Epigenetic regulation of carnitine metabolising enzymes in Proteus sp under aerobic conditions

Proteus sp. is able to catalyse the reversible transformation of crotonobet aine into L(-)-carnitine during aerobic growth. Contrary to other Enterobac teriaceae no reduction of crotonobetaine into gamma -butyrobetaine could be detected in the culture supernatants. Activities of L(-)-carnitine dehydra tase, carnitine racemasing system and crotonobetaine reductase could be det ermined enzymatically in cell-free extracts of Proteus sp. Small amounts of gamma -butyrobetaine were found in cell-free extracts, indicating that it accumulates in the cell and inhibits the crotonobetaine reductase. Crotonob etaine and L(-)-carnitine were able to induce enzymes of carnitine metaboli sm. gamma -Butyrobetaine and glucose repress carnitine metabolism in Proteu s sp. Other betaines are neither inducers nor repressors. Monoclonal antibo dies against purified CaiA from Escherichia coli O44K74 recognise an analog ous protein in cell-free extract of Proteus sp. No crossreactivity could be detected with monoclonal antibodies against purified CaiB and CaiD from E. coli O44K74. (C) 2001 Federation of European Microbiological Societies. Pu blished by Elsevier Science B.V. All rights reserved.