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The pathogenic Escherichia coli EDL933 is known to cause infection in the intestine. E. coli Nissle 1917 is used as a probiotic strain to prevent infection (63). When the mouse intestine is pre-colonized with E. coli Nissle 1917 it prevents E. coli EDL933 from growing up in the intestine. E. coli EDL933 is not eliminated from the intestine; it stays at the level in which it was fed to the mice. The P41L envZ missense mutation was previously shown to causes an increase in the level of phosporylated OmpR (OmpR~P) produced (67). E.coli MG1655 with the P41L missense envZ mutation is referred to as E. coli MG1655 mot-1. These changes result in an improvement of E. coli MG1655 colonization ability in the mouse intestine. The EnvZ/OmpR system positively regulates the small RNAs omrA and omrB (29). omrA and omrB were shown to negatively regulate a number of outer membrane genes including ompT, cirA, fepA, and fecA, (29). omrA and omrB work by hybridizing to mRNA thereby preventing translation from occurring (28). The mutant envZ gene was transferred to E. coli Nissle 1917 to create E. coli Nissle 1917 envZ(mot-1). The mutant envZ gene results in E. coli Nissle 1917 having improved colonization ability. E. coli Nissle 1917 envZ(mot-1) grows slower than E. coli Nissle 1917 wildtype on many sugars and in cecal mucus. The E. coli Nissle 1917 envZ(mot-1) mutant grows slower on galactose than E. coli Nissle 1917 wildtype. When the ability to utilize galactose is eliminated from E. coli Nissle 1917 envZ(mot1) it can no longer grow up in the mouse intestine in the presence of E. coli Nissle 1917 wildtype. This displays the importance of galactose utilization in the intestine for E. coli Nissle 1917 envZ(mot-1). E. coli Nissle 1917 envZ(mot-1) may have access to a niche where galactose is being utilized that E. coli Nissle 1917 is unable to inhabit. If E. coli Nissle 1917 was able to inhabit that niche then it would seem likely that E. coli Nissle 1917 would out compete E. coli Nissle 1917 envZ(mot-1) due to its superior ability to utilize galactose. E. coli Nissle 1917 envZ(mot-1) was then colonized against E. coli EDL933 to see if its improved colonization ability also results in improved probiotic potential. After performing multiple colonization experiments it is evident that E. coli Nissle 1917 envZ(mot-1) is not a better probiotic than E. coli Nissle 1917 wildtype.

MODIFICATION OF THE ESCHERICHIA coli NISSLE 1917 envZ GENE TO IMPROVE ITS PROBIOTIC POTENTIAL