A comparative study on the production of exopolysaccharides between two entomopathogenic fungi Cordyceps militaris and Cordyceps sinensis in submerged mycelial cultures

AIMS: The present study comparatively investigates the optimal culture conditions for the production of exopolysaccharides (EPS) and cordycepin during submerged mycelial culture of two entomopathogenic fungi Cordyceps militaris and Cordyceps sinensis. METHODS AND RESULTS: Fermentations were performed in flasks and in 5-l stirred-tank fermenters. In the case of C. militaris, the highest mycelial biomass (22.9 g l(-1)) and EPS production (5 g l(-1)) were achieved in a medium of 40 g l(-1) sucrose, 5 g l(-1) corn steep powder at 30 degrees C, and an initial pH 8.0. The optimum culture conditions for C. sinensis was shown to be (in g l(-1)) 20 sucrose, 25 corn steep powder, 0.78 CaCl2, 1.73 MgSO4.7H2O at 20 degrees C, and an initial pH 4.0, where the maximum mycelial biomass and EPS were 20.9 and 4.1 g l(-1) respectively. Cordycepin, another bioactive metabolite, was excreted at low levels during the early fermentation period (maximum 38.8 mg l(-1) in C. militaris; 18.2 mg l(-1) in C. sinensis). CONCLUSIONS: The two fungi showed different nutritional and environmental requirements in their submerged cultures. Overall, the concentrations of mycelial biomass, EPS and cordycepin achieved in submerged culture of C. militaris were higher than those of C. sinensis. SIGNIFICANCE AND IMPACT OF THE STUDY: C. militaris and C. sinensis are representative insect-born fungi which have been longstanding and widely used as traditional medicines in eastern Asia. Comparative studies between two fungi are currently not available and this is the first report on the optimum medium composition for submerged culture of C. sinensis.     

Influence of nutritional conditions on the mycelial growth and exopolysaccharide production in Paecilomyces sinclairii

AIMS: The objective of the study was to optimize the submerged culture conditions for the production of exopolysaccharide from Paecilomyces sinclairii. METHODS AND RESULTS: The optimal temperature and initial pH for exopolysaccharide production by Paecilomyces sinclairii in shake flask culture were found to be 30 degrees C and 6.0, respectively. Sucrose (60 g l(-1)) and corn steep powder (10 g l(-1)) were the most suitable carbon and nitrogen source for exopolysaccharide production. CONCLUSIONS: Under optimal culture medium, the maximum exopolysaccharide concentration in a 5-l stirred-tank fermenter indicated 7.4 g l(-1), which was approximately three times higher than that in basal medium. The maximum specific growth rates (micro max) and yield coefficient (Y(P/S)) in the optimal culture medium was 0.16 h(-1) and 0.19, respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: The optimal culture conditions reported in this article can be widely applied to the processes for submerged cultures of other mushrooms.     

Effect of agitation intensity on the exo-biopolymer production and mycelial morphology in Cordyceps militaris

AIMS: The influence of agitation intensity on Cordyceps militaris morphology and exo-biopolymer production was investigated in a 5 litre stirred vessel using a six-blade Rushton turbine impeller. METHODS AND RESULTS: The mycelial morphology of C. militaris was characterized by means of image analysis, which included mean diameter, circularity, roughness and compactness of the pellets. The morphological parameters of the pellets grown under different stirring conditions were significantly different, which correspondingly altered exo-biopolymer production yields. CONCLUSIONS: The compactness of the pellets was found to be the most critical parameter affecting exo-biopolymer biosynthesis; more compact pellets were formed at 150 rev min(-1) with maximum exo-biopolymer production (15 g l(-1)). SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study suggest that morphological change of pellets is a good indicator for identifying the cell activity for exo-biopolymer production.     

