科研之友
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摘要
The microbe-mediated marine biogeochemical cycles of carbon (C) and nitrogen (N) have an important impact on the global climate changes. The hopanoids of pentacyclic triterpenoids, including biological hopanoids (e.g., bacteriohopanepolyols (BHPs)) and geological hopanoids (e.g., hopanes), are important lipid biomarkers for indicating and reconstructing C and N cycles in modern and ancient environments. In this paper, we reviewed the biosynthetic pathways and physiological functions of hopanoids, and their roles as indicators in the key processes of the marine C and N cycles (i.e., nitrogen fixation, nitrification, anammox, methane oxidation and terrestrial organic matter input). The hopanoids in microbial membrane lipids are mainly regulated by enzymes of hopanoids synthesis and modification encoded with hpn gene, which are closely related to microbial physicochemical characteristics and environmental conditions. The oxygen permeability of cell membrane can be regulated by 2-methyl hopanoids, 2-methyl cyclitol ether and unsaturated cyclitol ether to protect nitrogenase, being able to indicate the diazotrophic cyanobacteria and N-fixation. Marine anammox bacteria Candidatus Scalindua is the only producer known as BHT-x (one of bacteriohopanetetrol isomers) so far, which can indicate marine anammox and hypoxic environment. Soil markers BHPs and terrestrial inputs indicator of Rsoil can track the input and migration of terrestrial organic matter to the ocean. Biomarkers 35-amino BHPs and 3-methyl (amino) BHPs can indicate aerobic methane oxidation. Bacteriohopanehexol and 3-methyl bacteriohopanehexol can indicate nitrite-reducing methanotrophy. With the development of molecular biology, genomics and instrumental analysis technology, hopanoids will play a more important role in indicating marine C and N cycles.
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