Screening of transporters to improve xylodextrin utilization in the yeast Saccharomyces cerevisiae

Abstract

The economic production of cellulosic biofuel requires efficient and full utilization of all abundant carbohydrates naturally released from plant biomass by enzyme cocktails. Recently, we reconstituted the Neurospora crassa xylodextrin transport and consumption system in Saccharomyces cerevisiae, enabling growth of yeast on xylodextrins aerobically. However, the consumption rate of xylodextrin requires improvement for industrial applications, including consumption in anaerobic conditions. As a first step in this improvement, we report analysis of orthologues of the N. crassa transporters CDT-1 and CDT-2. Transporter ST16 from Trichoderma virens enables faster aerobic growth of S. cerevisiae on xylodextrins compared to CDT-2. ST16 is a xylodextrin-specific transporter, and the xylobiose transport activity of ST16 is not inhibited by cellobiose. Other transporters identified in the screen also enable growth on xylodextrins including xylotriose. Taken together, these results indicate that multiple transporters might prove useful to improve xylodextrin utilization in S. cerevisiae. Efforts to use directed evolution to improve ST16 from a chromosomally-integrated copy were not successful, due to background growth of yeast on other carbon sources present in the selection medium. Future experiments will require increasing the baseline growth rate of the yeast population on xylodextrins, to ensure that the selective pressure exerted on xylodextrin transport can lead to isolation of improved xylodextrin transporters.

Crosstalk of Cellulose and Mannan Perception Pathways Leads to Inhibition of Cellulase Production in Several Filamentous Fungi

“…The S. cerevisiae strain used in this study was D452-2 transformed with pRS316- CDT1 or pRS316- CDT2 (66). The strain was grown as described previously (48).…”

“…For the yeast cell-based uptake, yeast strain D452-2 cells transformed with pRS316- CDT1 or pRS316- CDT2 (66) were used. Uptake assays in S.…”

Xylo-Oligosaccharide Utilization by Engineered Saccharomyces cerevisiae to Produce Ethanol

“…The success of these strategies enables new perspectives on the carbon-source range assimilated by S. cerevisiae to be considered. Since xylose assimilation by engineered S. cerevisiae strains has become well-established, new approaches have been adopted to enable S. cerevisiae to consume XOS instead of xylose and glucose ( La Grange et al, 2000 , 2001 ; Fujita et al, 2002 ; Qian et al, 2003 ; Katahira et al, 2004 ; Lee et al, 2009 ; Sun et al, 2012 ; Li et al, 2015 ; dos Reis et al, 2016 ; Sekar et al, 2016 ; Zhang et al, 2017a ). Scientific interest in this field is increasing steadily, but still much must be done to obtain an efficient XOS-consuming S. cerevisiae strain.…”

Enhancing the Co-utilization of Biomass-Derived Mixed Sugars by Yeasts

“…Reconstituting this pathway in S. cerevisiae enabled slow cell growth on xylodextrin. An ortholog of N. crassa xylodextrin transporter, ST16 from Trichoderma virens , enabled S. cerevisiae to grow more rapidly on xylodextrins as sole carbon source (Zhang et al, 2017). Moreover, ST16 was not subjected to cellobiose inhibition, making it a promising candidate for the co-fermentation of cellobiose and xylodextrins.…”