Amino acids promote black carbon aggregation and microbial colonization in coastal waters off Vietnam.

The combustion of fossil fuels and biomass produces pyrogenic organic matter usually known as ‘black carbon’ (BC), which are transported across the atmosphere as particulate aerosol, eventually deposited on land and oceans. Soil studies have investigated the potential microbial colonization and remineralization of BC particles, but this process has been seldom studied in marine waters. BC provides a significant input of organic carbon to the oceans, yet its fate and role in biogeochemical cycling remains unknown. Here we explored the microbial colonization of BC particles in coastal seawater samples collected in Halong Bay (northern Vietnam). Using high-resolution mass spectrometry and microscopy methods, we observed an increasing colonization of BC particles by marine microbes in the presence of amino acids. Our results suggest that natural organic matter (NOM) present in seawater may promote the microbial colonization and eventual remineralization of BC particles. Future experiments should explore the potential microbial remineralization of BC particles to unveil the role of this massive source of carbon to marine ecosystems.