Microbially induced calcium precipitation driven by denitrification: Performance, metabolites, and molecular mechanisms

Multiple effects of microbially induced calcium precipitation on bacteria under different molar volumes of organic pollutants

Microbially induced calcium precipitation (MICP) has been extensively discussed as a water treatment method. However, the impact of MICP on the selective adsorption of different organic contaminants in industrial wastewater and the metabolism and growth of bacteria has not been elucidated in detail. In this study, by comparing the differences in the metabolism and removal of bacteria by phenol, bisphenol A (BPA), and tetracycline (TC), it was found that bioprecipitates had significant differences in the adsorption capacity of organic pollutants with different molar volumes. Concurrently, bacteria produced more extracellular polymeric substances (EPS) under the influence of organic pollutants, and the self-protection mechanism of bacteria would reduce the amount of gaseous nitrogen. However, the points on the surface of EPS promoted the process of MICP, and MICP encapsulated bacteria to form precipitates to regulate bacteria in water and further improve the removal of carbon and nitrogen in water through biomineralization. This experiment provides new insights into the selective adsorption of bioprecipitates and its multiple effects on bacteria.

Genomic analysis and functional properties of Lactobacillus johnsonii GJ231 isolated from healthy beagles

Probiotics are one of the management tools to improve the host's healthy microbiota. The positive effects of probiotics on host health are species-specific, so probiotics isolated from host's own gut may be most beneficial. Many of the metabolites (e.g., short-chain fatty acids, bacteriocins, and hydrogen peroxide) produced by Lactobacillus johnsonii have specific inhibitory profiles against invading pathogens. In this study, we isolated L. johnsonii GJ231 from the intestinal tract of healthy female beagles. The genome size of 1.763 M encoded a total of 1,691 predicted genes. Many carbohydrate-active enzymes responsible for carbohydrate degradation and the production of short-chain fatty acids were also predicted. The metabolic profile of short-chain fatty acids in L. johnsonii GJ231 was determined using LC-MS/MS. The bacteriocin-producing gene bacteriocin (lactacin F) in L. johnsonii GJ231 was also predicted. In vitro, experiments demonstrated that GJ231 can thrive in weak acids, 0.3% bile salts, and artificial gastrointestinal fluid models. It was tolerant of to high temperatures up to 70°C, was non- hemolytic, inhibited pathogenic bacteria, and had a high antioxidant capacity. In vivo safety experiments conducted in mice revealed that oral administration of GJ231 not only had no toxic side effect but also increased their antioxidant capacity. In conclusion, combining the above test results, which collectively demonstrate that canine-derived L. johnsonii GJ231 was a non-pathogenic, acid-tolerant and bile-salt-tolerant probiotic strain that inhibits pathogenic bacteria and improves host antioxidant function. This may make it a promising candidate for the development of innovative functional foods for pets.

Understanding microbial biomineralization at the molecular level: recent advances

Microbial biomineralization is a phenomenon involving deposition of inorganic minerals inside or around microbial cells as a direct consequence of biogeochemical cycling. The microbial metabolic processes often create environmental conditions conducive for the precipitation of silicate, carbonate or phosphate, ferrate forms of ubiquitous inorganic ions. Till date the fundamental mechanisms underpinning two of the major types of microbial biomineralization such as, microbially controlled and microbially induced remains poorly understood. While microbially-controlled mineralization (MCM) depends entirely on the genetic makeup of the cell, microbially-induced mineralization (MIM) is dependent on factors such as cell morphology, cell surface structures and extracellular polymeric substances (EPS). In recent years, the organic template-mediated nucleation of inorganic minerals has been considered as an underlying mechanism based on the principles of solid-state bioinorganic chemistry. The present review thus attempts to provide a comprehensive and critical overview on the recent progress in holistic understanding of both MCM and MIM, which involves, organic-inorganic biomolecular interactions that lead to template formation, biomineral nucleation and crystallization. Also, the operation of specific metabolic pathways and molecular operons in directing microbial biomineralization have been discussed. Unravelling these molecular mechanisms of biomineralization can help in the biomimetic synthesis of minerals for potential therapeutic applications, and facilitating the engineering of microorganisms for commercial production of biominerals.

Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially -induced calcite precipitation (MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined Castellaniella denitrificans and Sporosarcina pasteurii to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results show that the dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional and interlocking forces, so that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength. At a water-solid ratio of 1 : 1.2 and a solid ratio of 15%, initial and final setting times were 67.2 and 96 h, respectively, which prolonged the initial setting time and final setting time by nearly 70% and 110% compared with that of the slurry without MICP treatment, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs.

Immobilization of Pb(II) by Bacillus megaterium-based microbial-induced phosphate precipitation (MIPP) considering bacterial phosphorolysis ability and Ca-mediated alleviation of lead toxicity

Inappropriate handling of lead (Pb)-containing wastewater that is produced as a result of smelting activities threatens the surrounding environment and human health. The microbial-induced phosphate precipitation (MIPP) technology was applied to immobilize Pb2+ in an aqueous solution considering bacterial phosphorolysis ability and Ca-mediated alleviation of lead toxicity. Pb immobilization was accompanied by sample characterization in order to explore the inherent mechanism that affected the immobilization efficiency. Results showed that Ca2+ use elevated the immobilization efficiency through the prevention of bacterial physisorption and chemisorption, an enhancement to the phosphatase activity and the degree of SGP hydrolysis, and the provision of nucleation sites for Pb2+ to attach. The formation of the Pb-GP complex helped the bacteria to maintain its activity at the commencement of catalyzing SGP hydrolysis. The nucleated minerals that were precipitated in a columnar shape through a directional stacking manner under MIPP featured higher chemical stability compared to non-nucleated minerals. As a result, there were three pathways, namely, bacterial physisorption, bacterial chemisorption, and substrate chelation, applied for Pb immobilization. The immobilization efficiency of 99.6% is achieved by precipitating bioprecipitates including Pb5(PO4)3Cl, Pb10(PO4)6Cl2, and Ca2Pb3(PO4)3Cl. The findings accentuate the potential of applying the MIPP technology to Pb-containing wastewater remediation.

Two decades of research trends in microbial-induced carbonate precipitation for heavy metal removal: a bibliometric review and literature review

Amidst the increasing significance of innovative solutions for bioremediation of heavy metal removal, this paper offers a thorough bibliometric analysis of microbial-induced carbonate precipitation (MICP) for heavy metal removal, as a promising technology to tackle this urgent environmental issue. This study focused on articles published from 1999 to 2022 in the Scopus database. It assesses trends, participation, and key players within the MICP for heavy metal sequestration. Among the 930 identified articles, 74 countries participated in the field, with China being the most productive. Varenyam Achal, the Chinese Academy of Sciences, and Chemosphere are leaders in the research landscape. Using VOSviewer and R-Studio, keyword hotspots like "MICP", "urease", and "heavy metals" underscore the interdisciplinary nature of MICP research and its focus on addressing a wide array of environmental and soil-related challenges. VOSviewer emphasises essential terms like "calcium carbonate crystal", while R-Studio highlights ongoing themes such as "soil" and "organic" aspects. These analyses further showcase the interdisciplinary nature of MICP research, addressing a wide range of environmental challenges and indicating evolving trends in the field. This review also discusses the literature concerning the potential of MICP to immobilise contaminants, the evolution of the research outcome in the last two decades, MICP treatment techniques for heavy metal removal, and critical challenges when scaling from laboratory to field. Readers will find this analysis beneficial in gaining valuable insights into the evolving field and providing a solid foundation for future research and practical implementation.

