Acthi, a thiazole biosynthesis enzyme, is essential for thiamine biosynthesis and CPC production in Acremonium chrysogenum

Yan Liu,Liping Xie,Youjia Hu,Baoquan Zhu,Hong Liu,Wei Zhang,Guihua Gong

doi:10.1186/s12934-015-0235-3

Abstract

BackgroundThe filamentous fungus Acremonium chrysogenum is an important industrial fungus and is used in the production of the β-lactam antibiotic cephalosporin C. Little is known regarding the molecular and biological mechanisms of how this industrial strain was improved by mutagenesis and molecular breeding. Comparative proteomics is one of the most powerful methods to evaluate the influence of gene expression on metabolite production.ResultsIn this study, we used comparative proteomics to investigate the molecular mechanisms involved in the biosynthesis of cephalosporin C between a high-producer (HY) strain and a wide-type (WT) strain. We found that the expression levels of thiamine biosynthesis-related enzymes, including the thiazole biosynthesis enzyme (Acthi), pyruvate oxidase, flavin adenine dinucleotide (FAD)-dependent oxidoreductase and sulfur carrier protein-thiS, were up-regulated in the HY strain. An Acthi-silencing mutant of the WT strain grew poorly on chemically defined medium (MMC) in the absence of thiamine, and its growth was recovered on MMC medium supplemented with thiamine. The intracellular thiamine content was changed in the Acthi silencing or over-expression mutants. In addition, we demonstrated that the manipulation of the Acthi gene can affect the hyphal growth of Acremonium chrysogenum, the transcription levels of cephalosporin C biosynthetic genes, the quantification levels of precursor amino acids for cephalosporin C synthesis and the expression levels of thiamine diphosphate-dependent enzymes. Over-expression of Acthi can significantly increase the cephalosporin C yield in both the WT strain and the HY mutant strain.ConclusionsUsing comparative proteomics, four differently expressed proteins were exploited, whose functions may be involved in thiamine diphosphate metabolism. Among these proteins, the thiazole biosynthesis enzyme (ActhiS) may play an important role in cephalosporin C biosynthesis. Our studies suggested that Acthi might be involved in the transcriptional regulation of cephalosporin C biosynthesis. Therefore, the thiamine metabolic pathway could be a potential target for the molecular breeding of this cephalosporin C producer for industrial applications.

Highlights

The filamentous fungus Acremonium chrysogenum is an important industrial fungus and is used in the production of the β-lactam antibiotic cephalosporin C
We examined the transcriptional levels of the Cephalosporin C (CPC) biosynthetic genes pcbAB (L-α-aminodipyl-L-cysteinyl-Dvaline synthetase gene), The isopenicillin N-synthetase gene (pcbC), The bifunctional deacetoxycephalosporin C synthase/hydroxylase gene (cefEF), and cef (DAC acetyltranferase gene) in the WT and mutant strains (Figure 7B)
Consistent with the CPC production, the transcriptional levels of pcbAB, pcbC, DAC acetyltranferase gene (cefG) and cefEF were significantly down- and up-regulated in the Acthi(−) and Acthi(+) strains, respectively. These results showed that the silencing and overexpression of the Acthi gene in A. chrysogenum altered the CPC biosynthesis during fermentation

Summary

Introduction

The filamentous fungus Acremonium chrysogenum is an important industrial fungus and is used in the production of the β-lactam antibiotic cephalosporin C. Cephalosporin C (CPC) is an important intermediate and is produced by the fermentation of the filamentous fungus Acremonium chrysogenum. This fungus, first isolated in 1948 from Sardinian coastal. CPC biosynthesis and transportation and their regulation patterns have been identified, and considerable progress has been made in understanding CPC biosynthesis in A. chrysogenum [4,5,6,7,8] In this fungus, global regulators, such as AcVEA, CPCR1, CRE1 and PACC, regulate. AcVEA, CPCR1 and AcsepH are involved in cellular differentiation and arthrospore formation in A. chrysogenum, both of which affect CPC biosynthesis [4,6,13]

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