Metatranscriptomics of the prokaryotic community in response to atmospheric deposition in the Western North Pacific Ocean

Atmospheric deposition represents a major vector of both macro- and micro-nutrients to the oligotrophic open oceans, potentially imposing a profound impact on the functioning of the microbial community. Whereas responses of the prokaryotes to atmospheric deposition are being studied at the community level, corresponding functional changes are essentially unknown. Here we used metatranscriptomic approaches to elucidate taxonomic and functional profiles of the prokaryotic community in response to Asian aerosols in the Western North Pacific Ocean. While Bacteria were downrepresented, Virus and Archaea were overrepresented in the aerosol treatment compared to the control. Within Bacteria , transcripts related to Cyanobacteria , including Prochlorococcus , Trichodesmium and Synechococcus , decreased dramatically, whereas transcripts related to Proteobacteria , Bacteroidetes , Actinobacteria and Firmicutes showed differential increases in the aerosol treatment. Nutrients and organic matters were enriched as evidenced by an overexpression of transporters for amino acids and utilization of various carbohydrates and a down-expression of transcripts related with phosphorus metabolism. Increased expression included transcripts involved in tricarboxylic acid cycle, pentose phosphate pathway, glycolysis and gluconeogenesis. Unexpectedly, the expression of transcripts associated with Fe metabolism suggested that Fe limitation was intensified. Transcripts associated with N fixation declined, corresponding to the decline of diazotroph-related transcripts. This result is against the paradigm of Fe fertilization from atmospheric deposition but may represent an extreme case that Fe was scavenged after aerosol addition. Negative effects included impaired sugar utilization and the stimulation of oxidative stress and heavy metal toxicity. All these changes lead the community to an energy-conserving lifestyle and promoted motility, chemotaxis and interspecies competition and interaction. The results provide new insights into the biogeochemical impacts of atmospheric deposition in the Western North Pacific Ocean.