Enhancing the production of cephalosporin C through modulating the autophagic process of Acremonium chrysogenum.

BACKGROUND: Autophagy is used for degradation of cellular components and nutrient recycling. Atg8 is one of the core proteins in autophagy and used as a marker for autophagic detection. However, the autophagy of filamentous fungi is poorly understood compared with that of Saccharomyces cerevisiae. Our previous study revealed that disruption of the autophagy related gene Acatg1 significantly enhanced cephalosporin C yield through reducing degradation of cephalosporin biosynthetic proteins in Acremonium chrysogenum, suggesting that modulation of autophagic process is one promising way to increase antibiotic production in A. chrysogenum. RESULTS: In this study, a S. cerevisiae ATG8 homologue gene Acatg8 was identified from A. chrysogenum. Acatg8 could complement the ATG8 mutation in S. cerevisiae, indicating that Acatg8 is a functional homologue of ATG8. Microscope observation demonstrated the fluorescently labeled AcAtg8 was localized in the cytoplasm and autophagosome of A. chrysogenum, and the expression of Acatg8 was induced by nutrient starvation. Gene disruption and genetic complementation revealed that Acatg8 is essential for autophagosome formation. Disruption of Acatg8 significantly reduced fungal conidiation and delayed conidial germination. Localization of GFP-AcAtg8 implied that autophagy is involved in the early phase of conidial germination. Similar to Acatg1, disruption of Acatg8 remarkably enhanced cephalosporin C yield. The cephalosporin C biosynthetic enzymes (isopenicillin N synthase PcbC and isopenicillin N epimerase CefD2) and peroxisomes were accumulated in the Acatg8 disruption mutant (∆Acatg8), which might be the main reasons for the enhancement of cephalosporin C production. However, the biomass of ΔAcatg8 decreased drastically at the late stage of fermentation, suggesting that autophagy is critical for A. chrysogenum cell survival under nutrition deprived condition. Disruption of Acatg8 also resulted in accumulation of mitochondria, which might produce more reactive oxygen species (ROS) which promotes fungal death. However, the premature death is unfavorable for cephalosporin C production. To solve this problem, a plasmid containing Acatg8 under control of the xylose/xylan-inducible promoter was introduced into ∆Acatg8. Conidiation and growth of the recombinant strain restored to the wild-type level in the medium supplemented with xylose, while the cephalosporin C production maintained at a high level even prolonged fermentation. CONCLUSIONS: Our results demonstrated inducible expression of Acatg8 and disruption of Acatg8 remarkably increased cephalosporin C production. This study provides a promising approach for yield improvement of cephalosporin C in A. chrysogenum.

Is the root-colonizing endophyte Acremonium strictum an ericoid mycorrhizal fungus?

In previous investigations, we found that Acremonium strictum (strain DSM 100709) developed intracellular structures with similarity to mycelia of ericoid mycorrhizal fungi in the rhizodermal cells of flax plants and in hair roots of Rhododendron plantlets. A. strictum had also been isolated from roots of ericaceous salal plants and was described as an unusual ericoid mycorrhizal fungus (ERMF). As its mycorrhizal traits were doubted, we revised the hypothesis of a mycorrhizal nature of A. strictum. A successful synthesis of mycorrhiza in hair roots of inoculated ericaceous plants was a first step of evidence, followed by fluorescence microscopy with FUN(®)1 cell stain to observe the vitality of the host cells at the early infection stage. In inoculation trials with in vitro-raised mycorrhiza-free Rhododendron plants in axenic liquid culture and in greenhouse substrate culture, A. strictum was never observed in living hair root cells. As compared to the ERMF Oidiodendron maius and Rhizoscyphus ericae that invaded metabolically active host cells and established a symbiotic unit, A. strictum was only found in cells that were dead or in the process of dying and in the apoplast. In conclusion, A. strictum does not behave like a common ERMF-if it is one at all. A comparison of A. strictum isolates from ericaceous and non-ericaceous hosts could reveal further identity details to generalize or specify our findings on the symbiotic nature of A. strictum. At least, the staining method enables to discern between true mycorrhizal and other root endophytes-a tool for further studies.

