Campylobacter jejuni Group III Phage CP81 Contains Many T4-Like Genes without Belonging to the T4-Type Phage Group: Implications for the Evolution of T4 Phages

Abstract

CP81 is a virulent Campylobacter group III phage whose linear genome comprises 132,454 bp. At the nucleotide level, CP81 differs from other phages. However, a number of its structural and replication/recombination proteins revealed a relationship to the group II Campylobacter phages CP220/CPt10 and to T4-type phages. Unlike the T4-related phages, the CP81 genome does not contain conserved replication and virion modules. Instead, the respective genes are scattered throughout the phage genome. Moreover, most genes for metabolic enzymes of CP220/CPt10 are lacking in CP81. On the other hand, the CP81 genome contains nine similar genes for homing endonucleases which may be involved in the attrition of the conserved gene order for the virion core genes of T4-type phages. The phage apparently possesses an unusual modification of C or G bases. Efficient cleavage of its DNA was only achieved with restriction enzymes recognizing pure A/T sites. Uncommonly, phenol extraction leads to a significant loss of CP81 DNA from the aqueous layer, a property not yet described for other phages belonging to the T4 superfamily.Campylobacteriosis is a worldwide zoonosis. There are probably more than two million Campylobacter infections in humans annually in the United States. Also, in developing countries, infections with Campylobacter jejuni are very frequent in children, and symptomatic infections early in life are followed later by asymptomatic infections. The bacteria are common commensals of the gastrointestinal tract of various mammals and birds. Consumption of undercooked meats, especially poultry, has been associated with Campylobacter infections (44). The prevalence of Campylobacter-positive chicken is generally high, and transmission of Campylobacter from bird to bird occurs rapidly (25). Intervention strategies mainly focus on biosecurity measures (e.g., improvement of personal hygiene, avoiding of mixed farming, and control of rodents and insects) and postslaughter decontamination of poultry carcasses (19). Since these measures are expensive and not always efficient and since suitable vaccines are not available, bacteriophages have been proposed to reduce the Campylobacter counts on chicken. Indeed, phage administration in the laboratory reduced C. jejuni colonization of the broiler gut and the contamination on chicken skin by several orders of magnitude (3,6,16,20,29,50).Phages intended for therapeutic applications or for the control of pathogens in food production have to fulfill a number of requirements. First and foremost, phages have to be safe in order to avoid any undesired side effect. Therefore, a basic understanding of the biology and genetics of the phage to be used is mandatory. A minimal standard is the acquisition of the genome sequence of the phage to exclude undesired genes. Unfortunately, up to now, genome sequences of Campylobacter phages are scarce. Most Campylobacter phages have been investigated only with respect to their host ranges, morphology, and genome size (3,4,11,16,22,26,30). Almost all Campyloba...

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