THE ROLE OF THE OUTER-MEMBRANE IN FORMALDEHYDE TOLERANCE IN ESCHERICHIA-COLI VU3695 AND HALOMONAS SP MAC

To investigate the mechanism of formaldehyde tolerance in Gram-negativ e bacteria, two formaldehyde-tolerant strains, Escherichia coli VU3695 and Halomonas sp. MAC (DSM 7328), and formaldehyde-sensitive revertan ts obtained by ethidium bromide or novobiocin treatment were studied. The presence of high levels of formaldehyde dehydrogenase activity alo ne proved insufficient to confer tolerance to high formaldehyde concen trations, as shown by the high activity displayed by formaldehyde-sens itive revertants of Halomonas MAC. Moreover, formaldehyde-tolerant str ains also proved to be tolerant to high concentrations of acetaldehyde and glutaraldehyde, which are not oxidized by formaldehyde dehydrogen ase. Treatment with sublethal concentrations of EDTA rendered the resi stant strains highly sensitive to formaldehyde without affecting the a ctivity of formaldehyde dehydrogenase. Comparison of the outer membran e proteins of formaldehyde-resistant strains with those of their sensi tive revertants showed the presence of at least one additional high mo lecular mass protein in the tolerant strains. It is concluded that for maldehyde tolerance in the bacteria studied depends on the composition and structure of the outer membrane.