Garduño R A, Phipps B M, Kay W W
Department of Biochemistry and Microbiology, University of Victoria, BC, Canada.
Can J Microbiol. 1994 Aug;40(8):622-9. doi: 10.1139/m94-099.
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.
S层是覆盖许多细菌物种整个细胞表面的准晶体蛋白质多聚体。杀鲑气单胞菌中S层（也称为A层）的存在使该细菌易于出现明显不相关的生理后果：在30℃下生长受抑制，在37℃下细胞丝化增强，以及疏水性抗生素链黑菌素和氯霉素的摄取增加。当天然A层缺失或其排列改变时，如在钙限制或钙和镁限制的细胞中、在人工重组A层的A层阴性（A-）细胞中或在无法正确组装该层的突变体中，未观察到生长抑制或丝化增强。A层阳性细胞（A+）比A-细胞对细胞内作用的抗生素链黑菌素和氯霉素敏感得多，并且链黑菌素抗性突变体主要是A-。血红素是一种已知能特异性结合A层的化合物，可减轻链黑菌素对A+细胞的毒性，但对A-细胞无效。同样，钙和镁限制的细胞或具有A层缺陷的突变体对链黑菌素的敏感性降低，并且具有重组A层的A-细胞对链黑菌素和氯霉素仍具有抗性。因此，细胞表面天然A层排列的存在，而不仅仅是A层蛋白质亚基的存在，使杀鲑气单胞菌易于出现上述生理后果。有人认为A层通过A层亚基与外膜的特异性相互作用，特别是链黑菌素或氯霉素的渗透，来特异性地影响这些后果。
