The pathogenicity of Shiga-like toxin (stx)-producing Escherichia coli (STEC), notably serotype O157, the causative agent of hemorrhagic colitis, hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura, is based partly on the presence of genes (stx 1 and/or stx 2 ) that are known to be carried on temperate lambdoid bacteriophages. Stx phages were isolated from different STEC strains and found to have genome sizes in the range of 48 to 62 kb and to carry either stx 1 or stx 2 genes. Restriction fragment length polymorphism patterns and sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles were relatively uninformative, but the phages could be differentiated according to their immunity profiles. Furthermore, these were sufficiently sensitive to enable the identification and differentiation of two different phages, both carrying the genes for Stx2 and originating from the same STEC host strain. The immunity profiles of the different Stx phages did not conform to the model established for bacteriophage lambda, in that the pattern of individual Stx phage infection of various lysogens was neither expected nor predicted. Unexpected differences were also observed among Stx phages in their relative lytic productivity within a single host. Two antibiotic resistance markers were used to tag a recombinant phage in which the stx genes were inactivated, enabling the first reported observation of the simultaneous infection of a single host with two genetically identical Stx phages. The data demonstrate that, although Stx phages are members of the lambdoid family, their replication and infection control strategies are not necessarily identical to the archetypical bacteriophage , and this could be responsible for the widespread occurrence of stx genes across a diverse range of E. coli serotypes.

Bacteriophages are viruses whose hosts are bacterial cells. Like all viruses, phages are metabolically inert in their extra-cellular form, reproducing only after infecting suitable host bacteria. Discovered over 80 years ago, they have played a key role in the development of modern biotechnology. Their initial isolation appeared to offer the ®rst therapeutic for the control of infectious disease. The discovery of antibiotics in the 1940s eclipsed bacteriophage-based therapies although, with the increase in multiply drug-resistant pathogens, bacteriophages are being re-evaluated as the basis of new therapeutic strategies. Their de®ned host speci®city facilitated their application in the typing and identi®cation of a wide range of bacteria. Bacteriophage typing schemes were developed for most groups of pathogenic of bacteria and more recently their host speci®city has been applied to the development of bacterial detection and diagnostic strategies. The advance in molecular biology over the past 30 years has been built on the study of phage structure and genetics carried out through the 1950s and 1960s. Restriction endonucleases which form the basis of molecular cloning were developed following studies of phage infection and many phage enzymes provide tools for the molecular biologist. The technique of phage display has more recently provided a powerful technique for the identi®cation and optimisation of ligands for antibodies and other biomolecules. In the environment they have been widely applied as tracers, as indicators of pollution and in the monitoring and validation of biological ®lters. While providing a valuable resource to the development of modern biotechnology, their ability to mobilise and transfer toxin genes in the environment is viewed with concern. They also present a continuing challenge to the fermentation and in particular, the dairy industry, where phage infection can prove commercially disastrous.

The dehalogenation of lindane by a range of hemoproteins, porphyrins, and corrins has been tested under reducing conditions in the presence of dithiothreitol. In addition, a series of porphyrin-metal ion complexes have been prepared and have also been screened for the capacity to dehalogenate lindane. Hemoglobin, hemin, hematin, and chlorophyll a all catalyzed the dehalogenation of lindane, as did all of the corrins tested. The porphyrins which did not contain metal centers-coproporphyrin, hematoporphyrin, protoporphyrin, and uroporphyrin-were inactive. However, when these porphyrins were then complexed with Co, Fe, Mg, Mo, Ni, or V, lindane dehalogenation was observed. In all cases, the reaction proceeded by an initial dechlorination to produce tetrachlorocyclohexene, which was further dehalogenated to yield chlorobenzene as the end product.

A mixed population, enriched and established in a defined medium, from a sewage sludge inoculum was capable of complete mineralization of 4-chlorobenzoate. An organism, identified as Arthrobacter sp., was isolated from the consortium and shown to be capable of utilizing 4-chlorobenzoate as the sole carbon and energy source in pure culture. This organism (strain TM-1), dehalogenated 4-chlorobenzoate as the initial step in the degradative pathway. The product, 4-hydroxybenzoate, was further metabolized via protocatechuate. The ability of strain TM-1 to degrade 4-chlorobenzoate in liquid medium at 25°C was improved by the use of continuous culture and repeated sequential subculturing. Other chlorinated benzoates and the parent compound benzoate did not support growth of strain TM-I. An active cell extract was prepared and shown to dehalogenate 4-chloro-, 4-fluoro-, and 4-bromobenzoate. Dehalogenase activity had an optimum pH of 6.8 and an optimum temperature of 20°C and was inhibited by dissolved oxygen and stimulated by manganese (Mn2+). Strain improvement resulted in an increase in the specific activity of the cell extract from 0.09 to 0.85 nmol of 4-hydroxybenzoate per min per mg of protein and a decrease in the doubling time of the organism from 50 to 1.6 h.

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