David E. Block, Ph. D.
Professor and Marvin Sands Department Chair
Viticulture and Enology
B.S., 1986, University of Pennsylvania
Ph.D., 1992, University of Minnesota
Elucidating Ethanol Tolerance Mechanisms in Yeast
Stuck and sluggish alcoholic fermentations are an important problem in both the wine and biofuel industries. Many times, microbial strains with desirable traits such as flavor qualities (in the wine industry) or the ability to use both five- and six-carbon sugars (in the biofuels industry) are less ethanol tolerant. Therefore, it is our goal to understand the fundamental basis of alcohol tolerance in yeast and bacteria so that this tolerance can be increased in otherwise desirable production strains. Early on in our modeling of this system, it appeared that inactivation of yeast (i.e. lack of tolerance) could be a result of the composition and structure of the lipid bilayer composing the cell membrane. This hypothesis led to a collaboration with Prof. M. Longo in CEMS at UC Davis to examine potential physical effects of ethanol on the lipid bilayer found in the cell membrane. Studies from this work gave strong evidence that this could, in fact, be the case. Further, these studies pointed to the phenomenon of membrane bilayer interdigitation (complete overlap of the fatty acid side chains) as potentially responsible for physiological behavior of yeast in response to alcohol. This led to a larger collaborative effort to evaluate the influence of membrane composition on alcohol tolerance in Saccharomyces yeast. As part of this project, we developed a high-resolution liquid chromatography/mass spectrometer (LC/MS) method for identifying and quantifying membrane composition in microbes and relating this composition to ethanol tolerance. This has allowed us to assess the lipid composition in a range of 25 industrial Saccharomyces strains during alcoholic fermentation. As these strains had varying alcohol tolerance levels, we were able to use the data to show that there are likely to be two complementary mechanisms for alcohol tolerance, higher tolerance per cell and higher maximum cell concentration during fermentation. Our data show that both of these mechanisms are related to membrane composition. We have now expanded this work to include metabolomics measurements during alcoholic fermentations and are working toward a metabolic model to incorporate this knowledge.
Wine Process Optimization
Our group also works in the general area of wine process optimization. For example, we have worked toward measuring and understanding the effects of filtration, including sterile membrane filtration, depth filters, and crossflow filtration, on the sensory and chemical characteristics of wine. We initiated this project because there is a wide-spread idea in the wine industry and popular wine press that filtration may negatively affect wine quality. However, the pore size of even sterile membranes should not filter out molecules with sensory impact. We continue to work on these projects in conjunction with Prof. Hildegarde Heymann, focusing also on the sensory impact of pumping and bottling practices. We also are working on a series of projects (with Anita Oberholster, and Doug Adams, among other V&E collaborators and collaborators at E&J Gallo) to try to understand cap extraction in red wine fermentations. Red wines are fermented with grape skins in order to extract color, tannins, and other flavor impact molecules. During the fermentation, the skins float to the top of the fermentation and form a “cap.” The mechanisms of extraction from this cap are not well understood, nor are the influence of temperature and ethanol concentrations. It is clear, however, that red wine fermentations present a heterogeneous environment that complicate this analysis. We are working on experiments from bench-scale through pilot scale to understand the underlying phenomena.
Conversion of Lignocellulosic Waste into Value Added Products
In collaboration with Prof. Bruce Gates in Chemical Engineering and Materials Science at UC Davis, we are examining the conversion of prototypical molecules found in biomass pyrolysis oils (produced from agricultural lignocellulosic waste) using commercially-available catalysts such as zeolites, supported metals, and bifunctional catalysts. Initially, our work focused on removing the oxygen from these molecules to make them better and more stable fuels. However, the scope of the work grew to include production of high-value chemical intermediates as well. We have used the approach of low conversion plug flow reactors (gas over solid catalyst) to examine conversion of single prototypical bio-oil components. Using our analytical tools, we have been able to elucidate reaction mechanisms for several of the lignin-derived compounds including anisole, 4-methylanisole, guaiacol, cyclohexanone, and eugenol. We have also begun to approximate the kinetics for these reactions, in some cases for multiple catalysts. We are working on a compounds derived from sugars as well, including furan and butanone and have begun to look at binary combinations of reactants. These types of studies are necessary precursors to scale-up and commercialization of the important routes of biomass to fuels.
C. M. Henderson and D. E. Block. “Examining the role of membrane lipid composition in determining ethanol tolerance in Saccharomyces cerevisiae,” Appl. Environ. Microbiol. (In Press).
T. Nimmanwudipong, R. C. Runnebaum, K. C. Brodwater, J. Heelan, D. E. Block, and B. C. Gates, “Design of a High-Pressure Flow-Reactor System for Catalytic Hydrogenation: Guaiacol Conversion Catalyzed by Platinum Supported on MgO,” Energy & Fuels, 28, 1090-1096 (2014).
C. M. Henderson, W. Zeno, L. Lerno, M. Longo, D. E. Block, “Fermentation Temperature Modulates Phosphatidylethanolamine and Phosphatidylinositol Levels in the Cell Membrane of Saccharomyces cerevisiae,” Appl. Environ. Microbiol., 79, 5345-5356 (2013).
C. M. Henderson, M. Lozada-Contreras, V. Jiranek, M. Longo, D. E. Block, “Ethanol Production and Maximum Cell Growth Are Highly Correlated with Membrane Lipid Composition during Fermentation as Determined by Lipidomic Analysis of 22 Saccharomyces cerevisiae Strains,” Appl. Environ. Microbiol., 79, 91-104 (2013).
