BackgroundBiopolymers have various applications in medicine, food and petroleum industries. The ascomycetous fungus Ophiocordyceps dipterigena BCC 2073 produces an exobiopolymer, a (1→3)-β-D-glucan, in low quantity under screening conditions. Optimization of O. dipterigena BCC 2073 exobiopolymer production using experimental designs, a scale-up in 5 liter bioreactor, analysis of molecular weight at different cultivation times, and levels of induction of interleukin-8 synthesis are described in this study.ResultsIn order to improve and certify the productivity of this strain, a sequential approach of 4 steps was followed. The first step was the qualitative selection of the most appropriate carbon and nitrogen sources (general factorial design) and the second step was quantitative optimization of 5 physiological factors (fractional factorial design). The best carbon and nitrogen source was glucose and malt extract respectively. From an initial production of 2.53 g·L-1, over 13 g·L-1 could be obtained in flasks under the improved conditions (5-fold increase). The third step was cultivation in a 5 L bioreactor, which produced a specific growth rate, biomass yield, exobiopolymer yield and exobiopolymer production rate of 0.014 h-1, 0.32 g·g-1 glucose, 2.95 g·g biomass-1 (1.31 g·g-1 sugar), and 0.65 g.(L·d)-1, respectively. A maximum yield of 41.2 g·L-1 was obtained after 377 h, a dramatic improvement in comparison to the initial production. In the last step, the basic characteristics of the biopolymer were determined. The molecular weight of the polymer was in the range of 6.3 × 105 - 7.7 × 105 Da. The exobiopolymer, at 50 and 100. μg·mL-1, induced synthesis in normal dermal human fibroblasts of 2227 and 3363 pg·mL-1 interleukin-8 respectively.ConclusionsHigh exobiopolymer yield produced by O. dipterigena BCC 2073 after optimization by qualitative and quantitative methods is attractive for various applications. It induced high IL-8 production by normal dermal fibroblasts, which makes it promising for application as wound healing material. However, there are still other possible applications for this biopolymer, such as an alternative source of biopolymer substitute for hyaluronic acid, which is costly, as a thickening agent in the cosmetic industry due to its high viscosity property, as a moisturizer, and in encapsulation.

Optimization of exopolysaccharides (EPS) produced by three strains of entomopathogenic fungi (Beauveria bassiana BCC 2692, Ophiocordyceps dipterigena BCC 2073, and Paecilomyces tenuipes BCC 2656) was carried out together with analyses of their prebiotic properties. B. bassiana BCC 2692 produced 6.27±0.22 g/L EPS on optimal medium using two-level fractional factorial design and 4.7 g/L EPS in bioreactor. EPS productions of O. dipterigena BCC 2073 were 13.2 g/L and 41.2 g/L in shake flask and bioreactor, respectively. For P. tenuipes BCC 2656, 1.47±0.21 g/L EPS in shake flask and 28.1 g/L EPS in bioreactor were obtained. These EPS were previously characterized as glucan with differences in molecular weights and degree of branching. They were resistant to hydrolysis by both hydrochloric acid and porcine pancreatic α-amylase. Furthermore, when used as the sole carbon source, all three types of EPS supported growth in vitro of two different probiotic bacteria (Lactobacillus acidophilus BCC 13839 and bifid bacterium animals ATCC 25527). A constant viability of L. acidophilus BCC 13839 was maintained throughout the cultivation period (48 hours) on all three entomopatogenic fungal EPS. All EPS also supported better growth and maintained longer growth period of B. animalis ATCC 25527 than glucose or inulin. Thus these entomopathogenic fungi EPS are promising candidates in prebiotic industry, expanding the pool of current commercial prebiotics.