Global transcriptional analysis of Cr(VI)-adapted cells of Klebsiella sp. AqSCr. 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 Overall design: mRNA profiles of Klebsiella sp. AqSCr grown in LB medium pH 8 with and without Cr(VI) 11mM, in triplicate, using Illumina Genome Analyzer Iix

六价铬（Hexavalent chromium, Cr(VI)）是一种剧毒污染物，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Cr(VI)污染地下水分离得到的克雷伯氏菌属（Klebsiella sp.）菌株AqSCr，可在有氧与厌氧条件下还原Cr(VI)，且能耐受最高达35 mM的Cr(VI)；在Cr(VI)存在下对AqSCr进行传代培养，有助于其获得适应性。本研究对Cr(VI)适应阶段的菌株开展了RNA测序（RNA-Seq），结果显示相较于无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响应、DNA修复与复制、硫饥饿应激响应、包膜-渗透应激响应、脂肪酸代谢、核糖体亚基及能量代谢相关。其中，此前未被报道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fecl、rpoE和rpoS在Cr(VI)适应细胞中表达上调，它们参与协调AqSCr菌株的Cr(VI)抗性机制。实验设计：本研究采用Illumina Genome Analyzer Iix平台，对在pH 8的LB培养基中培养、添加与不添加11 mM Cr(VI)的克雷伯氏菌AqSCr的mRNA转录组进行测序分析，每组设置3个生物学重复。