D. Garrido, S. Ruiz-Moyano, R. Jimenez-Espinoza, H. J. Eom, D. E. Block, and D. A. Mills. “Utilization of galactooligosaccharides by Bifidobacterium longum subsp. infantis isolates.” Food Microbiol., 33, 262-70 (2013).
T. Nimmanwudipong, C. Aydin, J. Lu, R. C. Runnebaum, K. C. Brodwater, N. D. Browning, D. E. Block, and B. C. Gates, “Selective Hydrodeoxygenation of Guaiacol Catalyzed by Platinum Supported on Magnesium Oxide,” Catalysis Letters, 142, 1190-1196 (2012).
R. C. Runnebaum, T. Nimmanwudipong, J. Doan, D. E. Block, and B. C. Gates, “Catalytic Conversion of Furan to Gasoline-Range Aliphatic Hydrocarbons via Ring Opening and Decarbonylation Reactions Catalyzed by Pt/gamma-Al2O3,” Catalysis Letters, 142, 664-666 (2012).
T. Nimmanwudipong, R. C. Runnebaum, S. E. Ebeler, D. E. Block, B. C. Gates, “Upgrading of Lignin-Derived Compounds: Reactions of Eugenol Catalyzed by HY Zeolite and Pt/γ-Al2O3,” Catal. Lett, 142, 151-160 (2012).
R. C. Runnebaum, T. Nimmanwudipong, R.R. Limbo, D. E. Block, B. C. Gates, “Conversion of 4-Methylanisole Catalyzed by Pt/γ-Al2O3 and by Pt/SiO2-Al2O3: Reaction Networks and Evidence of Oxygen Removal,” Catal. Lett, 142, 7-15 (2012).
R. C. Runnebaum, T. Nimmanwudipong, D. E. Block, B. C. Gates, “Catalytic Conversion of Compounds Representative of Lignin-derived Bio-oils: A Reaction Network for Guaiacol, Anisole, 4-Methylanisole, and Cyclohexanone Conversion Catalysed by Pt/γ-Al2O3,” Catal. Sci. Technol., 2, 113-118 (2012).
C. M. Henderson, M. Lozada-Contreras, Y. Naravane, M. L. Longo, and D. E. Block, “Analysis of Major Phospholipid Species and Ergosterol in Fermenting Industrial Yeast Strains Using Atmospheric Pressure Ionization Ion-Trap Mass Spectrometry,” Journal of Agricultural and Food Chemistry, 59, 12761-12770, 2011.
R. C. Runnebaum, R.J. Lobo-Lapidus, T. Nimmanwudipong, D. E. Block, B. C. Gates, “Conversion of Anisole Catalyzed by Platinum Supported on Alumina: The Reaction Network", Energy & Fuels, 25, 4776-4785 (2011).
T. Nimmanwudipong, R. C. Runnebaum, D. E. Block, B. C. Gates, “Catalytic Conversion of Guaiacol Catalyzed by Platinum Supported in Alumina: Reaction Network Including Hydrodeoxygenation Reactions”, Energy & Fuels, 25, 3417-3427 (2011).
T. Nimmanwudipong, R. C. Runnebaum, D. E. Block, B. C. Gates, “Cyclohexanone Conversion Catalyzed by Pt/γ-Al2O3: Evidence of Oxygen Removal and Coupling Reactions”, Catal. Lett, 141, 779–783 (2011).
R. C. Runnebaum, T. Nimmanwudipong, D. E. Block, B. C. Gates, “Catalytic Conversion of Anisole: Evidence of Oxygen Removal in Reactions with Hydrogen”, Catal. Lett, 141, 817–820 (2011).
T. Nimmanwudipong, R. C. Runnebaum, D. E. Block, B. C. Gates, “Catalytic Reactions of guaiacol: reaction network and Evidence of Oxygen Removal in Reactions with Hydrogen”, Catal. Lett, 141, 779–783 (2011).
Kim, J-H. D. E. Block and D. A. Mills. “Simultaneous consumption of pentose and hexose sugars: An optimal microbial phenotype for efficient fermentation of lignocellulosic biomass.” Applied Microbiology and Biotechnology, 88, 1077-1085, 2010.
Kim, J-H. D. E. Block, S. P. Shoemaker and D. A. Mills. “Atypical ethanol production by carbon catabolite derepressed lactobacilli.” BioResource Technology, 101: 8790-8797, 2010.
Marcobal, A., M. Barboza, J. Froehlich, D. E. Block, J. B. German, C. B. Lebrilla, and D. A. Mills. “Consumption of human milk oligosaccharides by gut-related microbes.” Journal of Agricultural and Food Chemistry, 58:5334-40, 2010.
Kim, J-H. D. E. Block, S. P. Shoemaker and D. A. Mills. “Conversion of rice straw to bio-based chemicals: an integrated process using Lactobacillus brevis.” Applied Microbiology and Biotechnology, 86:1375-1385, 2010.
Zhang, G. and D.E. Block. “Using Highly Efficient Nonlinear Experimental Design Methods for Optimization of Lactococcus lactis Fermentation in Chemically Defined Media.” Biotechnology Progress, 25:1587-1597, 2010.
Oddone, G.M., D.A. Mills, and D.E. Block. “A Dynamic, Genome-Scale Flux Model of Lactococcus lactis to Increase Specific Recombinant Protein Expression.” Metabolic Engineering, 11:367-381, 2009.