Enhancement of cephalosporin C production by cultivation of Cephalosporium acremonium M25 using a mixture of inocula

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.

The Online Morphology Control and Dynamic Studies on Improving Vitamin B12 Production by Pseudomonas denitrificans with Online Capacitance and Specific Oxygen Consumption Rate

The relationship between the morphological character of Pseudomonas denitrificans and vitamin B12 synthesis based on real-time capacitance measurement and online specific oxygen consumption rate (Q O2) control was established for enhancing vitamin B12 production. Results demonstrated that the threshold Q O2 value lower than 2.0 mmol/gDCW/l would greatly stimulate the state transfer from the cell number growth phase to the cell elongation phase and promote rapid vitamin B12 biosynthesis, while the vitamin B12 biosynthesis rate could also be inhibited when the rate of cell's length-to-width ratio (ratio-LW) was higher than 10:1. Furthermore, the optimal morphology controlling strategy was achieved based on online Q O2 control, which increases the appropriate active cell numbers at the former phase, and then control the elongation of ratio-LW no more than 10:1 at the vitamin B12 biosynthesis phase. The maximal vitamin B12 production reached 239.7 mg/l at 168 h, which was improved by 14.7 % compared with the control (208 mg/l). This online controlling strategy would be effectively applied for improving industrial vitamin B12 fermentation.

[Research progress on strain improvement of Acremonium chrysogenum by genetic engineering]

Acremonium chrysogenum, cephalosporin C (CPC) producing strain, is an important industrial microorganism. CPC is used to produce 7-ACA, a major intermediate for manufacturing of many first-line anti-infectious cephalosporin-antibiotics. The fermentation level of CPC determines the production, quality and cost of its downstream products. Therefore, it is necessary to develop the strains of A. chrysogenum. Along with the development of molecular biology, genetic manipulation technique is becoming more and more important in the field of molecular breeding. This paper reviews the latest research progresses on CPC biosynthesis and its regulation. Genetic manipulations of A. chrysogenum were summarized and concluded. We suggested that strain improvement of A. chrysogenum by means of induction and expression of biosynthetic and regulatory genes, as well as exogenous genes, and further optimization could be applied to different aspects including CPC production enhancement and metabolic pathway elongation, etc. Future direction of this field is also proposed. We believed that incorporation of comparative proteomics and genomic shuffling with molecular breeding could lead the achievements close to industry promptly.

Differentiation of Acremonium chrysogenum M35 in submerged culture with glass beads or silicone rubbers

In this study, we investigated the effects of glass beads and silicone rubbers on the differentiation and morphological changes of A. chrysogenum M35 in submerged culture. Differentiation in the center of the cell pellets was improved by the addition of glass beads or silicone rubbers to the primary medium. The fragmentation rate constant (k(frag)), which is used to estimate the tensile strength of fungal hyphae, was increased by more than 40% in baffled flasks containing glass beads. The maximum fragmentation rate was also increased by 48% when silicone rubbers were added to a 5 L bioreactor containing the culture. During the cultivation in the main medium with 6 glass beads, the value of the fractal dimension increased by about 8% when it was compared with baffled flasks without glass beads. Additionally, the number of arthrospores and the dry cell weight were increased by more than 10% in baffled flasks containing beads. The degree of roundness, which is the ratio of the object area to the longest Feret diameter, was decreased from 0.85 at day 1 to 0.77 at day 5. The differentiation of A. chrysogenum M35 was also supposedly closely related with the enlargement of the cell surfaces. Taken together, these results indicate that complex changes in morphology resulted in increased cell growth and differentiation in the culture broth containing glass beads and silicone rubbers.

Rapid quantification of lipids in Acremonium chrysogenum using Oil red O

A method based on staining condition and volume of culture broth for the rapid estimation of the level of intracellular lipids in Acremonium chrysogenum using Oil red O was developed. Lipids in A. chrysogenum were strongly stained by the modified Oil red O after treatment for 10 min at 75°C. The results of the study indicated that the Oil red O staining method developed here is useful for the quantification of 0.1-5 mg ml(-1) of lipids in A. chrysogenum.

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.

Fatty acids reduce the tensile strength of fungal hyphae during cephalosporin C production in Acremonium chrysogenum

Fragmentation rate constants, which can be used to estimate the tensile strength of fungal hyphae, were used to elucidate relationships between morphological changes and addition of fatty acids during cephalosporin C production in Acremonium chrysogenum M35. The number of arthrospores increased gradually during fermentation, and, in particular, was higher in the presence of rice oil, oleic acid or linoleic acid than in their absence. Because supplementation of rice oil or fatty acids increased cephalosporin C, we concluded that differentiation to arthrospores is related to cephalosporin C production. To estimate the relative tensile strengths of fungal hyphae, fragmentation rate constants (k (frag)) were measured. When rice oil, oleic acid, or linoleic acid were added into medium, fragmentation rate constants were higher than for the control, and hyphal tensile strengths reduced. The relative tensile strength of fungal hyphae, however was not constant presumably due to differences in physiological state.

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.