Mycelial growth and exo-biopolymer production by submerged culture of various edible mushrooms under different media

AIMS: The effect of synthetic media on the submerged mycelial growth and exo-biopolymer production in various edible mushrooms was investigated in shake flask culture. METHODS AND RESULTS: Among 19 mushrooms examined, the relatively high yield in mycelial biomass and exo-biopolymer production was achieved in potato malt peptone (PMP) medium. In particular, Ganoderma lucidum NO. 1 and Phellinus linteus KCTC 6190 showed favourable growth in PMP medium with exo-biopolymer concentration of 1170 and 1520 mg l(-1), respectively. CONCLUSIONS: Enhanced exo-biopolymer production was achieved from Ganoderma lucidum NO. 1 and Phellinus linteus KCTC 6190 in a 5L batch fermentor, indicating approximately 5000 and 2410 mg l(-1), respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: The exo-biopolymer production and mycelial growth from various mushrooms were found to be strongly controlled by different complex media.     

Production and characterization of exopolysaccharides from an enthomopathogenic fungus Cordyceps militaris NG3

Optimization of the submerged culture conditions for the mycelial growth and production of exopolysaccharide (EPS) from a newly isolated Cordyceps species (C. militaris NG3) was studied in flask cultures. The optimal temperature and initial pH for EPS production were 30 degrees C and 8.0, respectively. Sucrose (30 g/L) and corn steep powder (10 g/L) were the most suitable carbon and nitrogen source for both mycelial growth and EPS production. There was a distinguishable morphological changes in mycelium grown between organic and inorganic nitrogen sources. A smooth pellet growth with heavy hyphal thickness was observed in the medium containing organic nitrogen sources, whereas irregular pellets with less hairy region were formed in the medium containing inorganic nitrogen sources. More highly branched cells appearing in the medium of organic nitrogen sources seemed a favorable morphological form for both EPS production and mycelial growth. Under optimal culture conditions, the maximum concentrations of mycelial growth and EPS were 17.6 and 3.4 g/L in a 5-L stirred-tank fermenter. Four groups of EPSs (designated as Fr-I, Fr-II, Fr-III, and Fr-IV) were obtained from the culture filtrates by size exclusion chromatography (SEC), and their molecular characteristics were examined by a multiangle laser-light scattering (MALLS) and refractive index (RI) detector system. The weight-average molar masses of the Fr-I, Fr-II, Fr-III, and Fr-IV of EPS were determined to be 2.262 x 10(6), 3.348 x 10(5), 1.049 x 10(5), and 5.059 x 10(4) g/mol, respectively. All four EPSs showed very low polydispersity indices ranging from 1.00 to 1.18. The SEC/MALLS analysis revealed that the molecular shape of the Fr-I was a rigid sphere suspected to be an aggregate of complex polysaccharides, the Fr-II and Fr-III were nearly globular in shape, and the Fr-IV was an almost rodlike structure.     

Production and molecular characteristics of four groups of exopolysaccharides from submerged culture of Phellinus gilvus

AIMS: The objective of the present study was to determine the optimal culture conditions for the production of four groups of exopolysaccharides (EPSs) in Phellinus gilvus by submerged culture and to investigate their molecular properties by multi-angle laser-light scattering (MALLS) analysis. METHODS AND RESULTS: The optimal temperature and initial pH for the production of both mycelial biomass and EPSs in P. gilvus by submerged flask cultures were found to be 30 degrees C and pH 9.0, respectively. Glucose and corn steep powder were the most suitable carbon and nitrogen source for both mycelial biomass and EPS production. Optimal medium composition was determined to be glucose 30 g l-1, corn steep powder 5 g l-1, MgSO4 1.23 g l-1, KH2PO4 0.68 g l-1, and K2HPO4 0.87 g l-1. Four groups of EPSs (Fr-I, II, III, and IV) were obtained from the culture filtrates by gel filtration chromatography on Sepharose CL-4B and characterized by size exclusion chromatography (SEC) coupled with MALLS. The weight average molar mass (Mw) of Fr-I, Fr-II, Fr-III and Fr-IV were determined to be 8.628 x 106 (+/-129 420), 1.045 x 106 (+/-19 855), 61.09 x 104 (+/-1244), and 33.55 x 104 (+/-134) g mol-1, respectively. CONCLUSIONS: Under optimal culture conditions, the maximum EPS production in a 5-l stirred fermenter indicated 5.3 g l-1 after 11 days of fermentation. The SEC/MALLS analysis revealed that Fr-I, which has extremely high molecular weight, was presumably an aggregate of complex polysaccharides forming a compact globular shape; whereas Fr-II was nearly spherical, Fr-III and Fr-IV were rod-like chains in an aqueous solution. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on the production of high amounts of EPSs from liquid-culture of the basidiomycete, P. gilvus. The SEC/MALLS approach used in this study could be useful in providing greater insight into the characterization of the mushroom polysaccharides without carrying out elaborate fractionation procedures prior to analysis.     

