背景:Moonmilk代表复杂的二级结构和模型系统,以研究微生物与碳酸岩之间的相互作用。GrottaNera的特点是天花板上悬挂着许多特殊大小的月乳节,长度超过两米。在这项工作中,我们将微生物分析与分析热解和碳稳定同位素数据相结合,以确定这些复杂的月乳结构的分子组成以及相关微生物群的组成。
结果:在根尖解剖了三个月乳结构,横向,和核心零件,它们具有相似的微生物丰度值,丰富,和碳同位素,但不同的水含量,微生物群组成,和有机物。与基岩(未显示月乳发育迹象)和水域(在滴落的月乳下方收集)相比,月乳部分/生态位显示出更高的微生物生物量和生物多样性值,表明存在与碳酸盐岩相互作用和生物矿化过程相关的更复杂的微生物群落。尽管每个月乳生态位都具有特定的微生物群和独特的有机碳特征,统计分析将样本分为两个主要组,一个包括月光的侧面部分和基岩,另一个包括蛇形体的核心和顶端部分。这两个基团的有机质分布都显示出两个分化良好的有机碳基团,一种来自洞穴微生物活动,另一种来自洞穴上方维管植物凋落物的浸出。发现了不同月奶生态位中有机质组成与微生物类群的相关性,将根尖部分中缩合有机化合物的存在与亚硝基螺旋藻和亚硝多酚的顺序联系起来,虽然不同的类群与芳香相关,木质素,和月光核心中的多糖。这些发现与这些微生物类群的代谢潜力一致,这表明保存的有机物的分子组成如何驱动微生物群定居在不同的月乳壁ni位。此外,已知参与无机氮和C1气体(CO2和CH4)代谢的不同细菌和古细菌类群(Nitrospira,亚硝基科,Nitrosomonadaceae,亚硝基球藻科,以及新的Methylomirabilota和Methanomasiliicoccales分类群)富集在月乳的核心和顶端部分,可能与它们对GrottaNera生态系统和月乳发育的生物地球化学循环的贡献有关。
结论:根据氧气和水的梯度,月光沉积物可以分为不同的生态位,其特征在于特定的微生物类群和源自微生物活动或源自洞穴上方的土壤和植被的有机质成分。允许复杂聚合物从洞穴上方的植被中生物降解的代谢能力以及无机氮和大气气体的使用可能推动了复杂微生物群落的发展,通过与碳酸盐岩相互作用,导致了这些巨大的月乳齿叶在GrottaNera中的形成。
BACKGROUND: Moonmilk represents complex secondary structures and model systems to investigate the interaction between microorganisms and carbonatic rocks. Grotta Nera is characterized by numerous moonmilk speleothems of exceptional size hanging from the ceiling, reaching over two meters in length. In this work we combined microbiological analyses with analytical pyrolysis and carbon stable isotope data to determine the molecular composition of these complex moonmilk structures as well as the composition of the associated microbiota.
RESULTS: Three moonmilk structures were dissected into the apical, lateral, and core parts, which shared similar values of microbial abundance, richness, and carbon isotopes but different water content, microbiota composition, and organic matter. Moonmilk parts/niches showed higher values of microbial biomass and biodiversity compared to the bedrock (not showing moonmilk development signs) and the waters (collected below dripping moonmilk), indicating the presence of more complex microbial communities linked to carbonate rock interactions and biomineralization processes. Although each moonmilk niche was characterized by a specific microbiota as well as a distinct organic carbon profile, statistical analyses clustered the samples in two main groups, one including the moonmilk lateral part and the bedrock and the other including the core and apical parts of the speleothem. The organic matter profile of both these groups showed two well-differentiated organic carbon groups, one from cave microbial activity and the other from the leaching of vascular plant litter above the cave. Correlation between organic matter composition and microbial taxa in the different moonmilk niches were found, linking the presence of condensed organic compounds in the apical part with the orders Nitrospirales and Nitrosopumilales, while different taxa were correlated with aromatic, lignin, and polysaccharides in the moonmilk core. These findings are in line with the metabolic potential of these microbial taxa suggesting how the molecular composition of the preserved organic matter drives the microbiota colonizing the different moonmilk niches. Furthermore, distinct bacterial and archaeal taxa known to be involved in the metabolism of inorganic nitrogen and C1 gases (CO2 and CH4) (Nitrospira, Nitrosopumilaceae, Nitrosomonadaceae, Nitrosococcaceae, and novel taxa of Methylomirabilota and Methanomassiliicoccales) were enriched in the core and apical parts of the moonmilk, probably in association with their contribution to biogeochemical cycles in Grotta Nera ecosystem and moonmilk development.
CONCLUSIONS: The moonmilk deposits can be divided into diverse niches following oxygen and water gradients, which are characterized by specific microbial taxa and organic matter composition originating from microbial activities or deriving from soil and vegetation above the cave. The metabolic capacities allowing the biodegradation of complex polymers from the vegetation above the cave and the use of inorganic nitrogen and atmospheric gases might have fueled the development of complex microbial communities that, by interacting with the carbonatic rock, led to the formation of these massive moonmilk speleothems in Grotta Nera.