AcstuA, which encodes an APSES transcription regulator, is involved in conidiation, cephalosporin biosynthesis and cell wall integrity of Acremonium chrysogenum.

A transcriptional regulatory gene AcstuA was identified from Acremonium chrysogenum. AcstuA encodes a basic helix-loop-helix protein with similarity to StuA which regulates the core developmental processes of Aspergillus nidulans. Like disruption of stuA in A. nidulans, deficiency of AcstuA blocked the conidiation of A. chrysogenum through severely down-regulating the expression of AcbrlA and AcabaA which encode orthologs of the key fungal developmental regulators BrlA and AbaA. Disruption of AcstuA also drastically reduced cephalosporin production of A. chrysogenum. In agreement, the transcriptions of pcbAB, pbcC, cefD1, cefD2, cefEF and cefG were remarkably decreased in the AcstuA disruption mutant (ΔAcstuA). In addition to defects in conidiation and cephalosporin biosynthesis, ΔAcstuA produced abnormal swollen and fragmented hyphal cells during fermentation. The phenotypic alterations of hyphal cells caused by AcstuA deletion were restored by supplementation of NaCl in the medium, indicating that the deficiency of AcstuA has an influence on the cell wall integrity of A. chrysogenum. The transcriptions of two putative mannoprotein encoding genes Acmp2 and Acmp3 significantly reduced in ΔAcstuA, further indicating that cell wall integrity of the mutant is impaired. These results strongly suggested that AcstuA is involved in conidiation, cephalosporin production, hyphal fragmentation and cell wall integrity in A. chrysogenum.

Acremonium kiliense: case report and review of published studies.

Changes in the spectrum of clinically important fungal infection have been observed in recent years. Acremonium species has been responsible for eumycotic mycetomas but has also been increasingly implicated in systemic fungal diseases. A case of Acremonium kiliense fungemia with proven involvement of the lungs in an allogeneic hematopoietic stem cell patient is reported. A high-resolution computed tomography scan of the lungs showed nodules in both lungs. Multiple cultures of blood demonstrated narrow septate hyphae, cylindrical conidia, and solitary tapering phialides and microconidia that remained grouped in slimy heads. The isolate was identified as A. kiliense based on its morphological characteristics and DNA sequence analysis. Susceptibility testing of the clinical isolate was performed to four antifungal agents. Amphotericin B, fluconazole and itraconazole were found to be inactive in vitro against the isolate; however, it was found to be sensitive to voriconazole. This last drug was indicated, and a high-resolution computed tomography scan of the lungs was normal after 10 days. One year later, the patient was free of symptoms and her blood culture was negative for fungi. Thus, voriconazole was effective in treatment for life-threatening A. kiliense infections. In this work, we performed an overview of worldwide clinical infections caused by A. kiliense.

[Chromosomal polymorphism of Acremonium chrysogenum strains producing cephalosporin C].

Using pulse electrophoresis in controlled homogenous electric field we conducted molecular karyotyping of highly-productive and laboratory strains of Acremonium chrysogenum generating antibiotic cephalosporin C (cefC). Differences in size of several chromosomes of highly active strain CB26/8 compared to the wild-type strain ATCC 11550 were revealed. It was shown that chromosomal polymorphism in the highly active strain was not associated with alteration of localization and copy number ofcephalosporin C biosynthesis and transport genes. A cluster of "early" cefC biosynthesis genes is located on chromosome VI (4.4 Mb); a cluster of the "late genes", on chromosome II (2.3 Mb). Both clusters are presented as a single copy perA. chrysogenum genome in the wild-type and in CB26/8 producer strains. Based on comparative analysis of laboratory and industrial cefC producers, a karyotype scheme for A. chrysogenum strains of various origins was designed.

A novel impeller configuration to improve fungal physiology performance and energy conservation for cephalosporin C production.

