To better understand heavy metal tolerance in Chlamydomonas acidophila, an extremophilic green alga, we assembled its transcriptome and measured transcriptomic expression before and after Cd exposure in this and the neutrophilic model microalga Chlamydomonas reinhardtii. Genes possibly related to heavy metal tolerance and detoxification were identified and analyzed as potential key innovations that enable this species to live in an extremely acid habitat with high levels of heavy metals. In addition we provide a data set of single orthologous genes from eight green algal species as a valuable resource for comparative studies including eukaryotic extremophiles.

Our results based on differential gene expression, detection of unique genes and analyses of codon usage all indicate that there are important genetic differences in C. acidophila compared to C. reinhardtii. Several efflux family proteins were identified as candidate key genes for adaptation to acid environments. This study suggests for the first time that exposure to cadmium strongly increases transposon expression in green algae, and that oil biosynthesis genes are induced in Chlamydomonas under heavy metal stress. Finally, the comparison of the transcriptomes of several acidophilic and non-acidophilic algae showed that the Chlamydomonas genus is polyphyletic and that acidophilic algae have distinctive aminoacid usage patterns.

为了更好地了解嗜极端衣藻绿藻嗜盐衣藻对重金属的耐受性，我们在该模型和中性模型微藻莱茵衣藻中组装了其转录组并测量了镉暴露前后的转录组表达。鉴定和分析了可能与重金属耐受性和排毒有关的基因，这是使该物种能够在具有高重金属含量的极端酸性生境中生活的潜在关键创新。此外，我们提供了来自八个绿色藻类物种的单个直系同源基因的数据集，作为包括真核极端微生物在内的比较研究的宝贵资源。

我们基于差异基因表达，独特基因检测和密码子使用分析的结果均表明，与莱茵衣藻相比，嗜酸衣杆菌有重要的遗传差异。几种外排家族蛋白被鉴定为适应酸性环境的候选关键基因。这项研究首次表明，暴露于镉会大大增加绿藻中的转座子表达，并且在重金属胁迫下衣藻中会诱导出石油生物合成基因。最后，对几种嗜酸和非嗜酸藻类的转录组的比较表明，衣藻属是多系的，嗜酸藻类具有独特的氨基酸使用模式。