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Journal of Bacteriology, March 2004, p. 1287-1296, Vol. 186, No. 5
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.5.1287-1296.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Transcriptional Regulation of Genes Encoding Arabinan-Degrading Enzymes in Bacillus subtilis

Maria Paiva Raposo,^1, José Manuel Inácio,¹ Luís Jaime Mota,^1, and Isabel de Sá-Nogueira^1,2*

Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, 2781-901 Oeiras,¹ Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal²

Received 25 August 2003/ Accepted 14 November 2003

Bacillus subtilis produces hemicellulases capable of releasing arabinosyl oligomers and arabinose from plant cell walls. In this work, we characterize the transcriptional regulation of three genes encoding arabinan-degrading enzymes that are clustered with genes encoding enzymes that further catabolize arabinose. The abfA gene comprised in the metabolic operon araABDLMNPQ-abfA and the xsa gene located 23 kb downstream most probably encode -L-arabinofuranosidases (EC 3.2.1.55). Here, we show that the abnA gene, positioned immediately upstream from the metabolic operon, encodes an endo--1,5-arabinanase (EC 3.2.1.99). Furthermore, by in vivo RNA studies, we inferred that abnA and xsa are monocistronic and are transcribed from ^A-like promoters. Transcriptional fusion analysis revealed that the expression of the three arabinases is induced by arabinose and arabinan and is repressed by glucose. The levels of induction by arabinose and arabinan are higher during early postexponential growth, suggesting a temporal regulation. Moreover, the induction mechanism of these genes is mediated through negative control by the key regulator of arabinose metabolism, AraR. Thus, we analyzed AraR-DNA interactions by in vitro quantitative DNase I footprinting and in vivo analysis of single-base-pair substitutions within the promoter regions of xsa and abnA. The results indicate that transcriptional repression of the abfA and xsa genes is achieved by a tightly controlled mechanism but that the regulation of abnA is more flexible. We suggest that the expression of genes encoding extracellular degrading enzymes of arabinose-containing polysaccharides, transport systems, and intracellular enzymes involved in further catabolism is regulated by a coordinate mechanism triggered by arabinose via AraR.

Present address: Department of Biochemistry and Molecular Biology, University of Miami, School of Medicine, Miami, FL 33136.

Present address: Biozentrum der Universität Basel, 50-70 CH-Basel, Switzerland.

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