Effects of impeller configuration on fungal physiology and cephalosporin C production were investigated by an industrial strain Acremonium chrysogenum in a 12 m(3) bioreactor equipped with conventional and novel impeller configuration, respectively. The cell growth and oxygen uptake rate (OUR) profiles were little affected by the impeller configurations. However, differing impeller combinations significantly affected the morphology, which in turn influenced cephalosporin C production. Under the novel impeller configuration, the production of cephalosporin C was 10% higher and an excessive amount of dispersed arthrospores was also observed. Computational fluid dynamics (CFD) simulation further revealed that poor mass and energy exchange as well as inhomogeneous environment existed in the bioreactor equipped with conventional impeller configuration. For equivalent power dissipation, the volume oxygen transfer coefficient (K(L)a) could be enhanced by 15% compared with that of conventional impeller configuration. Power consumption was dramatically decreased by 25% by using novel impeller configuration.

Two new species of Acremonium from Spanish soils.

In a survey on the diversity of microfungi in Spanish soils, two new species of Acremonium were found. Both species were characterized as having more or less erect, mostly branched conidiophores bearing whorls of acicular phialides. In addition, one of these species, Acremonium asperulatum, produced abundant chlamydospores and globose rough-walled conidia. The other species, Acremonium variecolor, produced a brownish diffusible pigment and smooth-walled, subglobose conidia with apiculate base; sessile conidia inserted directly on vegetative hyphae also were present. The analysis of the sequences of the ITS region, the D1/D2 domains of the 28S rRNA gene and a fragment of the actin gene revealed relationships of both species with members of the Bionectriaceae (Hypocreales). Genetic differences were observed with morphologically similar species.

Acremonium kiliense: reappraisal of its clinical significance.

A case of Acremonium kiliense peritonitis is described. Diagnosis was established by repeated isolation of the fungus from peritoneal dialysate and by its identification on the basis of morphological characteristics and sequencing of internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA). This report and available literature suggest that A. kiliense may have a greater clinical significance than hitherto recognized.

Efficient production of cellulase in the culture of Acremonium cellulolyticus using untreated waste paper sludge.

Cellulase was produced by Acremonium cellulolyticus using untreated waste paper sludge (PS) as the carbon source. The clay present in PS did not show any inhibitory effect on cellulase production but did alter the pH during fermentation. On the flask scale, the maleate buffer concentration and pH were key factors that affected the efficiency of cellulase production from PS cellulose. Optimum cellulase production in a 3-L fermentor of working volume 1.5 L was achieved by controlling the pH value at 6.0 using 2 M NaOH and 2 M maleic acid, and the productivity reached 8.18 FPU/mL. When 40.89 g/L PS cellulose, 2.2 g/L (NH(4) )(2) SO(4) , and 4.4 g/L urea were added to a 48-h culture, the cellulase activity was 9.31 FPU/mL at the flask scale and 10.96 FPU/mL in the 3-L fermentor. These values are ∼80% of those obtained when pure cellulose is used as the carbon source. The method developed here presents a new route for the utilization of PS.

Spectrum of clinically relevant Acremonium species in the United States.

Some species in the polyphyletic fungal genus Acremonium are important opportunist pathogens. Determining the actual spectrum of species and their incidence in the clinical setting, however, has long been hampered because of the difficulties encountered in phenotypic species-level identification. The goal of this study was to re-identify a large number of clinical isolates morphologically and to confirm the identifications by comparing sequences of the internal transcribed spacer region of the rRNA gene of these isolates to those of type or reference strains of well-known Acremonium species. Of the 119 isolates referred to a United States reference laboratory under the name Acremonium, only 75 were identified morphologically as belonging to that genus. The remainder (44 isolates) were identified as belonging to other morphologically similar genera. The Acremonium clinical isolates were related to species of Hypocreales, Sordariales, and of an incertae sedis family of ascomycetes, Plectosphaerellaceae. A total of 50 of the 75 Acremonium isolates (67%) could be identified by molecular means, the prevalent species being Acremonium kiliense (15 isolates), A. sclerotigenum-A. egyptiacum (11 isolates), A. implicatum (7 isolates), A. persicinum (7 isolates), and A. atrogriseum (4 isolates). One of the most interesting findings of our study was that we identified several species among this large collection of clinical isolates that had not previously been reported from human infections, and we failed to confirm other Acremonium species, such as A. potronii, A. recifei, and A. strictum, that had been considered significant. The most common anatomic sites for Acremonium isolates were the respiratory tract (41.3%), nails (10.7%), and the eye (9.3%). Antifungal susceptibility testing demonstrated high MICs for all agents tested, except for terbinafine. Since numerous isolates could not be identified, we concluded that the list of opportunistic Acremonium species is far from be complete and that a considerable number of additional species will be discovered.

