A New ICE clc Subfamily Integrative and Conjugative Element Responsible for Horizontal Transfer of Biphenyl and Salicylic Acid Catabolic Pathway in the PCB-Degrading Strain Pseudomonas stutzeri KF716.

Integrative and conjugative elements (ICEs) are chromosomally integrated self-transmissible mobile genetic elements. Although some ICEs are known to carry genes for the degradation of aromatic compounds, information on their genetic features is limited. We identified a new member of the ICE clc family carrying biphenyl catabolic bph genes and salicylic acid catabolic sal genes from the PCB-degrading strain Pseudomonas stutzeri KF716. The 117-kb ICE _bph-sal KF716 contains common core regions exhibiting homology with those of degradative ICE clc from P. knackmussii B13 and ICE _XTD from Azoarcus sp. CIB. A comparison of the gene loci collected from the public database revealed that several putative ICEs from P. putida B6-2 , P, alcaliphila JAB1, P. stutzeri AN10 , and P. stutzeri 2A20 had highly conserved core regions with those of ICE _bph-sal KF716, along with the variable region that encodes the catabolic genes for biphenyl, naphthalene, toluene, or phenol. These data indicate that this type of ICE subfamily is ubiquitously distributed within aromatic compound-degrading bacteria. ICE _bph-sal KF716 was transferred from P. stutzeri KF716 to P. aeruginosa PAO1 via a circular extrachromosomal intermediate form. In this study, we describe the structure and genetic features of ICE _bph-sal KF716 compared to other catabolic ICEs.