Systems and methods for producing biofuels and related materials

Abstract

Clostridium phytofermentans cells (American Type Culture Collection 700394^T) and all other strains of the species can ferment materials such as biomass into useful products and coproducts, such as ethanol, hydrogen and organic acids. Compositions that include Clostridium phytofermentans are also disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of priority from U.S. Provisional Patent Application No. 60 / 762,813, filed on Jan. 27, 2006, the contents of which is incorporated herein by reference in its entirety.STATEMENT AS TO FEDERALLY SPONSORED RESEARCH[0002]This invention was made with Government support under Grant No. DE-FG02-02ER15330, awarded by the United States Department of Energy (DOE). The Government thus has certain rights in the invention.TECHNICAL FIELD[0003]This invention relates to compositions, and to systems and methods for producing biofuels such as ethanol, and related materials.BACKGROUND[0004]There is an interest in developing methods of producing usable energy from renewable and sustainable biomass resources. Energy in the form of carbohydrates can be found in waste biomass, and in dedicated energy crops, such as grains (e.g., corn or wheat) or grasses (e.g., switchgrass). Cellulosic and lignocellulosic materials, are produ...

AI Technical Summary

Benefits of technology

[0022]In another aspect, the invention features kits, e.g., for seeding a fermentor, that include Clostridium phytofermentans. The kits can further include any one or more of any of the other microbes described herein. For example, the microbes in the kits can be combined in a single container or multiple containers. The microbes in the kits can be dispersed in a medium, or they can be freeze-dried. The kits can further include starter materials, such as nutrients.

[0023]Clostridium phytofermentans (American Type Culture Collection 7003941) is defined based on the phenotypic and genotypic characteristics of a cultured strain, ISDgT (Warrick et al., International Journal of Systematic and Evolutionary Microbiology, 52:1155-60, 2002). The invention generally relates to systems, and methods and compositions for producing fuels and / or other useful organic products involving strain ISDgT and / or any other strain of the species Clostridium phytofermentans, which may be derived from strain ISDgT or separately isolated. The species is defined using standard taxonomic considerations (Stackebrandt and Goebel, International Journal of Systematic Bacteriology, 44:846-9, 1994): Strains with 16S rRNA sequence homology values of 97% and higher as compared to the type strain (ISDgT) are considered strains of Clostridium phytofermentans, unless they are shown to have DNA re-association values of less than 70%. Considerable evidence exists to indicate that microbes which have 70% or greater DNA re-association values also have at least 96% DNA sequence identity and share phenotypic traits defining a species. Analyses of the genome sequence of Clostridium phytofermentans strain ISDgT indicate the presence of large numbers of genes and genetic loci that are likely to be involved in mechanisms and pathways for plant polysaccharide fermentation, giving rise to the unusual fermentation properties of this microbe. Based on the above-mentioned taxonomic considerations, all strains of the species Clostridium phytofermentans would also possess all, or nearly all, of these fermentation properties. Clostridium phytofermentans strains can be natural isolates, or genetically modified strains.

