Yen K M, Serdar C M
AMGEN, Inc., Thousand Oaks, California.
Crit Rev Microbiol. 1988;15(3):247-68. doi: 10.3109/10408418809104459.
In pseudomonads, naphthalene is catabolized in a series of reactions to salicylic acid, which is further degraded via the catechol meta-cleavage, ortho-cleavage, or gentisic acid pathway to Krebs cycle intermediates. The naphthalene catabolic genes have been located on self-transmissible plasmids, in most cases, and implicated to have chromosomal locations in other cases. The best-studied naphthalene catabolic plasmid is NAH7. It carries two operons, one of which enables the host to utilize naphthalene and the other to utilize salicylate as a carbon and energy source. The product of another NAH7 gene, nahR, is required to turn on both operons in the presence of the inducer, salicylate. Several different naphthalene and salicylate catabolic plasmids have been shown to share sequence homology with NAH7. These plasmids can undergo structural alterations involving insertions and deletions during conjugations and changes in nutritional conditions. Available evidence suggests that salicylate catabolic plasmids can form from the naphthalene catabolic plasmids by structural alterations of the plasmid DNA. The gene organization and regulation, as well as the genetic instability of the naphthalene catabolic plasmids, are reminiscent of the TOL plasmids and suggest that the naphthalene catabolic plasmids and other catabolic plasmids may have evolved in a short period of time by acquiring and modifying preevolved gene clusters from host chromosomes or other plasmids.
在假单胞菌中，萘通过一系列反应被分解代谢为水杨酸，水杨酸再通过儿茶酚间位裂解、邻位裂解或龙胆酸途径进一步降解为三羧酸循环中间体。在大多数情况下，萘分解代谢基因位于自我传递质粒上，而在其他情况下则与染色体位置有关。研究得最透彻的萘分解代谢质粒是NAH7。它携带两个操纵子，其中一个使宿主能够利用萘，另一个使宿主能够利用水杨酸盐作为碳源和能源。另一个NAH7基因nahR的产物是在诱导剂水杨酸盐存在的情况下开启这两个操纵子所必需的。已证明几种不同的萘和水杨酸盐分解代谢质粒与NAH7具有序列同源性。这些质粒在接合过程中以及营养条件变化时会发生涉及插入和缺失的结构改变。现有证据表明，水杨酸盐分解代谢质粒可以通过质粒DNA的结构改变由萘分解代谢质粒形成。萘分解代谢质粒的基因组织和调控以及遗传不稳定性让人联想到TOL质粒，这表明萘分解代谢质粒和其他分解代谢质粒可能是通过从宿主染色体或其他质粒获取并修饰预先演化的基因簇在短时间内进化而来的。