Optimization of physical parameters for exo-biopolymer production in submerged mycelial cultures of two entomopathogenic fungi Paecilomyces japonica and Paecilomyces tenuipes

AIMS: In the present study, two different optimization techniques were used to determine the suitable operating parameters for exo-biopolymer production in submerged mycelial cultures of two entomopathogenic fungi Paecilomyces japonica and Paecilomyces tenuipes. METHODS AND RESULTS: First, the rotating simplex method, a nonstatistical optimization technique, was employed to obtain the best combination of physical parameters (viz. pH, agitation intensity, aeration rate) for maximum exo-biopolymer production by P. japonica in a batch bioreactor. The optimal combination was determined to be a pH of 8.06, an aeration of 3 vvm, without any impeller agitation, producing a 17-time increase in exopolymer production (34.5 g l(-1)) when compared with that achieved in unoptimized flask cultures. Second, the uniform design method, a statistical optimization technique, was employed to determine the best operating parameters for submerged culture of P. tenuipes. The optimal combination for mycelial growth was determined to be a pH of 4.88, an aeration of 2 vvm and an agitation of 350 rpm, while a pH of 4, an aeration of 2 vvm and an agitation of 150 rpm was best for exo-biopolymer production. CONCLUSIONS: The exo-biopolymer production in P. japonica optimized by the rotating simplex method was strikingly improved (max. 34.5 g l(-1)), and the exo-biopolymer production in P. tenuipes optimized by the uniform design method was also significantly increased (max. 3.4 g l(-1)). SIGNIFICANCE AND IMPACT OF THE STUDY: The successful application of these two different optimization techniques in this study implies that these methods are worthy of applying to other fermentation systems for the production of bioactive mycelial biomass and exo-biopolymers in liquid culture of higher fungi.     

Optimization of submerged culture requirements for the production of mycelial growth and exopolysaccharide by Cordyceps jiangxiensis JXPJ 0109

AIMS: The objective of the present study was to investigate the optimal culture requirements for mycelial growth and exopolysaccharide production by Cordyceps jiangxiensis JXPJ 0109 in submerged culture. METHODS AND RESULTS: The effects of medium ingredients (i.e. carbon and nitrogen sources, and growth factor) and other culture requirements (i.e. initial pH, temperature, etc.) on the production of mycelia and exopolysaccharide were observed using a one-factor-at-a-time method. More suitable culture requirements for mycelial growth and exopolysaccharide production were proved to be maltose, glycerol, tryptone, soya bean steep powder, yeast extract, medium capacity 200 ml in a 500-ml flask, agitation rate 180 rev min(-1), seed age 4-8 days, inoculum size 2.5-7.5% (v/v), etc. The optimal temperatures and initial pHs for mycelial growth and exopolysaccharide production were at 26 degrees C and pH 5 and at 28 degrees C and pH 7, respectively, and corresponding optimal culture age were observed to be 8 and 10 days respectively. According to the primary results of the one-factor-at-a-time experiments, the optimal medium for the mycelial growth and exopolysaccharide production were obtained using an orthogonal layout method to optimize further. Herein the effects of medium ingredients on the mycelial growth of C. jiangxiensis JXPJ 0109 were in the order of yeast extract > tryptone > maltose > CaCl2 > glycerol > MgSO4 > KH2PO4 and the optimal concentration of each composition was 15 g maltose (food-grade), 10 g glycerol, 10 g tryptone, 10 g yeast extract, 1 g KH2PO4, 0.2 g MgSO4, and 0.5 g CaCl2 in 1 l of distilled water, while the order of effects of those components on exopolysaccharide production was yeast extract > maltose > tryptone > glycerol > KH2PO4 > CaCl2 > MgSO4, corresponding to the optimal concentration of medium was as follows: 20 g maltose (food-grade), 8 g glycerol, 5 g tryptone, 10 g yeast extract, 1 g KH2PO4, and 0.5 g CaCl2 in 1 l of distilled water. CONCLUSIONS: Under the optimal culture requirements, the maximum exopolysaccharide production reached 3.5 g l(-1) after 10 days of fermentation, while the maximum production of mycelial growth achieved 14.5 g l(-1) after 8 days of fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on the submerged culture requirements for mycelial growth and exopolysaccharide in C. jiangxiensis, and this two-step optimization strategy in this study can be widely applied to other microbial fermentation processes.     

