Cephalosporin C production by Cephalosporium acremonium: the methionine story

Exploring Antimicrobials from the Flora and Fauna of Marine: Opportunities and Limitations

About 95% of earth living space lies deep below the ocean's surface and it harbors extraordinary diversity of marine organisms. Marine biodiversity is an exceptional reservoir of natural products, bioactive compounds, nutraceuticals and other potential compounds of commercial value. Timeline for the development of the drug from a plant, synthetic and other alternative sources is too lengthy. Exploration of the marine environment for potential bioactive compounds has gained focus and huge opportunity lies ahead for the exploration of such vast resources in the ocean. Further, the evolution of superbugs with increasing resistance to the currently available drugs is alarming and it needs coordinated efforts to resolve them. World Health Organization recommends the need and necessity to develop effective bioactive compounds to combat problems associated with antimicrobial resistance. Based on these factors, it is imperative to shift the focus towards the marine environment for potential bioactive compounds that could be utilized to tackle antimicrobial resistance. Current research trends also indicate the huge strides in research involving marine environment for drug discovery. The objective of this review article is to provide an overview of marine resources, recently reported research from marine resources, challenges, future research prospects in the marine environment.

A Review on the Feedstocks for the Sustainable Production of Bioactive Compounds in Biorefineries

Since 2015, the sustainable development goals of the United Nations established a route map to achieve a sustainable society, pushing the industry to aim for sustainable processes. Biorefineries have been studied as the technological scheme to process integrally renewable resources. The so-called “bioactive” compounds (BACs) have been of high interest, given their high added value and potential application in pharmaceutics and health, among others. However, there are still elements to be addressed to consider them as economic drivers of sustainable processes. First, BACs can be produced from many sources and it is important to identify feedstocks for this purpose. Second, a sustainable production process should also consider valorizing the remaining components. Finally, feedstock availability plays an important role in affecting the process scale, logistics, and feasibility. This work consists of a review on the feedstocks for the sustainable production of BACs in biorefineries, covering the type of BAC, composition, and availability. Some example biorefineries are proposed using wheat straw, hemp and grapevine shoots. As a main conclusion, multiple raw materials have the potential to obtain BACs that can become economic drivers of biorefineries. This is an interesting outlook, as the integral use of the feedstocks may not only allow obtaining different types of BACs, but also other fiber products and energy for the process self-supply.

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.

Extending the "One Strain Many Compounds" (OSMAC) Principle to Marine Microorganisms

Genomic data often highlights an inconsistency between the number of gene clusters identified using bioinformatic approaches as potentially producing secondary metabolites and the actual number of chemically characterized secondary metabolites produced by any given microorganism. Such gene clusters are generally considered as “silent”, meaning that they are not expressed under laboratory conditions. Triggering expression of these “silent” clusters could result in unlocking the chemical diversity they control, allowing the discovery of novel molecules of both medical and biotechnological interest. Therefore, both genetic and cultivation-based techniques have been developed aimed at stimulating expression of these “silent” genes. The principles behind the cultivation based approaches have been conceptualized in the “one strain many compounds” (OSMAC) framework, which underlines how a single strain can produce different molecules when grown under different environmental conditions. Parameters such as, nutrient content, temperature, and rate of aeration can be easily changed, altering the global physiology of a microbial strain and in turn significantly affecting its secondary metabolism. As a direct extension of such approaches, co-cultivation strategies and the addition of chemical elicitors have also been used as cues to activate “silent” clusters. In this review, we aim to provide a focused and comprehensive overview of these strategies as they pertain to marine microbes. Moreover, we underline how changes in some parameters which have provided important results in terrestrial microbes, but which have rarely been considered in marine microorganisms, may represent additional strategies to awaken “silent” gene clusters in marine microbes. Unfortunately, the empirical nature of the OSMAC approach forces scientists to perform extensive laboratory experiments. Nevertheless, we believe that some computation and experimental based techniques which are used in other disciplines, and which we discuss; could be effectively employed to help streamline the OSMAC based approaches. We believe that natural products discovery in marine microorganisms would be greatly aided through the integration of basic microbiological approaches, computational methods, and technological innovations, thereby helping unearth much of the as yet untapped potential of these microorganisms.

Study on genetic engineering of Acremonium chrysogenum, the cephalosporin C producer

Acremonium chrysogenum is an important filamentous fungus which produces cephalosporin C in industry. This review summarized the study on genetic engineering of Acremonium chrysogenum, including biosynthesis and regulation for fermentation of cephalosporin C, molecular techniques, molecular breeding and transcriptomics of Acremonium chrysogenum. We believe with all the techniques available and full genomic sequence, the industrial strain of Acremonium chrysogenum can be genetically modified to better serve the pharmaceutical industry.

Comparative expression profiling of genes involved in primary metabolism in high-yield and wild-type strains of Acremonium chrysogenum

Cephalosporin C (CPC) productivity of Acremonium chrysogenum has been improved significantly through classical strain improvement programs. Here, we used transcription and metabolite profiling to address mechanisms underlying CPC production in a high yield (HY) strain. Transcription and metabolite profiling indicated that enzymes involved in amino acid production are higher in abundance in the HY strain. Moreover, results indicate a higher flow of precursors from the glycolysis and gluconeogenesis pathways to serine synthesis at the late stage of fermentation in the HY strain. In addition, less pyruvate would enter the TCA cycle thus favoring valine synthesis. Amino acid production would also benefit from a more active pentose phosphate pathway and γ-amino butyric acid shunt both generating NADPH. Moreover the glyoxylate pathway seems to be more active in the HY strain. These results may provide new leads for CPC strain improvement in industry.

