An integrated process and system for employing low conversion rWGS to prepare a gas fermentation feed stream from a CO.sub.2 source and a hydrogen source in order to produce at least one gas fermentation product. Low conversion rWGS reactors may (1) employ a wider selection of inorganic catalysts then rWGS reactors requiring high temperature operation, (2) allow for use of an electric heater instead of a fired heater to preheat feed stream to the low conversion rWGS reactor, and (3) extend rWGS catalyst life by reducing the amount of water produced in the rWGS reaction.

An integrated process and system for employing low conversion rWGS to prepare a gas fermentation feed stream from a CO.sub.2 source and a hydrogen source in order to produce at least one gas fermentation product. Low conversion rWGS reactors may (1) employ a wider selection of inorganic catalysts then rWGS reactors requiring high temperature operation, (2) allow for use of an electric heater instead of a fired heater to preheat feed stream to the low conversion rWGS reactor, and (3) extend rWGS catalyst life by reducing the amount of water produced in the rWGS reaction.

The invention provides recombinant microorganisms and methods for the production of acetone from gaseous substrates. For example, the recombinant microorganism may be modified to express an exogenous thiolase, an exogenous CoA transferase, and an exogenous decarboxylase.

The invention provides recombinant microorganisms and methods for the production of acetone from gaseous substrates. For example, the recombinant microorganism may be modified to express an exogenous thiolase, an exogenous CoA transferase, and an exogenous decarboxylase.

Multi-stage, biological processes and systems for converting a C1 carbon source to desired end products are described. The processes comprise dividing a gaseous C1-containing substrate, in parallel, among multiple bioreactor stages. Liquid products are successively fed, in series, from a first bioreactor stage to downstream bioreactor stages. Operation can be simplified by avoiding the requirement for microorganism separation and recycle at each stage. In addition, overall vapor-liquid mass transfer for the combined stages is very favorable, leading to high end product productivity with comparably low byproduct metabolite productivity.

Methods, systems and compositions for producing at least one light-boiling, volatile, organic product using at least a portion of one or more carbon containing substances from a non-biosynthetic process in a biosynthetic process are provided. These methods, systems and compositions are useful in reducing waste treatment load of carbon containing chemical process waste streams.

Methods, systems and compositions for producing at least one light-boiling, volatile, organic product using at least a portion of one or more carbon containing substances from a non-biosynthetic process in a biosynthetic process are provided. These methods, systems and compositions are useful in reducing waste treatment load of carbon containing chemical process waste streams.

This invention provides optimized fermentation of cellulosic and hemicellulosic sugars. Biomass-derived hemicellulosic and cellulosic sugars are independently conditioned and separately fermented, utilizing reuse and recycle of microorganisms, metabolic intermediates, and nutrients. Conditioned sugars can be fermented in separate vessels, where excess cells from glucose fermentation are conveyed to hemicellulose sugar fermentation along with raffinate from solvent recovery, to enhance productivity and product yield. Some variations provide a method of fermenting C.sub.5 and C.sub.6 sugars to fermentation products, the method comprising: fermenting a C.sub.6-rich sugar feed to a first fermentation product; fermenting a C.sub.5-rich sugar feed to a second fermentation product; removing microorganism cells from the first fermentor, to maintain a cell concentration within a selected range; conveying microorganism cells to a second fermentor; and removing microorganism cells from the second fermentor, to maintain a microorganism cell concentration that is greater than that in the C.sub.6-rich fermentor.

This invention provides optimized fermentation of cellulosic and hemicellulosic sugars. Biomass-derived hemicellulosic and cellulosic sugars are independently conditioned and separately fermented, utilizing reuse and recycle of microorganisms, metabolic intermediates, and nutrients. Conditioned sugars can be fermented in separate vessels, where excess cells from glucose fermentation are conveyed to hemicellulose sugar fermentation along with raffinate from solvent recovery, to enhance productivity and product yield. Some variations provide a method of fermenting C.sub.5 and C.sub.6 sugars to fermentation products, the method comprising: fermenting a C.sub.6-rich sugar feed to a first fermentation product; fermenting a C.sub.5-rich sugar feed to a second fermentation product; removing microorganism cells from the first fermentor, to maintain a cell concentration within a selected range; conveying microorganism cells to a second fermentor; and removing microorganism cells from the second fermentor, to maintain a microorganism cell concentration that is greater than that in the C.sub.6-rich fermentor.

An acetyl-CoA producing microorganism obtained by imparting at least one enzymatic activity selected from the group consisting of malate thiokinase, malyl-CoA lyase, glyoxylate carboligase, 2-hydroxy-3-oxopropionate reductase, and hydroxypyruvate reductase, to a microorganism that does not have any of the following (a), (b), (c), (d) or (e): (a) a carbon dioxide fixation cycle including an enzymatic reaction from malonyl-CoA to malonate semialdehyde or 3-hydroxypropionate; (b) a carbon dioxide fixation cycle including an enzymatic reaction from acetyl-CoA and CO.sub.2 to pyruvate; (c) a carbon dioxide fixation cycle including an enzymatic reaction from crotonyl-CoA and CO.sub.2 to ethylmalonyl-CoA or glutaconyl-CoA; (d) a carbon dioxide fixation cycle including an enzymatic reaction from CO.sub.2 to formate; or (e) at least one selected from the group consisting of malate thiokinase and malyl-CoA lyase.