Targeted gene deletions for polysaccharide slime formers
The present invention provides improved polysaccharides (e.g., gellan and diutan) produced by mutant gene R, M or N Sphingomonas strains containing at least one genetic modification that favors slime-forming polysaccharide production. Methods of making the mutant Sphingomonas strains and the culture broth containing such mutant Sphingomonas strains are also provided.
1. A Sphingomonas mutant strain comprising a mutation in gelM gene, wherein said Sphingomonas mutant strain has been genetically engineered to eliminate expression of gene gelM, wherein said mutant strain produces gellan, wherein said gellan is a slime form polysaccharide, and wherein said gellan has improved rheology, as compared to gellan naturally produced by the wild-type Sphingomonas strain ATCC 31461.
2. The Sphingomonas mutant strain of claim 1 , wherein said mutation in gene gelM comprises an insertion, deletion, or substitution in gene gelM so as to inactivate gene gelM.
3. The Sphingomonas mutant strain of claim 2 , wherein said mutation comprises a deletion in gene gelM.
4. The Sphingomonas mutant strain of claim 1 , further comprising a second gene mutation, comprising an insertion, deletion, or substitution.
5. The Sphingomonas mutant strain of claim 4 , wherein second gene mutation is in gene gelN.
6. The Sphingomonas mutant strain of claim 4 , wherein said second gene mutation is in gene gelI.
7. The Sphingomonas mutant strain of claim 4 , wherein said gellan has improved gel strength, as compared to gellan naturally produced by the wild-type Sphingomonas strain ATCC 31461.