Effect of biosurfactant sophorolipids on Rhizomucor miehei lipase fermentation by Aspergillus oryzae

Qianqian Zhang,Ju Chu,Guiwei Tian,Yiming Yang,Yonghong Wang,Lei Sun,Xiwei Tian,Xu Li,Zhiyue Xiong

doi:10.1186/s40643-021-00433-y

Abstract

In this study, the effect of biosurfactant sophorolipids (SLs) on Rhizomucor miehei lipase (RML) fermentation by Aspergillus oryzae was investigated. With the exogenous addition of 0.3% (w/v) SLs in the initial medium, the RML activity reached 430.0 U/mL, an increase of 25.0% compared to the control group. Subsequently, the physiological metabolic responses of A. oryzae to the addition of SLs were further explored. The results showed that though SLs had almost no effect on the RML secretion, it would affect the morphology of the cells. During the late phase of the fermentation, the proportion of middle pellets, which was generally considered as an energetic and stable state for enzyme production was increased with the addition of SLs. Simultaneously, the viscosity of fermentation broth was reduced, which facilitated the increase of oxygen transfer, thereby improving the RML production. Finally, it could be found that the addition of SLs significantly increased the contents of precursor amino acids, especially for those rank first and second of the RML composition, and it could promote the synthesis of RML.

Highlights

Rhizomucor miehei lipase (RML) is an α/β-type singlechain polypeptide composed of 269 amino acids with a Ser-Asp-His catalytic triad structure (Boel et al 1988; Huge-Jensen et al 1989; Turkenburg et al 1990)
Acacia, polyvinyl alcohol and Triton X-100 could not increase the RML activity, which might be due to that the mechanism of surfactants on the enzyme is closely relevant to the non-homologous structure of lipase, extracellular secretion, enzymatic properties and physiological metabolic characteristics of the host
It was worth noting that compared to the control group, the proportion of small pellets was lower in SLs addition group, while the proportion of middle pellets was higher (Fig. 4c). These results indicated that the autolysis of the aging cells in SLs addition group provided more nutrients for small pellets to become middle pellets faster

Summary

Introduction

Rhizomucor miehei lipase (RML) is an α/β-type singlechain polypeptide composed of 269 amino acids with a Ser-Asp-His catalytic triad structure (Boel et al 1988; Huge-Jensen et al 1989; Turkenburg et al 1990). The lipase production capacity of wild type R. miehei is relatively low, and the composition of the Aspergillus oryzae, which is generally recognized as safe, is one of the important cell factories for protein production. Compared with P. pastoris as the expression host of heterologous RML production, which could reach approximate 1200 U/mL (Huang et al 2014), the expression level in A. oryzae seems to be much lower. Wang et al (2009) successfully expressed RML in A. oryzae and obtained the integrated positive transformant A. oryzae ONL1, the enzyme activity of the fermentation supernatant measured by alkali titration was only 2.5 U/mL after 7 days cultivation.

Methods

Results

Conclusion