One-pot bioethanol production from cellulose by co-culture of Acremonium cellulolyticus and Saccharomyces cerevisiae

Abstract

BackgroundWhile the ethanol production from biomass by consolidated bioprocess (CBP) is considered to be the most ideal process, simultaneous saccharification and fermentation (SSF) is the most appropriate strategy in practice. In this study, one-pot bioethanol production, including cellulase production, saccharification of cellulose, and ethanol production, was investigated for the conversion of biomass to biofuel by co-culture of two different microorganisms such as a hyper cellulase producer, Acremonium cellulolyticus C-1 and an ethanol producer Saccharomyces cerevisiae. Furthermore, the operational conditions of the one-pot process were evaluated for maximizing ethanol concentration from cellulose in a single reactor.ResultsEthanol production from cellulose was carried out in one-pot bioethanol production process. A. cellulolyticus C-1 and S. cerevisiae were co-cultured in a single reactor. Cellulase producing-medium supplemented with 2.5 g/l of yeast extract was used for productions of both cellulase and ethanol. Cellulase production was achieved by A. cellulolyticus C-1 using Solka-Floc (SF) as a cellulase-inducing substrate. Subsequently, ethanol was produced with addition of both 10%(v/v) of S. cerevisiae inoculum and SF at the culture time of 60 h. Dissolved oxygen levels were adjusted at higher than 20% during cellulase producing phase and at lower than 10% during ethanol producing phase. Cellulase activity remained 8–12 FPU/ml throughout the one-pot process. When 50–300 g SF/l was used in 500 ml Erlenmeyer flask scale, the ethanol concentration and yield based on initial SF were as 8.7–46.3 g/l and 0.15–0.18 (g ethanol/g SF), respectively. In 3-l fermentor with 50–300 g SF/l, the ethanol concentration and yield were 9.5–35.1 g/l with their yields of 0.12–0.19 (g/g) respectively, demonstrating that the one-pot bioethanol production is a reproducible process in a scale-up bioconversion of cellulose to ethanol.ConclusionA. cellulolyticus cells produce cellulase using SF. Subsequently, the produced cellulase saccharifies the SF, and then liberated reducing sugars are converted to ethanol by S. cerevisiae. These reactions were carried out in the one-pot process with two different microorganisms in a single reactor, which does require neither an addition of extraneous cellulase nor any pretreatment of cellulose. Collectively, the one-pot bioethanol production process with two different microorganisms could be an alternative strategy for a practical bioethanol production using biomass.

Production of cellulolytic enzymes from ascomycetes: Comparison of solid state and submerged fermentation

“…However the biological conversion of lignocellulose is still a much slower process than the enzymatic hydrolysis, especially the biological pretreatment of biomass is rate limiting [188]. For CBP, challenges also arise when aerobic microbes (ascomycetes) are used for cellulase production in combination with anaerobic fermentation by S. cerevisiae for bioethanol [189]. An onsite enzyme production applying a waste stream from a biorefinery setup as substrate might be just as economical and efficient as a CBP setup, especially with the many SSF bioreactor designs that enable the application of waste streams.…”

Transforming biomass conversion with ionic liquids: process intensification and the development of a high-gravity, one-pot process for the production of cellulosic ethanol

“…6 It was also reported that ethanol could be fermented from SolkaFloc (powdered cellulose) by using a co-culture in a one-pot process scheme. 7 A recent report used a mixture of acid-pretreated (i.e., HCl) and base-pretreated (NaOH) rice straw for ethanol production, but the pretreatment had to be conducted in different reactors. 8 Until now, the production of biofuels from lignocellulose using a one-pot conversion technology that includes pretreatment, saccharification, and fermentation has not been reported because of the significant technical challenges present.…”

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…Their results confirmed that all three Bacillus/yeast co-culture systems could achieve the cellulose saccharification and ethanol conversion simultaneously better than KR5 alone, and therefore, this microbial consortium could be of great potentials for integrating into a CBP system (Ho et al, 2012). Park et al (2012) developed co-culture system for one-pot bioethanol production, in which Acidothermus cellulolyticus C-1 and S. cerevisiae were co-cultured in a single reactor. After production of cellulase by A. cellulolyticus C-1, subsequently, S. cerevisiae was added to produce ethanol.…”