A Single Nucleotide Exchange in the wzy Gene Is Responsible for the Semirough O6 Lipopolysaccharide Phenotype and Serum Sensitivity of Escherichia coli Strain Nissle 1917

Abstract

Structural analysis of lipopolysaccharide (LPS) isolated from semirough, serum-sensitiveLipopolysaccharide (LPS) is a key component of the outer membrane of gram-negative bacteria. It is comprised of three distinct regions: lipid A, the oligosaccharide core, and commonly a long-chain polysaccharide O antigen that causes a smooth phenotype. Lipid A is the most conserved part of LPS. It is connected to the core part, which links it to the O repeating units. In Escherichia coli, five different core structures (K-12 and R1 to R4) have been described (2, 18, 43). The O repeating units are highly polymorphic, and more than 190 serologically distinguished forms in E. coli are known today (35).The LPS core-encoding genes are located at a conserved position on the E. coli K-12 chromosomal map (81 to 82 min) (5). The wa‫ء‬ (formerly called rfa) gene clusters contain the genes which code for the enzymes required for the core assembly and consist of three operons (defined by the first genes in the operons; gmhD, waaQ, and waaA). Although the O-unitencoding gene cluster is extremely polymorphic in the E. coli species, it is localized at a conserved position on the E. coli K-12 chromosome between the galF and gnd genes (45.4 min) (5). These determinants consist of several sugar transferase-, epimerase-, and isomerase-encoding genes, the O-antigen flippase gene (wzx), the O-antigen polymerase gene (wzy [formerly called rfc]), as well as the genes coding for enzymes involved in carbohydrate biosynthesis pathways. Until now, several E. coli O-antigen-encoding gene clusters have been studied, e.g., those of serotypes O7, O111, O113, and O157 (32, 38, 54, 55). These gene clusters show no significant nucleotide homology with each other, with the exception of some common genes such as manC and manB. However, they contain a conserved range of predicted enzyme activities. The O6 antigen is widely distributed among pathogenic and nonpathogenic fecal E. coli isolates and is often found in uropathogenic E. coli strains. It is associated with R1-type core LPS and has not been investigated in detail so far.E. coli strain Nissle 1917 (DSM 6601, serotype O6:K5:H1) is a nonpathogenic fecal isolate, which is used as a probiotic agent in medicine (7), mainly for treatment of various gastroenterological indications (23,26,30,33,41). This strain exhibits a serum-sensitive, semirough phenotype. Since colonies of this strain on agar plates show a special smooth-and-rough

Construction of recombinant E. coli Nissle 1917 (EcN) strains for the expression and secretion of defensins

“…coli Nissle 1917 has been thoroughly analyzed by means of microbiological, biochemical and molecular genetic methods (Blum-Oehler et al 2003, Blum et al 1995, Grozdanov et al 2004, Grozdanov et al 2002. The strain does not exhibit any virulence factors, but has gene clusters located on genomic islands (GEIs) responsible for the synthesis of several so-called `fitness factors´, which contribute to the strain's probiotic nature.…”

“…The strain does not exhibit any virulence factors, but has gene clusters located on genomic islands (GEIs) responsible for the synthesis of several so-called `fitness factors´, which contribute to the strain's probiotic nature. Serologically, EcN belongs to the E. coli O6 group and is of serotype O6:K5:H1 (Blum et al 1995, Grozdanov et al 2002. EcN is a typical gram-negative enterobacterium containing lipopolysaccharide (LPS) as a structural component of its outer cell membrane.…”

Bacteria as tumor therapeutics?

“…This in turn results from a point mutation in the wzy gene encoding the O-antigen polymerase. 16 EcN in contrast to S. typhimurium has not to be genetically altered to achieve a very high selectivity for tumor colonization in mice. In fact, EcN did not colonize liver and spleen at all and even almost exclusively the tumor tissue, even in immunocompromised animals.…”

The effect of probiotic Escherichia coli strain Nissle 1917 lipopolysaccharide on the 5-aminosalicylic acid transepithelial transport across Caco-2 cell monolayers

“…In this study, one of the best characterized probiotics, nonpatogenic Escherichia coli strain Nissle 1917 O6:K5:H1 (EcN) exhibiting a serum-sensitive, semirough phenotype (Grozdanov et al 2002) was used. As for EcN efficacy, there are several clinical trials comparing the oral EcN and 5-ASA formulations in maintenance of remission of UC.…”