The chromosome of Bacteroides fragilis strain YCH46 was shown to be a single circular DNA molecule of about 5.3 Mb having 16 Noti, seven Ascl, and six I-Ceul sites. A physical map of the chromosome was constructed by four independent experimental approaches: linking clone analysis. cross-Southern hybridization, partial restriction digestion, and two-dimensional pulsed-Field get electrophoresis. Six rRNA operons and 10 known genes were localized on the physical map. (C) 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.