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1. Mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation in the presence of seawater ions and varying soil materials

   https://doi.org/10.1038/s41598-022-21268-3  

   Burdalski, Robert J.; Ribeiro, Bruna G. O.; Gomez, Michael G.; Gorman-Lewis, Drew (October 2022, Scientific Reports)

   Abstract Microbially-induced calcium carbonate precipitation (MICP) is a bio-cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO₃) minerals on soil particle surfaces and contacts. The technology has advanced rapidly as an environmentally conscious soil improvement method, however, our understanding of the effect of changes in field-representative environmental conditions on the physical and chemical properties of resulting precipitates has remained limited. An improved understanding of the effect of subsurface geochemical and soil conditions on process reaction kinetics and the morphology and mineralogy of bio-cementation may be critical towards enabling successful field-scale deployment of the technology and improving our understanding of the long-term chemical permanence of bio-cemented soils in different environments. In this study, thirty-five batch experiments were performed to specifically investigate the influence of seawater ions and varying soil materials on the mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation. During experiments, differences in reaction kinetics were quantified to identify conditions inhibiting CaCO₃precipitation and ureolysis. Following experiments, scanning electron microscopy, x-ray diffraction, and chemical composition analyses were employed to quantify differences in mineralogical compositions and material morphology. Ions present in seawater and variations in soil materials were shown to significantly influence ureolytic activity and precipitate mineralogy and morphology, however, calcite remained the predominant CaCO₃polymorph in all experiments with relative percentages exceeding 80% by mass in all precipitates. 

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2. Subsurface hydrocarbon degradation strategies in low- and high-sulfate coal seam communities identified with activity-based metagenomics

   https://doi.org/10.1038/s41522-022-00267-2  

   Schweitzer, Hannah D.; Smith, Heidi J.; Barnhart, Elliott P.; McKay, Luke J.; Gerlach, Robin; Cunningham, Alfred B.; Malmstrom, Rex R.; Goudeau, Danielle; Fields, Matthew W. (February 2022, npj Biofilms and Microbiomes)

   Abstract Environmentally relevant metagenomes and BONCAT-FACS derived translationally active metagenomes from Powder River Basin coal seams were investigated to elucidate potential genes and functional groups involved in hydrocarbon degradation to methane in coal seams with high- and low-sulfate levels. An advanced subsurface environmental sampler allowed the establishment of coal-associated microbial communities under in situ conditions for metagenomic analyses from environmental and translationally active populations. Metagenomic sequencing demonstrated that biosurfactants, aerobic dioxygenases, and anaerobic phenol degradation pathways were present in active populations across the sampled coal seams. In particular, results suggested the importance of anaerobic degradation pathways under high-sulfate conditions with an emphasis on fumarate addition. Under low-sulfate conditions, a mixture of both aerobic and anaerobic pathways was observed but with a predominance of aerobic dioxygenases. The putative low-molecular-weight biosurfactant, lichysein, appeared to play a more important role compared to rhamnolipids. The methods used in this study—subsurface environmental samplers in combination with metagenomic sequencing of both total and translationally active metagenomes—offer a deeper and environmentally relevant perspective on community genetic potential from coal seams poised at different redox conditions broadening the understanding of degradation strategies for subsurface carbon. 

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3. Investigating the Effect of Microbial Activity and Chemical Concentrations on the Mineralogy and Morphology of Ureolytic Bio-Cementation

   https://doi.org/10.1061/9780784482834.010  

   Burdalski, Robert J.; Gomez, Michael G. (February 2020, GeoCongress 2020)

