ISCce1 and ISCce2, two novel insertion sequences in Clostridium cellulolyticum

Two new insertion sequences,ISCce1 and ISCce2, were found to be inserted into the cipC gene of spontaneous mutants of Clostridium cellulolyticum. In these insertional mutants, the cipC gene was disrupted either by ISCce1 alone or by both ISCcel and ISCce2. ISCcel is 1,292 bp long and has one open reading frame. The open reading frame encodes a putative 348-amino-acid protein with significant levels of identity with putative proteins having unknown functions and with some transposases belonging to the IS481 and IS3 families. Imperfect 23-bp inverted repeats were found near the extremities of ISCcel. ISCce2 is 1,359 bp long, carries one open reading frame, and has imperfect 35-bp inverted repeats at its termini. The open reading frame encodes a putative 398-amino-acid protein. This protein shows significant levels of identity with transposases belonging to the IS256 family. Upon transposition, both ISCcel and ISCce2 generate 8-bp direct repeats of the target sequence, but no consensus sequences could be identified at either insertion site. ISCcel is copied at least 20 times in the genome, as assessed by Southern blot analysis. ISCce2 was found to be mostly inserted into ISCcel. In addition, as neither of the elements was detected in seven other Clostridium species, we concluded that they may be specific to the C. cellulolyticum strain used.