Inhibitory Effects of Lignocellulosic Degradation Compounds From Hydrolysate On Microbial Oil Production

Inhibitory effects of lignocellulosic degradation compounds from hydrolysate on microbial oil production.

Jijiao Zeng, Xiaochen Yu, Yubin Zheng, Shulin Chen*

Department of Biological Systems Engineering, Washington State University, Pullman, Washington 99164-6120, USA

*Corresponding author. Tel: +1 509 335 3743; fax: +1 509 335 2722.

E-mail address: chens@wsu.edu

Abstract:

Recently microbe based lipid has attracted great attentions due to its high potential for "drop in" fuel production. Differentiation with phototrophic algal lipid, oleaginous yeast/fungi shows notably capability to accumulate lipid on utilization of lignocellulosic biomass which are recognized as most promising renewable resource for bio-fuel production. However, traditional pretreatment technologies, such as dilute acid, producing hydrolysate contain various carbonhydrate and lignin derivative compounds. These weak acids, furan aldehydes and phenolic aldehydes extensively inhibit microbial fermentation. Therefore, understanding their inhibitory effects to oleaginous yeast/fungi gives critical information to guide hydrolysis process for microbial oil production. In this study, the lipid accumulation by Cryptococcus curvatus and Mortierella isabellina was prudently investigated in the presence of eight representative inhibitors.  The results showed that these two strains have unexpectable tolerance to inhibitors in wide range of concentrations which overridden most reported value in lignocellulosic hydrolysate. Among the inhibitors, furfural and three phenolic aldehydes strongly repressed the growth of both yeast and fungus when the concentrations rose to 2 g/L (Fig.1A). The best performances on specific inhibitors were also observed with slight difference between yeast and fungi that might be resulted from their enzyme system and cultural conditions. Furthermore, the inhibitory effects indicated dependence on inoculum size and had minor influences on lipid content and fatty acid composition (Fig 1B). In short, our work demonstrated that Cryptococcus curvatus and Mortierella isabellina can tolerate high concentration of inhibitors which imply their possibility on economically competitive lipid production using non-detoxified hydrolysate.

 

Figure 1. Effects of inhibitors on biomass (A) and lipid (B) production by Cryptococcus curvatus