THE GENES FOR BUTANOL AND ACETONE FORMATION IN CLOSTRIDIUM-ACETOBUTYLICUM ATCC-824 RESIDE ON A LARGE PLASMID WHOSE LOSS LEADS TO DEGENERATION OF THE STRAIN

Degeneration is the process whereby Clostridium acetobutylicum ATCC 82 4 loses the capacity to produce acetone and butanol after repeated veg etative transfers or in continuous culture. Two degenerate mutants (M5 and DG1) of C.acetobutylicum ATCC 824 do not contain the four genes ( ctfA, ctfB, adc, and aad) for acetone and butanol formation. Strain AT CC 824 contains a 210-kb plasmid (pSOL1) which is absent in M5 and DG1 . pSOL1 carries the four acetone and butanol formation genes. A restri ction map of pSOL1 was constructed by using ApaI, SmaI, SstII, and Nar I digestions. M5 and DG1 could be complemented for acetone and butanol formation by expressing the corresponding genes (ctfA, ctfB, and ade for acetone; aad for butanol) on the plasmid. Degeneration of this str ain thus appears to be the result of pSOL1 loss.