Araki Naoto, Niikura Yuji, Miyauchi Keisuke, Kasai Daisuke, Masai Eiji, Fukuda Masao
Department of Bioengineering, Nagaoka University of Technology, Nagaoka, Japan.
J Mol Microbiol Biotechnol. 2011;20(1):53-62. doi: 10.1159/000323509. Epub 2011 Feb 18.
Rhodococcus jostii RHA1, a Gram-positive polychlorinated biphenyl (PCB) degrader, exhibited biphasic growth in a medium containing biphenyl (BPH) and glucose (Glc), with consumption of Glc and low 2,3-dihydroxybiphenyl 1,2-dioxygenase activity in the first growth stage. These results suggested the repression of BPH metabolism in the presence of Glc, in which RHA1 preferentially utilized Glc in the first growth stage and BPH in the second stage. A reporter assay using a transcriptional fusion of the bphAa promoter (P(bphAa)) and the luxAB luciferase genes was performed, and lower luciferase activity was observed during the first growth stage, indicating transcriptional repression of P(bphAa) activity in the presence of Glc. Transcription levels of the representative genes of five BPH catabolic enzyme gene clusters (bph/etb gene clusters) and their transcriptional regulatory genes (bphST) were examined by real-time reverse transcription PCR. The results obtained indicate that transcription of the targeted bph/etb genes, which were upregulated by BPH, was repressed in the presence of Glc. Among the substrates examined, fructose in addition to Glc induced the repression of P(bphAa) transcription. These results indicate that BPH utilization in RHA1 is under the control of carbon catabolite repression at the transcriptional level in addition to BphST-dependent transcriptional regulation.
约氏红球菌RHA1是一种革兰氏阳性多氯联苯（PCB）降解菌，在含有联苯（BPH）和葡萄糖（Glc）的培养基中呈现双相生长，在第一个生长阶段消耗Glc且2,3-二羟基联苯1,2-双加氧酶活性较低。这些结果表明在Glc存在的情况下BPH代谢受到抑制，其中RHA1在第一个生长阶段优先利用Glc，在第二个阶段利用BPH。使用bphAa启动子（P(bphAa)）与luxAB荧光素酶基因的转录融合进行了报告基因检测，在第一个生长阶段观察到较低的荧光素酶活性，表明在Glc存在的情况下P(bphAa)活性受到转录抑制。通过实时逆转录PCR检测了五个BPH分解代谢酶基因簇（bph/etb基因簇）及其转录调控基因（bphST）的代表性基因的转录水平。获得的结果表明，受BPH上调的靶向bph/etb基因的转录在Glc存在的情况下受到抑制。在所检测的底物中，除了Glc之外，果糖也诱导了P(bphAa)转录的抑制。这些结果表明，除了BphST依赖性转录调控之外，RHA1中BPH的利用在转录水平上还受到碳分解代谢物阻遏的控制。
