Effect of Geobacillus toebii GT-02 addition on composition transformations and microbial community during thermophilic fermentation of bean dregs

Bean dregs can be prepared into organic fertilizer by microbial fermentation. Geobacillus toebii GT-02, which has promoting effect on bean dregs fermentation, was isolated from horse dung and it grows within a range of 40–75 °C and pH 6.50–9.50. The effectiveness of GT-02 addition on composition transformations and the microbial community in bean dregs thermophilic fermentation at 70 °C for 5 days was investigated (T1). Fermentation of bean dregs without GT-02 served as control (CK). The results showed that T1 (the germination index (GI) = 95.06%) and CK (GI = 86.42%) reached maturity (defined by GI ≥ 85%) on day 3 and day 5, respectively. In addition, the total nitrogen loss of T1 (18.46%) on day 3 was lower than that in CK (24.12%). After thermophilic fermentation, the total organic carbon and dry matter loss of T1 (53.51% and 54.16%) was higher than that in CK (41.72% and 42.82%). The mean microbial number in T1 was 4.94 × 10 7 CFUs/g dry matter, which was 5.37 times higher than that in CK. 16S rDNA sequencing identified Bacillus , Geobacillus and Thermobacillus as dominant in CK, while Bacillus , Ammoniibacillus and Geobacillus were dominant in T1. A canonical correspondence analysis showed that Geobacillus and Ammoniibacillus were positively correlated with the GI. Thus, thermophilic fermentation with GT-02 can promote the maturity of bean dregs, which indicated the potential application value of GT-02 in thermophilic fermentation.