Schmiedel D, Hillen W
Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik der Friedrich-Alexander Universität Erlangen-Nürnberg, FRG.
Mol Gen Genet. 1996 Feb 25;250(3):259-66. doi: 10.1007/BF02174383.
Bacillus megaterium shows diauxic growth in minimal medium containing glucose and xylose. We have examined the influence of three elements that regulate xyl operon expression on diauxic growth and expression of a xylA-lacZ fusion. xylA is 13-fold repressed during growth on glucose. Induction occurs at the onset of the lag phase after glucose is consumed. Inactivation of xylR yields a two-fold increase in expression of xylA on glucose. Deletion of the catabolite responsive element (cre) has a more pronounced effect, reducing glucose repression from 13-fold in the wild type to about 2.5-fold. When xylR and cre are inactivated together a residual two-fold repression of xylA is found. Inactivation of xylR affects diauxic growth by shortening the lag phase from 70 to 40 min. In-frame deletion of ccpA results in the loss of diauxic growth, an increase in doubling time and simultaneous use of both sugars. In contrast, a strain with an inactivated cre site in xylA exhibits diauxic growth without an apparent lag phase on glucose and xylose, whereas fructose and xylose are consumed simultaneously.
巨大芽孢杆菌在含有葡萄糖和木糖的基本培养基中呈现双相生长。我们研究了调节木糖操纵子表达的三个元件对双相生长和木糖A-乳糖Z融合蛋白表达的影响。在以葡萄糖为碳源生长时，木糖A的表达被抑制了13倍。在葡萄糖消耗完后的延迟期开始时发生诱导。木糖R失活会使木糖A在葡萄糖上的表达增加两倍。分解代谢物反应元件（cre）的缺失有更显著的影响，将野生型中的葡萄糖阻遏从13倍降低到约2.5倍。当木糖R和cre一起失活时，发现木糖A仍有两倍的残留阻遏。木糖R的失活通过将延迟期从70分钟缩短到40分钟来影响双相生长。ccpA的框内缺失导致双相生长丧失、倍增时间增加以及两种糖的同时利用。相比之下，木糖A中cre位点失活的菌株在葡萄糖和木糖上呈现双相生长，且在葡萄糖上没有明显的延迟期，而果糖和木糖是同时消耗的。
