Factors affecting production of Scopulariopsis brevicaulis spores for use in self-healing concrete

Concrete durability is compromised by its susceptibility to cracking, necessitating innovative solutions like self-healing concrete (SHC). Scopulariopsis brevicaulis is capable of biomineralization and its spores were found to hold high potential for use in SHC. Realizing this potential requires clean and effective production of S. brevicaulis spores, which remains unexplored. Here the factors and processes conducive to high productivity of S. brevicaulis spores were investigated. Suitability of cheap, renewable soy-based substrates: soy molasses (SM), soy hull (SH), and soy flour (SF) were first evaluated, and SH was found suitable. The comparison of SH-based solid-state fermentation (SSF) with submerged fermentation (SmF) revealed SSF's superiority, producing spores earlier and with a more than 4.5-fold higher rate. Further study of SSF parameters, including initial spore inoculum, moisture, SH particle size, sugar supplementation, N-source supplementation, pH, salt addition, light (vs. dark) condition, and occasional mixing/shaking plus water addition, highlighted conditions that significantly boost spore production. Optimal moisture content (60-67%) and elevated medium pH (10-11) and salt addition (15 g/L NaCl) were key to enhancing yield, the latter likely induced stress-driven sporulation. Using larger SH particles (> 850 µm) also proved beneficial, improving oxygen transfer. Electron microscopy confirmed the effective attachment and penetration of spore chains into SH particles. This work significantly improved the technical and economic feasibility of producing S. brevicaulis spores for industrial SHC development.