Open AccessCharaterization of cryptic prophages (monocins) in Listeria and sequence analysis of a holin/endolysin gene
Author(s) -
Ralf Zink,
Martin J. Loessner,
Siegfried Scherer
Publication year - 1995
Publication title -
microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.019
H-Index - 179
eISSN - 1465-2080
pISSN - 1350-0872
DOI - 10.1099/13500872-141-10-2577
Subject(s) - prophage , lytic cycle , biology , lysin , bacteriophage , listeria , lysogenic cycle , microbiology and biotechnology , gene , escherichia coli , dna , nucleic acid sequence , extrachromosomal dna , phagemid , listeria monocytogenes , genetics , plasmid , bacteria , virus
Monocins in Listeria were induced by UV-irradiation of liquid cultures, and defective phage particles were purified from the lysates. Electron microscopy showed flexible, non-contractile bacteriophage-tail-like particles, consisting of specific proteins of molecular mass 20-45 kDa and pI 4.6-6.7. These particles were able to lyse listerial cells. DNA sequence homologies between chromosomal DNA of monocin-producing strains and labelled Listeria phage DNAs were inferred from DNA/DNA hybridizations, suggesting that most of the prophage DNA is still present in the listerial chromosome. An endolysin gene cpl2438 was cloned from listerial chromosomal DNA and was identified by its expression of lytic activity against Listeria cells in a bioassay. The gene consists of 864 nt encoding a protein of 287 aa with a calculated molecular mass of 32975 Da (CPL2438). This is in good agreement with the size of a protein observed in SDS-PAGE after overexpression of the lytic protein in Escherichia coli. The nucleotide sequence of a putative holin gene (hol2438, 291 nt) upstream of cpl2438 was determined after PCR-amplification of listerial DNA and it shows typical features common to the holin gene family. Expression of the encoded protein (HOL2438, 95 aa, 10.1 kDa) in E. coli was found to be lethal for the host cells. The results underline the close relationship between monocins and intact Listeria bacteriophages, indicating that monocins are incompletely assembled phage particles derived from cryptic prophages of Listeria, probably including the phage lysin.