Global transcriptional analysis of Cr(VI)-adapted cells of Klebsiella sp. AqSCr

Hexavalent chromium (Cr(VI)) is a highly toxic contaminant, some bacteria are able to transform it to less toxic and less soluble trivalent chromium (Cr(III)). Klebsiella sp. strain AqSCr, isolated from Cr(VI)-polluted groundwater, reduces Cr(VI) both aerobically and anaerobically, and resists up 35 mM of Cr(VI); Subculturing of AqSCr in the presence of Cr(VI) conduces to adaptation. In this study, we performed RNA-Seq of Cr(VI) adapted stage, finding 255 genes upregulated and 240 downregulated with respect to controls without Cr(VI). Genes differentially expressed are mostly associated with oxidative stress response, DNA repair and replication, sulfur starvation response, envelope-osmotic stress response, fatty acid metabolism, ribosomal subunits and energy metabolism. Among them, genes not previously associated with chromium resistance as cybB, encoding a putative superoxide oxidase, gltA2, encoding an alternative citrate synthase, and des, encoding a fatty acid desaturase were upregulated. The alternative sigma factors fecl, rpoE and rpoS were upredgulated in Cr(VI) adapted cells, then they participate in orchestate the Cr(VI)-resistance mechanisms in AqSCr strain六价铬（Hexavalent chromium, Cr(VI)）是一类剧毒污染物，部分细菌可将其转化为毒性更低、溶解度更弱的三价铬（trivalent chromium, Cr(III)）。从受Cr(VI)污染的地下水中分离得到的克雷伯氏菌属（Klebsiella sp.）菌株AqSCr，可在有氧与无氧条件下还原Cr(VI)，且能耐受最高35 mM的Cr(VI)；在Cr(VI)存在的环境中对AqSCr进行传代培养，有助于菌株产生适应性。本研究对处于Cr(VI)适应阶段的菌株开展了RNA测序（RNA-Seq），结果显示相较于未添加Cr(VI)的对照组，共有255个基因上调表达，240个基因下调表达。差异表达基因主要与氧化应激应答、DNA修复与复制、硫饥饿应答、包膜-渗透压应激应答、脂肪酸代谢、核糖体亚基及能量代谢相关。其中，此前未被发现与铬抗性相关的基因，如编码推定超氧化物氧化酶的cybB、编码替代柠檬酸合酶的gltA2以及编码脂肪酸去饱和酶的des均出现上调表达。替代σ因子（sigma factor）fecl、rpoE和rpoS在Cr(VI)适应的细胞中呈上调表达，它们参与协调AqSCr菌株的Cr(VI)抗性调控机制。