Identification, Expression and Activity of Candidate Nitrite Reductases From Orange Beggiatoaceae, Guaymas Basin
Identification, Expression and Activity of Candidate Nitrite Reductases From Orange Beggiatoaceae, Guaymas Basin
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DOI：
10.3389/fmicb.2019.00644
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发表时间：
2019-03-29
影响因子：
5.2
通讯作者：
Teske, Andreas
中科院分区：
文献类型：
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作者：
Buckley, Andrew;MacGregor, Barbara;Teske, Andreas
瓜伊马斯盆地热液沉积物中橙色丝状Beggiatoaceae形成大量微生物席；这些细菌被认为用硝酸盐和亚硝酸盐作为电子受体来氧化硫化物。从先前分析的橙Beggiatoaceae细丝的基因组中，克隆并在大肠杆菌中表达了三个具有亚硝酸盐还原功能的酶的候选基因——橙八血红素细胞色素、nirS亚硝酸盐还原酶和亚硝酸盐/四硫酸还原八血红素细胞色素。与从微生物席中获得的多功能天然蛋白相比，表达和纯化的橙色细胞色素的亚硝酸盐还原活性降低。nirS基因产物在体外表现出亚硝酸盐还原活性，但在凝胶中无还原活性；亚硝酸盐/四硫酸还原八血红素细胞色素在体外同时还原亚硝酸盐和四硫酸。系统发育分析表明，与其他候选亚硝酸盐还原酶相比，橙色Beggiatoaceae nirS不与其他大型硫氧化细菌中的对应物形成单系谱系，很可能是最近通过横向基因转移获得的。橙Beggiatoaceae的亚硝酸盐/四硫酸还原酶与亚硝酸盐和四硫酸还原酶有关，这些还原酶主要由gamma变形菌（包括热液喷口管虫的专性内共生体）所拥有。因此，橙瓜伊马斯盆地Beggiatoaceae具有至少三种不同的亚硝酸盐还原功能酶的曲目。通过展示在亚硝酸盐还原中具有潜在作用的酶的不同寻常的多样性，我们表明在高动态，富含硫化物的热液喷口栖息地中的细菌适应这些通常禁止硝酸盐和亚硝酸盐还原的条件。在橙瓜（Guaymas Beggiatoaceae）的情况下，经典的反硝化作用似乎被不同的多功能酶所取代，用于亚硝酸盐和四硫酸盐的还原；由此产生的生态生理灵活性为这些Beggiatoaceae在热液热点地区的优势提供了新的关键。
Orange filamentous Beggiatoaceae form massive microbial mats on hydrothermal sediments in Guaymas Basin; these bacteria are considered to oxidize sulfide with nitrate and nitrite as electron acceptors. From a previously analyzed genome of an orange Beggiatoaceae filament, three candidate genes for enzymes with nitrite-reducing function - an orange octaheme cytochrome, a nirS nitrite reductase, and a nitrite/tetrathionate-reducing octaheme cytochrome - were cloned and expressed in Escherichia coll. The expressed and purified orange cytochrome showed reduced nitrite-reducing activity compared to the multifunctional native protein obtained from microbial mats. The nirS gene product showed in vitro but no in-gel nitrite-reducing activity; and the nitrite/tetrathionate-reducing octaheme cytochrome was capable of reducing both nitrite and tetrathionate in vitro. Phylogenetic analysis shows that the orange Beggiatoaceae nirS, in contrast to the other candidate nitrite reductases, does not form monophyletic lineages with its counterparts in other large sulfur-oxidizing bacteria, and most likely represents a recent acquisition by lateral gene transfer. The nitrite/tetrathionate-reducing enzyme of the orange Beggiatoaceae is related to nitrite- and tetrathionate reductases harbored predominantly by Gammaproteobacteria, including obligate endosymbionts of hydrothermal vent tubeworms. Thus, the orange Guaymas Basin Beggiatoaceae have a repertoire of at least three different functional enzymes for nitrite reduction. By demonstrating the unusual diversity of enzymes with a potential role in nitrite reduction, we show that bacteria in highly dynamic, sulfide-rich hydrothermal vent habitats adapt to these conditions that usually prohibit nitrate and nitrite reduction. In the case of the orange Guaymas Beggiatoaceae, classical denitrification appears to be replaced by different multifunctional enzymes for nitrite and tetrathionate reduction; the resulting ecophysiological flexibility provides a new key to the dominance of these Beggiatoaceae in hydrothermal hot spots.