Nutritional requirements of mycelial growth of Cordyceps sinensis in submerged culture

AIMS: The nutritional requirements for mycelial growth of Cordyceps sinensis in semi-synthetic liquid media were investigated. The results provide a basis for further physiological study and industrial fermentation of the fungus. METHODS AND RESULTS: Nutritional requirements, including 17 carbohydrates, 16 nitrogen compounds, nine vitamins, four macro-elements, four trace-elements and eight ratios of carbon to nitrogen, were studied for their effects on the mycelial growth in submerged cultures of C. sinensis by using one-factor-at-a-time and orthogonal matrix methods. Among these variables, sucrose, peptone, folic acid, calcium, zinc and a carbon to nitrogen ratio 12 : 1 were identified as the requirements for the optimum mycelial growth. The concentrations of sucrose, peptone and yeast extract were optimized and the effects of medium composition on mycelial growth were found to be in the order sucrose > yeast extract > peptone. The optimal concentration for mycelial growth was determined as 50 g l(-1) sucrose, 10 g l(-1) peptone and 3 g l(-1) yeast extract. CONCLUSIONS: Under optimal culture conditions, over 22 g l(-1) of mycelial biomass could be obtained after 40 days in submerged cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: Cordyceps sinensis, one of the most valued medicinal fungi, is shown to grow in axenic culture. This is the first report on nutritional requirements and design of a simplified semi-synthetic medium for mycelial growth of this psychrophilic species, which grows slowly below 20 degrees C. The results of this study will facilitate research on mass production of the fungus under defined culture conditions.     

蛹虫草蓝光诱导两步法发酵产类胡萝卜素

采用黑暗摇瓶发酵和蓝光照射静置培养的两步培养法,进行蛹虫草(Cordyceps militaris L.)液体发酵产类胡萝卜素的蓝光诱导。结果表明蛹虫草在2d的黑暗培养和5d的蓝光照射静置培养后,其类胡萝卜素的含量可达到最高值558.4μg/gFW。而以黑暗摇瓶培养2d后,进行不同时间的蓝光照射静置培养。结果表明,蓝光照射最初2d,蛹虫草类胡萝卜素含量变化不明显,随后快速增加,并在第5天达到最大值558.4μg/gFW,随后类胡萝卜素的含量并无明显变化。通过研究解决了蛹虫草液体发酵产类胡萝卜素的培养过程中蓝光的给光问题。     

Optimization of submerged culture process for the production of mycelial biomass and exo-polysaccharides by Cordyceps militaris C738

