Abstract：
Hopanoid lipids, bacteriohopanols and bacteriohopanepolyols, are membrane components exclusive to bacteria. Together with their diagenetic derivatives, they are commonly used as biomarkers for specific bacterial groups or biogeochemical processes in the geologic record. However, the sources of hopanoids to marine and freshwater environments remain inadequately constrained. Recent marker gene studies suggest a widespread potential for hopanoid biosynthesis in marine bacterioplankton, including nitrifying (i.e., ammonia- and nitrite-oxidizing) bacteria. To explore their hopanoid biosynthetic capacities, we studied the distribution of hopanoid biosynthetic genes in the genomes of cultivated and uncultivated ammonia-oxidizing (AOB), nitrite-oxidizing (NOB), and complete ammonia-oxidizing (comammox) bacteria, finding that biosynthesis of diverse hopanoids is common among seven of the nine presently cultivated clades of nitrifying bacteria. Hopanoid biosynthesis genes are also conserved among the diverse lineages of bacterial nitrifiers detected in environmental metagenomes. We selected seven representative NOB isolated from marine, freshwater, and engineered environments for phenotypic characterization. All tested NOB produced diverse types of hopanoids, with some NOB producing primarily diploptene and others producing primarily bacteriohopanepolyols. Relative and absolute abundances of hopanoids were distinct among the cultures and dependent on growth conditions, such as oxygen and nitrite limitation. Several novel nitrogen-containing bacteriohopanepolyols were tentatively identified, of which the so called BHP-743.6 was present in all NOB. Distinct carbon isotopic signatures of biomass, hopanoids, and fatty acids in four tested NOB suggest operation of the reverse tricarboxylic acid cycle in Nitrospira spp. and Nitrospina gracilis and of the Calvin-Benson-Bassham cycle for carbon fixation in Nitrobacter vulgaris and Nitrococcus mobilis. We suggest that the contribution of hopanoids by NOB to environmental samples could be estimated by their carbon isotopic compositions. The ubiquity of nitrifying bacteria in the ocean today and the antiquity of this metabolic process suggest the potential for significant contributions to the geologic record of hopanoids.
摘要：
Hopanoid脂质，细菌啤酒花醇和细菌啤酒花醇，是细菌独有的膜成分。连同它们的成岩作用衍生物，它们通常用作地质记录中特定细菌群或生物地球化学过程的生物标志物。然而,海洋和淡水环境中的类大麻的来源仍然没有受到足够的限制。最近的标记基因研究表明，海洋浮游细菌中的类hopanoid生物合成具有广泛的潜力，包括硝化(即，氨氧化和亚硝酸盐氧化)细菌。为了探索它们的生物合成能力，我们研究了hopanoid生物合成基因在培养和未培养氨氧化（AOB）基因组中的分布，亚硝酸盐氧化（NOB），和完全的氨氧化（Comammox）细菌，发现在目前培养的9个硝化细菌分支中，有7个常见的生物合成不同的hopanoids。Hopanoid生物合成基因在环境宏基因组中检测到的细菌硝化剂的不同谱系中也是保守的。我们选择了七个从海洋中分离的代表性NOB，淡水,和用于表型表征的工程环境。所有测试的NOB都产生了不同类型的类大麻，其中一些NOB主要生产二溴烯，另一些主要生产细菌酚多元醇。hopanoids的相对和绝对丰度在培养物中是不同的，并且依赖于生长条件。如氧和亚硝酸盐的限制。初步确定了几种新型含氮细菌的醇，其中所谓的BHP-743.6存在于所有NOB中。生物质的不同碳同位素特征，类大麻,和四个测试的NOB中的脂肪酸建议在硝基螺旋体中进行反向三羧酸循环。和亚硝基球藻和卡尔文-本森-巴斯舍姆循环的普通硝化细菌和移动亚硝酸球菌的碳固定。我们建议，可以通过其碳同位素组成来估算NOB对环境样品的贡献。当今海洋中硝化细菌的普遍存在以及这种代谢过程的古老性表明，有可能对类野菜的地质记录做出重大贡献。
