Optimization of sporulation and germination of self-healing bacterium Bacillus sp. for concrete crack

Abstract

The single factor experimental results of spore production of a self-healing bacterial strain, Bacillus sp.B8, show that the optimal inoculation volume is 1×107 mL-1. The suitable carbon and nitrogen source are starch and yeast extract and the corresponding optimal concentrations being 0.5 g/L and 2 g/L, respectively. The presence of Mg2+ (0.24 g/L) and Mn2+ (4.8 mg/L) is beneficial for spore formation. Furthermore, based on the above results, orthogonal experiment is carried out to optimize the influential factors. The result shows that the inoculation volume and yeast extract concentration are the significant factors affecting spore yield. Under the optimized condition in which the concentrations of inoculation cells, starch, yeast extract, Mg2+ and Mn2+ are 1×107 mL-1, 5, 5, 0.48 and 4.8×10-3 g/L, respectively, the final spore concentration reaches up to 1.54×109 mL-1, showing more than 150 times enhancement. On the other hand, the results of spore germination indicate that spores need about 4 h to complete germination process. The most suitable germinant is inosine, and the optimal concentration is 2 g/L. The suitable pH is 10. Na+ could promote the germination of spores, whereas Ca2+ shows a severe inhibition on the germination of spores. However, we find, for the first time, that the presence of Na+ at a certain concentration (the optimal concentration is 24 g/L) can alleviate the inhibition of Ca2+ on spore germination to a large extent.