Cell-wall lipopolysaccharide of the 'Shigella-like' Escherichia coli 058. Structure of the polysaccharide chain.

Two lipopolysaccharide preparations were obtained from Escherichia coli 058 by extraction with 45% aqueous phenol and fractional precipitation with cetyltrimethyl ammonium bromide (Cetavlon). Chemical analysis and polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate showed that the two preparations differed only in the extent of the O-specific polysaccharide moiety. The O-specific polysaccharide was characterized with proton magnetic resonance and infrared spectroscopy, optical rotation and paper electrophoresis. Using gas-liquid chromatography and ion-exchange chromatography, it was shown to contain D-mannose, 2-acetamido-2-deoxy-D-glucose, 3-O-(R-1'-carboxyethyl)-L-rhamnose (rhamnolactylic acid), and O-acetyl groups in the molar ratios of 2:1:1:1. The polysaccharide and oligosaccharides obtained from it were subjected to methylation and chromic acid oxidation. The results obtained indicated that the polysaccharide consists of tetrasaccharide repeating units in which the trisaccharide beta-GlcNAc1 - 4alphaMan-1 - 4(2/3-O-Ac)-Man is substituted at C-3 of the non-acetylated mannose with rhamnolactylic acid. The repeating units are joined through alpha-mannosyl-1 - 3-glucosamine bonds. This structure is identical with that of the cell wall polysaccharide of Shigella dysenteriae type 5.     

Influence of growth temperature on the development of Escherichia coli polysaccharide K antigens

The established seventy-one Escherichia coli polysaccharide capsular K antigenic test strains were examined for the development of the K antigen after growth at 37 degrees C and 18 degrees C. Twenty-eight K antigens were not detectable after growth of bacteria at 18 degrees C, while the remaining 43 antigens were developed at both temperatures. Most of the temperature-dependent antigens belonged to electrophoretically fast-moving K polysaccharides of rather low molecular weight, characteristically found among the common K antigens from extraintestinal disease isolates. Lipopolysaccharide O antigens were developed at both growth temperatures.     

Cell-wall lipopolysaccharide of Escherichia coli 0114:H2. Structure of the polysaccharide chain

The O-specific polysaccharide of the 0114 antigen (lipopolysaccharide) of Escherichia coli 0114 and oligosaccharides obtained from it by Smith degradation and hydrogen fluoride solvolysis were analyzed, using proton and 13C nuclear magnetic resonance spectroscopy and methylation. The results indicated that the 0114 polysaccharide has the tetrasaccharide repeating unit alpha-N-acetylglucosamine(1 leads to 4) beta-3,6-dideoxy-3-(N-acetyl-L-seryl)aminoglucose(1 leads to 3) beta-ribofuranose(1 leads to 4)galactose. In the polysaccharide the repeating units are joined through beta 1 leads to 3-galactosyl linkages. This structure is compared with that of the serologically cross-reacting Shigella boydii 08 antigen and the serological similarity is discussed.     

Optimization of Escherichia coli growth by controlled addition of glucose

During aerobic growth of Escherichia coli (recombinant K-12 and strain B) on protein hydrolysate (L-broth) and a carbon source (glucose), acetic acid is produced via glucose metabolism until the late log phase. At this point, the culture pH starts to increase and the growth rate decreases. In cultures without further glucose supplementation, these changes are associated with the accumulation of ammonia, the utilization of acetic acid, the depletion of amino acids, and the complete depletion of glucose. We hypothesize that, after depletion of the glucose, the bacteria catabolize amino acids for energy and carbon and give off the nitrogen as ammonia. Also contributing to the overall increase in pH is the depletion of the acetic acid produced earlier as it is metabolized upon exhaustion of glucose. However, there is a lag time of about 1 hour after the initial pH increase before the sustained accumulation of ammonia begins. This lag indicates that an unidentified factor, in addition to the increase in ammonia, contributes to the increase in pH. Advantage was taken of the turnaround from acid production to base production as reflected in the culture pH to implement the addition of glucose. In growth experiments during which the pH was controlled in the basic direction by glucose addition, the observed decrease in growth rate was significantly postponed and the pH change in the basic direction was reversed as a result of acid production by the cells from the newly added glucose. Furthermore, coll densities of twice that obtained without glucose feeding were demonstrated. Based on the media cost per unit cell density, the data indicate a 31% cost savings.     

Effects of temperature shift on growth rate of Escherichia coli BB at lower glucose concentration

Although a shift in nutritinal conditins brings about transient unbalanced growth in normally grown Escherichia coli, a shift in temperature without changing the nutritional conditions results in immediate adaptation to the new conditions. However, when a medium contained an insufficient amount of nutrient, such as glucose, a temperature shift caused a lag time in temperature shiftup was primarily determined by the postshift temperature. These situatins were quite similar to those observed in nutrient shiftup, but a growth profile during the lag time was more distorted than that found in the nutrient shiftup. The transient unbalanced growth appeared to be caused by a difference in physiological states of bacteria, as expressed by macromolecule content per cell characterized by the pre and postshift environments, and was capable of expressing theoretically its profile and duration according to the model of Cooper and Helmstetter. On the other hand, the shiftdown in temperature in the presence of a limiting concentration of glucose caused extraordinarily long lag time, and transient cessation of cell division during that period. This response was unable to explain by the Cooper and Helmstetter model. In contrast to the temperature shiftup, the duration of lag time in the shiftdown was expresed as functions of the poshift temperature and the difference in physiological states of the pre- and postshift environments.     

Wide distribution of O157-antigen biosynthesis gene clusters in Escherichia coli

Most Escherichia coli O157-serogroup strains are classified as enterohemorrhagic E. coli (EHEC), which is known as an important food-borne pathogen for humans. They usually produce Shiga toxin (Stx) 1 and/or Stx2, and express H7-flagella antigen (or nonmotile). However, O157 strains that do not produce Stxs and express H antigens different from H7 are sometimes isolated from clinical and other sources. Multilocus sequence analysis revealed that these 21 O157:non-H7 strains tested in this study belong to multiple evolutionary lineages different from that of EHEC O157:H7 strains, suggesting a wide distribution of the gene set encoding the O157-antigen biosynthesis in multiple lineages. To gain insight into the gene organization and the sequence similarity of the O157-antigen biosynthesis gene clusters, we conducted genomic comparisons of the chromosomal regions (about 59 kb in each strain) covering the O-antigen gene cluster and its flanking regions between six O157:H7/non-H7 strains. Gene organization of the O157-antigen gene cluster was identical among O157:H7/non-H7 strains, but was divided into two distinct types at the nucleotide sequence level. Interestingly, distribution of the two types did not clearly follow the evolutionary lineages of the strains, suggesting that horizontal gene transfer of both types of O157-antigen gene clusters has occurred independently among E. coli strains. Additionally, detailed sequence comparison revealed that some positions of the repetitive extragenic palindromic (REP) sequences in the regions flanking the O-antigen gene clusters were coincident with possible recombination points. From these results, we conclude that the horizontal transfer of the O157-antigen gene clusters induced the emergence of multiple O157 lineages within E. coli and speculate that REP sequences may involve one of the driving forces for exchange and evolution of O-antigen loci.