title: Controlling microbial contamination during hydrolysis of AFEX-pretreated corn stover and switchgrass: effects on hydrolysate composition, microbial response and fermentation.
abstract: BACKGROUND
  Microbial conversion of lignocellulosic feedstocks into biofuels remains an attractive means to produce sustainable energy. It is essential to produce lignocellulosic hydrolysates in a consistent manner in order to study microbial performance in different feedstock hydrolysates. Because of the potential to introduce microbial contamination from the untreated biomass or at various points during the process, it can be difficult to control sterility during hydrolysate production. In this study, we compared hydrolysates produced from AFEX-pretreated corn stover and switchgrass using two different methods to control contamination: either by autoclaving the pretreated feedstocks prior to enzymatic hydrolysis, or by introducing antibiotics during the hydrolysis of non-autoclaved feedstocks. We then performed extensive chemical analysis, chemical genomics, and comparative fermentations to evaluate any differences between these two different methods used for producing corn stover and switchgrass hydrolysates.
  
  
  RESULTS
  Autoclaving the pretreated feedstocks could eliminate the contamination for a variety of feedstocks, whereas the antibiotic gentamicin was unable to control contamination consistently during hydrolysis. Compared to the addition of gentamicin, autoclaving of biomass before hydrolysis had a minimal effect on mineral concentrations, and showed no significant effect on the two major sugars (glucose and xylose) found in these hydrolysates. However, autoclaving elevated the concentration of some furanic and phenolic compounds. Chemical genomics analyses using Saccharomyces cerevisiae strains indicated a high correlation between the AFEX-pretreated hydrolysates produced using these two methods within the same feedstock, indicating minimal differences between the autoclaving and antibiotic methods. Comparative fermentations with S. cerevisiae and Zymomonas mobilis also showed that autoclaving the AFEX-pretreated feedstocks had no significant effects on microbial performance in these hydrolysates.
  
  
  CONCLUSIONS
  Our results showed that autoclaving the pretreated feedstocks offered advantages over the addition of antibiotics for hydrolysate production. The autoclaving method produced a more consistent quality of hydrolysate, and also showed negligible effects on microbial performance. Although the levels of some of the lignocellulose degradation inhibitors were elevated by autoclaving the feedstocks prior to enzymatic hydrolysis, no significant effects on cell growth, sugar utilization, or ethanol production were seen during bacterial or yeast fermentations in hydrolysates produced using the two different methods.
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Serate
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Xie
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Pohlmann
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Donald
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI USA.
authors.forename: Mahboubeh
authors.initials: M
authors.lastname: Shabani
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Li
authors.initials: L
authors.lastname: Hinchman
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Alan
authors.initials: A
authors.lastname: Higbee
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Mick
authors.initials: M
authors.lastname: Mcgee
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Alex
authors.initials: A
authors.lastname: La Reau
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Grace E
authors.initials: GE
authors.lastname: Klinger
authors.affiliation: RIKEN Center for Sustainable Resource Science, Wako, Saitama Japan.
authors.forename: Sheena
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Computer Science and Engineering, University of Minnesota-Twin Cities, Minneapolis, MN USA.
authors.forename: Chad L
authors.initials: CL
authors.lastname: Myers
authors.affiliation: Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: Boone
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Donna M
authors.initials: DM
authors.lastname: Bates
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI USA.
authors.forename: Dave
authors.initials: D
authors.lastname: Cavalier
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Dustin
authors.initials: D
authors.lastname: Eilert
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Oates
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Gregg
authors.initials: G
authors.lastname: Sanford
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Trey K
authors.initials: TK
authors.lastname: Sato
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI USA.
authors.forename: Bruce
authors.initials: B
authors.lastname: Dale
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Landick
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Jeff
authors.initials: J
authors.lastname: Piotrowski
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI USA.
authors.forename: Rebecca Garlock
authors.initials: RG
authors.lastname: Ong
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI USA.
authors.forename: Yaoping
authors.initials: Y
authors.lastname: Zhang
keywords: Biomass feedstock; Chemical genomics; Fermentation; Inhibitors; Lignocellulosic hydrolysate; Saccharomyces cerevisiae; Sterility; Zymomonas mobilis