Performance analyses of a pH-shift and DOT-shift integrated fed-batch fermentation process for the production of ganoderic acid and Ganoderma polysaccharides by medicinal mushroom Ganoderma lucidum Ya-Jie Tang a,b, * , Wei Zhang a , Jian-Jiang Zhong c a Hubei Provincial Key Laboratory of Industrial Microbiology, College of Bioengineering, Hubei University of Technology, Wuhan 430068, China b National Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, China c Key Laboratory of Microbial Metabolism (Ministry of Education), College of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China article info Article history: Received 21 July 2008 Received in revised form 1 October 2008 Accepted 3 October 2008 Available online 17 November 2008 Keywords: Ganoderma lucidum pH-shift culture DOT-shift culture Fed-batch culture Integrated strategy abstract Investigations on Ganoderma lucidum fermentation suggested that the responses of the cell growth and metabolites biosynthesis to pH and dissolved oxygen tension (DOT) were different. The ganoderic acid (GA) production of 321.6 mg/L was obtained in the pH-shift culture by combining a 4-day culture at pH 3.0 with the following 6-day culture at pH 4.5, which was higher by 45% and 300% compared with the culture at pH 3.0 and 4.5, respectively. The GA production of 487.1 mg/L was achieved in the DOT- shift culture by combining a 6-day culture at 25% of DOT with a following 6-day culture at 10% of DOT, which was higher by 43% and 230% compared with the culture at 25% and 10% of DOT, respectively. A fed-batch fermentation process by combining the above-mentioned pH-shift and DOT-shift strategies resulted in a significant synergistic enhancement of GA accumulation up to 754.6 mg/L, which is the highest reported in the submerged fermentation of G. lucidum in stirred-tank bioreactor. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Medicinal mushrooms are abundant sources of a wide range of useful native products and new compounds with interesting bio- logical activities ( Wasser, 2002; Lindequist et al., 2005). Ganoderma lucidum (Fr.) Krast (Polyporaceae) is a famous traditional Chinese medicinal mushroom. Ganoderic acid (GA) and Ganoderma polysac- charides are two of its major bioactive components (Paterson, 2006). Interestingly, recent studies show that GA has new biological activities including suppressing the growth of human solid tumor and the proliferation of a highly metastatic lung cancer cell line (95-D) (Tang et al., 2006), and anti-HIV-1 (El-Mekkawy et al., 1998). Currently, commercial products from medicinal mushrooms are mostly obtained through the field-cultivation of the fruiting body. However, in this case it is difficult to control the quality of the final product. So, mushroom submerged fermentation is viewed as a promising alternative for the efficient production of their valu- able products (Zhong and Tang, 2004; Tang et al., 2007). In G. lucidum fermentation, Zhong together with his colleagues demonstrated the response of the cell growth and metabolites bio- synthesis to process parameters (i.e., pH, dissolved oxygen tension, substrate feeding) was different. In the shake flask fermentation of G. lucidum, Fang and Zhong (2002a) found an initial pH of 6.5 was the best for mycelial growth and GA biosynthesis, while an initial pH of 3.5 was beneficial for the accumulation of Ganoderma poly- saccharides. In the stirred-tank bioreactor cultivation of G. lucidum, Tang and Zhong (2003a) observed that 25% of dissolved oxygen tension (DOT) was beneficial for G. lucidum growth, while 10% of DOT was favorable for the specific GA biosynthesis (i.e., GA content). Based on the favorable effect of oxygen limitation on the specific GA biosynthesis, Fang and Zhong (2002b) developed a two-stage fermentation process by combining conventional shake flask fermentation (i.e., the first-stage culture) with static culture (i.e., the second-stage culture), and GA production was greatly enhanced in the two-stage culture process. Then, the first-stage culture was scaled-up in the conventional stirred-tank bioreactor (Tang and Zhong, 2003a), and the second-stage culture was successfully scaled-up in the novel multi-layer static bioreac- tor (Tang and Zhong, 2003b). Tang and Zhong (2002) demonstrated the inhibition of GA biosynthesis by a relatively higher initial lac- tose concentration (i.e., >35 g/L) was avoided and GA production markedly improved by lactose supplementation when its residual level was around 10–5 g/L. Medicinal mushroom cells have the ability to respond to envi- ronment alterations. Provided that these alterations proceed with 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.10.005 * Corresponding author. Address: Hubei Provincial Key Laboratory of Industrial Microbiology, College of Bioengineering, Hubei University of Technology, Wuhan 430068, China. Tel./fax: +86 27 88015108. E-mail address: yajietang@hotmail.com (Y.-J. Tang). Bioresource Technology 100 (2009) 1852–1859 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech