ISOLATION OF 2 PHYSIOLOGICALLY INDUCED VARIANT STRAINS OF BACILLUS-STEAROTHERMOPHILUS NRS 2004 3A AND CHARACTERIZATION OF THEIR S-LAYER LATTICES/

During growth of Bacillus stearothermophilus NRS 2004/3a in continuous culture on complex medium, the chemical properties of the S-layer gly coprotein and the characteristic oblique lattice were maintained only if glucose was used as the sole carbon source. With increased aeration , amino acids were also metabolized, accompanied by liberation of ammo nium and by changes in the S-layer protein. Depending on the stage of fermentation at which oxygen limitation was relieved, two different va riants, one with a more delicate oblique S-layer lattice (variant 3a/V 1) and one with a square S-layer lattice (variant 3a/V2), were isolate d. During the switch from the wild-type strain to a variant or from va riant 3a/V2 to variant 3a/V1, monolayers of two types of S-layer latti ces could be demonstrated on the surfaces of single cells. S-layer pro teins from variants had different molecular sizes and a significantly lower carbohydrate content than S-layer proteins from the wild-type st rain did. Although the S-layer lattices from the wild-type and variant strains showed quite different protein mass distributions in two- and three-dimensional reconstructions, neither the amino acid composition nor the pore size, as determined by permeability studies, was signifi cantly changed. Peptide mapping and N-terminal sequencing results stro ngly indicated that the three S-layer proteins are encoded by differen t genes and are not derived from a universal precursor form.