## 4 Discussion  
BOF produced by antagonistic microbes can effectively control soil-borne diseases of tobacco, cucumber, watermelon and other crops [14; 15; 16]. Agricultural straw, livestock manure and soybean meal are conventional raw materials for BOF production, while PAS is rarely used. The current study showed that using PAS as a substitute for soybean powder is feasible for _B. subtilis_ Tpb55 production. The final number of bacteria in PBB was more than 10\({}^{10}\) cfu/mL under the optimal PAS fermentation formula, which is equal to that produced by 100% of soybean powders. However, the growth of the Tpb55 strain was very low in PAS with no biochar addition, indicating that biochar has a great influence on the fermentation process. The promotion of biochar in microbial fermentation has been widely reported. The promotional effect can be associated with the pore structure and low density of biochar, which can increase the oxygen flux of the fermentation substrate [6; 17]. It is especially important for the fermentation of PAS, harboring high fat content and low air permeability. Alleviating the pH decline may be another important role of biochar in fermentation. Additionally, the biochar also significantly increased the final pH of PBB. To the best of our knowledge, this is the first report to produce BOF by PAS with biochar addition and _B. subtilis_ inoculation. BOF is considered to have advantages of both organic fertilizers and antagonistic microbes. Organic fertilizers can provide nutrients for antagonistic microbes and promote their colonization in soil [18; 19]. These nutrients are also beneficial for plant growth [20; 21]. [PERSON] et al. [22] found that BOF fortified with Bacillus licheniformis X-1 and Bacillus methylotrophicus Z-1 showed a significant preventive effect against strawberry Fusarium wilt disease. [PERSON] et al. [23] reported that a BOF produced from spent grain waste with _Azospirillium brasilense_ inoculation enhanced soil fertility and corn growth. Consistently, PBB showed inhibitory activity against _P. nicotianae_, reduced the survival of pathogens in soil and decreased the disease severity of tobacco black shank. The soil pH, OC, AN and AK were also increased with PBB application. These results indicated for alkaline  
Figure 3: Canonical correspondence analysis (CCA) diagram illustrating the relationship between fungal (**a**) and bacterial (**b**) composition at genus level from different samples and environmental variables. hydrolyzed N that pathogen inhibition and soil nutrient improvement were involved in the effects of PBB. Soil microbial community structure not only affects plant growth but also has a close relationship with plant diseases [24; 25]. The ability of BOF in the regulation of the soil microbial community has been widely reported, and they are considered an important disease prevention strategy [26; 27]. [PERSON] et al. [27] reported that BOF treatment shifted the soil microbial community and enhanced the populations of some beneficial microorganisms, such as _Gemmatimonas_ and _Sphingomonas_. [PERSON] et al. [16] found that the application of BOF enriched with _B. amyloliquefaciens_ increased the bacterial diversity but decreased the fungal diversity in soil, and populations of some potential beneficial taxa such as Firmicutes (_Bacillus_) and Basidiomycota were enhanced. In line with these results, PBB treatment reduced the richness and diversity of the fungal community but had no significant effect on that of bacteria. PBB application also altered the microbial structure in tobacco rhizosphere soil. As expected, the relative abundance of _Bacillus_ increased with PBB treatment. In addition, some potential beneficial genera were also enriched, including _Mucor_, _Rhizopus_, _Cunninghamella_, _Chitinophaga_ and _Phenylobacterium_[28; 29; 30; 31; 32]. Nine genera were significantly decreased, including _Fusarium_, which includes pathogens that can cause a variety of crop diseases [15; 16].