ENHANCED HYDROGEN-PEROXIDE SENSITIVITY AND ALTERED STRESS PROTEIN EXPRESSION IN IRON-STARVED MYCOBACTERIUM-SMEGMATIS

Mycobactericum smegmatis ATCC 607 became iron starved and did not reac h maximum population density when grown at an iron concentration of 0. 1 mu M, or less, Iron deficient cells were more susceptible than iron replete cells to H2O2 killing; 9 mM H2O2 killed about 80% of the popul ation of cultures grown at 0.05 mu M iron, while about 25 mM H2O2 was required for similar killing of cultures grown at 1 or 20 mu M iron, I n response to H2O2 iron sufficient cells produced major oxidative stre ss proteins of molecular masses of 90, 75, 65, 62, and 43 kDa (the 75 and 65 kDa proteins were identified as DnaK and GroEL homologs, respec tively), Iron deficient M. smegmatis did not upregulate the DnaK and G roEL proteins when stressed with H2O2 Both iron deficient and iron suf ficient M. smegmatis produced (at 48 degrees C) major heat shock prote ins of molecular masses of 90, 75 (DnaK), 65 (GroEL), 62, 43, and 16 k Da, The stress protein response induced by 2M ethanol challenge was si milar to the heat shock response except that ethanol induced a unique 55 kDa protein and the 16 kDa heat shock protein was not apparent, Ind uction of ethanol stress proteins was identical in high iron and low i ron cells, All of the stress agents induced expression of a 62 kDa pro tein which may also be induced by iron insufficiency, The heat and eth anol shock responses of M. smegmatis were unchanged by iron deficiency ; therefore, the absence of DnaK and GroEL from the response of iron s tarved M. smegmatis to H2O2 may be due to a specific defect (or altera tion) of the oxidative stress response during iron starvation.