Glass Jennifer B, Kretz Cecilia B, Ganesh Sangita, Ranjan Piyush, Seston Sherry L, Buck Kristen N, Landing William M, Morton Peter L, Moffett James W, Giovannoni Stephen J, Vergin Kevin L, Stewart Frank J
School of Earth and Atmospheric Sciences, Georgia Institute of Technology Atlanta, GA, USA ; School of Biology, Georgia Institute of Technology Atlanta, GA, USA.
School of Earth and Atmospheric Sciences, Georgia Institute of Technology Atlanta, GA, USA.
Front Microbiol. 2015 Sep 28;6:998. doi: 10.3389/fmicb.2015.00998. eCollection 2015.
Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is known about the metalloenyzme inventory of anaerobic marine microbial communities despite their importance to the nitrogen cycle. We compared dissolved O2, NO[Formula: see text], NO[Formula: see text], Fe and Cu concentrations with nucleic acid sequences encoding Fe and Cu-binding proteins in 21 metagenomes and 9 metatranscriptomes from Eastern Tropical North and South Pacific oxygen minimum zones and 7 metagenomes from the Bermuda Atlantic Time-series Station. Dissolved Fe concentrations increased sharply at upper oxic-anoxic transition zones, with the highest Fe:Cu molar ratio (1.8) occurring at the anoxic core of the Eastern Tropical North Pacific oxygen minimum zone and matching the predicted maximum ratio based on data from diverse ocean sites. The relative abundance of genes encoding Fe-binding proteins was negatively correlated with O2, driven by significant increases in genes encoding Fe-proteins involved in dissimilatory nitrogen metabolisms under anoxia. Transcripts encoding cytochrome c oxidase, the Fe- and Cu-containing terminal reductase in aerobic respiration, were positively correlated with O2 content. A comparison of the taxonomy of genes encoding Fe- and Cu-binding vs. bulk proteins in OMZs revealed that Planctomycetes represented a higher percentage of Fe genes while Thaumarchaeota represented a higher percentage of Cu genes, particularly at oxyclines. These results are broadly consistent with higher relative abundance of genes encoding Fe-proteins in the genome of a marine planctomycete vs. higher relative abundance of genes encoding Cu-proteins in the genome of a marine thaumarchaeote. These findings highlight the importance of metalloenzymes for microbial processes in oxygen minimum zones and suggest preferential Cu use in oxic habitats with Cu > Fe vs. preferential Fe use in anoxic niches with Fe > Cu.
铁（Fe）和铜（Cu）是微生物金属酶的必需辅因子，但尽管厌氧海洋微生物群落对氮循环很重要，人们对其金属酶组成却知之甚少。我们比较了东热带北太平洋和南太平洋海洋氧含量最小值区域的21个宏基因组和9个宏转录组以及百慕大大西洋时间序列站的7个宏基因组中溶解氧、一氧化氮、亚硝酸盐、铁和铜的浓度，以及编码铁和铜结合蛋白的核酸序列。溶解铁浓度在有氧-缺氧过渡带上部急剧增加，在东热带北太平洋海洋氧含量最小值区域的缺氧核心处铁与铜的摩尔比最高（1.8），与基于不同海洋站点数据预测的最大比值相符。编码铁结合蛋白的基因相对丰度与氧气呈负相关，这是由缺氧条件下参与异化氮代谢的铁蛋白编码基因显著增加所驱动的。编码细胞色素c氧化酶（有氧呼吸中含铁和铜的末端还原酶）的转录本与氧气含量呈正相关。对海洋氧含量最小值区域中编码铁和铜结合蛋白与大量蛋白的基因分类进行比较后发现，浮霉菌门在铁基因中占比更高，而奇古菌门在铜基因中占比更高，特别是在氧跃层。这些结果与海洋浮霉菌基因组中编码铁蛋白的基因相对丰度较高以及海洋奇古菌基因组中编码铜蛋白的基因相对丰度较高的情况大致一致。这些发现突出了金属酶对海洋氧含量最小值区域微生物过程的重要性，并表明在铜含量大于铁含量的有氧生境中优先使用铜，而在铁含量大于铜含量的缺氧生态位中优先使用铁。
