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Applied and Environmental Microbiology, March 2007, p. 1842-1850, Vol. 73, No. 6
0099-2240/07/$08.00+0     doi:10.1128/AEM.02082-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Analysis of the Mechanism and Regulation of Lactose Transport and Metabolism in Clostridium acetobutylicum ATCC 824{triangledown}

Yang Yu,1,{dagger} Martin Tangney,2 Hans C. Aass,1 and Wilfrid J. Mitchell1*

School of Life Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, United Kingdom,1 School of Life Sciences, Merchiston Campus, Napier University, Edinburgh EH10 5DT, United Kingdom2

Received 4 September 2006/ Accepted 21 December 2006

Although the acetone-butanol-ethanol fermentation of Clostridium acetobutylicum is currently uneconomic, the ability of the bacterium to metabolize a wide range of carbohydrates offers the potential for revival based on the use of cheap, low-grade substrates. We have investigated the uptake and metabolism of lactose, the major sugar in industrial whey waste, by C. acetobutylicum ATCC 824. Lactose is taken up via a phosphoenolpyruvate-dependent phosphotransferase system (PTS) comprising both soluble and membrane-associated components, and the resulting phosphorylated derivative is hydrolyzed by a phospho-ß-galactosidase. These activities are induced during growth on lactose but are absent in glucose-grown cells. Analysis of the C. acetobutylicum genome sequence identified a gene system, lacRFEG, encoding a transcriptional regulator of the DeoR family, IIA and IICB components of a lactose PTS, and phospho-ß-galactosidase. During growth in medium containing both glucose and lactose, C. acetobutylicum exhibited a classical diauxic growth, and the lac operon was not expressed until glucose was exhausted from the medium. The presence upstream of lacR of a potential catabolite responsive element (cre) encompassing the transcriptional start site is indicative of the mechanism of carbon catabolite repression characteristic of low-GC gram-positive bacteria. A pathway for the uptake and metabolism of lactose by this industrially important organism is proposed.

* Corresponding author. Mailing address: School of Life Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, United Kingdom. Phone: 44 131 451 3459. Fax: 44 131 451 3009. E-mail: w.j.mitchell{at}hw.ac.uk.

{triangledown} Published ahead of print on 5 January 2007.

{dagger} Present address: Mascoma Corporation, 16 Cavendish Court, Suite 2A, Lebanon, NH 03766.

Applied and Environmental Microbiology, March 2007, p. 1842-1850, Vol. 73, No. 6
0099-2240/07/$08.00+0     doi:10.1128/AEM.02082-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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