Stimulation of cephalosporin C production in Acremonium chrysogenum M35 by glycerol.

In this study, the effects of glycerol on cephalosporin C production by Acremonium chrysogenum M35 were evaluated. The addition of glycerol increased cephalosporin production by up to 12-fold. Glycerol caused the upregulation of the transcription of the isopenicillin synthase (pcbC) and transporter (cefT) genes in early exponential phase, and affected the cell morphology since hyphal fragments differentiated into arthrospores. These results indicate that glycerol effectively enhances cephalosporin C production via stimulation of cell differentiation.

A homologue of the Aspergillus velvet gene regulates both cephalosporin C biosynthesis and hyphal fragmentation in Acremonium chrysogenum.

The Aspergillus nidulans velvet (veA) gene encodes a global regulator of gene expression controlling sexual development as well as secondary metabolism. We have identified the veA homologue AcveA from Acremonium chrysogenum, the major producer of the beta-lactam antibiotic cephalosporin C. Two different disruption strains as well as the corresponding complements were generated as a prelude to detailed functional analysis. Northern hybridization and quantitative real-time PCR clearly indicate that the nucleus-localized AcVEA polypeptide controls the transcriptional expression of six cephalosporin C biosynthesis genes. The most drastic reduction in expression is seen for cefEF, encoding the deacetoxycephalosporine/deacetylcephalosporine synthetase. After 120 h of growth, the cefEF transcript level is below 15% in both disruption strains compared to the wild type. These transcriptional expression data are consistent with results from a comparative and time-dependent high-performance liquid chromatography analysis of cephalosporin C production. Compared to the recipient, both disruption strains have a cephalosporin C titer that is reduced by 80%. In addition to its role in cephalosporin C biosynthesis, AcveA is involved in the developmentally dependent hyphal fragmentation. In both disruption strains, hyphal fragmentation is already observed after 48 h of growth, whereas in the recipient strain, arthrospores are not even detected before 96 h of growth. Finally, the two mutant strains show hyperbranching of hyphal tips on osmotically nonstabilized media. Our findings will be significant for biotechnical processes that require a defined stage of cellular differentiation for optimal production of secondary metabolites.

Secretion systems for secondary metabolites: how producer cells send out messages of intercellular communication.

Many secondary metabolites (e.g. antibiotics and mycotoxins) are toxic to the microorganisms that produce them. The clusters of genes that are responsible for the biosynthesis of secondary metabolites frequently contain genes for resistance to these toxic metabolites, such as different types of multiple drug resistance systems, to avoid suicide of the producer strains. Recently there has been research into the efflux systems of secondary metabolites in bacteria and in filamentous fungi, such as the large number of ATP-binding cassette transporters found in antibiotic-producing Streptomyces species and that are involved in penicillin secretion in Penicillium chrysogenum. A different group of efflux systems, the major facilitator superfamily exporters, occur very frequently in a variety of bacteria that produce pigments or antibiotics (e.g. the cephamycin and thienamycin producers) and in filamentous fungi that produce mycotoxins. Such efflux systems include the CefT exporters that mediate cephalosporin secretion in Acremonium chrysogenum. The evolutionary origin of these efflux systems and their relationship with current resistance determinants in pathogenic bacteria has been analyzed. Genetic improvement of the secretion systems of secondary metabolites in the producer strain has important industrial applications.

Morphology and kinetics studies on cephalosporin C production by Cephalosporium acremonium M25 in a 30-l bioreactor using a mixture of inocula.

