Bischoff M, Entenza J M, Giachino P
Institute of Medical Microbiology, University of Zürich, CH-8028 Zürich, Switzerland.
J Bacteriol. 2001 Sep;183(17):5171-9. doi: 10.1128/JB.183.17.5171-5179.2001.
The growth phase-dependent activity profile of the alternate transcription factor sigma(B) and its effects on the expression of sar and agr were examined in three different Staphylococcus aureus strains by Northern blot analyses and by the use of reporter gene fusion experiments. Significant sigma(B) activity was detectable only in the clinical isolates MSSA1112 and Newman, carrying the wild-type rsbU allele, but not in the NCTC8325 derivative BB255, which is defective in rsbU. sigma(B) activity peaked in the late exponential phase and diminished towards the stationary phase when bacteria were grown in Luria-Bertani medium. Transcriptional analysis and a sarP1-sarP2-sarP3 (sarP1-P2-P3)-driven firefly luciferase (luc+) reporter gene fusion demonstrated a strong sigma(B) activity- and growth phase-dependent increase in sar expression that was totally absent in either rsbU or Delta rsbUVWsigB mutants. In contrast, expression of the agr locus, as measured by RNAIII levels and by an hldp::luc+ fusion, was found to be higher in the absence of sigma(B) activity, such as in rsbU or Delta rsbUVWsigB mutants, than in wild-type strains. Overexpression of sigma(B) in BB255 derivatives resulted in a clear increase in sarP1-P2-P3::luc+ expression as well as a strong decrease in hldp::luc+ expression. The data presented here suggest that sigma(B) increases sar expression while simultaneously reducing the RNAIII level in a growth phase-dependent manner.
通过Northern印迹分析和使用报告基因融合实验，在三种不同的金黄色葡萄球菌菌株中检测了交替转录因子σ(B)的生长阶段依赖性活性谱及其对sar和agr表达的影响。仅在携带野生型rsbU等位基因的临床分离株MSSA1112和Newman中检测到显著的σ(B)活性，而在rsbU有缺陷的NCTC8325衍生物BB255中未检测到。当细菌在Luria-Bertani培养基中生长时，σ(B)活性在指数后期达到峰值，并在稳定期逐渐降低。转录分析和sarP1-sarP2-sarP3（sarP1-P2-P3）驱动的萤火虫荧光素酶（luc+）报告基因融合表明，sar表达呈现出强烈的σ(B)活性和生长阶段依赖性增加，而在rsbU或Delta rsbUVWsigB突变体中则完全不存在这种增加。相反，通过RNAIII水平和hldp::luc+融合测量发现，在没有σ(B)活性的情况下，如在rsbU或Delta rsbUVWsigB突变体中，agr位点的表达高于野生型菌株。在BB255衍生物中过表达σ(B)导致sarP1-P2-P3::luc+表达明显增加，同时hldp::luc+表达强烈降低。此处提供的数据表明，σ(B)以生长阶段依赖性方式增加sar表达，同时降低RNAIII水平。
