Understanding microbially induced calcite formation by Bacilli for application in bio-based, green construction materials

The construction industry, particularly the use of cement-based materials, has become a concern amid growing unrest over climate issues. Cement production and use accounts for 8% of global anthropogenic CO2 emissions. One exciting approach to reduce the use of cement is to take advantage of Microbially Induced Calcite Precipitation (MICP). This describes the ability of some bacteria to form calcium carbonate minerals, specifically calcite, the main component of limestone. Application of spore-forming MICP-bacteria into concrete, for example, can be used to develop self-healing technologies that autonomously heal microcracks in structures and thus prevent further deterioration and the need for repairs. Other uses include consolidation of soils, or, more recently, the development of engineered living materials, where bacterial activity replaces the use of cement entirely, e.g. for the production of bricks.

A major drawback of current technologies is the use of expensive complex nutrients, which leads to high costs of the biobased materials, reducing economic feasibility. Optimisation, however, is hampered by a limited understanding of the molecular and physiological mechanisms of MICP. Here, we report on detailed profiling of environmental Bacillus sp. and close relatives to identify optimally suited MICP-strains. Exploration of the relationship between MICP and the metabolism of organic acids showed that acetate metabolism is a key driver of precipitation in some species, leading to rapid and almost complete precipitation of soluble calcium nitrate to insoluble calcite. Our findings further indicate that calcium homeostasis in bacteria may play a role in MICP. Detailed insights into how bacteria contribute to or even control the formation of calcite minerals opens the way for targeted design of economically viable self-healing or de novo-built construction materials. Bio-based cement alternatives could thus pave the road towards a greener, more sustainable infrastructure of the future.