AIMS: In this study, the relationship between morphology and cephalosporin C (CPC) production in a 30-l bioreactor culture of Cephalosporium acremonium M25 using a 3:7 seed mixture was investigated. In addition, the kinetic model was established and applied. METHODS AND RESULTS: CPC production was performed in a 30-l bioreactor using a 3:7 seed mixture. It was recognized that a 3:7 seed mixture was able to reduce lag phase and enhance CPC production. The maximum CPC production and cell mass were 1.96 and 81.5 g l-1 respectively. Through a morphology study by observation using image analysis, it was concluded that changes of morphological features predicted the progressive production of CPC and that a morphology study could be useful in monitoring the CPC fermentation by C. acremonium M25. In the kinetics study, a kinetic model of CPC fermentation was developed and applied. The proposed model could adequately describe the fermentation of C. acremonium M25 in a 30-l bioreactor. CONCLUSIONS: CPC productivity was improved by using a 3:7 seed mixture in a 30-1 bioreactor. The changes in morphological features showed a very similar tendency with CPC production. A kinetic model of CPC fermentation was successfully established. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the present study suggest that the use of a 3:7 seed mixture inocula has considerable possibilities for improving CPC productivity if applied to industrial scale fermentations. Through morphology and kinetics study, the kinetic model to describe the morphological differentiation and CPC production by C. acremonium M25 was established.

Classification of the guava wilt fungus Myxosporium psidii, the palm pathogen Gliocladium vermoesenii and the persimmon wilt fungus Acremonium diospyri in Nalanthamala.

Psidium guajava wilt is known from South Africa, Malaysia and Taiwan. The fungus causing this disease, Myxosporium psidii, forms dry chains of conidia on surfaces of pseudoparenchymatous sporodochia, which develop in blisters on bark. Similar sporodochia are characteristic of Nalanthamala madreeya, the type species of Nalanthamala. Nalanthamala, therefore, is the appropriate anamorph genus for Myxosporium psidii, while Myxosporium is a nomen nudum (based on M. croceum). For M. psidii the combination Nalanthamala psidii is proposed. Nalanthamala psidii, the palm pathogen Gliocladium (Penicillium) vermoesenii, another undescribed anamorphic species from palm, two species of Rubrinectria and the persimmon pathogen Acremonium diospyri are monophyletic and belong to the Nectriaceae (Hypocreales) based on partial nuclear large subunit ribosomal DNA (LSU rDNA) analyses. Rubrinectria, therefore, is the teleomorph of Nalanthamala, in which the anamorphs are classified as N. vermoesenii, N. diospyri or Nalanthamala sp. Nalanthamala squamicola, the only other Nalanthamala species, has affinities with the Bionectriaceae and is excluded from this group. Rubrinectria/Nalanthamala species form dimorphic conidiophores and conidia in culture. Fusiform, cylindrical, or allantoid conidia arise in colorless liquid heads on acremonium-like conidiophores; ovoidal conidia with somewhat truncated ends arise in long, persistent, dry chains on penicillate conidiophores. No penicillate but irregularly branched conidiophores were observed in N. diospyri. Conidia of N. psidii that are held in chains are shorter than those of N. madreeya, of which no living material is available. Nalanthamala psidii and N. diospyri are pathogenic specifically to their hosts. They form pale yellow to pale orange or brownish orange colonies, respectively, and more or less white conidial masses. Most strains of Rubrinectria sp., Nalanthamala sp. and N. vermoesenii originate from palm hosts, form mostly greenish or olive-brown colonies and white-to-salmon conidial masses. They form a monophyletic clade to which Nalanthamala psidii and N. diospyri are related based on analyses of the internal transcribed spacer regions and 5.8S rDNA (ITS rDNA), LSU rDNA, and partial beta-tubulin gene. Few polymorphic sites in the ITS rDNA and beta-tubulin gene indicate that Nalanthamala psidii comprises two lineages, one of which has been detected only in South Africa.

Investigations of the production of cephalosporin C by Acremonium chrysogenum.

A review is given on the morphology of Acremonium chrysogenum and the biosynthesis of cephalosporin C based on the published references. Investigations are presented on the comparison of cultivation media carried out by means of shake flask cultures. The process performance of a standard cultivation in well controlled bioreactor is presented and compared with other cultivations, which were executed with the same strain and bioreactor, but with various carbon-, nitrogen- and sulphur-sources keeping the concentrations of the key components at definite levels. Also the influence of dilution and enrichment of the medium on the process performance is explored. Mathematical models for the growth of Acremonium chrysogenum and production of cephalosporin C are reviewed and their application for control of industrial processes with complex cultivation media are discussed.

