Microbially Induced Carbonates Precipitation (MICP) is a promising technique for enhancing the self-healing properties of cementitious composites. Despite numerous studies on the subject, there is a limited focus on the comprehensive analysis of the various components in treatment solutions influencing precipitation in MICP. This study aimed to investigate Bacillus subtilis bacteria's ability to precipitate carbonates via ureolytic and heterotrophic pathways in controlled conditions and within the cement mortar environment using different combinations of calcium and magnesium compounds. The assessment included crack-sealing capability, determination of precipitate masses, and microstructure analysis (XRD, SEM, Raman spectroscopy). The results confirmed B. subtilis' effective precipitation of various crystalline forms of calcium carbonates and magnesium carbonates under controlled conditions. However, in the presence of the cement matrix, only solutions with magnesium compounds exhibited sediment precipitation in mortar cracks, indicating limited bacterial activity in the cement composite environment. Microstructural analyses characterized all precipitate forms, supporting the conclusions drawn.