In-depth profiling of calcite precipitation by environmental bacteria reveals fundamental mechanistic differences with relevance to application

Abstract

Microbial-induced calcite precipitation (MICP) has not only helped to shape our planets 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 ureolytic ability, where urease-positive bacteria caused rapid, widespread increases in pH, while non-ureolytic strains produced such changes slowly and locally. These pH shifts correlated well with patterns of precipitation on solid media. 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 non-ureolytic strains were larger with a mixed organic/inorganic composition. When representative strains were tested in application for crack healing in cement mortars, non-ureolytic bacteria gave robust results, while ureolytic strains showed more variation. This may be explained by our observation that urease activity varied between growth conditions, or by the different nature and therefore material performance of the precipitate. Our results shed light on the breadth of biomineralization activity among environmental bacteria, an important step towards the rational design of bacteria-based engineering solutions.