of urease specific activity, and a sharp increase in the urea-containing medium pH resulted in efficient CaCO₃ biomineralization. In the urea-deficient medium, all ureolytic bacteria also induced CaCO₃ precipitation although at lower pH values. Five strains (B. licheniformis DSMZ 8782, B. cereus 4b, S. epidermidis 4a, M. luteus BS52, M. luteus 6) were found to completely repair micro-cracks in the cement samples. Detailed studies of the most promising strain B. licheniformis DSMZ 8782 revealed a slower rate of the polymorph transformation in the urea-deficient medium than in urea-containing one. We suppose that a ureolytic microorganism retains its ability to induce CaCO₃ biomineralization regardless the origin of carbonate ions in a cell environment by switching between mechanisms of urea-degradation and metabolism of calcium organic salts.

Study on Physical Properties of Mortar for Section Restoration Using Calcium Nitrite and CO2 Nano-Bubble Water

This study investigated the physical properties of section-restoration mortar with calcium nitrite (Ca(NO2)2) and carbon dioxide (CO2) nanobubble mixing water to develop materials and methods for the repair and reinforcement of cracks in reinforced concrete (RC) structures. As the calcium nitrite content increased, the generation rate and generated amount of nitrite-based hydration products also increased, owing to the rapid reaction between NO2- ions in calcium nitrite and C3A(Al2O3). Further, the reaction with C3S and C2S was accelerated, thereby increasing the generation rates of Ca(OH)2 and C-S-H. The large amount of Ca2+ ions in these hydration products reacted with CO32- ions in CO2 nanobubble water, thereby increasing the generation of calcite-based CaCO3 in the cement matrix. This appears to have affected strength development and durability improvement via the densification of the structure. These results suggest that the performance of polymer cement mortar for repairing concrete structures can be improved if calcium nitrite and CO2 nanobubble water are properly combined and applied.

Bioaugmentation of Vibrio alginolyticus in phytoremediation of aluminium-contaminated soil using Scirpus grossus and Thypa angustifolia

This research analyses the performance of bacteria-assisted phytoremediation of aluminium (Al)-contaminated soil using native Indonesian plants namely, Scirpus grossus and Thypa angustifolia. A range finding test (RFT) was carried out for 14 days to obtain the tolerable Al concentration for both plants. A total of 2% and 5% (v/v) of Vibrio alginolyticus were bioaugmented during the 28-day phytoremediation test to enhance the overall Al removal. Result of the RFT showed that both plants can tolerate up to 500 mg/kg Al concentration. The addition of V. alginolyticus to the reactors resulted in a significant increment of Al removal from the contaminated soil (p < 0.05). Such addition of V. alginolyticus increased the Al removal by up to 14.0% compared with that without-bacteria addition. The highest Al removal was obtained for S. grossus with 5% V. alginolyticus with an efficiency of 35.1% from 500 mg/kg initial concertation. T. angustifolia with 500 mg/kg initial concentration showed the highest removal of 26.2% by the addition of 5% V. alginolyticus. The increase of Al removal by the bioaugmentation of V. alginolyticus was due to the interaction in the plant's rhizosphere. Exudates of both plants provided a good environment for bacteria to live in the root area. Meanwhile, the bacteria increased the bioavailability of Al to be further extracted by plants. Certain mechanisms, such as rhizostabilisation, phytostimulation and phytoextraction, were considered to be the main processes that occurred during the treatment. S. grossus and T. angustifolia displayed promising ability to act as Al hyperaccumulators with bioaccumulation factor values up to 5.308 and 3.068, respectively. Development of the design of the ex-situ soil phytoremediation reactors is suggested as a future research direction because it can significantly enhance the current obtained finding.

First reported case of Gilbertella persicaria in human stool: outcome of a community study from Segamat, Johor, Malaysia

Species of fungi belonging to the order Mucorales can be found everywhere in the environment. Gilbertella persicaria, which belongs to this order, have often been isolated from fruits and in water systems. However, there has been no report of isolation of this fungus from human samples. During a gut mycobiome study, from the Segamat community, Gilbertella persicaria was isolated from a human fecal sample and was characterized through a series of morphological assessment, biochemical tests, and molecular techniques. The isolate produced a white velvety surface that turned grayish after 24 h. Although no biofilm production was observed, the results indicated that the isolate could form calcium oxalate crystals, produced urease, and was resistant to low pH. The isolate was sensitive to amphotericin but resistant to voriconazole and itraconazole. The features of this fungus that could help in its survival in the human gut are also discussed.

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

Research on Improving Concrete Durability by Biomineralization Technology

The interfacial transition zone (ITZ) around aggregates in concrete is a weak area with higher porosity than the matrix; it breaks easily under stress and is not conducive to the durability of concrete. However, the ITZ in concrete is full of calcium hydroxide crystals, which can provide the calcium source required for biomineralization. In view of this, this study aims to use the biological activity (i.e., biomineralization technology) existing in nature to enhance the ITZ in concrete and repair concrete cracks to improve the strength and durability of concrete. In this study, the bacterial strain Sporosarcina pasteurii, which is environmentally friendly, was selected. In addition, lightweight aggregate was used as a bacterial carrier. The bacteria were first sporulated. To protect the strains, the biological species were fixed in porous lightweight aggregates. These lightweight aggregates were then used as concrete aggregates. The planned tests included concrete engineering properties (i.e., compressive strength, chloride ion penetration, and water permeability tests) and residual strength after crack repair. The test results show that the use of lightweight aggregate as a carrier and the implantation of Sporosarcina pasteurii can induce biomineralization, strengthen the ITZ, and repair small internal cracks in concrete, thereby improving the strength and durability of the concrete.

Self-Healing Concrete by Biological Substrate

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.