Summary auto-generated
This study investigated the mechanism of formaldehyde tolerance in two Gram-negative bacteria: Escherichia coli VU3695 and Halomonas sp. MAC. The researchers compared formaldehyde-tolerant strains with formaldehyde-sensitive revertants obtained through mutagenesis. While both tolerant and sensitive strains possessed formaldehyde dehydrogenase enzyme activity, the enzyme alone was insufficient to confer tolerance, as sensitive revertants also displayed high enzyme activity. Notably, tolerant strains showed cross-tolerance to acetaldehyde and glutaraldehyde, aldehydes not metabolized by formaldehyde dehydrogenase, further evidence that enzyme activity alone cannot explain tolerance. EDTA treatment, which disrupts the outer membrane, rendered tolerant strains highly sensitive to formaldehyde without affecting enzyme activity. Outer membrane protein analysis revealed that tolerant strains possessed additional high molecular mass proteins (>143 kDa in E. coli, 98-143 kDa in Halomonas) absent or reduced in sensitive revertants. For Halomonas MAC, a 15 kb plasmid was present but not required for tolerance, as plasmid-free tolerant strains existed. The findings conclusively demonstrate that formaldehyde tolerance depends on outer membrane composition and structure rather than enzymatic activity alone.
Key findings
- Formaldehyde dehydrogenase activity alone is insufficient for formaldehyde tolerance, as sensitive revertants possess comparable enzyme levels to tolerant strains
- EDTA-induced disruption of outer membrane integrity sensitizes tolerant bacteria to formaldehyde without affecting dehydrogenase activity, implicating the outer membrane as the critical barrier
- Tolerant strains possess additional high molecular mass proteins in their outer membrane (>143 kDa in E. coli, 98-143 kDa in Halomonas) that are absent or reduced in sensitive revertants
- Cross-tolerance to acetaldehyde and glutaraldehyde, which are not oxidized by formaldehyde dehydrogenase, demonstrates that tolerance is not enzyme-dependent
- Formaldehyde tolerance in Halomonas MAC is not plasmid-mediated, as plasmid-free tolerant strains were isolated through novobiocin treatment
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Abstract
To investigate the mechanism of formaldehyde tolerance in Gram-negative bacteria, two formaldehyde-tolerant strains, Escherichia coli VU3695 and Halomonas sp. MAC (DSM 7328), and formaldehyde-sensitive revertants obtained by ethidium bromide or novobiocin treatment were studied. The presence of high levels of formaldehyde dehydrogenase activity alone proved insufficient to confer tolerance to high formaldehyde concentrations, as shown by high activity displayed by formaldehyde- sensitive revertants of Halomonas MAC. Moreover, formaldehyde-tolerant strains also proved to be tolerant to high concentrations of acetaldehyde and glutaraldehyde, which are not oxidized by formaldehyde dehydrogenase. Treatment with sublethal concentrations of EDTA rendered the resistant strains highly sensitive to formaldehyde without affecting the activity of formaldehyde dehydrogenase. Comparison of the outer membrane proteins of formaldehyde-resistant strains with those of their sensitive revertants showed the presence of at least one additional high molecular mass protein in the tolerant strains. It is concluded that formaldehyde tolerance in the bacteria studied depends on the composition and structure of the outer membrane.