An investigation into the structure and functional aspects of the cell wall of Desulfovibrio

Satisfactory preparations of cell walls from Desulfovibrio vulgaris cells grown in iron rich (C+Fe) and iron poor (C-Fe) media were obtained by partial detergent solubilisation of the cell envelopes. Polyacrylamide gel electrophoresis (PAGE) has shown the presence in the outer membrane (OM) of three major proteins (OMPs l, 2 and 3) and a relatively homogeneous lipopolysaccharide (LPS) containing no ketodeoxyoctonate (KDO). A protein of OMP 1 PAGE mobility is readily removed by the EDTA treatment of cells showing its loose association with the cell surface. Only a portion of OMP l is removed by digestion or acetate extraction indicating the existence of two proteins, OMP la and lb which comigrate in PAGE. 1251 lactoperoxidase labelling of whole cells shows proteins of OMP 1 and 3 mobility to be exposed on the cell surface. OMPs do not show hydrogenase activity and this enzyme is inactive in C-Fe cells. Numerous minor proteins are present in C+Fe OM but are absent from C-Fe OM indicating ’protection’ of the cell wall by iron to detergent solubilisation. In response to iron limitation D.vulgaris Woolwich shows an increase in the proportion of carbohydrate in the cell wall and in the yield of extractable LPS. HPLC studies have shown changes in the LPS sugars with iron limitation indicating an interaction between Fed I) and the LPS. Studies on the release of LPS from Intact cells by an EDTA washing procedure have shown a selective interaction between Fe2+ and LPS In D.vulgaris. Fe(II) appears to have an important role in the stabilisation in vivo of the OM and this selective interaction may play a part in iron uptake. In vitro OM reconstitutions using extracted material have given further support to this selective interaction. The incorporation of acetate extracted OMPs into reconstituted OM has indicated a possible iron transport function for one or more of these proteins. Calculations of Fe2+ :LPS molar binding ratios based on compositional data and these in vivo and in vitro studies show two forms of iron binding to the surface LPS, which may be applicable to the parameters at work in the natural environment of the bacteria