Study of genome of pesticide-degrading bacteria as a representative of environmental bacterium

环境细菌的适应机制是人们非常感兴趣的。日本鞘氨醇单胞菌（以前称为少动鞘氨醇单胞菌）UT 26利用重要的杀虫剂γ-六氯环己烷（HCH）作为唯一的碳和能量来源。在这项研究中，它被证明是UT 26基因组由三个大的环状复制子的3.6 Mb，670 kb，和185 kb。3.6 Mb和670 kb的复制子分别具有一个和两个拷贝的16 S核糖体RNA基因，这些复制子分别被指定为染色体（Chr）I和II。Chr Ⅰ是携带dnaA基因的一条主染色体。将γ-HCH转化为2，5-二氯氢醌的前三个lin基因（linA至linC）分散在Chr I上。185 kb质粒pCHQ 1携带用于将2，5-二氯氢醌转化为马来酰乙酸的linRED操纵子，并接合转移到另一种鞘氨醇单胞菌菌株中。编码马来酰乙酸还原酶的linF基因位于Chr II上。这些结果表明，γ-六氯环己烷完全降解的基因分散在UT 26的三个大复制子上。UT 26的内源性插入序列ISsp 1被鉴定，其可能参与UT 26基因组的重排。此外，还发现γ-六氯环己烷的代谢物对UT 26具有毒性作用，并确定了UT 26利用γ-六氯环己烷所必需的ABC型转运蛋白。这些结果表明，除了催化酶之外，其他因素对UT 26中γ-六氯环己烷的同化作用也很重要。

Mechanism for adaptation of environmental bacteria is of great interest. Sphingobium japonicum (formerly Sphingomonas paucimobilis) UT26 utilizes the important insecticide gamma-hexachlorocyclohexane (HCH) as a sole source of carbon and energy. In this study it was demonstrated that the UT26 genome consists three large circular replicons of 3.6 Mb, 670 kb, and 185 kb. The 3.6 Mb and the 670 kb replicons had one and two copies, respectively, of the 16S ribosomal RNA gene, and these replicons were designated as chromosomes (Chr) I and II, respectively. Chr I was indicated to be a main chromosome carrying the dnaA gene. The first three lin genes, linA to linC, for conversion of gamma-HCH to 2, 5-dichlorohydroquinone, were dispersed on Chr I. The 185 kb plasmid, pCHQ1, carried the linRED operon for the conversion of 2,5-dichlorohydroquinone to maleylacetate and was conjugatively transferred to another sphingomonad strain. The linF gene encoding maleylacetate reductase was located on Chr II. These results indicated that the genes for the complete gamma-HCH degradation are dispersed on the three large replicons of UT26. An endogenous insertion sequence of UT26, ISsp1, was identified, which may be involved in the rearrangement of the UT26 genome. Furthermore, it was revealed that metabolites of gamma-HCH had toxic effect on UT26, and a ABC-type transporter which was essential for the utilization of gamma-HCH in UT26 was identified. These results demonstrated the importance of factors except the catalyzing enzymes for the gamma-HCH assimilation in UT26.