Antimicrobial properties and morphological characteristics of two Photorhabdus luminescens strains

The biological properties of two Photorhabdus luminescens isolates (MU1 and MU2) of environmental source and the activity of antimicrobial agar diffus ible agents (AADA) produced by the same are reported. With regard to cultur al features, two variant forms for P. luminescens MU1 and three for P. lumi nescens MU2 (including an intermediate phase I-like form) have been found. These three forms differ in biological and biochemical properties: P-lactam ase, urease, bioluminescence and antimicrobial agar diffusible substance pr oduction associated with the phase I form, were less evident in the interme diate phase I-like MU2 and were absent in phase II form. Antimicrobial acti vity was present in both strains, with the production of a large amount of a diffusible compound with a wide spectrum of action against bacteria of ot her genera; a reduced activity against correlated species was also observed . Examination by electron microscopy of MU1 and MU2 purified broth cultures revealed the presence of particles belonging to the class of the phage tai l-like bacteriocins, described in recent studies as responsible for antibac terial activity against correlated bacteria, a result never confirmed "in v itro". A plasmid of 21 Mdal was observed in all the form variants of P. lum inescens MU2, suggesting that plasmids are not involved in the transition f rom primary to secondary phase; no plasmid was detected in P. luminescens M U1.