Spent Mushroom Substrate (SMS) as a Potential Casing Material for Commercial Cultivation of Calocybe indica: Improved Mineral Profile and Microbial Advantages

Recent prolonged summer seasons have posed significant challenges for mushroom cultivation, underscoring the need for summer-adapted commercial varieties like C alocybe indica . Casing plays a crucial role in its cultivation, which traditionally uses loamy soil (LS). However, given the non-renewable nature of LS and the environmental concerns associated with spent mushroom substrate (SMS), our study explored SMS as a potential alternative. We examined the physio-chemical properties, and microbial flora especially bacterial composition using MALDI-TOF in both LS and SMS, along with the total yield, biological efficiency, mineral content, and total phenolic and flavonoid contents of mushrooms grown on these substrates. While most of the physio-chemical properties of SMS align with the ideal casing properties, it exhibits higher electrical conductivity (EC) and a greater C/N ratio. The dominating bacterial flora in SMS, including Bacillus, Priestia, and Lysinbacillus , contribute to the mushrooms’ temperature tolerance and facilitate nutrient uptake especially phosphorous (P). The yields and biological efficiency were significantly higher in LS, likely due to its superior mechanical support. Furthermore, the results found that element levels, especially copper (Cu), zinc (Zn), and phosphorous (P), were significantly higher in mushrooms grown on SMS except iron (Fe). Notably, phosphorus (P) levels were significantly elevated in mushrooms grown in SMS, highlighting the role of phosphorous-solubilizing bacteria in SMS. The PCA biplot results further supported these findings. Interestingly, Calocybe indica consistently exhibited higher iron (Fe) content than Pleurotus ostreatus, regardless of the casing material used. The metal bioaccumulation factors (BCF) reveal that Calocybe indica is a hyperaccumulator of potassium (K) but does not bioaccumulate manganese (Mn). It also showed a low calcium (Ca) and iron (Fe) accumulation level, suggesting a synergistic interaction between Ca and Fe. No significant difference in total phenolic and flavonoid content was observed between the LS and SMS. In conclusion, LS proved more effective in maximizing yield, while SMS emerged as a sustainable alternative with the enhanced nutritional quality of mushrooms, making it a viable option for environmentally conscious mushroom cultivation.