Evaluation of different strategies for efficient sporulation and germination of the MICP bacterium Lysinibacillus sphaericus strain MB284 (ATCC 13805)

Environmental harsh conditions are one of the main challenges to the survivability of bacteria during the microbially induced calcium carbonate precipitation (MICP) process. Due to the high resistivity of endospores against inhospitable conditions in comparison with vegetative cells, different sporulation methods were applied to Lysinibacillus sphaericus strain MB284 by changing the environmental conditions to investigate the growth of germinated cells. It was found that the sporulation yield was more when both carbon source starvation and the thermal shock process were applied to this bacterium. In addition, extending the sporulation time of cells into the minimal medium at 2 °C for a couple of weeks had a great impact on improving the sporulation yield. Comparing the growth rate of germinated endospores in natural conditions (pH 7 and 25 °C) and harsh conditions (pH 12, temperature of -10 to 60 °C, salinity up to 100 g/l) showed that endospores generated by thermal shock are able to germinate in almost every inhospitable condition except at low pH (~3). Finally, exposing generated endospores before germination to harsh conditions (carbon source starving, high and low pH and temperature, and desiccation) for a nearly long period (to 100 days) showed that only low pH(~3) had a negative effect on the germination process and bacterial growth curve that indicated endospore of strain MB284 can be an appropriate solution for the problem of the survivability of bioagents in MICP. These results will provide helpful information about preparing and applying endospores of L. sphaericus for crack healing in concrete.