Physical and genetic map of the genome of Buchnera, the primary endosymbiont of the pea aphid Acyrthosiphon pisum

The genome of Buchnera, an endosymbiotic bacterium of the pea aphid Acyrtho siphon pisum, was characterized by pulse-field gel electrophoresis (PFGE) a s a circular DNA molecule of 657 kb. The enzymes I-CeuI, CpoI, ApaI, SmaI, NaeI, SacII, MluI, FspI, and NruI were used to cleave the DNA of Buchnera i nto fragments of suitable size for PFGE analysis. A physical map of the Buc hnera genome, including restriction fragments from seven of these enzymes, was constructed using double cutting, partial digestion, and hybridization with linking fragments, and 29 genes and operons were localized on the map. In addition, the genomic map of Buchnera was compared with those of Escher ichia coli and Haemophilus influenzae. The gene order in Buchnera is more s imilar to that of E. coli than to H. influenzae. The dramatic shrinkage of the Buchnera genome compared with those of other members of the closely rel ated Enterobacteriaceae family is discussed in terms of evolution under the influence of the intracellular symbiotic association.