GNPS - Metabolite release by marine nitrifiers

Microbial chemoautotroph-heterotroph interactions may play a pivotal role in the cycling of carbon in the deep ocean, reminiscent of phytoplankton-heterotroph associations in surface waters. Nitrifiers are the most abundant chemoautotrophs in the global ocean, yet very little is known about nitrifier metabolite production, release, and transfer to heterotrophic microbial communities. To elucidate which organic compounds are released by nitrifiers and potentially available to heterotrophs, we characterized the endo- and exometabolomes of the ammonia-oxidizing archaeon Nitrosopumilus adriaticus CCS1 and the nitrite-oxidizing bacterium Nitrospina gracilis Nb-211. Nitrifier endometabolome composition was not a good predictor of exometabolite availability, indicating that metabolites were predominately released by mechanisms other than cell death/lysis. While both nitrifiers released labile organic compounds, N. adriaticus preferentially released amino acids, in particular glycine, suggesting that its cell membranes might be more permeable to small, hydrophobic amino acids. We further initiated co-culture systems between each nitrifier and a heterotrophic alphaproteobacterium, and compared exometabolite and transcription patterns of nitrifiers grown axenically to those in co-culture. Particularly, B vitamins exhibited dynamic production and consumption patterns in co-cultures, including a higher release of pantothenic acid (vitamin B5) in both co-culture systems, and increased amounts of riboflavin (vitamin B2) and the vitamin B12 ligand dimethylbenzimidazole in co-cultures with N. adriaticus and N. gracilis, respectively. In contrast, the heterotroph likely consumed the vitamin B7 precursor dethiobiotin in co-culture with N. gracilis. Our results indicate that B vitamins and their precursors could play a particularly important role in governing specific metabolic interactions between nitrifiers and heterotrophic microbes in the ocean.

The work (proposal:https://doi.org/10.46936/10.25585/60001318) conducted by the U.S. Department of Energy Joint Genome Institute (https://ror.org/04xm1d337), a DOE Office of Science User Facility, is supported by the Office of Science of the U.S. Department of Energy operated under Contract No. DE-AC02-05CH11231.