Microbially induced calcium carbonate precipitation through CO2 sequestration via an engineered Bacillus subtilis.

BACKGROUND: Microbially induced calcium carbonate precipitation has been extensively researched for geoengineering applications as well as diverse uses within the built environment. Bacteria play a crucial role in producing calcium carbonate minerals, via enzymes including carbonic anhydrase-an enzyme with the capability to hydrolyse CO2, commonly employed in carbon capture systems. This study describes previously uncharacterised carbonic anhydrase enzyme sequences capable of sequestering CO2 and subsequentially generating CaCO3 biominerals and suggests a route to produce carbon negative cementitious materials for the construction industry. RESULTS: Here, Bacillus subtilis was engineered to recombinantly express previously uncharacterised carbonic anhydrase enzymes from Bacillus megaterium and used as a whole cell catalyst allowing this novel bacterium to sequester CO2 and convert it to calcium carbonate. A significant decrease in CO2 was observed from 3800 PPM to 820 PPM upon induction of carbonic anhydrase and minerals recovered from these experiments were identified as calcite and vaterite using X-ray diffraction. Further experiments mixed the use of this enzyme (as a cell free extract) with Sporosarcina pasteurii to increase mineral production whilst maintaining a comparable level of CO2 sequestration. CONCLUSION: Recombinantly produced carbonic anhydrase successfully sequestered CO2 and converted it into calcium carbonate minerals using an engineered microbial system. Through this approach, a process to manufacture cementitious materials with carbon sequestration ability could be developed.

Effect of (in)organic additives on microbially induced calcium carbonate precipitation.

AIM: This study aimed to understand the morphological effects of (in)organic additives on microbially induced calcium carbonate precipitation (MICP). METHODS AND RESULTS: MICP was monitored in real time in the presence of (in)organic additives: bovine serum albumin (BSA), biofilm surface layer protein A (BslA), magnesium chloride (MgCl2), and poly-l-lysine. This monitoring was carried out using confocal microscopy to observe the formation of CaCO3 from the point of nucleation, in comparison to conditions without additives. Complementary methodologies, namely scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction, were employed to assess the visual morphology, elemental composition, and crystalline structures of CaCO3, respectively, following the crystals' formation. The results demonstrated that in the presence of additives, more CaCO3 crystals were produced at 100 min compared to the reaction without additives. The inclusion of BslA resulted in larger crystals than reactions containing other additives, including MgCl2. BSA induced a significant number of crystals from the early stages of the reaction (20 min) but did not have a substantial impact on crystal size compared to conditions without additives. All additives led to a higher content of calcite compared to vaterite after a 24-h reaction, with the exception of MgCl2, which produced a substantial quantity of magnesium calcite. CONCLUSIONS: The work demonstrates the effect of several (in)organic additives on MICP and sets the stage for further research to understand additive effects on MICP to achieve controlled CaCO3 precipitation.