Biological production of multi-carbon compounds from methane
Multi-carbon compounds such as ethanol, n-butanol, sec-butanol, isobutanol, tert-butanol, fatty (or aliphatic long chain) alcohols, fatty acid methyl esters, 2,3-butanediol and the like, are important industrial commodity chemicals with a variety of applications. The present invention provides metabolically engineered host microorganisms which metabolize methane (CH 4 ) as their sole carbon source to produce multi-carbon compounds for use in fuels (e.g., bio-fuel, bio-diesel) and bio-based chemicals. Furthermore, use of the metabolically engineered host microorganisms of the invention (which utilize methane as the sole carbon source) mitigate current industry practices and methods of producing multi-carbon compounds from petroleum or petroleum-derived feedstocks, and ameliorate much of the ongoing depletion of arable food source “farmland” currently being diverted to grow bio-fuel feedstocks, and as such, improve the environmental footprint of future bio-fuel, bio-diesel and bio-based chemical compositions.
1. A method for producing isobutanol from a methane substrate comprising the steps of:
(a) providing a methanotrophic host microorganism that metabolizes methane (CH 4 ) to methanol (CH 3 OH) and methanol to formaldehyde (H 2 C═O);
(b) introducing into the methanotroph host and expressing at least one exogenous polynucleotide open reading frame (ORF) under the control of suitable regulatory-sequences, wherein the at least one polynucleotide ORF encodes a polypeptide that catalyzes a reaction in an isobutanol pathway,
wherein the at least one polynucleotide ORF is selected from the group consisting of acetolactate synthase (ALS), ketol-acid reductoisomerase (KARI), dihydroxy-acid dehydratase (DHAD), ketoacid decarboxylase (KDC) and alcohol dehydrogenase (ADH), and wherein the ALS polypeptide comprises an amino acid sequence having at least 90% sequence homology to SEQ ID NO:2, the KARI polypeptide comprises an amino acid sequence having at least 90% sequence homology to SEQ ID NO:4, the DHAD polypeptide comprises an amino acid sequence having at least 90% sequence homology to SEQ ID NO:6, the KDC polypeptide comprises an amino acid sequence having at least 90% sequence homology to SEQ ID NO:8 and the ADH polypeptide comprises an amino acid sequence having at least 90% sequence homology to SEQ ID NO:10;
(c) feeding the methanotroph host produced according to step (b) a methane substrate under suitable growth conditions, wherein the host metabolizes methane to formaldehyde as set forth in step (a), wherein the formaldehyde is converted to pyruvate by means of an endogenous type I RuMP pathway or a type II serine pathway and the host metabolizes pyruvate to produce isobutanol; and
(d) recovering the isobutanol produced.
2. The method of claim 1 , wherein the one or more polynucleotide ORFs introduced in step (b) encode an isobutanol pathway polypeptide selected from an Enzyme Class (EC) comprising EC 2.2.1.6, EC 1.1.1.86, EC 4.2.1.9, EC 4.1.1.72 and EC 1.1.1.1.
3. The method of claim 1 , wherein the ALS polypeptide catalyzes the substrate to product conversion of pyruvate to acetolactate; the KARI polypeptide catalyzes the substrate to product conversion of acetolactate to 2,3-dihydroxyisovalerate; the DHAD polypeptide catalyzes the substrate to product conversion of 2,3-dihydroxyisovalerate to ketoisovalerate; the KDC polypeptide catalyzes the substrate to product conversion of ketoisovalerate to isobutyraldehyde and ADH polypeptide catalyzes the substrate to product conversion of isobutyraldehyde to isobutanol.
4. The method of claim 1 , wherein the one or more polynucleotide ORFs introduced in step (b) encode the complete isobutanol pathway comprising an ALS polypeptide, a KARI polypeptide, a DHAD polypeptide, a KDC polypeptide and an ADH polypeptide.
5. The method of claim 1 , wherein the methanotroph host microorganism is selected from genus consisting of Methylobacter, Methylomicrobium, Methylomonas, Methylocaldum, Methylococcus, Methylosoma, Methylosarcina, Methylothermus, Methylohalobius, Methylogaea, Methylovulum, Crenothrix, Clonothrix, Methylosphaera, Methylocapsa, Methylocella, Methylosinus, Methylocystis , and Methyloacidophilum.