Cloning and sequencing of IS1086, an Alcaligenes eutrophus insertion element related to IS30 and IS4351

A new insertion sequence (IS), designated IS1086, was isolated from Alcaligenes eutrophus CH34 by being trapped in plasmid pJV240, which contains the Bacillus subtilis sacB and sacR genes. The 1,106-bp IS1086 element contains partially matched (22 of 28 bp) terminal-inverted repeats and a long open reading frame. Hybridization data suggest the presence of one copy of IS1086 in the strain CH34 heavy-metal resistance plasmid pMOL28 and at least two copies in its chromosome. Analysis of the IS1086 nucleotide sequence revealed striking homology with two other IS elements, IS30 and IS4351, suggesting that they are three close members in a family of phylogenetically related insertion sequences. One open reading frame of the Spiroplasma citri phage SpV1-R8A2 B was also found to be related to this IS family but to a lesser extent. Comparison of the G+C contents of IS30 and IS1086 revealed that they conform to their respective hosts (46 versus 50% for IS30 and Escherichia coli and 64.5% for IS1086 and A. eutrophus). The pressure on the AT/GC ratio led to a very different codon usage in these two closely related IS elements. Results suggesting that IS1086 transposition might be activated by some forms of stress are discussed.