| Microbial ecological agents are effective alternatives to feed antibiotics.Spores with strong resistance to the extreme environment could be formed by Bacillus subtilis,which benefit its preparation and application.Improving the effective biomass of B.subtilis is the key to ensure the quality of B.subtilis microbial ecological agents.In this study,variations of physicochemical properties of solid medium,expression of spore formation regulatory genes,and microbial growth and sporulation during fermentation were systematically investigated.Effects of different pretreatments on effective biomass of B.subtilis and its mechanisms were revealed.The main results are shown as follows:（1）Steam explosion pretreatment improved B.subtilis solid-state fermentation performance.Glucose content reached 35.82 mg/g dry medium in the steam explosion pretreated medium（i.e.,172℃,2min-134℃,3 min）.After fermentation for 72 h,effective biomass reached 2.83×1010CFU/g dry medium,which was 25.78%higher than that with the pretreatment at 134℃for 3min without steam explosion.（2）High-temperature and short-term pretreatment is an effective strategy for promoting effective biomass of the microbial ecological agents.Glucose content reached 32.43 mg/g dry medium and specific surface area was 1.37 m2/g in the medium pretreated at 134℃for 2min.These medium properties provided sufficient nutrients and living space for microbial cells during the initial stage of fermentation.After fermentation for 72 h,effective biomass reached 2.92×1010CFU/g in the medium pretreated at 134℃for 2 min,which was 1.30-fold higher than that pretreated at 134℃for 3 min.（3）The principal component analysis（PCA）showed that glucose content was negatively correlated with the expression of the key genes（e.g.,spo0A,sig F,sig E）that regulate sporulation.With the consumption of nutrients,expressions of key genes facilitated spore formation,which increased effective biomass efficiently. |