AIMS: The objective of the present study was to determine the optimal culture conditions for mycelial biomass and exo-polysaccharide (EPS) by Cordyceps militaris C738 in submerged culture. METHODS AND RESULTS: The optimal temperatures for mycelial biomass and EPS production were 20 degrees C and 25 degrees C, respectively, and corresponding optimal initial pHs were found to be 9 and 6, respectively. The suggested medium composition for EPS production was as follows: 6% (w/v) sucrose, 1% (w/v) polypeptone, and 0.05% (w/v) K2HPO4. The influence of pH on the fermentation broth rheology, morphology and EPS production of C. militaris C738 was carried out in a 5-l stirred-tank fermenter. The morphological properties were comparatively characterized by pellet roughness and compactness by use of image analyser between the culture conditions with and without pH control. The roughness and compactness of the pellets indicated higher values at pH-stat culture (pH 6.0), suggesting that larger and more compact pellets were desirable for polysaccharide production (0.91 g g(-1) cell d(-1). CONCLUSIONS: Under the optimized culture conditions (with pH control at 6), the maximum concentration of biomass and EPS were 12.7 g l(-1) and 7.3 g l(-1), respectively, in a 5-l stirred-tank fermenter. SIGNIFICANCE AND IMPACT OF THE STUDY: The critical effect of pH on fungal morphology and rheology presented in this study can be widely applied to other mushroom fermentation processes.     

Optimization of submerged culture condition for the production of mycelial biomass and exopolysaccharides by Agrocybe cylindracea

The optimization of submerged culture conditions and nutritional requirements was studied for the production of exopolysaccharide (EPS) from Agrocybe cylindracea ASI-9002 using the statistically based experimental design in a shake flask culture. Both maximum mycelial biomass and EPS were observed at 25 degrees C. The optimal initial pH for the production of mycelial biomass and EPS were found to be pH 4.0 and pH 6.0, respectively. Subsequently, optimum concentration of each medium component was determined using the orthogonal matrix method. The optimal combination of the media constituents for mycelial growth was as follows: maltose 80 g/l, Martone A-1 6 g/l, MgSO4 x 7H2O 1.4 g/l, and CaCl2 1.1 g/l; for EPS production: maltose 60 g/l, Martone A-1 6 g/l, MgSO4 x 7H2O 0.9 g/l, and CaCl2 1.1 g/l. Under the optimal culture condition, the maximum EPS concentration achieved in a 5-l stirred-tank bioreactor indicated 3.0 g/l, which is about three times higher than that at the basal medium.     

Production of red pigment by submerged culture of Paecilomyces sinclairii

AIMS: From a survey of submerged culture of edible mushrooms, a high pigment-producing fungus Paecilomyces sinclairii was selected and its optimal culture conditions investigated. METHODS AND RESULTS: The optimal culture conditions for pigment production were as follows: inoculum age, 3 d; temperature, 25 degrees C; initial pH, 6.0; carbon source, 1.5% (w/v) soluble starch; nitrogen source, 1.5% (w/v) meat peptone. Although addition of 10 mmol l(-1) CaCl2 to the culture medium slightly increased pigment production, most of the bio-elements examined had no notable or detrimental effect on pigment production. CONCLUSIONS: Under the optimal conditions obtained in the flask culture tested, a ninefold increase in pigment production (4.4 g l(-1)) was achieved using a 5(-l) batch fermenter. Paecilomyces sinclairii secreted water-soluble red pigment into the culture medium. The pigment colour was strongly dependent on the pH of the solution: red at pH 3-4, violet at pH 5-9 and pink at pH 10-12. SIGNIFICANCE AND IMPACT OF THE STUDY: The high concentration of pigment (4.4 g l(-1)) produced by P. sinclairii demonstrates the possibility of commercial production of pigment by this strain, considering its relatively high production yield and light stability.     

Exopolysaccharide production and mycelial growth in an air-lift bioreactor using Fomitopsis pinicola

