酸性土壤（pH<5.5）在我国分布面积广泛，是我国热带亚热带粮食和经济作物的重要产地。一直以来，氨氧化细菌（AOB）被认为是土壤硝化作用的主要驱动者，但在多数酸性土壤中检测不到AOB，或发现AOB的存在与硝化作用无关，酸性土壤硝化作用的机理一直不够清楚。
中国科学院生态环境研究中心贺纪正研究员课题组于2007年在Environmental Microbiology上首次报道了酸性土壤中存在大量氨氧化古菌（AOA），且AOA的数量与土壤硝化潜势呈显著正相关关系，该成果在国际上引起关注，被SCI期刊广泛引用。最近，他们利用稳定性同位素探针技术（SIP），结合经典的分子生态学手段，对我国强酸性土壤中的硝化作用机理开展了深入研究。
根据氨氧化微生物氧化氨时进行化能自养生长固定CO2为碳源的牲征，研究人员在实验室微宇宙培养条件下，分别用13C-CO2和12C-CO2对酸性土壤进行标记培养，通过密度梯度超速离心，将结合了13C和12C的微生物DNA加以分离，并对这些DNA进行分子生物学分析，发现属于奇古菌门(Thaumarchaeota)中的氨氧化古菌(AOA)能固定13CO2，且其丰度变化与活跃的氨氧化速率呈显著正相关。在代表微生物多样性组成的DGGE指纹图谱上，两个AOA类群在培养后显著增加，而相应的氨氧化细菌则变化不明显，表明AOA是该酸性土壤硝化作用的主要贡献者。
这一发现为AOA在酸性土壤硝化作用中发挥主导作用提供了直观证据，为重新认识酸性土壤中的硝化作用机理提供了重要参考。
该研究成果发表于5月出版的国际微生物生态学会会刊The ISME Journal上(Ammonia-oxidizing archaea have more important role than ammonia-oxidizing bacteria in ammonia oxidation of strongly acidic soils. The ISME J, 6(5): 1032-1045)。奇古菌门是最近定义的一个新的古菌类群，贺纪正等在最近一期的中文期刊《微生物学报》上对奇古菌门也作了专门介绍（张丽梅和贺纪正，2012，52：411-421）。（生物谷Bioon.com）
doi:10.1038/ismej.2011.168
PMC:
PMID:
Ammonia-oxidizing archaea have more important role than ammonia-oxidizing bacteria in ammonia oxidation of strongly acidic soils
Li-Mei Zhang1,3, Hang-Wei Hu1,2,3, Ju-Pei Shen1 and Ji-Zheng He1
Increasing evidence demonstrated the involvement of ammonia-oxidizing archaea (AOA) in the global nitrogen cycle, but the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation are still in debate. Previous studies suggest that AOA would be more adapted to ammonia-limited oligotrophic conditions, which seems to be favored by protonation of ammonia, turning into ammonium in low-pH environments. Here, we investigated the autotrophic nitrification activity of AOA and AOB in five strongly acidic soils (pH<4.50) during microcosm incubation for 30 days. Significantly positive correlations between nitrate concentration and amoA gene abundance of AOA, but not of AOB, were observed during the active nitrification. 13CO2-DNA-stable isotope probing results showed significant assimilation of 13C-labeled carbon source into the amoA gene of AOA, but not of AOB, in one of the selected soil samples. High levels of thaumarchaeal amoA gene abundance were observed during the active nitrification, coupled with increasing intensity of two denaturing gradient gel electrophoresis bands for specific thaumarchaeal community. Addition of the nitrification inhibitor dicyandiamide (DCD) completely inhibited the nitrification activity and CO2 fixation by AOA, accompanied by decreasing thaumarchaeal amoA gene abundance. Bacterial amoA gene abundance decreased in all microcosms irrespective of DCD addition, and mostly showed no correlation with nitrate concentrations. Phylogenetic analysis of thaumarchaeal amoA gene and 16S rRNA gene revealed active 13CO2-labeled AOA belonged to groups 1.1a-associated and 1.1b. Taken together, these results provided strong evidence that AOA have a more important role than AOB in autotrophic ammonia oxidation in strongly acidic soils.
