THE MATRIX IS EVERYWHERE: CACO₃BIOMINERALIZATION BY THEBACILLUS LICHENIFORMISPLANKTONIC CELLS

Abstract

To date, the mechanisms of CaCO3 nucleus formation and crystal growth induced by bacterial cells still remain debatable. Here, an insight on the role of planktonic cells of Bacillus licheniformis DSMZ 8782 in the biomineralization is presented. We showed that during 14-days bacterial growth in a liquid urea/Ca2+-containing medium the transformation of CaCO3 polymorphs followed the classical pathway "ACC-vaterite-calcite/aragonite". By microscopic techniques, we detected the formation of extracellular matrix (ECM) around the cells at the stage of exponential growth and appearance of electron-dense inclusions at 24 h after the inoculation. The cells formed filaments and created a network, the nodes of which served as sites for further crystal growth. The ECM formation accompanied with the expression of proteins required for biofilm formation, the aldehyde/alcohol dehydrogenase, stress-associated Clp family proteins, and a porin family protein (ompA ortholog) associated with bacterial extracellular vesicles. We demonstrated that urea and CaCl2 acted as denaturing agents causing matrix formation in addition to their traditional role as a source of carbonate and Ca2+ ions. We showed that CaCO3 nucleation occured inside B. licheniformis cells and further crystal growth and polymorphic transformations took place in the extracellular matrix without attaching to the cell surface. The spatial arrangement of the cells was important for the active crystal growth and dependent on environmental factors. The extracellular matrix played a double role being formed as a stress response and providing a favorable microenvironment for biomineralization (a high concentration of ions necessary for CaCO3 crystal aggregation, fixation and stabilization).

Comprehensive Profiling of Microbiologically Induced CaCO3 Precipitation by Ureolytic Bacillus Isolates from Alkaline Soils

“…Wei et al [ 35 ] showed induction of calcite by B. lentus , while, different scientific groups reported that B. licheniformis can form only calcite pure precipitate [ 33 , 53 ]. In agreement with the obtained results also, a difference in XRD pattern during the incubation period of 14 days is observed by Ivanova et al [ 54 ], where sediment isolate B. licheniformis induced vaterite single-phase structure formation at the beginning of the MICP process, while at the end of the observed period predominant calcite phase was detected.…”

Modification of Surfaces with Vaterite CaCO3 Particles

“…The process of bacteria induced CaCO 3 precipitation has received a lot of consideration from researchers working in various disciplines. Consequently, one of the most studied subjects is the advancement in technologies the use microorganisms to induce the formation of CaCO 3 polymorphs to restore concrete structures [ 81 ]. Findings on the stability and formation of bacterially induced CaCO 3 has gained importance for the understanding of the mechanism of CaCO 3 mineralization.…”