Abstract
Bacillus amyloliquefaciens-9 (GBacillus-9), which is isolated from the intestinal tract of the white-spotted bamboo shark (Chiloscyllium plagiosum), can secrete potential antibacterial materials, such as β-1,3-1,4-glucanase and some antimicrobial peptides. However, the low fermentation production has hindered the development of GBacillus-9 as biological additives. In this study, the Plackett–Burman design and response surface methodology were used to optimize the fermentation conditions in a shake flask to obtain a higher yield and antibacterial activity of GBacillus-9. On the basis of the data from medium screening, M9 medium was selected as the basic medium for fermentation. The data from the single-factor experiment showed that sucrose had the highest antibacterial activity among the 10 carbon sources. The Plackett–Burman design identified sucrose, NH4Cl, and MgSO4 as the major variables altering antibacterial activity. The optimal concentrations of these compounds to enhance antibacterial activity were assessed using the central composite design. Data showed that sucrose, NH4Cl, and MgSO4 had the highest antibacterial activities at concentrations of 64.8, 1.84, and 0.08 g L−1, respectively. The data also showed that the optimal fermentation conditions for the antibacterial material production of GBacillus-9 were as follows: Inoculum volume of 5%, initial pH of 7.0, temperature of 36 °C, rotating speed of 180 rpm, and fermentation time of 10 h. The optimal fermentation medium and conditions achieved to improve the yield of antibacterial materials for GBacillus-9 can enhance the process of developing biological additives derived from GBacillus-9.
Highlights
The wide usage of antibiotics in the world has rapidly increased the risk of antibiotic-resistant pathogens
The growth curve showed that a high GBacillus-9 density did not result in high antibacterial activity
The three-dimensional response surfaces and contour plots illustrated in Figure 4 depict the interactions of sucrose, NH4 Cl, and MgSO4 on antibacterial material yield by using TG1 and BS168 as substrates [23,24]
Summary
The wide usage of antibiotics in the world has rapidly increased the risk of antibiotic-resistant pathogens. The B. amyloliquefaciens BTSS-3 isolated from a deep-sea shark (Centroscyllium fabricii) has shown antimicrobial activity against pathogenic bacteria, including Salmonella typhimurium, Proteus vulgaris, Clostridium perfringens, and Staphylococcus aureus [9]. The bacteria in the shark, those in the digestive tract, produce inhibitory compounds responsible for controlling the colonization of potential pathogens in fish [10,11]. GFP-2), a strain of B. amyloliquefaciens, was isolated from the intestinal tract of the whitespotted bamboo shark (C. plagiosum) [12]. All these data suggest that the antibacterial material in GBacillus-9 can be used as a “drug” in the fish farm, which can help decrease the use of antibiotics in agriculture. The idea of developing a “drug” by using GBacillus-9 is hindered by its low antibacterial material production. Were used to optimize the fermentation conditions of GBacillus-9, achieve high antibacterial activity, and overcome the limited fermentation efficiency of GBacillus-9
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