Metabolic insights into microbially induced calcite formation by Bacillaceae for application in bio-based construction materials

Microbially induced calcite precipitation (MICP) offers promising solutions for sustainable, low-cement infrastructure materials. While it is known how urea catabolism leads to biomineralisation, the non-ureolytic pathways of MICP are less clear. This limits the use of the latter in biotechnology, despite its clear benefit of avoiding toxic ammonia release. To address this knowledge gap, the present study explored the interdependence between carbon source utilisation and non-ureolytic MICP. We show that acetate can serve as the carbon source driving calcite formation in several environmental Bacillaceae isolates. This effect was particularly clear in a Solibacillus silvestris strain, which could precipitate almost all provided calcium when provided with a 2:1 acetate-to-calcium molar ratio, and we show that this process was independent of active cell growth. Genome sequencing and gene expression analyses revealed an apparent link between acetate catabolism and calcite precipitation in this species, suggesting MICP may be a calcium stress response. Development of a simple genetic system for S. silvestris led to the deletion of a proposed calcium binding protein, although this showed minimal effects on MICP. Taken together, this study provides insights into the physiological processes leading to non-ureolytic MICP, paving the way for targeted optimisation of biomineralisation for sustainable materials development.