Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai, 980-8577, Japan.
Environ Microbiol Rep. 2019 Oct;11(5):630-644. doi: 10.1111/1758-2229.12762. Epub 2019 May 21.
Bacterial strains capable of degrading man-made xenobiotic compounds are good materials to study bacterial evolution towards new metabolic functions. Lindane (γ-hexachlorocyclohexane, γ-HCH, or γ-BHC) is an especially good target compound for the purpose, because it is relatively recalcitrant but can be degraded by a limited range of bacterial strains. A comparison of the complete genome sequences of lindane-degrading sphingomonad strains clearly demonstrated that (i) lindane-degrading strains emerged from a number of different ancestral hosts that have recruited lin genes encoding enzymes that are able to channel lindane to central metabolites, (ii) in sphingomonads lin genes have been acquired by horizontal gene transfer mediated by different plasmids and in which IS6100 plays a role in recruitment and distribution of genes, and (iii) IS6100 plays a role in dynamic genome rearrangements providing genetic diversity to different strains and ability to evolve to other states. Lindane-degrading bacteria whose genomes change so easily and quickly are also fascinating starting materials for tracing the bacterial evolution process experimentally in a relatively short time period. As the origin of the specific lin genes remains a mystery, such genes will be useful probes for exploring the cryptic 'gene pool' available to bacteria.
能够降解人为合成的外来化合物的细菌菌株是研究细菌向新代谢功能进化的良好材料。林丹（γ-六氯环己烷，γ-HCH 或 γ-BHC）是一种特别适合该目的的目标化合物，因为它相对难以降解，但可以被有限数量的细菌菌株降解。对降解林丹的鞘氨醇单胞菌菌株的完整基因组序列的比较清楚地表明：（i）降解林丹的菌株来自许多不同的原始宿主，这些宿主招募了编码能够将林丹转化为中心代谢物的酶的 lin 基因，（ii）在鞘氨醇单胞菌中，lin 基因通过不同的质粒介导的水平基因转移获得，其中 IS6100 在基因的招募和分布中发挥作用，（iii）IS6100 在动态基因组重排中发挥作用，为不同菌株提供遗传多样性和进化到其他状态的能力。基因组变化如此容易和迅速的降解林丹的细菌也是追踪细菌在相对较短时间内的进化过程的有趣的起始材料。由于特定 lin 基因的起源仍然是一个谜，因此这些基因将是探索细菌可用的隐藏“基因库”的有用探针。
