Abstract
BackgroundEthanol production from non-crop materials, such as Jerusalem artichokes, would make a great contribution to the energy industry. The non-conventional yeast, Kluyveromyces marxianus, is able to carry out ethanol fermentation of sugar molecules obtained from inulin-containing materials by consolidated bioprocessing. Lower inulin concentrations and micro-aeration can lead to a relatively fast and ideal fermentation process; however, it is unclear what causes the inhibition of higher concentrations of inulin and the promotion effect of aeration.ResultsNext-generation sequencing technology was used to study the global transcriptional response of K. marxianus Y179 under three fermentation conditions, including 120 g/L inulin without aeration (120-N), 230 g/L inulin without aeration (230-N), 230 g/L inulin with aeration by ORP controlling at −130 mV (230-130mV). A total of 35.55 million clean reads were generated from three samples, of which 4,820 predicted that open reading frames were annotated. For differential expression analysis, 950 and 1,452 differentially expressed genes were discovered under the conditions of 230-130mV and 120-N, respectively, and the sample 230-N was used as the control. These genes are mainly associated with the pathways of central carbon metabolism and ethanol formation. Increased expression of inulinase and the low activity of the autophagy-related gene, ATG8, ensured fast and ideal fermentation processes.ConclusionsDespite being reported as the “crabtree-negative” species, K. marxianus Y179 could achieve favorable ethanol fermentation profiles under micro-aeration and high inulin concentrations. K. marxianus Y179 cells responded to inulin concentrations and micro-aeration that is involved in the whole ethanol metabolism network. These results will serve as an important foundation for further exploration of the regulatory mechanisms involved in ethanol fermentation from inulin by consolidated bioprocessing and also provide a valuable reference for future studies on optimization and reconstruction of the metabolism network in K. marxianus.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0295-y) contains supplementary material, which is available to authorized users.
Highlights
Ethanol production from non-crop materials, such as Jerusalem artichokes, would make a great contribution to the energy industry
Physiological diversity for ethanol fermentation among various K. marxianus strains Though S. cerevisiae has been widely applied in industrial ethanol production, K. marxianus is attracting an increasing amount of attention for its specific physiological diversity
K. marxianus was known to have a poor ethanol tolerance compared to S. cerevisiae [12], the maximum ethanol concentration for K. marxianus fermentation broth is more than 100 g/L
Summary
Ethanol production from non-crop materials, such as Jerusalem artichokes, would make a great contribution to the energy industry. The non-conventional yeast, Kluyveromyces marxianus, is able to carry out ethanol fermentation of sugar molecules obtained from inulin-containing materials by consolidated bioprocessing. Lower inulin concentrations and micro-aeration can lead to a relatively fast and ideal fermentation process; it is unclear what causes the inhibition of higher concentrations of inulin and the promotion effect of aeration. The previous results of ethanol fermentation from the inulin of Jerusalem artichokes showed some problems under high inulin concentration conditions, such as residual inulin and a long fermentative time [7]. These problems did not happen under micro-aeration or lower inulin concentration conditions (our unpublished data). The molecular mechanisms of the inhibition of higher inulin concentrations and the effects of aeration are still unclear
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