Isolation and characterization of hemin-permeable, envelope-defective mutants of Salmonella typhimurium

From Salmonella typhimurium LT2 hemA (δ-aminolevulinic acid requiring) 15 mutants were isolated which grew on the hydrophobic compound hemin. All had increased sensitivity to antibiotics such as vancomycin, bacitracin, novobiocin, erythromycin, rifampin, and oleandomycin, and were considered to be envelope mutants (Env−). Half the mutants were rough, based on altered bacteriophage sensitivity and deoxycholate sensitivity, whereas the remainder were smooth; three of the smooth mutants were studied in detail. They gave increased uptake of gentian violet but no increase in leakage of a periplasmic protein, RNase I. The total membranes and fractions from sucrose gradient centrifugations representing inner and outer membranes of the wild type and three mutants were examined by sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS–PAGE) and isoelectric focussing – PAGE (IEF–PAGE). The major outer membrane proteins (molecular weights (MW)33 000, 34 000, 35 000, and 36 000) showed no or very little alterations in the Env− mutants. In SA1926 (env-52) one protein spot at MW 48 000, proven to be an outer membrane protein, was missing, whereas a new spot appeared nearby, and other proteins in this area of the gel were reduced. An Env+ transductant selected from this strain had the wild-type protein pattern restored. The two other Env− mutants had similar but not identical changes in protein composition.