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Effect of Helium Gas at Elevated Pressure on Iron Transport and Growth of Escherichia coli

¹ Department of Microbiology, Naval Medical Research Institute, Bethesda, Maryland 20014

ABSTRACT

Helium at an ambient pressure of 68 at m with 0.2 atm of O₂ shortened by 1 to 1.5 h the lag phase for growth of Escherichia coli in minimal medium supplemented with 2 µliters of cell-free culture filtrate (CFF) per ml or with 1 µM 2,3-dihydroxybenzoylserine (DHBS), an iron chelator. The lag phase of cultures not exposed to helium could be shortened by use of supplements, but higher concentrations were required—10 to 30 µliters of CFF per ml or 10 to 50 µM DHBS. Strain AN 193 of E. coli, which requires the DHBS precursor 2,3-dihydroxybenzoic acid (DHBA), grew well in media with 10 µM DHBA when exposed to helium at 68 atm, whereas 100 µM DHBA was required for growth in unexposed cultures. In the presence of 100 µM DHBA plus 1.0 µM ethylenediaminetetraactic acid, growth was inhibited at 1 and 68 atm. Growth was restored, however, by the addition of 0.1 µM FeSO₄ at 68 atm and 1.0 µM FeSO₄ at 1 atm, but lag times were invariably shorter in the pressurized cultures. Hydrostatic pressures of 68 atm did not reduce the lag phase in the presence of CFF, DHBS, or DHBA. Our results suggest that 68 atm of helium pressure, but not hydrostatic pressure, elicited a more rapid transport of iron into the cells.