In-Depth Profiling of Calcite Precipitation by Environmental Bacteria Reveals Fundamental Mechanistic Differences with Relevance to Application

Abstract

Microbially induced calcite precipitation (MICP) has not only helped to shape our planet’s geological features but is also a promising technology to address environmental concerns in civil engineering applications. However, limited understanding of the biomineralization capacity of environmental bacteria impedes application. We therefore surveyed the environment for different mechanisms of precipitation across bacteria. The most fundamental difference was in ureolytic ability, where urease-positive bacteria caused rapid, widespread increases in pH, whereas nonureolytic strains produced such changes slowly and locally. These pH shifts correlated well with patterns of precipitation on solid medium. Strikingly, while both mechanisms led to high levels of precipitation, we observed clear differences in the precipitate. Ureolytic bacteria produced homogenous, inorganic fine crystals, whereas the crystals of nonureolytic strains were larger and had a mixed organic/inorganic composition. When representative strains were tested in application for crack healing in cement mortars, nonureolytic bacteria gave robust results, while ureolytic strains showed more variation. This may be explained by our observation that urease activity differed between growth conditions or by the different natures and therefore different material performances of the precipitates. Our results shed light on the breadth of biomineralization activity among environmental bacteria, an important step toward the rational design of bacterially based engineering solutions. IMPORTANCE Biomineralization triggered by bacteria is important in the natural environment and has many applications in industry and in civil and geotechnical engineering. The diversity in biomineralization capabilities of environmental bacteria is, however, not well understood. This study surveyed environmental bacteria for their ability to precipitate calcium carbonate minerals and investigated both the mechanisms and the resulting crystals. We show that while urease activity leads to the fastest precipitation, it is by no means essential. Importantly, the same quantities of calcium carbonate are produced by nonureolytic bacteria, and the resulting crystals appear to have larger volumes and more organic components, which are likely beneficial in specific applications. Testing both precipitation mechanisms in a self-healing concrete application showed that nonureolytic bacteria delivered more robust results. Here, we performed a systematic study of the fundamental differences in biomineralization between environmental bacteria, and we provide important information for the design of bacterially based engineering solutions.

Self-Healing Concrete and Cementitious Materials

“…Common encapsulating shell materials are glass [23,24] and polymers [1,25,26]. Healing agents in autonomic self-healing are epoxy resins, cyanoacrylates (super glues), alkali-silica solutions [23,24,27,28], methyl methacrylate [24,28], expansive minerals [16,29], hydrogel [30] and bacteria-based microorganisms [31][32][33]. Self-healing performance in concrete is assessed using visual observation, mechanical strength recovery, permeability, durability improvement and microstructural evaluation (Figure 3).…”

“…Examples of these bacteria are B. cohnii, B. pseudofirmus and B. sphaericus. The process involved in calcite production is termed as microbiologically induced calcite precipitation (MICP) [32]. There are two conventional MICP processes: firstly, the urease system, which [64]).…”

Integrating Self-Sensing in Self-Healing Concrete: Towards a Biomimetic Approach to Repair

“…Research at Bath has performed a comparison between how ureolytic and non-ureolytic environmental bacteria precipitate calcium carbonate in order to understand how these mechanisms differ and how we can apply this knowledge to the improvement of self-healing concrete (Reeksting et al, 2020). In this study, environmental bacteria were surveyed for their ability to precipitate calcium carbonate and both the mechanism and resulting precipitates were examined.…”

Field detection of urease and carbonic anhydrase activity using rapid and economical tests to assess microbially induced carbonate precipitation

“…Microbially‐induced calcium carbonate precipitation (MICP) is a widespread environmental process that affects the carbon cycle and that has been explored as an alternative solution for several engineering and environmental challenges, such as restoration of concrete structures, soil consolidation, pollutant bioremediation and CO 2 sequestration (Sarayu et al ., 2014; Li et al ., 2015; Bose and Satyanarayana, 2017; Krajewska, 2018; Reeksting et al ., 2020). Despite its environmental relevance and multiple applications, MICP can be difficult to assess and identify in a given environment.…”