Reassembly in vitro of hexagonal surface arrays in a protein-producing bacterium, Bacillus brevis 47

Abstract

Bacillus brevis 47 had two protein layers (the outer and middle walls) and a peptidoglycan layer (the inner wall) and contained two major proteins with approximate molecular weights of 130,000 and 150,000 in the cell wall. Both the total and Triton-insoluble envelopes revealed a hexagonal lattice array with a lattice constant of 14.5 nm. The proteins of 130,000 and 150,000 molecular weight isolated from the Triton-insoluble envelopes were serologically different from each other and assembled in vitro on the peptidoglycan layer. A mixture of 130,000- and 150,000-molecular-weight proteins led to the formation of a five-layered cell wall structure, two layers on each side of the peptidoglycan layer, which resembled closely the Triton-insoluble envelopes. A three-layered cell wall structure, one layer on each side of the peptidoglycan layer, was reconstituted when only the 150,000-molecular-weight protein was used. Both five- and three-layered cell walls reconstituted in vitro also contained hexagonally arranged arrays with the same lattice constant as that of the total and Triton-insoluble envelopes. A mutant, strain 47-57, which was isolated as a phage-resistant colony, had a two-layered cell wall consisting of the middle and inner wall layers and contained only 150,000-molecular-weight protein as the major cell wall protein. The cell envelopes of the mutant revealed the hexagonal arrays with the same lattice constant as that of the wild-type cell envelopes. We conclude that the outer and middle wall layers consist of proteins with approximate molecular weights of 130,000 and 150,000, respectively. Furthermore, the 150,000-molecular-weight protein formed the hexagonal arrays in the middle wall layer.