Stimulation of cephalosporin C production in Acremonium chrysogenum M35 by glycerol

Carbon catabolite regulation of secondary metabolite formation, an old but not well-established regulatory system

Secondary microbial metabolites have various functions for the producer microorganisms, which allow them to interact and survive in adverse environments. In addition to these functions, other biological activities may have clinical relevance, as diverse as antimicrobial, anticancer and hypocholesterolaemic effects. These metabolites are usually formed during the idiophase of growth and have a wide diversity in their chemical structures. Their synthesis is under the impact of the type and concentration of the culture media nutrients. Some of the molecular mechanisms that affect the synthesis of secondary metabolites in bacteria (Gram‐positive and negative) and fungi are partially known. Moreover, all microorganisms have their peculiarities in the control mechanisms of carbon sources, even those belonging to the same genus. This regulatory knowledge is necessary to establish culture conditions and manipulation methods for genetic improvement and product fermentation. As the carbon source is one of the essential nutritional factors for antibiotic production, its study has been imperative both at the industrial and research levels. This review aims to draw the utmost recent advances performed to clarify the molecular mechanisms of the negative effect exerted by the carbon source on the secondary metabolite formation, emphasizing those found in Streptomyces, one of the genera most profitable antibiotic producers.

A Myb transcription factor represses conidiation and cephalosporin C production in Acremonium chrysogenum

Acremonium chrysogenum is the industrial producer of cephalosporin C (CPC). We isolated a mutant (AC554) from a T-DNA inserted mutant library of A. chrysogenum. AC554 exhibited a reduced conidiation and lack of CPC production. In consistent with it, the transcription of cephalosporin biosynthetic genes pcbC and cefEF was significantly decreased in AC554. Thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR) was performed and sequence analysis indicated that a T-DNA was inserted upstream of an open reading frame (ORF) which was designated AcmybA. On the basis of sequence analysis, AcmybA encodes a Myb domain containing transcriptional factor. Observation of red fluorescent protein (RFP) tagged AcMybA showed that AcMybA is naturally located in the nucleus of A. chrysogenum. Transcriptional analysis demonstrated that the AcmybA transcription was increased in AC554. In contrast, the AcmybA deleted mutant (ΔAcmybA) overproduced conidia and CPC. To screen the targets of AcmybA, we sequenced and compared the transcriptome of ΔAcmybA, AC554 and the wild-type strain at different developmental stages. Twelve differentially expressed regulatory genes were identified. Taken together, our results indicate that AcMybA negatively regulates conidiation and CPC production in A. chrysogenum.

Improved FK506 production by the precursors and product-tolerant mutant of Streptomyces tsukubaensis based on genome shuffling and dynamic fed-batch strategies

FK506, a secondary metabolite produced by Streptomyces tsukubaensis, is well known for its immunosuppressant properties to prevent rejection of transplanted organs and treat autoimmune diseases. However, the low titer of FK506 in the original producer strain limits the further industrialization efforts and restricts its clinical applications. To address this issue, a highly efficient method combined genome shuffling and dynamic fed-batch strategies was systematically performed in this work. Firstly, after five rounds of genome shuffling based on precursors and product resistances, a higher yielding strain TJ-P325 was successfully acquired, whose production reached 365.6 mg/L, 11-fold increase compared with the original strain. Then, the possible mechanism of different production capabilities between TJ-P325 and the wild type was explored through comparative gene expression analysis of key genes. Results showed that the transcription level of key genes was altered significantly in the mutant. Moreover, precursors addition enhanced the FK506 production by 28 %, as well as reduced the by-products biosynthesis. Finally, the disodium malonate and disodium methylmalonate dynamic fed-batch strategies dramatically led to the production of 514.5 mg/L in a 7.5-L bioreactor. These results demonstrated that genome shuffling and dynamic fed-batch strategies could be successfully applied to generate high-yield strains with value-added natural products during industrial microbial fermentation.

Production of cephalosporin C using crude glycerol in fed-batch culture of Acremonium chrysogenum M35

In this study, cephalosporin C production by Acremonium chrysogenum M35 cultured with crude glycerol instead of rice oil and methionine was investigated. The addition of crude glycerol increased cephalosporin C production by 6-fold in shake-flask culture, and also the amount of cysteine. In fed-batch culture without methionine, crude glycerol resulted only in overall improvement in cephalosporin C production (about 700%). In addition, A. chrysogenum M35 became highly differentiated in fed-batch culture with crude glycerol, compared with the differentiation in batch culture. The results presented here suggest that crude glycerol can replace methionine and plant oil as cysteine and carbon sources during cephalosporin C production by A. chrysogenum M35.