Metabolic engineering of Acremonium chrysogenum for improving cephalosporin C production independent of methionine stimulation

Jiajia Liu,Wenyan Gao,Yuanyuan Pan,Gang Liu

doi:10.1186/s12934-018-0936-5

Abstract

BackgroundCephalosporin C (CPC) produced by Acremonium chrysogenum is one of the most important drugs for treatment of bacterial infectious diseases. As the major stimulant, methionine is widely used in the industrial production of CPC. In this study, we found methionine stimulated CPC production through enhancing the accumulation of endogenous S-adenosylmethionine (SAM). To overcome the methionine dependent stimulation of CPC production, the methionine cycle of A. chrysogenum was reconstructed by metabolic engineering.ResultsThree engineered strains were obtained by overexpressing the SAM synthetase gene AcsamS and the cystathionine-γ-lyase gene mecB, and disrupting a SAM dependent methyltransferase gene Acppm1, respectively. Overexpression of AcsamS resulted in fourfold increase of CPC production which reached to 129.7 µg/mL. Disruption of Acppm1 also increased CPC production (up to 135.5 µg/mL) through enhancing the accumulation of intracellular SAM. Finally, an optimum recombinant strain (Acppm1DM-mecBOE) was constructed through overexpressing mecB in the Acppm1 disruption mutant. In this strain, CPC production reached to the maximum value (142.7 µg/mL) which was 5.5-fold of the wild-type level and its improvement was totally independent of methionine stimulation.ConclusionsIn this study, we constructed a recombinant strain in which the improvement of CPC production was totally independent of methionine stimulation. This work provides an economic route for improving CPC production in A. chrysogenum through metabolic engineering.

Highlights

Cephalosporin C (CPC) produced by Acremonium chrysogenum is one of the most important drugs for treatment of bacterial infectious diseases
Since methionine is the precursor of SAM which has been proved to stimulate antibiotic production in bacteria [25], the intracellular SAM concentration of A. chrysogenum was measured during fermentation in the MDFA medium with or without addition of methionine
The result showed that the intracellular concentration of SAM dropped remarkably after 4 days fermentation without addition of exogenous methionine, probably the endogenous methionine as the precursor has been exhausted at this time

Summary

Introduction

Cephalosporin C (CPC) produced by Acremonium chrysogenum is one of the most important drugs for treatment of bacterial infectious diseases. We found methionine stimulated CPC production through enhancing the accumulation of endogenous S-adenosylmethionine (SAM). Homocysteine, locating at an important metabolic branch point, can be removed sulfur to generate l-cysteine through transsulfuration pathway. The sulfur atom is provided for l-cysteine formation through a reverse transsulfuration pathway [12]. The formation of l-cysteine could be increased through enhancing the intracellular SAM concentration. It could be one of the reasons for methionine stimulation on CPC production. It was reported that the autotrophic sulfur assimilation is important for CPC production in A. chrysogenum A3/2 strain [13]

Methods

Results

Conclusion