[0024]Advantages of the new systems and methods include any one of, or combinations of, the following. Clostridium phytofermentans can ferment a broad spectrum of materials into fuels with high efficiency. Advantageously, waste products, e.g., lactose, waste paper, leaves, grass clippings, and / or sawdust, can be used to make fuels. Clostridium phytofermentans remains active even at high concentrations of carbohydrates. Often materials that include carbohydrates can be used raw, without pretreatment. For example, in some instances, it is not necessary to pretreat the cellulosic material with an acid, a base, or an enzyme to release the lower molecular weight sugars that form part of the cellulosic material prior to fermentation. Instead, Clostridium phytofermentans can ferment the raw cellulosic material into a fuel directly. In some instances, lignocellulosic materials, e.g., sawdust or switchgrass, can be used without removal of lignin, and / or hemicelluloses. Clostridium phytofermentans cells grow and ferment under a wide range of temperatures and pH ranges. The pH of the fermentation medium may not need to be adjusted during fermentation. In some instances, Clostridium phytofermentans cells can be used in combination with one or more other microbes to increase the yield of a desired product, e.g., ethanol. In addition, Clostridium phytofermentans can ferment high concentrations of 5-carbon sugars, or polymers that include 5-carbon sugar repeat units, to combustible fuels. Five-carbon sugars, such as xylose, or polymers that include 5-carbon sugar repeat units, such as xylan and other components of the “hemicellulose” fraction of plant cell walls, are hydrolyzed and fermented by Clostridium phytofermentans concomitantly with other polymeric components of lignocellulosic materials yielding products such as ethanol and hydrogen. The 5-carbon sugars, or polymers that include 5-carbon sugar repeat units, do not appear to divert metabolic resources of Clostridium phytofermentans. Furthermore, Clostridium phytofermentans ferments higher cellulose concentrations, e.g., greater than 40 mM (glucose equivalents), with increasing ethanol yield. Other cellulose-fermenting microbes generally do not ferment higher concentrations of cellulose, above about 20 mM (glucose equivalents), and ethanol production decreases at higher cellulose concentrations (Desvaux et al., Appl. Environ. Microbiology, 66, 2461-2470, 2000).

[0025]Carbohydrates can be polymeric, oligomeric, dimeric, trimeric, or monomeric. When the carbohydrates are formed from more than a single repeat unit, each repeat unit can be the same or different. Examples of polymeric carbohydrates include cellulose, xylan, pectin, and starch, while cellobiose and lactose are examples of dimeric carbohydrates. Example of a monomeric carbohydrates include glucose and xylose. The term “low molecular weight carbohydrate” as used herein is any carbohydrate with a formula weight, or a number average molecular weight of less than about 1,000, as determined using a universal calibration curve. Generally, the term “high molecular weight carbohydrate” is any carbohydrate having a molecular weight of greater than 1,000, e.g., greater than 5,000, greater than 10,000, greater than 25,000, greater than 50,000, greater than 100,000, greater than 150,000, or greater than 250,000.

[0026]For carbohydrates having a defined single structure with a defined and computable formula weight, e.g., monomeric, or dimeric carbohydrates (e.g., arabinose and cellobiose, respectively), concentrations are calculated using the formula weight of the carbohydrate. For carbohydrates not having a defined single structure, e.g., polymeric carbohydrates (e.g., cellulose), concentrations are calculated assuming that the entire mass of the polymeric carbohydrate can be hydrolyzed to the monomeric carbohydrate unit from which the polymeric carbohydrate is formed. The formula weight of the monomeric carbohydrate unit is then applied to calculate the concentration in monomer equivalent units. For example, pure cellulose is made up entirely of glucose repeat units. 10 grams of cellulose would give 10 grams of glucose, assuming that the entire mass of the cellulose is hydrolyzed to glucose. Glucose (C6H12O6) has a formula weight of 180.16 amu. 10 grams of glucose is 0.056 moles of glucose. If this amount of glucose is in 1 L of solution, the concentration would be 0.056 M or 56 mM. If the polymer has more than one repeat unit, the concentration would be calculated as a total average carbohydrate concentration by assuming that the entire mass of the polymeric carbohydrate can be hydrolyzed to the monomeric carbohydrate units from which the polymeric carbohydrate is formed. For example, if the polymeric carbohydrate is made up entirely of the two repeat units, hydrolysis of X grams of polymeric carbohydrate gives X grams of monomeric carbohydrates. A composite formula weight is the sum of the product of the mole fraction of the first monomeric carbohydrate and its formula weight and the product of the mole fraction of the second monomeric carbohydrate and its formula weight. The average number of moles of carbohydrates is then X grams divided by the composite formula weight. The average carbohydrate concentration is found by dividing the average number of moles by the quantity of solution in which they reside.

[0027]A “fermentable material” is one that Clostridium phytofermentans (e.g., ISDgT) can, at least in part, convert into a fuel, e.g., ethanol, propanol or hydrogen and / or another useful product, e.g., an organic acid.

Problems solved by technology

A current challenge is to develop viable and economical strategies for the conversion of carbohydrates into usable energy forms.

Images