Direct bioethanol production by amylolytic yeast Candida albicans

• Published in: Letters in applied microbiology Vol. 60; no. 3; pp. 229 - 236
• Main Authors: Aruna, A, Nagavalli, M, Girijashankar, V, Ponamgi, S.P.D, Swathisree, V, Venkateswar Rao, L
• Format: Journal Article
• Language: English
• Published: England Published for the Society for Applied Bacteriology by Blackwell Scientific Publications [c1985-] 01.03.2015; Oxford University Press
• Subjects: alpha-amylase; alpha-Amylases - genetics; alpha-Amylases - metabolism; bioethanol; bioethanol production; Biofuels; biomass; Candida albicans; Candida albicans - enzymology; Candida albicans - genetics; Cells, Immobilized; corn steep liquor; energy; ethanol; Ethanol - metabolism; ethanol production; ethidium; fermentation; Fermentation - physiology; fossil fuels; glucan 1,4-alpha-glucosidase; glucoamylase; Hydrolysis; maltose; Maltose - metabolism; mutagenesis; mutants; Mutation; octoxynol; optimization of fermentation; potato starch; secretion; sodium chloride; Solanum tuberosum - metabolism; starch; Starch - metabolism; ultraviolet radiation; yeasts; Zea mays - metabolism; Candida albicans; bioethanol production; mutagenesis; glucoamylase; optimization of fermentation
• ISSN: 0266-8254; 1472-765X
• DOI: 10.1111/lam.12348

An attempt was made to produce bioethanol using optimized fermentation parameters and mutationally improved strain of Candida albicans. The mutant strain OMC3E6 obtained by UV irradiation followed by ethidium bromide successive mutations showed 2·6 times more glucoamylase secretion and 1·5 times more bioethanol production via direct conversion of starch. Enhanced hydrolysis of insoluble starch (72%) and potato starch (70%) was achieved with glucoamylase enzyme preparation from mutant C. albicans. In fermentation medium, the use of maltose, corn steep liquor, NaH₂PO₄, NaCl + MgSO₄and Triton X‐100 has increased the glucoamylase production by the microbe. Under optimized conditions, C. albicans eventually produced 437 g ethanol kg⁻¹potatoes. Earlier reports mentioned the use of thrice the quantity of starch as reported by us followed by more fermentation period (3–4 days) and demanded pretreatment of starch sources with alpha‐amylase as well. Here, we simplified these three steps and obtained 73% conversion of insoluble starch into ethanol via direct conversion method in a period of 2 days without the involvement of cell immobilizations or enzyme pretreatment steps. SIGNIFICANCE AND IMPACT OF THE STUDY: Due to fast depletion of fossil fuels in the modern world, bioethanol usage as an alternate energy source is the need of the hour. For the first time, we report bioethanol production by Candida albicans via direct conversion of starchy biomass into ethanol along with enhanced starch‐hydrolysing capacity and ethanol conversion ratio. So far, C. albicans was dealt in the field of clinical pathology, but here we successfully employed this organism to produce bioethanol from starchy agri‐substrates. Optimizing fermentation parameters and improving the microbial strains through successive mutagenesis can improve the end product yield.