Targeted gene deletions for polysaccharide slime formers
View Patent ↗The present invention provides improved polysaccharides (e.g., gellan and diutan) produced by mutant gene M or gene N Sphingomonas strains containing at least one genetic modification that favors slime-forming polysaccaride production. Methods of making the mutant Sphingomonas strains and the culture broth containing such mutant Sphingomonas strains are also provided.
1. An isolated slime forming mutant Sphingomonas strain comprising a substitution, insertion or deletion in gene dpsN in a diutan biosynthetic gene cluster that inactivates gene dpsN and favors the production of a slime form polysaccharide, wherein said dpsN comprises the nucleotide sequence of nucleotides 1321-2019 as set forth in SEQ ID NO:14.
2. The isolated slime forming mutant Sphingomonas strain of claim 1 , wherein said slime forming mutant Sphingomonas strain produces diutan.
3. The isolated slime forming mutant Sphingomonas strain of claim 2 , wherein said diutan is a slime form polysaccharide.
4. The isolated slime forming mutant Sphingomonas strain of claim 3 , wherein said diutan comprises longer fibers than diutan as naturally produced by a wild-type strain ATCC 53159.
5. The isolated slime forming mutant Sphingomonas strain of claim 3 , wherein said diutan imparts to a fluid an increased viscosity relative to an equivalent amount of diutan as naturally produced by a wild-type Sphingomonas strain ATCC 53159.
6. The isolated slime forming mutant Sphingomonas strain of claim 5 , wherein the increased viscosity is at least 30% more than an equivalent amount of diutan produced by the wild-type strain ATCC 53159.
7. The isolated slime forming mutant Sphingomonas strain of claim 5 , wherein the increased viscosity is at least 50% more than an equivalent amount of diutan produced by the wild-type strain ATCC 53159.
8. The isolated slime forming mutant Sphingomonas strain of claim 5 , wherein the increased viscosity is at least 80% more than an equivalent amount of diutan produced by the wild-type strain ATCC 53159.
9. The isolated slime forming mutant Sphingomonas strain of claim 5 , wherein the increased viscosity is at least 90% more than an equivalent amount of diutan produced by the wild-type strain ATCC 53159.
10. The isolated slime forming mutant Sphingomonas strain of claim 1 , further comprising a second gene mutation, insertion or deletion in gene I (dpsI) comprising a nucleotide sequence of 501-1472 as set forth in SEQ ID NO:29, in gene R (dpsR) comprising a nucleotide sequence of 501-2498 as set forth in SEQ ID NO:31, or in gene M (dpsM) comprising a nucleotide sequence of 456-1337 as set forth in SEQ ID NO:14.
11. The isolated slime forming mutant Sphingomonas strain of claim 1 , wherein said mutant Sphingomonas strain is a variant of a wild-type Sphingomonas strain ATCC 53159, wherein said variant has been genetically engineered to eliminate an expression of said dpsN.