title: Physiological consequences of the S-layer of Aeromonas salmonicida in relation to growth, temperature, and outer membrane permeation.
abstract: S-layers are paracrystalline protein multimers that cover the entire cell surface of many bacterial species. The presence of an S-layer in Aeromonas salmonicida (also known as A-layer) predisposed this bacterium to apparently unrelated physiological consequences: inhibition of growth at 30 degrees C, enhanced cell filamentation at 37 degrees C, and enhanced uptake of the hydrophobic antibiotics streptonigrin and chloramphenicol. Growth inhibition or enhanced filamentation was not observed when the native A-layer was missing or its arrangement altered, as in Ca(2+)-limited or Ca(2+)- and Mg(2+)-limited cells, in A-layer-negative (A-) cells with an artificially reconstituted A-layer, or in mutants unable to correctly assemble this layer. A-layer-positive cells (A+) were far more sensitive to the intracellularly acting antibiotics streptonigrin and chloramphenicol than were A- cells, and streptonigrin-resistant mutants were predominantly A-. Hemin, a compound known to specifically bind to the A-layer, alleviated streptonigrin toxicity to A+, but not A-, cells. As well, Ca(2+)- and Mg(2+)-limited cells, or mutants harboring A-layer defects had a reduced sensitivity to streptonigrin, and A- cells with reconstituted A-layers remained resistant to streptonigrin and chloramphenicol. Thus, the presence of a native A-layer arrangement on the cell surface, and not the mere presence of A-layer protein subunits, predisposed A. salmonicida toward the aforementioned physiological consequences. The A-layer is suggested to specifically effect these consequences, in particular the permeation of streptonigrin or chloramphenicol, by a specific interaction of A-layer subunits with the outer membrane.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, BC, Canada.
authors.forename: R A
authors.initials: RA
authors.lastname: Garduño
authors.forename: B M
authors.initials: BM
authors.lastname: Phipps
authors.forename: W W
authors.initials: WW
authors.lastname: Kay
mesh_terms: D000333:Aeromonas / Q000502:physiology* / Q000648:ultrastructure; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D001426:Bacterial Proteins; D001692:Biological Transport; D002455:Cell Division; D002462:Cell Membrane / Q000502:physiology* / Q000648:ultrastructure; D002463:Cell Membrane Permeability; D002701:Chloramphenicol / Q000633:toxicity; D006358:Hot Temperature; D008826:Microbial Sensitivity Tests; D011166:Porphyrins / Q000494:pharmacology; D013045:Species Specificity; D013308:Streptonigrin / Q000633:toxicity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D011166:Porphyrins; C070683:surface layer protein A, Bacteria; D013308:Streptonigrin; D002701:Chloramphenicol