Nitrous oxide reduction by two partial denitrifying bacteria requires denitrification intermediates that cannot be respired
Nitrous oxide reduction by two partial denitrifying bacteria requires denitrification intermediates that cannot be respired
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DOI：
10.1128/aem.01741-23
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发表时间：
2023-12-11
影响因子：
4.4
通讯作者：
McKinlay，James B.
中科院分区：
文献类型：
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作者：
LaSarre，Breah;Morlen，Ryan;McKinlay，James B.
反硝化作用是一种厌氧呼吸，其中硝酸盐（NO3-）依次通过亚硝酸盐（NO2-），一氧化氮和一氧化二氮（N2 O）被四种还原酶还原为二氮气体（N2）。部分分解细菌仅拥有这四种还原酶中的一种或几种，并将它们用作独立的呼吸模块。然而，目前尚不清楚部分反硝化酶是否能感知并响应其还原酶库之外的反硝化中间产物。本文对两株紫色非硫细菌Rhodobacter palustrisCGA 0092和Rhodobacter capsulatusSB 1003的脱硫能力进行了研究。每一种都有与它们的基因组注释相匹配的分解能力; CGA 0092将NO2-还原为N2，SB 1003将N2 O还原为N2。对于每一种细菌，N2 O还原可以用于在光下在富电子有机化合物上生长期间的电子平衡和在黑暗中通过呼吸进行能量转化。然而，N2 O还原需要补充反硝化中间体，包括那些没有相关的反硝化酶。对于CGA 0092，NO3−是一种稳定的、不可催化的分子，足以激活N2 O还原。使用β-半乳糖苷酶报告基因，我们发现NO3−至少部分通过刺激N2 O还原酶基因表达而起作用。在SB 1003中，NO2-而不是NO3-激活了N2 O还原，但NO2-被缓慢去除，可能是通过混杂的酶活性。我们的研究结果表明，部分反硝化菌仍然可以受到调节的反硝化中间体，他们不能使用。重要反硝化是一种形式的微生物呼吸，其中硝酸盐通过几个氮氧化物中间体转化为无害的二氮气体。部分反硝化细菌，其中个别地有一些但不是全部的反硝化酶，可以实现完全的反硝化作为一个群体通过交叉喂养氮氧化物中间体。然而，最后一个中间体一氧化二氮（N2 O）是一种经常逃逸的强效温室气体，这促使人们努力了解和提高脱氮效率。在这里，我们发现，至少有一些部分分解N2 O还原剂可以感知和响应氮氧化物中间体，否则他们不能使用。因此，氮氧化物对部分硝化细菌的调节作用是理解和应用硝化细菌群落对抗温室气体排放的重要考虑因素。
Denitrification is a form of anaerobic respiration wherein nitrate (NO3−) is sequentially reduced via nitrite (NO2−), nitric oxide, and nitrous oxide (N2O) to dinitrogen gas (N2) by four reductase enzymes. Partial denitrifying bacteria possess only one or some of these four reductases and use them as independent respiratory modules. However, it is unclear if partial denitrifiers sense and respond to denitrification intermediates outside of their reductase repertoire. Here, we tested the denitrifying capabilities of two purple nonsulfur bacteria,Rhodopseudomonas palustrisCGA0092 andRhodobacter capsulatusSB1003. Each had denitrifying capabilities that matched their genome annotation; CGA0092 reduced NO2−to N2, and SB1003 reduced N2O to N2. For each bacterium, N2O reduction could be used both for electron balance during growth on electron-rich organic compounds in light and for energy transformation via respiration in darkness. However, N2O reduction required supplementation with a denitrification intermediate, including those for which there was no associated denitrification enzyme. For CGA0092, NO3−served as a stable, non-catalyzable molecule that was sufficient to activate N2O reduction. Using a β-galactosidase reporter, we found that NO3−acted, at least in part, by stimulating N2O reductase gene expression. In SB1003, NO2−but not NO3−activated N2O reduction, but NO2−was slowly removed, likely by a promiscuous enzyme activity. Our findings reveal that partial denitrifiers can still be subject to regulation by denitrification intermediates that they cannot use.IMPORTANCEDenitrification is a form of microbial respiration wherein nitrate is converted via several nitrogen oxide intermediates into harmless dinitrogen gas. Partial denitrifying bacteria, which individually have some but not all denitrifying enzymes, can achieve complete denitrification as a community by cross-feeding nitrogen oxide intermediates. However, the last intermediate, nitrous oxide (N2O), is a potent greenhouse gas that often escapes, motivating efforts to understand and improve the efficiency of denitrification. Here, we found that at least some partial denitrifying N2O reducers can sense and respond to nitrogen oxide intermediates that they cannot otherwise use. The regulatory effects of nitrogen oxides on partial denitrifiers are thus an important consideration in understanding and applying denitrifying bacterial communities to combat greenhouse gas emissions.