Assessment of enduracidin production from sweet sorghum juice by Streptomyces fungicidicus M30
Graphical abstract
Introduction
As a novel cyclic peptide antibiotic, the demand for enduracidin, including enduracidin A and enduracidin B, has been increasing due to its promising applications, especially as an animal growth-promoting additive (Chan et al., 2015; Hu et al., 2012; Yin and Zabriskie, 2006; Zhong et al., 2018). For commercial enduracidin production, Streptomyces fungicidicus is regarded as the most efficient enduracidin producer and the production of enduracidin mainly depends on expensive carbohydrate sources, such as glucose (Chan et al., 2015; Liu et al., 2014). Currently, the breeding of high-yielding strains, process optimization, and pH shift feeding strategies are the main approaches to improve enduracidin production and reduce production costs (Chan et al., 2015; Liu et al., 2019; Zhang et al., 2015; Zhong et al., 2018). In general, the cost of raw materials accounts for the majority of the total cost in the commercial production of biochemicals via microbial conversion (Dai et al., 2017; Zhang et al., 2018b). Therefore, the development of a cheaper fermentation process for enduracidin production from low-cost carbohydrate sources has received much attention.
Besides sweet potato (Dioscorea esculenta) and cassava (Manihot esculenta), sweet sorghum (Sorghum bicolor) is another low-cost non-food energy crop in China (Fu et al., 2019) that can be cultivated in marginal soil. As large areas of such marginal lands are available in China (Eggleston et al., 2015; Fu et al., 2019; Vasilakoglou et al., 2011; Zhuang et al., 2011), their efficient utilization for the cultivation of sweet sorghum is encouraged by the Chinese government (Zhang et al., 2018a), and the production of chemicals from sweet sorghum has attracted much interest. The fermentable carbohydrates in sweet sorghum stalk mainly comprise glucose, fructose, and sucrose (Billa et al., 1997; Gao et al., 2010), making sweet sorghum an ideal substrate for producing value-added biochemicals through microbial bioconversion. Moreover, when compared with other low-cost materials (such as lignocellulosic biomass), the production of biochemicals from sweet sorghum juice is a better choice due to its easier treatment and lower cost (Zhang et al., 2018a). Hence, the biosynthesis of biochemicals from sweet sorghum juice represents a promising approach.
As a high-biomass and sugar-enriched bioenergy crop, sweet sorghum has been utilized as a low-cost plant-derived feedstock for the production of fuels and chemicals (Cai et al., 2018; Cui and Liang, 2015; Gao et al., 2010; Liu and Shen, 2008; Rolz, 2016; Wang et al., 2017). However, the utilization of sweet sorghum juice for enduracidin production has not been reported. Therefore, in this study, the feasibility of using sweet sorghum juice as a feedstock to produce enduracidin through bioconversion by S. fungicidicus was explored. The objective of the study was to develop a cheaper fermentation process for enduracidin production from sweet sorghum juice. The biomass and enduracidin productivities, as well as reducing sugar utilization were evaluated.
Section snippets
Microorganisms, media, and culture conditions
The S. fungicidicus M30, used in this study was screened after heavy ion mutagenesis (Liu et al., 2019). The strain was cultivated on an agar slant at 28 °C for 7 d, as described in our previous report (Liu et al., 2019). The mature spores were washed off using sterile water and suspended at a concentration of 3 × 107 cells/mL. Then, 1 mL of the spore suspension was transferred into a 250-mL shake flask with 50 mL of seed medium, as indicated in our previous study (Liu et al., 2019). The flask
Growth of S. fungicidicus M30 on glucose and crude sweet sorghum juice
In our previous study, S. fungicidicus M30 derived from heavy ion mutagenesis exhibited high ability to producing enduracidin (Liu et al., 2019), and will be used to produce enduracidin using sweet sorghum juice as a feedstock as well as the optimized glucose concentration for enduracidin production by M30 was 40 g/L (Liu et al., 2019). Prior to the addition to the fermentation medium, sucrose in the crude sweet sorghum juice was first hydrolyzed to a reducing sugar via acid hydrolysis, and the
Conclusion
In the present study, the clarification treatment of sweet sorghum juice was demonstrated to enhance the enduracidin production efficiency of S. fungicidicus M30. Thus, low-cost sweet sorghum juice could be an ideal alternative to expensive glucose for enduracidin production. By combining the clarification treatment and fed-batch strategies, 1.01 ± 0.05 g/L enduracidin was generated by S. fungicidicus M30 in 250-mL flask with a productivity of 0.09 g/L/d.
Declarations of interest
The authors report no ‘conflict of interest’ in connection with this manuscript.
Acknowledgements
The study was supported financially by the National Natural Science Foundation of China (No.11605259), the western talents program of the Chinese Academy of Sciences (Y706030XB0). Partially supported by Open Funds of the Key Laboratory of Biopesticide and Chemical Biology, Ministry of Education, Fujian Agriculture and Forestry University (Keylab2018-02).
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