Escherichia coli

About: Escherichia coli is a research topic. Over the lifetime, 59041 publications have been published within this topic receiving 2050337 citations. The topic is also known as: E. coli & E coli jdj.

Production of optically pure D-lactic acid in mineral salts medium by metabolically engineered Escherichia coli W3110.

Abstract: The resistance of polylactide to biodegradation and the physical properties of this polymer can be controlled by adjusting the ratio of l-lactic acid to d-lactic acid. Although the largest demand is for the l enantiomer, substantial amounts of both enantiomers are required for bioplastics. We constructed derivatives of Escherichia coli W3110 (prototrophic) as new biocatalysts for the production of d-lactic acid. These strains (SZ40, SZ58, and SZ63) require only mineral salts as nutrients and lack all plasmids and antibiotic resistance genes used during construction. d-Lactic acid production by these new strains approached the theoretical maximum yield of two molecules per glucose molecule. The chemical purity of this d-lactic acid was ∼98% with respect to soluble organic compounds. The optical purity exceeded 99%. Competing pathways were eliminated by chromosomal inactivation of genes encoding fumarate reductase (frdABCD), alcohol/aldehyde dehydrogenase (adhE), and pyruvate formate lyase (pflB). The cell yield and lactate productivity were increased by a further mutation in the acetate kinase gene (ackA). Similar improvements could be achieved by addition of 10 mM acetate or by an initial period of aeration. All three approaches reduced the time required to complete the fermentation of 5% glucose. The use of mineral salts medium, the lack of antibiotic resistance genes or plasmids, the high yield of d-lactate, and the high product purity should reduce costs associated with nutrients, purification, containment, biological oxygen demand, and waste treatment.

Conditional Lethality of recA and recB Derivatives of a Strain of Escherichia coli K-12 with a Temperature-Sensitive Deoxyribonucleic Acid Polymerase I

Abstract: We have isolated a strain of Escherichia coli K-12 carrying a mutation, polA12, that results in the synthesis of a temperature-sensitive deoxyribonucleic acid (DNA) polymerase I. The double mutants polA12 recA56 and polA12 recB21, constructed at 30 C, are inviable at 42 C. About 90% of the cells of both double mutants die after 2 hr of incubation at 42 C. Both double mutants filament at 42 C and show a dependence on high cell density for growth at 30 C. In polA12 recB21 cells at 42 C, DNA and protein synthesis gradually stop in parallel. In polA12 recA56 cells, DNA synthesis continues for at least 1 hr at 42 C, and there is extensive DNA degradation. The results suggest that the primary lesion in these double mutants is not in DNA replication per se.

The tol gene products and the import of macromolecules into Escherichia coli.

Abstract: Genetic studies have identified a number of genes whose products appear to be required for the transport of the group A colicins and the single-stranded DNA of certain filamentous bacteriophages into Escherichia coli. Mutations in these genes allow normal binding of the colicins to their outer-membrane receptors and of the bacteriophage of the tip of specific conjugative pili, but do not allow translocation of the macromolecules to their target. These mutations have been designed 'tolerant' (tol) mutations and the protein products specified by these genes appear to comprise part of a transport system known as the Tol import system. Some of these genes have been isolated, sequenced and their protein products localized to the membranes or periplasm of E. coli. Information is also available regarding the domains of the colicins or phage proteins which interact with the Tol proteins. A preliminary model of the location and possible interactions of the Tol proteins is presented.

DNA probes for Shiga-like toxins I and II and for toxin-converting bacteriophages.

Abstract: A set of DNA probes has been developed to study the genes for Shiga-like toxins (SLT) and the bacteriophage from which these toxin genes were isolated. Under stringent conditions of hybridization (80 to 90% homology), these probes detect strains containing (i) SLT I-related genes, (ii) SLT II-related genes, (iii) phage sequences from the SLT I-converting phage H19A/933J, and (iv) phage sequences from the SLT II-converting phage 933W. Strain characterization by hybridization with the toxin gene probes was as accurate as methods that used toxin-specific antibody to determine toxin synthesis. Screening of different gram-negative bacteria with the toxin probes revealed that only two species carry sequences related to the SLT genes, Escherichia coli and Shigella dysenteriae 1. These results indicated that the lower levels of toxin activity observed in shigellae other than S. dysenteriae 1 are due to a gene(s) that is genetically distinct from that which encodes Shiga toxin. Analysis of enterotoxigenic, enteroinvasive, enteropathogenic, and enterohemorrhagic E. coli indicated that SLT genes are found primarily in the enterohemorrhagic E. coli strain group. Use of both the toxin and the phage probes has identified a variety of genotypic combinations of phage and toxin sequences which differ from those observed for the original toxin-converting phage isolates, for E. coli O157:H7 strain 933, and for E. coli O26:H11 strain H19.