Pseudomonas syringae pv. savastanoi lipopolysaccharide as receptor of a new bacteriophage

Abstract

A new bacteriophage was found growing on Pseudomonas syringae pv. savastanoi isolates from knots of diseased Spanish olive trees. The bacteriophage had a contractile tail (type A1 of Bradley's classification: Myoviridae) of 60 × 14 nm and an icosahedral head (diameter, 45 nm) which contains DNA. Lipopolysaccharide from the outer membrane of the host bacteria was found to be the specific receptor for the bacteriophage. Phage inactivation was measured as a percentage decrease in plaque-forming units and by electron microscopy. This lipopolysaccharide showed an ultrastructure and chemical composition very similar to those obtained from other Gram-negative pathogenic bacteria. Mild hydrolysis of the lipopolysaccharide with 1% acetic acid liberated the carbohydrate moiety (degraded polysaccharide) from the lipid A. After hydrolysis, monosaccharides and fatty acids were studied by gas–liquid chromatography. The polysaccharide was mainly composed of rhamnose, glucose, and 2-keto-3-deoxyoctulosonic acid; the lipid A contained glucosamine, phosphate, and fatty acids, both hydroxylated (3-OH 10:0, 2-OH 12:0, and 3-OH 12:0) and nonhydroxylated (12:0, 16:1, and 16:0).