For effective exopolysaccharide production and mycelial growth by a liquid culture of Fomitopsis pinicola in an air-lift bioreactor, the culture temperature, pH, carbon source, nitrogen source, and mineral source were initially investigated in a flask. The optimal temperature and pH for mycelial growth and exopolysaccharide production were 25degrees C and 6.0, respectively. Among the various carbon sources tested, glucose was found to be the most suitable carbon source. In particular, the maximum mycelial growth and exopolysaccharide production were achieved in 4% glucose. The best nitrogen sources were yeast extract and malt extract. The optimal concentrations of yeast extract and malt extract were 0.5 and 0.1%, respectively. K2HPO4 and MgSO4 x 7H2O were found to be the best mineral sources for mycelial growth and exopolysaccharide production. In order to investigate the effect of aeration on mycelial growth and exopolysaccharide production in an air-lift bioreactor, various aerations were tested for 8 days. The maximum mycelial growth and exopolysaccharide production were 7.9 g/l and 2.6 g/l, respectively, at 1.5 vvm of aeration. In addition, a batch culture in an air-lift bioreactor was carried out for 11 days under the optimal conditions. The maximum mycelial growth was 10.4 g/l, which was approximately 1.7-fold higher than that of basal medium. The exopolysaccharide production was increased with increased culture time. The maximum concentration of exopolysaccharide was 4.4 g/l, which was about 3.3-fold higher than that of basal medium. These results indicate that exopolysaccharide production increased in parallel with the growth of mycelium, and also show that product formation is associated with mycelial growth. The developed model in an air-lift bioreactor showed good agreement with experimental data and simulated results on mycelial growth and exopolysaccharide production in the culture of F pinicola.     

Optimization of culture conditions and medium components for the production of mycelial biomass and exo-polysaccharides with Cordyceps militaris in liquid culture

Both crude exo-biopolymers and mycelial biomass, produced by liquid culture of Cordyceps species, are believed to possess several potential health benefits. As a result of its known biological activities, Cordyceps militaris has been extensively characterized in regards to potential medicinal applications. However, optimized liquid culture conditions for enhanced polysaccharide productivity have yet to be developed, which is a necessary step for industrial applications. Therefore, in this study, the liquid culture conditions were optimized for maximal production of mycelial biomass and exo-polysaccharide (EPS) by C. militaris. The effects of medium composition, environmental factors, and C/N ratio were investigated. Among these variables 80 g, glucose; 10 g, yeast extract; 0.5 g, MgSO₄·7H₂O; and 0.5 g, KH₂PO₄ in 1 L distilled water were found to be the most suitable carbon, nitrogen, and mineral sources, respectively. The optimal temperature, initial pH, agitation, and aeration were determined to be 24°C, uncontrolled pH, 200 rpm, and 1.5 vvm, respectively. Under these optimal conditions, mycelial growth in shake flask cultures and 5 L jar bioreactors was 29.43 and 40.60 g/L, respectively, and polysaccharide production in shake flask cultures and 5 L jar bioreactors was 2.53 and 6.74 g/L, respectively.     

Utilization of chicory roots for microbial endoinulinase production

AIMS: The optimal culture conditions for endoinulinase production using chicory roots were studied in shake-flask culture. METHODS AND RESULTS: Much higher enzyme production was achieved with Xanthomonas sp. (15 U ml(-1)) than with Pseudomonas sp. (3 U ml(-1)). Optimized culture conditions of Xanthomonas sp. for endoinulinase production in flask culture were: chicory powder, 5 g l(-1); temperature, 37 degrees C; pH, 7.0; agitation speed, 100 rev min(-1). CONCLUSION: Maximum bacterial growth and enzyme production were 6.2 g l(-1) and 20 U ml(-1) under optimal conditions, respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: Chicory roots could be used as a fermentation substrate for the production of enndoinulinase.     

Effect of chemical and physical parameters on the production of L-asparaginase from a newly isolated Serratia marcescens SK-07

