Description
Peptidoglycan lytic enzymes (endolysins) of bacteriophages have a major role in
bacterial lysis at the end of the phage replication cycle. These endolysins turned out to be
potential antibacterial compounds to combat a broad range of Gram-positive pathogens,
yet Gram-negative bacteria remain unharmed due to their impermeable outer membrane.
With this background, we recently characterized three new endolysins from Gramnegative
origin: OBPgp279 (Pseudomonas fluorescens phage OBP), PVP-SElgpl46
(Salmonella Enteritidis phage PVP-SEl) and 20lphi2-lgp229 (Pseudomonas
chlororaphis phage 201phi2-1). These endolysins share a modular structure with anNterminal
cell wall binding domain and a C-terrninal catalytic domain, a unique property
of endolysins belonging to giant phiKZ related phages and some other giant, non-related
myoviruses. All three endolysins showed strong muralytic activity on the peptidoglycan
of a broad range of Gram-negative bacteria, a feature linked with their modular
composition. In case of OBPgp279, the presence of the cell wall binding domain is
responsible for 38 % of the total muralytic activity. Moreover, the binding domain of
PVP-SE1gp146 has a binding affinity for Salmonella peptidoglycan that falls within the
range of typical cell adhesion molecules. Remarkably, PVP-SElgp146 shows
thermoresistant properties up to temperatures of 90°C, making it a potential candidate as
antibacterial in hurdle technology for food preservation. OBPgp279, on the other hand. is
able to pass the outer membrane of P. aeruginosa PAO 1 using an unknown mechanism,
thereby gaining access to its peptidoglycan and reduce the bacterium with !logarithmic
unit. Addition of the outer membrane permeabilizer EDTA significantly increased the
antibacterial activity of the three endolysins up to 2-3 logarithmic units. This research
offers perspectives towards elucidation of the structural differences explaining the unique
biochemical and antibacterial properties ofOBPgp279, PVP-SE1gp146 and 201phi2-
lgp229. Furthermore, these endolysins extensively enlarge the pool of potential
antibacterial compounds used for treatment of Gram-negative bacterial infections.