Characterization and Role of tbuX in Utilization of Toluene by Ralstonia pickettii PKO1

Biotechnology Center for Agriculture and the Environment, Rutgers University, New Brunswick, New Jersey 08901-8520, USA.
Journal of Bacteriology (Impact Factor: 2.81). 04/2000; 182(5):1232-42. DOI: 10.1128/JB.182.5.1232-1242.2000
Source: PubMed


The tbu regulon of Ralstonia pickettii PKO1 encodes enzymes involved in the catabolism of toluene, benzene, and related alkylaromatic hydrocarbons. The first operon
in this regulon contains genes that encode the tbu pathway's initial catabolic enzyme, toluene-3-monooxygenase, as well as TbuT, the NtrC-like transcriptional activator for
the entire regulon. It has been previously shown that the organization of tbuT, which is located immediately downstream of tbuA1UBVA2C, and the associated promoter (PtbuA1) is unique in that it results in a cascade type of up-regulation of tbuT in response to a variety of effector compounds. In our efforts to further characterize this unusual mode of gene regulation,
we discovered another open reading frame, encoded on the strand opposite that of tbuT, 63 bp downstream of the tbuT stop codon. The 1,374-bp open reading frame, encoding a 458-amino-acid peptide, was designatedtbuX. The predicted amino acid sequence of TbuX exhibited significant similarity to several putative outer membrane proteins from
aromatic hydrocarbon-degrading bacteria, as well as to FadL, an outer membrane protein needed for uptake of long-chain fatty
acids inEscherichia coli. Based on sequence analysis, transcriptional and expression studies, and deletion analysis, TbuX seems to play an important
role in the catabolism of toluene inR. pickettii PKO1. In addition, the expression oftbuX appears to be regulated in a manner such that low levels of TbuX are always present within the cell, whereas upon toluene
exposure these levels dramatically increase, even more than those of toluene-3-monooxygenase. This expression pattern may
relate to the possible role of TbuX as a facilitator of toluene entry into the cell.

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Available from: Ronald H Olsen
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    • "The plates were incubated at 30°C for 3 days. Ctl refers to clone containing pBBR1MCS2, and pTcpY refers to the clones containing constitutively expressed tcpY Biodegradation a b-barrel outer membrane protein because of its structural similarity to characterized b-barrel outer membrane proteins, including FadL, TodX and TbuX (Wang et al. 1995; Kahng et al. 2000; van den Berg 2005). The toxicity and uptake studies support that TcpY facilitates the transport of polychlorophenols across the outer membrane of gram negative bacterium C. necator. "
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    • "The role of phenol as an inducer for TpMO is unclear in the literature. Early work indicates phenol is not an inducer for TpMO (Leahy et al ., 1997; Olsen et al ., 1994) whereas later works show it is an inducer, albeit a poor one compared with toluene and benzene (Kahng et al ., 2000). Therefore phenol is listed both as an inducer and a non-inducer in Table I. "
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