The genome and proteome of Serratia bacteriophage η which forms unstable lysogens

Background: Serratia marcescens phage η is a temperate unclassified member of the Siphoviridae which had been reported as containing hypermodified guanine residues. Methods: The DNA was characterized by enzymatic digestion followed by HPLC analysis of the nucleoside composition, and by DNA sequencing and proteomic analysis. Its ability to form stable lysogens and integrate was also investigated. Results: Enzymatic digestion and HPLC analysis revealed phage η DNA did not contain modified bases. The genome sequence of this virus, determined using pyrosequencing, is 42,724 nucleotides in length with a mol% GC of 49.9 and is circularly permuted. Sixty-nine putative CDSs were identified of which 19 encode novel proteins. While seven close genetic relatives were identified, they shared sequence similarity with only genes 40 to 69 of the phage η genome, while gp1 to gp39 shared no conserved relationship. The structural proteome, determined by SDS-PAGE and mass spectrometry, revealed seven unique proteins. This phage forms very unstable lysogens with its host S. marcescens.