Cephalosporin C production by immobilized Cephalosporium acremonium cells in a repeated batch tower bioreactor.

The industrial production of antibiotics with filamentous fungi is usually carried out in conventional aerated and agitated tank fermentors. Highly viscous non-Newtonian broths are produced and a compromise must be found between convenient shear stress and adequate oxygen transfer. In this work, cephalosporin C production by bioparticles of immobilized cells of Cephalosporium acremonium ATCC 48272 was studied in a repeated batch tower bioreactor as an alternative to the conventional process. Also, gas-liquid oxygen transfer volumetric coefficients, k(L)a, were determined at various air flow-rates and alumina contents in the bioparticle. The bioparticles were composed of calcium alginate (2.0% w/w), alumina ( < 44 micra), cells, and water. A model describing the cell growth, cephalosporin C production, oxygen, glucose, and sucrose consumption was proposed. To describe the radial variation of oxygen concentration within the pellet, the reaction-diffusion model forecasting a dead core bioparticle was adopted. The k(L)a measurements with gel beads prepared with 0.0, 1.0, 1.5, and 2.0% alumina showed that a higher k(L)a value is attained with 1.5 and 2.0%. An expression relating this coefficient to particle density, liquid density, and air velocity was obtained and further utilized in the simulation of the proposed model. Batch, followed by repeated batch experiments, were accomplished by draining the spent medium, washing with saline solution, and pouring fresh medium into the bioreactor. Results showed that glucose is consumed very quickly, within 24 h, followed by sucrose consumption and cephalosporin C production. Higher productivities were attained during the second batch, as cell concentration was already high, resulting in rapid glucose consumption and an early derepression of cephalosporin C synthesizing enzymes. The model incorporated this improvement predicting higher cephalosporin C productivity.

On-line and off-line monitoring of the production of cephalosporin C by Acremonium chrysogenum.

Process monitoring of cephalosporin C formation by Acremonium chrysogenum in laboratory investigations is considered. The goal of these investigations is the identification of bottlenecks in the biosynthesis and the improvement of the process performance. Based on reports of other research groups and own experience the key parameters were selected, which influence the process performance. They are: dissolved oxygen and pH values. In addition the concentrations of biomass, DNA, glucose and reducing sugars (glucose, maltose, maltotriose and oligosaccharides), methionine, other nitrogen sources (ammonium ion, other amino acids), organic acids, phosphate, sulfate, dissolved organic carbon, proteins, product and precursors in the cell free cultivation medium are monitored. In addition the intracellular concentrations of RNA, DNA, proteins, amino acids as well as the activities of the enzymes of the biosynthesis of cephalosporin C are determined. The influence of these parameters on the biosynthesis is discussed.

Morphologic criteria for the preliminary identification of Fusarium, Paecilomyces, and Acremonium species by histopathology.

Nontraditional human pathogenic fungi, including Fusarium, Paecilomyces, and Acremonium species, have been increasingly documented as agents of infection in immunocompromised patients and, occasionally, in normal hosts. Although definitive identification of these fungi requires culture, they often can be identified provisionally in tissue sections by a combination of histologic features, including hyaline septate hyphae and characteristic reproductive structures known as phialides and phialoconidia. These morphologic characteristics, although familiar to mycologists, are easily overlooked by histopathologists; as a result, Fusarium species and Paecilomyces lilacinus are frequently misidentified in tissue sections as Aspergillus or Candida species. We identified 19 culture-proved cases of infection with species of Fusarium, Paecilomyces, or Acremonium; retrospectively reviewed histologic specimens stained by routine hematoxylin and eosin, Gomori methenamine silver, and/or periodic acid-Schiff stains; and delineated morphologic criteria that will help pathologists make a preliminary identification of these fungi by histopathology. Adventitious sporulation was found in 9 of 9 infections caused by Paecilomyces species, 7 of 10 infections caused by Fusarium species, and in the single case of infection caused by Acremonium strictum. Histologic recognition of these morphologies may help clinicians select appropriate initial antifungal treatment and manage the infection.