Abstract
The kinetics of growth and α-amylase production of a novel Candida wangnamkhiaoensis yeast strain were studied in single-stage steady-state continuous cultures. This was performed in a split-cylinder internal-loop airlift bioreactor, using a variety of carbon sources as fermentation substrates. Results showed that the steady-state yields of cell mass from carbohydrates were practically constant for the range of dilution rates assayed, equaling 0.535 ± 0.030, 0.456 ± 0.033, and 0.491 ± 0.035 g biomass/g carbohydrate, when glucose, maltose, and starch, respectively were used as carbon sources. No α-amylase activity was detected when glucose was used as the carbon source in the influent medium, indicating that α-amylase synthesis of C. wangnamkhiaoensis is catabolically repressed by glucose. Contrastingly, maltose and starch induce synthesis of α-amylase in C. wangnamkhiaoensis, with starch being the best α-amylase inducer. The highest α-amylase volumetric and specific activities (58400 ± 800 U/L and 16900 ± 200 U/g biomass, respectively), and productivities (14000 ± 200 U/L·h and 4050 ± 60 U/g biomass·h, respectively) were achieved at a dilution rate of 0.24 h-1 using starch as the carbon source. In conclusion, single-stage steady-state continuous culture in an airlift bioreactor represents a powerful tool, both for studying the regulatory mechanisms of α-amylase synthesis by C. wangnamkhiaoensis and for α-amylase production. Furthermore, results showed that C. wangnamkhiaoensis represents a potential yeast species for the biotechnological production of α-amylase, which can be used for the saccharification of starch. This offers an attractive renewable resource for the production of biofuels (particularly bioethanol), representing an alternative to fossil fuels with reduced cost of substrates.
Highlights
IntroductionAmylases (α, β, and γ) are among the most versatile and important families of enzymes that have numerous biotechnological applications [1,2]
Yeasts offer several advantages for the commercial production of amylases, including: their easier cultivation, higher specific growth rate and shorter generation time than filamentous fungi ensure more productivity. Because of their GRAS status, their products are safe for human consumption, and yeasts are commonly deemed superior to bacteria in terms of their extracellular products
This work studied the regulatory mechanisms of α-amylase synthesis and the growth and αamylase production kinetics of C. wangnamkhiaoensis in single-stage steady-state continuous cultures in a split-cylinder internal-loop airlift bioreactor
Summary
Amylases (α, β, and γ) are among the most versatile and important families of enzymes that have numerous biotechnological applications [1,2]. Α-amylases can be obtained from several sources, such as animals, plants, and microorganisms, most industrial applications use microbial α-amylases, mainly from bacteria and filamentous fungi [5]. Yeasts offer several advantages for the commercial production of amylases, including: their easier cultivation, higher specific growth rate and shorter generation time than filamentous fungi ensure more productivity. Because of their GRAS (generally regarded as safe) status, their products are safe for human consumption, and yeasts are commonly deemed superior to bacteria in terms of their extracellular products. Enzymes-derived from yeast tend to be more economically relevant than enzymes derived from other sources [6–10]
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