JB Accepts, published online ahead of print on 23 October 2009

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J. Bacteriol. doi:10.1128/JB.01038-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The structure and regulation of the gab gene cluster involved in the GABA shunt controlled by a ⁵⁴ factor in Bacillus thuringiensis

Li Zhu, Qi Peng, Fuping Song^*, Yanan Jiang, Changpo Sun, Jie Zhang, and Dafang Huang^*

State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China; Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, China; Northeast Agriculture University, Harbin 150030, China

^* To whom correspondence should be addressed. Email: fpsong{at}ippcaas.cn. dfhuang{at}mail.caas.net.cn, dfhuang@ippcaas.cn.

The structure and regulation of gab gene cluster, involved in -aminobutyric acid (GABA) shunt, were studied by characterizing gabT and gabD genes cloned from Bacillus thuringiensis. Deletions of the gabT and gabD genes in B. thuringiensis strain HD-73 did not affect the growth of mutant strains in rich culture media, but the growth of a gabT deletion mutant strain was reduced in basic media (containing 0.2% GABA). Genome analysis indicates that the structure of gab gene cluster in B. thuringiensis HD-73 is different from that of Escherichia coli and Bacillus subtilis, but is common in strains of the Bacillus cereus group. This suggests that the gene cluster involved in GABA shunt is specific to the B. cereus group. Based on RT-PCR and transcriptional fusion analysis, we confirmed that the gabT and gabD genes belonged to different transcriptional units, while the gabD and gabR genes formed an operon. We also demonstrated that gabR gene played a positive regulatory role in gabD and gabT expression. GabR protein may be a ⁵⁴-dependent transcriptional activator according to the conserved domain search in NCBI, and it is highly conserved in the B. cereus group. The -24/-12 consensus sequence of a promoter upstream from gabT suggests that the promoter can be recognized by a ⁵⁴ factor. Further analysis of the genetic complementation also suggests that the expression of gabT gene is controlled by ⁵⁴ factor. Thus, the expression of the gab cluster is regulated by a ⁵⁴ factor by way of the transcription activator GabR.