Expression of the Acremonium chrysogenum cefT gene in Penicillum chrysogenum indicates that it encodes an hydrophilic beta-lactam transporter

The Acremonium chryrsogenum cefT gene encoding a membrane protein of the major facilitator superfamily implicated in the cephalosporin biosynthesis in A. chrysogenum was introduced into Penicillium chrysogenum Wisconsin 54-1255 (a benzylpenicillin producer), P. chrysogenum npe6 pyrG(-) (a derivative of Wisconsin 54-1255 lacking a functional penDE gene) and P. chrysogenum TA98 (a deacetylcephalosporin producer containing the cefD1, cefD2, cefEF and cefG genes from A. chrysogenum). RT-PCR analysis revealed that the cefT gene was expressed in P. chrysogenum strains. HPLC analysis of the culture broths of the TA98 transformants showed an increase in the secretion of deacetylcephalosporin C and hydrophilic penicillins (isopenicillin N and penicillin N). P. chrysogenum Wisconsin 54-1255 strain transformed with cefT showed increased secretion of the isopenicillin N intermediate and a drastic decrease in the benzylpenicillin production. Southern and northern blot analysis indicated that the untransformed P. chrysogenum strains contain an endogenous gene similar to cefT that may be involved in the well-known secretion of the isopenicillin N intermediate. In summary, the cefT transporter is a hydrophilic beta-lactam transporter that is involved in the secretion of hydrophilic beta-lactams containing alpha-aminoadipic acid side chain (isopenicillin N, penicillin N and deacetylcephalosporin C).

Yeast-like cell formation and glutathione metabolism in autolysing cultures of Penicillium chrysogenum

The bulk formation of yeast-like (arthrospore-like) cells were typical in carbon-depleted submerged cultures of the high beta-lactam producer Penicillium chrysogenum NCAIM 00237 strain independently of the nitrogen-content of the culture medium. This morphogenetic switch was still quite common in carbon-starving cultures of the low-penicillin-producer strain P. chrysogenum ATCC 28089 (Wis 54-1255) when the nitrogen-content of the medium was low but was a very rare event in wild-type P. chrysogenum cultures. The mycelium-->yeast-like cell transition correlated well with a relatively high glutathione concentration and a reductive glutathione/glutathione disulfite (GSH/GSSG) redox balance in autolysing cultures, which was a consequence of industrial strain development. Paradoxically, the development of high beta-lactam productivity resulted in a high intracellular GSH level and, concomitantly, in an increased y-glutamyltranspeptidase (i.e. GSH-decomposing) activity in the autolytic phase of growth of P. chrysogenum NCAIM 00237. The hypothesized causal connection between GSH metabolism and cell morphology, if verified, may help us in future metabolic engineering of industrially important filamentous fungi.

Involvement of nitrogen-containing compounds in beta-lactam biosynthesis and its control

Biosynthesis of beta-lactam antibiotics by fungi and actinomycetes is markedly affected by compounds containing nitrogen. The different processes employed by the spectrum of microbes capable of making these valuable compounds are affected differently by particular compounds. Ammonium ions, except at very low concentrations, exert negative effects via nitrogen metabolite repression, sometimes involving the nitrogen regulatory gene nre. Certain amino acids are precursors or inducers, whereas others are involved in repression and, in certain cases, as inhibitors of biosynthetic enzymes and of enzymes supplying precursors. The most important amino acids from the viewpoint of regulation are lysine, methionine, glutamate and valine. Surprisingly, diamines such as diaminopropane, putrescine and cadaverine induce cephamycin production by actinomycetes. In addition to penicillins and cephalosporins made by fungi and cephamycins made by actinomycetes, other beta-lactams are made by actinomycetes and unicellular bacteria. These include clavams (e.g., clavulanic acid), carbapenems (e.g., thienamycin), nocardicins and monobactams. Here also, amino acids are precursors and inhibitors, but only little is known about regulation. In the case of the simplest carbapenem made by unicellular bacteria, i.e., 1-carba-2-em-3-carboxylic acid, quorum sensors containing homoserine lactone are inducers.

Glutathione metabolism of Acremonium chrysogenum in relation to cephalosporin C production: is gamma-glutamyltransferase in the center?

Methionine increased the intracellular glutathione (reduced) (GSH) pool and the specific gamma-glutamyltransferase (gamma-GT) activity in the cephalosporin C (CPC) producer Acremonium chrysogenum. The accelerated turnover of GSH might be indicative of the existence of a functioning gamma-glutamate cycle, and might supply the CPC biosynthetic machinery with L-cysteine. The gamma-GT was not subject to nitrogen metabolic repression but was more active in cells exposed to different oxidative-stress-generating agents. Exogenous cysteine hindered both the uptake of methionine and the induction of gamma-GT, and was not beneficial for CPC production. There was no causal relationship between the redox status of the cells and the observed cell morphology.

Unraveling the methionine-cephalosporin puzzle in Acremonium chrysogenum

Methionine has long been known as the major stimulant of the formation of cephalosporin C in Acremonium chrysogenum. Enzymatic and genetic studies of methionine have revealed that it induces four of the enzymes of cephalosporin-C biosynthesis at the level of transcription. It is also converted to cysteine, one of three precursors of cephalosporin C, by cystathionine-gamma-lyase. The main effect of methionine on cephalosporin production results from its regulatory role, which can be duplicated by the non-sulfur analog norleucine. Eliminating cystathionine-gamma-lyase prevents the enhancing precursor effect of methionine on cephalosporin-C production, and cystathionine-gamma-lyase overproduction in moderate doses increases cephalosporin-C formation.