The transposable element IS4712 prevents S-layer gene (sbsA) expression inBacillus stearothermophilus and also affects the synthesis of altered surface layer proteins

Cell surface (S)-layer protein synthesis in Bacillus stearothermophilus PV7 2/p6 is blocked when cells are grown at elevated temperature. From a cultur e exhibiting the S-layer-negative phenotype, the S-layer deficient mutant T 5 (SbsA(-)) was isolated. Genetic analysis of the S-Layer-encoding gene (sb sA) of mutant T5 revealed an insertion element (IS4712) integrated into the upstream regulatory region of the S-layer gene, thereby blocking sbsA tran scription. The insertion element consists of 1371 base pairs which are flan ked by two perfect inverted terminal repeats. Sequence similarity to other transposases of the IS4 family was detected. DNA-DNA hybridizations demonst rated that multiple homologues of IS4712 were also present within the genom es of several other thermophilic bacillus isolates. Attempts to isolate Sbs A(+) revertants failed. Instead, cells with altered surface proteins were d etected. The synthesis of the altered S-layer proteins was correlated with the presence of IS4712 along with the occurrence of deletions in the sbsA c oding region. Furthermore imprecise excision of IS4712 was detected. This w ork demonstrated that B. stearothermophilus is able to express at least fou r different S-layer proteins and that blocking of sbsA transcription by the insertion element IS4712 is associated with the expression of altered surf ace proteins.