Proline auxotrophs

1. A non-naturally occurring proline auxotroph comprising an altered endogenous proC gene, wherein the proline auxotroph is Methylococcus capsulatus , and wherein the proline auxotroph exhibits a no growth phenotype when cultured in a proline-free culture medium and in the presence of a C 1 substrate.

2. The non-naturally occurring proline auxotroph of claim 1 , wherein the proline auxotroph exhibits a growth phenotype when cultured in a proline-containing medium comprising from about 10 μg/mL to about 500 μg/mL of proline.

3. The non-naturally occurring proline auxotroph of claim 1 , wherein the altered endogenous proC gene comprises a ΔproC mutation.

4. The non-naturally occurring proline auxotroph of claim 1 , wherein the proline auxotroph further comprises a heterologous polynucleotide that encodes a desired protein.

5. The non-naturally occurring proline auxotroph of claim 4 , wherein the encoded desired protein is:

(a) a lactate dehydrogenase;

(b) a propylene synthesis pathway enzyme;

(c) an isoprene synthesis pathway enzyme;

(d) a fatty acid converting enzyme;

(e) a fatty acid elongation pathway enzyme;

(f) an amino acid biosynthesis pathway enzyme; or

(g) a carbohydrate biosynthesis pathway enzyme.

6. The non-naturally occurring proline auxotroph of claim 5 , wherein:

(a) the encoded propylene synthesis pathway enzyme is a crotonase, a crotonyl CoA thioesterase, or a 4-oxalocrotonate decarboxylase;

(b) the encoded fatty acid converting enzyme is a fatty acyl-CoA reductase, a fatty alcohol forming acyl-ACP reductase, or a carboxylic acid reductase;

(c) the encoded fatty acid elongation pathway enzyme is a β-ketoacyl-CoA synthase, a β-ketoacy-CoA reductase, a β-hydroxy acyl-CoA dehydratase, or an enoyl-CoA reductase;

(d) the encoded amino acid biosynthesis pathway enzyme is a lysine biosynthesis enzyme, wherein the lysine biosynthesis enzyme is a, lysine-sensitive aspartokinase III (lysC), an aspartate kinase, an aspartate-semialdehyde dehydrogenase (asd), a dihydrodipicolinate synthase (dapA), a dihydrodipicolinate reductase (dapB), a 2,3,4,5-tetrahydropyridine-2,6-carboxylate N-succinyltransferase (dapD), an acetylornithine/succinyldiaminopimelateaminotransferase (argD), a succinyldiaminopimelate desuccinylase (dapE), a succinyldiaminopimelate transaminase, a diaminopimelate epimerase (dapF), or a diaminopimelate dicarboxylase (lysA);

(e) the encoded amino acid biosynthesis pathway enzyme is a tryptophan biosynthesis enzyme, wherein the tryptophan biosynthesis enzyme is a chorismate-pyruvate lyase (ubiC), an anthranilate synthase component I (trpE), an anthranilate synthase component II (trpG), an anthranilate phosphoribosyltransferase (trpD), a phosphoribosylanthranilate isomerase (trpC), a tryptophan biosynthesis protein (trpC), an N-(5′phosphoribosyl) anthranilate isomerase (trpF), an indole-3-glycerol phosphate synthase, a tryptophan synthase alpha chain (trpA), or a tryptophan synthase beta chain (trpB);

the encoded amino acid biosynthesis pathway enzyme is a methionine biosynthesis enzyme, wherein the methionine biosynthesis enzyme is a homoserine O-succinyltransferase (metA), a cystathionine gamma-synthase (metB), a protein MalY, a cystathionine beta-lyase (metC), a B12-dependent methionine synthase (metH), or a 5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase (metE);

(g) the encoded amino acid biosynthesis pathway enzyme is a cysteine biosynthesis enzyme, wherein the cysteine biosynthesis enzyme is a serine acetyltransferase (CysE), a cysteine synthase A, or a cysteine synthase B; or

(h) the encoded carbohydrate biosynthesis pathway enzyme is a pyruvate carboxylase, a phosphoenolpyruvate carboxykinase, an enolase, a phosphoglycerate mutase, a phosphoglycerate kinase, a glyceraldehyde-3-phosphate dehydrogenase, a Type A aldolase, a fructose 1,6-bisphosphatase, a phosphofructokinase, a phosphoglucose isomerase, a hexokinase, a glucose-6-phosphate, glucose-1-phosphate adenyltransferase, a glycogen synthase, or a glucan synthase.

7. The non-naturally occurring proline auxotroph of claim 4 , wherein the heterologous polynucleotide is incorporated into a self-replicating nucleic acid construct or is integrated into the chromosome of the Methylococcus capsulatus.

8. The non-naturally occurring proline auxotroph of claim 1 , wherein the proline auxotroph does not further comprise a recombinant polynucleotide encoding a proline transporter.

9. The non-naturally occurring proline auxotroph of claim 1 , wherein the Methylococcus capsulatus comprises Methylococcus capsulatus Bath.