Purification and disposition of a surface protein associated with virulence of Aeromonas salmonicida

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Abstract
Virulent strains of A. salmonicida observed by EM were characterized by an outer layer exhibiting a tetragonal repeat pattern. Attenuated strains had a 2.5 .times. 103- to 5 .times. 103-fold reduction in virulence and lost the outer layer, autoaggregating properties, and a 49 kdalton protein (A protein) simultaneously. The A protein is the major protein component of outer membrane fractions of virulent strains. A variety of radiolabeling studies showed that this protein was surface localized and that it provided an effective barrier against iodination of other outer membrane proteins with either lactoperoxidase or diazoiodosulfanilic acid; A protein was not labeled with lactoperoxidase but was specifically labeled with diazoiodosulfanilic acid. The A protein was purified by selective extraction with detergent and guanidine hydrochloride, and its amino acid composition was determined. The properties of A protein are compared with those of other bacterial surface layer proteins.