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J. Bacteriol. doi:10.1128/JB.01535-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Lactobacillus reuteri DSM 20016 produces cobalamin-dependent diol dehydratase in metabolosomes and metabolises 1,2-propanediol by disproportionation

Departments of Microbiology, and Pathology, University College Cork, Cork, Ireland; Department of Biochemistry, Department of Biosciences, University of Kent,Canterbury, Kent CT2 7NJ, UK; Dept of Vaccinology, Helmholtz Center of Infection Research, Braunschweig, D-16 38124, Germany

^* To whom correspondence should be addressed. Email: m.prentice{at}ucc.ie.

	Abstract

A Lactobacillus reuteri strain isolated from sourdough is known to produce the vitamin cobalamin. The organism requires this for glycerol co-fermentation by a cobalamin-dependent enzyme usually termed glycerol dehydratase in the synthesis of the antimicrobial substance reuterin. We show that the cobalamin-synthesizing capacity of another L. reuteri strain (20016, the type strain, isolated from the human gut and recently sequenced as F275) is genetically and phenotypically linked, as in Enterobacteriaceae, to the production of a cobalamin-dependent enzyme which is associated with a bacterial microcompartment (metabolosome) and known as diol dehydratase. We show that this enzyme allows L. reuteri to carry out a disproportionation reaction converting 1, 2-propanediol to propionate and propanol. The wide distribution of this operon suggests it is adapted to horizontal transmission between bacteria. However, significant genetic and phenotypic differences are noted in a Lactobacillus background compared to Enterobacteriaceae. Electron microscopy reveals that the bacterial microcompartment in L. reuteri occupies a smaller percentage of the cytoplasm than in Gram-negative bacteria. DNA sequence data shows evidence of a different regulatory control mechanism from that in Gram-negative bacteria with the presence of a catabolite responsive element (cre sequence) immediately upstream of the pdu operon encoding diol dehydratase and metabolosome structural genes in L. reuteri. The metabolosome-associated diol dehydratase we describe is the only candidate glycerol dehydratase present on inspection of the L. reuteri F275 genome sequence.