Abstract
SummaryAmmonia‐oxidizing archaea (AOA) constitute a considerable fraction of microbial biomass in the global ocean, comprising 20%–40% of the ocean's prokaryotic plankton. However, it remains enigmatic to what extent these chemolithoautotrophic archaea release dissolved organic carbon (DOC). A combination of targeted and untargeted metabolomics was used to characterize the exometabolomes of three model AOA strains of the Nitrosopumilus genus. Our results indicate that marine AOA exude a suite of organic compounds with potentially varying reactivities, dominated by nitrogen‐containing compounds. A significant fraction of the released dissolved organic matter (DOM) consists of labile compounds, which typically limit prokaryotic heterotrophic activity in open ocean waters, including amino acids, thymidine and B vitamins. Amino acid release rates corresponded with ammonia oxidation activity and the three Nitrosopumilus strains predominantly released hydrophobic amino acids, potentially as a result of passive diffusion. Despite the low contribution of DOC released by AOA (~0.08%–1.05%) to the heterotrophic prokaryotic carbon demand, the release of physiologically relevant metabolites could be crucial for microbes that are auxotrophic for some of these compounds, including members of the globally abundant and ubiquitous SAR11 clade.
Highlights
Dissolved organic matter (DOM) is one of the Earth’s largest reactive carbon pools, similar in magnitude to atmospheric CO2, and of major significance for the global carbon cycle and climate (Hedges, 1992; Hansell et al, 2009)
DOM was extracted from culture supernatant of three strains of Ammonia-oxidizing archaea (AOA), N. adriaticus NF5, N. piranensis D3C, and N. maritimus SCM1
Dissolved organic carbon (DOC) concentrations of solid-phase extracted DOM (SPE-DOM) from archaeal cultures harvested during late exponential growth ranged from 3.5 to 5.0 μM, which was on average 2–3 times higher than dissolved organic carbon (DOC) concentrations of medium blanks
Summary
Ammonia-oxidizing archaea (AOA) constitute a considerable fraction of microbial biomass in the global ocean, comprising 20%–40% of the ocean’s prokaryotic plankton. It remains enigmatic to what extent these chemolithoautotrophic archaea release dissolved organic carbon (DOC). A significant fraction of the released dissolved organic matter (DOM) consists of labile compounds, which typically limit prokaryotic heterotrophic activity in open ocean waters, including amino acids, thymidine and B vitamins. Amino acid release rates corresponded with ammonia oxidation activity and the three Nitrosopumilus strains predominantly released hydrophobic amino acids, potentially. Despite the low contribution of DOC released by AOA (~0.08%–1.05%) to the heterotrophic prokaryotic carbon demand, the release of physiologically relevant metabolites could be crucial for microbes that are auxotrophic for some of these compounds, including members of the globally abundant and ubiquitous SAR11 clade
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