Aims: The objective of this study is to optimize the levels of carbon and nitrogen sources of the medium in shake flask experiments and evaluate the effect of pH and dissolved oxygen (DO) on the production of l ‐asparaginase from a newly isolated Serratia marcescens SK‐07 in a batch bioreactor. Methods and Results: Central composite rotatable design (CCRD) was applied to optimize the levels of carbon and nitrogen sources of the medium in shake flask experiments. The optimal levels of l ‐asparagine, glucose, yeast extract and peptone were found to be 4·93, 3·81, 3·65 and 1·47 g l^?1, respectively, and maximal l ‐asparaginase production of 25·02 U mg^?1 was obtained under these conditions. Among the carbon sources tested, l ‐asparagine was identified to be the most favourable carbon source for enhanced production of l ‐asparaginase. The maximum l ‐asparaginase production of 29·89 U mg^?1 was achieved in a batch bioreactor at initial pH of 6·5 (uncontrolled) and DO level of 40% in the culture. Conclusions: We have isolated, screened and identified the potential micro‐organism, S. marcescens, for the production of l ‐asparaginase. An overall 5·55‐fold increase in the production was achieved under optimal levels of carbon and nitrogen sources, DO level and at initial pH of 6·5 (uncontrolled). Significance and Impact of the Study: The experiments illustrate the importance of statistical method for optimization of carbon and nitrogen sources and study the effect of physical process parameters on the production of l ‐asparaginase in shake flask and bioreactor, respectively. This study would be helpful for bioprocess development of bacterial l ‐asparaginase production.     

Optimisation of submerged culture conditions for the production of mycelial biomass and exopolysaccharide byPleurotus nebrodensis

The optimisation of submerged culture conditions and nutritional requirements was studied for the production of exopolysaccharide (EPS) fromPleurotus nebrodensis. The optimal temperature and initial pH for both mycelial growth and EPS production in shake flask cultures were 25 °C and 8.0, respectively. Maltose was found the most suitable carbon source for both mycelial biomass and EPS production. Yeast extract was favourable nitrogen source for both mycelial biomass and EPS production. Optimum concentration of each medium component was determined using the orthogonal matrix method. The optimal combination of the media constituents for mycelial growth and EPS production was as follows: 200 g l^?1 bran, 25 g l^?1 maltose, 3 g l^?1 yeast extract, 1 g l^?1 KH₂PO₄, 1 g l^?1 MgSO₄ 7H₂O. Under the optimal conditions, the mycelial biomass (4.13 g l^?1) and EPS content (2.40 g l^?1) ofPleurotus nebrodensis was 2.3 and 3.6 times compared to the control with basal medium respectively.     

Effects of culture conditions on the mycelial growth and bioactive metabolite production in submerged culture of Cordyceps militaris

The influence of initial pH value, various nitrogen sources, plant oils, and modes of propagation (shake-flask and static culture) on the production of biomass, exopolysaccharide (EPS), adenosine and, in particular, cordycepin, by Cordyceps militaris CCRC 32219 were investigated. Optimal conditions for mycelial growth, EPS and cordycepin production were observed at relatively low pH. Amongst organic sources, yeast extract (YE) was favorable for EPS and cordycepin production, while corn steep powder (CSP) was favorable for adenosine production. A lower C/N ratio was favorable for adenosine and cordycepin production; however, too low a C/N ratio led to diminished production. All plant oils tested stimulate mycelial growth and EPS production of C. militaris, but they did not show much effect on the adenosine and cordycepin production. A two-stage fermentation process by combining shake-flask fermentation with static culture significantly enhanced cordycepin production. A Box–Behnken experimental design was employed to optimize the production of cordycepin, which showed that the optimum conditions to produce cordycepin by C. militaris CCRC 32219 were at pH 6, YE concentration of 45 g/l and 8.0 day of the shake culture followed by 16 days of the static culture. Under the optimized conditions, the maximum production (2214.5 mg/l) of cordycepin was obtained, which is much higher than those reported up to date.     

蛹虫草液体培养条件优化及有效成分含量分析

为优化蛹虫草菌的液体培养条件,对蛹虫草菌丝体进行液体摇瓶培养。以干菌丝体得率为指标,对影响发酵产量的重要因子设计正交试验,得出最佳培养条件。在最优条件下扩大培养,检测此时菌丝体中虫草素及虫草多糖含量。结果表明:蛹虫草菌丝体液体发酵的最适条件为:接种量10 % (v/v) ,发酵初始pH7 0 ,发酵温度2 7℃,发酵时间96h。扩大培养后,测得菌丝体中虫草素的含量为5 1 785mg/10 0g ,虫草精多糖含量为1 92g/10 0g。