Microbial-induced calcium precipitation: Bibliometric analysis, reaction mechanisms, mineralization types, and perspectives

Microbial-induced calcium precipitation (MICP) refers to the formation of calcium precipitates induced by mineralization during microbial metabolism. MICP has been widely used as an ecologically sustainable method in environmental, geotechnical, and construction fields. This article reviews the removal mechanisms of MICP for different contaminants in the field of water treatment. The nucleation pathway is explained at both extracellular and intracellular levels, with a focus on evaluating the contribution of extracellular polymers to MICP. The types of mineralization and the regulatory role of enzyme genes in the MICP process are innovatively summarized. Based on this, the environmental significance of MICP is illustrated, and the application prospects of calcium precipitation products are discussed. The research hotspots and development trends of MICP are analyzed by bibliometric methods, and the challenges and future directions of MICP technology are identified. This review aims to provide a theoretical basis for further understanding of the MICP phenomenon in water treatment and the effective removal of multiple pollutants, which will help researchers to find the breakthroughs and innovations in the existing technologies, with a view to making significant progress in MICP technology.

Deciphering the potential role of quorum quenching in efficient aerobic denitrification driven by a synthetic microbial community

Low efficiency is one of the main challenges for the application of aerobic denitrification technology in wastewater treatment. To improve denitrification efficiency, a synthetic microbial community (SMC) composed of denitrifiers Acinetobacter baumannii N1 (AC), Pseudomonas aeruginosa N2 (PA) and Aeromonas hydrophila (AH) were constructed. The nitrate (NO3--N) reduction efficiency of the SMC reached 97 % with little nitrite (NO2--N) accumulation, compared to the single-culture systems and co-culture systems. In the SMC, AH proved to mainly contribute to NO3--N reduction with the assistance of AC, while PA exerted NO2--N reduction. AC and AH secreted N-hexanoyl-DL-homoserine lactone (C6-HSL) to promote the electron transfer from the quinone pool to nitrate reductase. The declined N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), resulting from quorum quenching (QQ) by AH, stimulated the excretion of pyocyanin, which could improve the electron transfer from complex III to downstream denitrifying enzymes for NO2--N reduction. In addition, C6-HSL mainly secreted by PA led to the up-regulation of TCA cycle-related genes and provided sufficient energy (such as NADH and ATP) for aerobic denitrification. In conclusion, members of the SMC achieved efficient denitrification through the interactions between QQ, electron transfer, and energy metabolism induced by N-acyl-homoserine lactones (AHLs). This study provided a theoretical basis for the engineering application of synthetic microbiome to remove nitrate wastewater.

Applying the first microcapsule-based self-healing microbial-induced calcium carbonate materials to prevent the migration of Pb ions

Lead (Pb) accumulation can lead to serious threats to surrounding environments and damage to the liver and kidneys. In the past few years, microbial-induced carbonate precipitation (MICP) technology has been widely applied to achieve Pb immobilization due to its environmentally friendly nature. However, harsh pH conditions can cause the instability of the carbonate precipitation to degrade or dissolve, increasing the potential of Pb2+ migration into nearby environments. In this study, microcapsule-based self-healing microbial-induced calcium carbonate (MICC) materials were applied to prevent Pb migration. The highest sporulation rate of 95.8% was attained at 7 g/L yeast extract, 10 g/L NH4Cl, and 3.6 g/L Mn2+. In the germination phase, the microcapsule not only prevented the bacterial spores from being threatened by the acid treatment but secured their growth and reproduction. Micro analysis also revealed that cerussite, calcite, and aragonite minerals were present, while extracellular polymeric substances (EPSs) were identified via Fourier transform infrared spectroscopy (FTIR). These results confirm their involvement in combining Pb2+ and Ca2+. The immobilization efficiency of above 90% applied to MICC materials was attained, while it of below 5% applied to no MICC use was attained. The findings explore the potential of applying microcapsule-based self-healing MICC materials to prevent Pb ion migration when the calcium carbonate degrades under harsh pH conditions.