Structures of two different surface layers found in six Bacteroides strains.

The structures of crystalline layers from six Bacteroides strains were studied by electron microscopy. Two different hexagonal crystalline surface layers were found, one with a unit cell spacing of 21.5 nm and another with a spacing of 7.7 nm. A three-dimensional structure of the 21.5-nm layer and a two-dimensional projection of the 7.7-nm layer were determined to 3.0- and 3.8-nm resolution, respectively, by computerized image processing of electron micrographs. Both of these two crystalline layers were found in all six strains studied: B. pentosaceus NP333T and WPH61, B. capillus ATCC 33690T and ATCC 33691, and B. buccae ATCC 33574T and ES57. This further supports the identity of B. pentosaceus, B. capillus, and B. buccae as suggested by M. Haapasalo, K. Lounatmaa, H. Ranta, H. Shah, and K. Ranta (Int. J. Syst. Bacteriol. 35:65-72, 1985). The surface layer with 21.5-nm spacing is an intricate network with two classes of pores through the layer.