CHARACTERIZATION OF NATRONOBACTERIUM-MAGADII PHAGE PHI-CH1, A UNIQUE ARCHAEAL PHAGE CONTAINING DNA AND RNA

A novel archaeal bacteriophage, Phi Ch1, was isolated from a haloalkal ophilic archaeon Natronobacterium magadii upon spontaneous lysis. The phage-cured strain N. magadii(L13) was used to demonstrate infectivity of phage Phi Ch1. The turbid-plaque morphology and the fact that N. m agadii cells isolated from plaques were able to produce phage indicate d that Phi Ch1 is a temperate phage. The phage morphology resembles ot her members of Myoviridae-infecting Halobacterium species. In solution below 2 M NaCl, the phage lost its morphological stability and infect ivity. One- and two-dimensional SDS-PAGE of phage particles revealed a t least four major and five minor proteins with molecular masses rangi ng from 15 to 80 kDa and acidic isoelectric points. Southern blot anal ysis of chromosomal DNA of a lysogenic N. magadii strain showed that P hi Chl exists as a chromosomally integrated prophage. The phage partic les contain both double-stranded, linear DNA (approx. 55 kbp) as well as several RNA species (80-700 nucleotides). Hybridization of labelled RNA fragments to total DNA from N. magadii and Phi Chl showed that th e virion-associated RNA is host encoded. Part of the phage DNA populat ion is modified and restriction analysis revealed evidence for adenine methylation. Phage Phi Chl is the first virus described for the genus Natronobacterium, and the first phage containing DNA and RNA in matur e phage particles.