Pseudomonas phage LKA1 of the subfamily Autographivirinae encodes a tailspike protein (LKA1gp49) which binds and cleaves B-band LPS (O-specific antigen, OSA) of Pseudomonas aeruginosa PAO1. The crystal structure of LKA1gp49 catalytic domain consists of a beta-helix, an insertion domain and a C-terminal discoidin-like domain. The putative substrate binding and processing site is located on the face of the beta-helix whereas the C-terminal domain is likely involved in carbohydrates binding. NMR spectroscopy and mass spectrometry analyses of degraded LPS (OSA) fragments show an O5 serotype-specific polysaccharide lyase specificity. LKA1gp49 reduces virulence in an in vivo Galleria mellonella infection model and sensitizes P. aeruginosa to serum complement activity. This enzyme causes biofilm degradation and does not affect the activity of ciprofloxacin and gentamicin. This is the first comprehensive report on LPS-degrading lyase derived from a Pseudomonas phage. Biological properties reveal a potential towards its applications in antimicrobial design and as a microbiological or biotechnological tool.

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This report describes the structure of a putative tail fiber protein of the Acinetobacter baumannii bacteriophage AP22. The target host range of strictly lytic bacteriophage AP22 includes many clinical isolates of A. baumannii from hospitals in Chelyabinsk, Nizhny Novgorod, Moscow and St. Petersburg (Russia), but its host cell binding apparatus remains uncharacterized. Here, we report the crystal structure of the C-terminal fragment of AP22 gene product 53 (gp53) one of its two putative host cell-binding proteins. We show that gp53 forms a trimeric fiber and binds ethylene glycol and glycerol molecules that represent known surrogates of the oligosaccharide backbone. However, despite its structural similarities to other phage/virus host cell-binding fibers and its binding to small sugar-like molecules, gp53 did not inhibit AP22 infection and its role in the infection process remains unclear.

The SOS response is a cascade of consecutive reactions induced by cell DNA damage. The genes directly involved in these reactions are regulated by LexA, which binds to specific nucleotide sequences in their upstream regions. The presence of such a sequence in the regulatory gene region can be used as a criterion to identify the genes potentially involved in the SOS response. A study was made of the genes whose regulation is specific to particular taxa (Enterobacteriales, Pasteurellales, Vibrionales, Pseudomonadales, and Alteromonadales). Some of the genes identified have not been implicated in the SOS response as yet but have a conserved LexA-binding site in the regulatory region and perform a function probably associated with the cell response to DNA damage. These genes include mfd , whose product facilitates DNA repair when transcription is arrested because of DNA damage; VC0082 , coding for recombinase; and VP2449 , which is responsible for xenobiotic resistance. The composition and evolution of the LexA regulon in γ-proteobacteria are considered.

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