Takemoto Kazuhiro, Yoshitake Ikumi
Department of Bioscience and Bioinformatics, Kyushu Institute of Technology, Kawazu 680-4, Iizuka, Fukuoka 820-8502, Japan.
Metabolites. 2013 Oct 16;3(4):979-92. doi: 10.3390/metabo3040979.
Oxygen is thought to promote species and biomolecule diversity. Previous studies have suggested that oxygen expands metabolic networks by acquiring metabolites with different chemical properties (higher hydrophobicity, for example). However, such conclusions are typically based on biased evaluation, and are therefore non-conclusive. Thus, we re-investigated the effect of oxygen on metabolic evolution using a phylogenetic comparative method and metadata analysis to reduce the bias as much as possible. Notably, we found no difference in metabolic network expansion between aerobes and anaerobes when evaluating phylogenetic relationships. Furthermore, we showed that previous studies have overestimated or underestimated the degrees of differences in the chemical properties (e.g., hydrophobicity) between oxic and anoxic metabolites in metabolic networks of unicellular organisms; however, such overestimation was not observed when considering the metabolic networks of multicellular organisms. These findings indicate that the contribution of oxygen to increased chemical diversity in metabolic networks is lower than previously thought; rather, phylogenetic signals and cell-cell communication result in increased chemical diversity. However, this conclusion does not contradict the effect of oxygen on metabolic evolution; instead, it provides a deeper understanding of how oxygen contributes to metabolic evolution despite several limitations in data analysis methods.
氧气被认为能促进物种和生物分子的多样性。先前的研究表明，氧气通过获取具有不同化学性质（例如更高的疏水性）的代谢物来扩展代谢网络。然而，此类结论通常基于有偏差的评估，因此并无定论。因此，我们使用系统发育比较方法和元数据分析重新研究了氧气对代谢进化的影响，以尽可能减少偏差。值得注意的是，在评估系统发育关系时，我们发现需氧生物和厌氧生物在代谢网络扩展方面并无差异。此外，我们表明先前的研究高估或低估了单细胞生物代谢网络中含氧和缺氧代谢物之间化学性质（如疏水性）的差异程度；然而，在考虑多细胞生物的代谢网络时并未观察到这种高估现象。这些发现表明，氧气对代谢网络中化学多样性增加的贡献低于先前的认识；相反，系统发育信号和细胞间通讯导致了化学多样性的增加。然而，这一结论并不与氧气对代谢进化的影响相矛盾；相反，尽管数据分析方法存在一些局限性，但它为理解氧气如何促进代谢进化提供了更深入的认识。
