Hetz Stefanie A, Horn Marcus A
Institute of Microbiology, Leibniz University Hannover, Hannover, Germany.
Front Microbiol. 2021 Feb 5;12:628269. doi: 10.3389/fmicb.2021.628269. eCollection 2021.
Cryoturbated peat circles (pH 4) in the Eastern European Tundra harbor up to 2 mM pore water nitrate and emit the greenhouse gas NO like heavily fertilized agricultural soils in temperate regions. The main process yielding NO under oxygen limited conditions is denitrification, which is the sequential reduction of nitrate/nitrite to NO and/or N. NO reduction to N is impaired by pH < 6 in classical model denitrifiers and many environments. Key microbes of peat circles are important but largely unknown catalysts for - and -cycling associated NO fluxes. Thus, we hypothesized that the peat circle community includes hitherto unknown taxa and is essentially unable to efficiently perform complete denitrification, i.e., reduce NO, due to a low pH. 16S rRNA analysis indicated a diverse active community primarily composed of the bacterial class-level taxa Alphaproteobacteria, Acidimicrobiia, Acidobacteria, Verrucomicrobiae, and Bacteroidia, as well as archaeal Nitrososphaeria. Euryarchaeota were not detected. C- and C-acetate supplemented anoxic microcosms with endogenous nitrate and acetylene at an near pH of 4 were used to assess acetate dependent carbon flow, denitrification and NO production. Initial nitrate and acetate were consumed within 6 and 11 days, respectively, and primarily converted to CO and N, suggesting complete acetate fueled denitrification at acidic pH. Stable isotope probing coupled to 16S rRNA analysis via Illumina MiSeq amplicon sequencing identified acetate consuming key players of the family during complete denitrification correlating with spp. The archaeal community consisted primarily of ammonia-oxidizing Archaea of Nitrososphaeraceae, and was stable during the incubation. The collective data indicate that peat circles (i) host acid-tolerant denitrifiers capable of complete denitrification at pH 4-5.5, (ii) other parameters like carbon availability rather than pH are possible reasons for high NO emissions , and (iii) are responsive key acetate assimilators co-occurring with sp. during denitrification, suggesting both organisms being associated with acid-tolerant denitrification in peat circles.
东欧冻原地区的冻融扰动泥炭圈（pH值为4）孔隙水中硝酸盐含量高达2 mM，并且像温带地区大量施肥的农业土壤一样排放温室气体一氧化氮（NO）。在氧气受限条件下产生NO的主要过程是反硝化作用，即硝酸盐/亚硝酸盐依次还原为NO和/或N。在经典模型反硝化菌和许多环境中，pH值<6会阻碍NO还原为N。泥炭圈中的关键微生物是与氮和碳循环相关的NO通量的重要催化剂，但很大程度上尚不为人所知。因此，我们推测泥炭圈群落包含迄今未知的分类群，并且由于pH值较低，基本上无法有效地进行完全反硝化作用，即还原NO。16S rRNA分析表明，活跃群落具有多样性，主要由细菌类群α-变形菌纲、酸微菌亚纲、酸杆菌门、疣微菌门和拟杆菌纲以及古菌亚硝化球菌纲组成。未检测到广古菌门。在接近pH值为4的条件下，用补充了内源性硝酸盐和乙炔的C-和C-乙酸盐培养缺氧微观世界，以评估乙酸盐依赖的碳流、反硝化作用和NO生成。初始硝酸盐和乙酸盐分别在6天和11天内被消耗，主要转化为CO和N，这表明在酸性pH条件下乙酸盐完全驱动了反硝化作用。通过Illumina MiSeq扩增子测序将稳定同位素探测与16S rRNA分析相结合，确定了在与 spp.相关的完全反硝化过程中消耗乙酸盐的关键菌属。古菌群落主要由亚硝化球菌科的氨氧化古菌组成，并且在培养过程中保持稳定。总体数据表明，泥炭圈（i）拥有能够在pH值4 - 5.5下进行完全反硝化作用的耐酸反硝化菌，（ii）碳可用性等其他参数而非pH值可能是NO高排放的原因，（iii）是反硝化过程中与 sp.共同出现的关键乙酸盐同化菌，这表明这两种生物都与泥炭圈中的耐酸反硝化作用有关。
