Phenotypic, Biochemical, and Structural Analysis of “S-layer” Mutants from Thermus thermophilus HB8

Abstract

S-layers are crystalline proteinaceous structures that surround a high number of wild type bacteria, being specially frequent among thermophiles (Sleytr and Messner, 1983). Their role and biochemical properties have been discussed extensively by a number of authors (Sàra and Sleytr, 1977; Baumeister and Engelhardt, 1987; Hövmoller et al., 1988), and, from these analyses, it could be concluded that there exist, at least, two well differentiated classes of S-layers, depending on the degree of interaction with the cell envelope. The first group is represented by bona fide Gram positive organisms, such as Bacillus brevis, B. stearothermophilus etc., in which the crystalline structure can be easily extracted from the envelope (Sleytr and Messner, 1983). In these bacteria, defective mutants in the S-layer synthesis with no apparent phenotypic defects can be obtained by spontaneous mutations (Ishiguro et al., 1981). Furthermore, it has been suggested that the presence of the S-layer is a counter-selected character under laboratory conditions for this group of organisms (Baumeister and Engelhardt, 1987).