Lava caves are an understudied ecosystem in the subterranean world, particularly in regard to nitrogen cycling. The diversity of ammonia oxidation (amoA) and nitrogen fixation (nifH) genes in bacterial mats collected from lava cave walls on the island of Terceira (Azores, Portugal) was investigated using denaturing gradient gel electrophoresis (DGGE). A total of 55 samples were collected from 11 lava caves that were selected with regard to surface land use. Land use types above the lava caves were categorized into pasture, forested, and sea/urban, and used to determine if land use influenced the ammonia oxidizing and nitrogen fixing bacterial communities within the lava caves. The soil and water samples from each lava cave were analyzed for total organic carbon, inorganic carbon, total nitrogen, ammonium, nitrate, phosphate and sulfate, to determine if land use influences either the nutrient content entering the lava cave or the nitrogen cycling bacteria present within the cave. Nitrosospira-like sequences dominated the ammonia-oxidizing bacteria (AOB) community, and the majority of the diversity was found in lava caves under forested land. The nitrogen fixation community was dominated by Klebsiella pneumoniae-like sequences, and diversity was evenly distributed between pasture and forested land, but very little overlap in diversity was observed. The results suggest that land use is impacting both the AOB and the nitrogen fixing bacterial communities.

中文翻译：

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葡萄牙亚速尔群岛特塞拉熔岩洞中氨氧化 (amoA) 和固氮 (nifH) 基因的多样性

熔岩洞穴是地下世界中一个未被充分研究的生态系统，特别是在氮循环方面。使用变性梯度凝胶电泳 (DGGE) 研究了从特塞拉岛（葡萄牙亚速尔群岛）熔岩洞穴壁收集的细菌垫中氨氧化 (amoA) 和固氮 (nifH) 基因的多样性。从根据地表土地利用选择的 11 个熔岩洞穴中收集了总共 55 个样本。熔岩洞穴上方的土地利用类型分为牧场、森林和海洋/城市，用于确定土地利用是否影响熔岩洞穴内的氨氧化和固氮细菌群落。对每个熔岩洞穴的土壤和水样进行了总有机碳、无机碳、总氮、铵、硝酸盐、磷酸盐和硫酸盐的分析，以确定土地利用是否影响进入熔岩洞穴的营养成分或洞穴内存在的氮循环细菌。亚硝化螺类序列占氨氧化细菌 (AOB) 群落的主导地位，大部分多样性在林地下的熔岩洞穴中发现。固氮群落以类肺炎克雷伯菌序列为主，多样性在牧场和林地之间分布均匀，但很少观察到多样性重叠。结果表明，土地利用正在影响 AOB 和固氮细菌群落。大多数多样性是在林地下的熔岩洞穴中发现的。固氮群落以类肺炎克雷伯菌序列为主，多样性在牧场和林地之间分布均匀，但很少观察到多样性重叠。结果表明，土地利用正在影响 AOB 和固氮细菌群落。大多数多样性是在林地下的熔岩洞穴中发现的。固氮群落以类肺炎克雷伯菌序列为主，多样性在牧场和林地之间分布均匀，但很少观察到多样性重叠。结果表明，土地利用正在影响 AOB 和固氮细菌群落。