title: Characterization of a dynamic S layer on Bacillus thuringiensis.
abstract: The surfaces of three Bacillus thuringiensis strains possess an S layer composed of linear arrays of small particles arranged with p2 symmetry and with a = 8.5 nm, b = 7.2 nm, and gamma = 73 degrees. Platinum shadows of whole cells and S-layer fragments revealed the outer surface of the array to be smooth and the inner surface to be corrugated. Treatment with 2 M guanidine hydrochloride at pH 2.5 to 4 best removed the S layer for chemical characterization; it was a relatively hydrophilic 91.4-kilodalton protein with a pI of 5, no detectable carbohydrate, cysteine, methionine or tryptophan, and 21.2% nonpolar residues. No N-terminal homology with other S-layer proteins was evident. Antibody labeling experiments confirmed that the amount of S layer was proportional to the growth phase in broth cultures. Late-exponential- and stationary-growth-phase cells typically sloughed off fragments of S layer, and this may be the result of wall turnover. Indigenous autolytic activity in isolated walls rapidly digested the wall fabric, liberating soluble S-layer protein. At the same time, proteases frequently reduced the molecular weight of the 91.4-kilodalton protein, but these polypeptides could still be identified as S-layer components by immunoblotting. As cultures were serially subcultured, the frequency of appearance of the S layer diminished, and it was eventually lost. The dynamic nature of this S layer makes it atypical of most previously identified S layers and made it unusually difficult to characterize.
authors.affiliation: Department of Microbiology, College of Biological Science, University of Guelph, Ontario, Canada.
authors.forename: M D
authors.initials: MD
authors.lastname: Luckevich
authors.forename: T J
authors.initials: TJ
authors.lastname: Beveridge
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000942:Antigens, Bacterial / Q000032:analysis; D001413:Bacillus thuringiensis / Q000648:ultrastructure*; D015153:Blotting, Western; D002473:Cell Wall / Q000187:drug effects / Q000648:ultrastructure; D002614:Chelating Agents / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D008565:Membrane Proteins / Q000032:analysis / Q000648:ultrastructure; D008623:Mercaptoethanol / Q000494:pharmacology; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012492:Salts
chemical_list: D000596:Amino Acids; D000942:Antigens, Bacterial; D002614:Chelating Agents; D003902:Detergents; D008565:Membrane Proteins; D012492:Salts; D008623:Mercaptoethanol; D004229:Dithiothreitol