Adaptation and acclimatization to formaldehyde in methylotrophs capable of high-concentration formaldehyde detoxification

1 Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK 2 Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK Correspondence Howard Dalton h.dalton{at}warwick.ac.uk Formaldehyde is a highly toxic chemical common in industrial effluents, and it is also an intermediate in bacterial metabolism of one-carbon growth substrates, although its role as a bacterial growth substrate per se has not been extensively reported. This study investigated two highly formaldehyde-resistant formaldehyde utilizers, strains BIP and ROS1; the former strain has been used for industrial remediation of formaldehyde-containing effluents. The two strains were shown by means of 16S rRNA characterization to be closely related members of the genus Methylobacterium . Both strains were able to use formaldehyde, methanol and a range of multicarbon compounds as their principal growth substrate. Growth on formaldehyde was possible up to a concentration of at least 58 mM, and survival at up to 100 mM was possible after stepwise acclimatization by growth at increasing concentrations of formaldehyde. At such high concentrations of formaldehyde, the cultures underwent a period of formaldehyde removal without growth before the formaldehyde concentration fell below 60 mM, and growth could resume. Two-dimensional electrophoresis and MS characterization of formaldehyde-induced proteins in strain BIP revealed that the pathways of formaldehyde metabolism, and adaptations to methylotrophic growth, were very similar to those seen in the well-characterized methanol-utilizing methylotroph Methylobacterium extorquens AM1. Thus, it appears that many of the changes in protein expression that allow strain BIP to grow using high formaldehyde concentrations are associated with expression of the same enzymes used by M. extorquens AM1 to process formaldehyde as a metabolic intermediate during growth on methanol. Abbreviations: 2DE, two-dimensional electrophoresis; H 4 F, tetrahydrofolate; H 4 MPT, tetrahydromethanopterin; IPG, immobilized pH gradient Three figures showing representative 2D gels of the various protein samples are available as supplementary material with the online version of this paper. Present address: Department of Agro-Industrial Technology, Faculty of Applied Science, King Mongkut's Institute of Technology (KMITNB), Piboonsongkram Rd, Bangsue, Bangkok 10800, Thailand.