   Numerous laboratory studies in the past decade have demonstrated the ability of microbially induced calcite precipitation (MICP), a bio-mediated soil improvement method, to favorably transform a soil’s engineering properties including increased shear strength and stiffness with reductions in hydraulic conductivity and porosity. Despite significant advances in treatment application techniques and characterization of post-treatment engineering properties, relationships between biogeochemical conditions during precipitation and post-treatment material properties have remained poorly understood. Bacterial augmentation, stimulation, and cementation treatments can vary dramatically in their chemical constituents, concentrations, and ratios between researchers, with specific formulas oftentimes perpetuating despite limited understanding of their engineering implications. In this study, small-scale batch experiments were used to systematically investigate how biogeochemical conditions during precipitate synthesis may influence resulting bio-cementation and related material engineering behaviors. Aqueous solution chemistry was monitored in time to better understand the relationship between the kinetics of ureolysis and calcium carbonate precipitation, and resulting precipitates. Following all experiments, precipitates were evaluated using x-ray diffraction and scanning electron microscopy to characterize mineralogy and morphology. Results obtained from these investigations are expected to help identify the primary chemical and biological factors during synthesis that may control bio-cementation material properties and 

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4. Mineralogy of microbially induced calcium carbonate precipitates formed using single cell drop-based microfluidics

   https://doi.org/10.1038/s41598-020-73870-y  

   Zambare, Neerja M.; Naser, Nada Y.; Gerlach, Robin; Chang, Connie B. (December 2020, Scientific Reports)

   null (Ed.)

   Abstract Microbe-mineral interactions are ubiquitous and can facilitate major biogeochemical reactions that drive dynamic Earth processes such as rock formation. One example is microbially induced calcium carbonate precipitation (MICP) in which microbial activity leads to the formation of calcium carbonate precipitates. A majority of MICP studies have been conducted at the mesoscale but fundamental questions persist regarding the mechanisms of cell encapsulation and mineral polymorphism. Here, we are the first to investigate and characterize precipitates on the microscale formed by MICP starting from single ureolytic E. coli MJK2 cells in 25 µm diameter drops. Mineral precipitation was observed over time and cells surrounded by calcium carbonate precipitates were observed under hydrated conditions. Using Raman microspectroscopy, amorphous calcium carbonate (ACC) was observed first in the drops, followed by vaterite formation. ACC and vaterite remained stable for up to 4 days, possibly due to the presence of organics. The vaterite precipitates exhibited a dense interior structure with a grainy exterior when examined using electron microscopy. Autofluorescence of these precipitates was observed possibly indicating the development of a calcite phase. The developed approach provides an avenue for future investigations surrounding fundamental processes such as precipitate nucleation on bacteria, microbe-mineral interactions, and polymorph transitions. 

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5. Investigating the Dissolution Behavior of Calcium Carbonate Bio-Cemented Sands

   https://doi.org/10.1061/9780784484012.040  

   Ribeiro, Bruna G.; Gomez, Michael G. (March 2022, Geo-Congress 2022 GSP 331)

   Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that uses microbial enzymatic activity to catalyze the precipitation of CaCO3 minerals on soil particle surfaces and contacts. Extensive research has focused on understanding various aspects of MICP-treated soils including soil behavioral enhancements and process reaction chemistry, however, almost no research has explored the permanence of bio-cemented geomaterials. As the technology matures, an improved understanding of the longevity of bio-cementation improved soils will be critical towards identifying favorable field applications, quantifying environmental impacts, and understanding their long-term performance. In this study, a series of batch experiments were performed to investigate the dissolution kinetics of CaCO3-based bio- cemented sands with the specific aim of incorporating these behaviors into geochemical models. All batch experiments involved previously bio-cemented poorly graded sands that were exposed to different dissolution treatments intended to explore the magnitude and rate of CaCO3 dissolution as a function of acid type, concentration, initial pH, and other factors. During experiments, changes in solution pH and calcium concentrations indicative of CaCO3 dissolution were monitored. After experiments, aqueous measurements were compared to those simulated using two different dissolution kinetic frameworks. While not exhaustive, the results of these experiments suggest that the dissolution behavior of bio-cementation can be well-approximated using existing chemically controlled kinetic models, particularly when surrounding solutions are more strongly buffered. 

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