Seasonal siderophore uptake and biosynthesis associated with carbon flux at Station ALOHA

Abstract

AbstractDissolved iron concentrations in the North Pacific subtropical oligotrophic gyre are low, in part due to biological consumption and seasonally restricted iron delivery to these waters. In this study, we examined seasonal changes in dissolved siderophore concentrations, uptake rates and biosynthesis at Station ALOHA to observe changes in iron acquisition by the microbial community. Genetic potential for siderophore biosynthesis was widespread throughout the upper water column (0-500 m) and peaked in spring and summer along with siderophore concentrations. Uptake rates were faster and residence times of siderophore-bound iron were shorter at 300 m compared to 15 m, suggesting differences in iron acquisition in the mesopelagic. Changes in siderophore production in the water column suggest that variations in primary production and carbon export impact iron acquisition of the microbial community over the seasonal cycle and provides initial evidence that iron demand may change in association with carbon export at Station ALOHA.Scientific Significance StatementMicrobial community production in the subtropical oligotrophic North Pacific is limited by macronutrients such as nitrogen and phosphorous. However, dissolved iron is another important micronutrient that has seasonal inputs from dust and passing eddies, keeping the availability of iron low and episodic. Little attention has been paid to the microbial strategies for dealing with low iron to support primary production in the oligotrophic ocean, or how limited iron availability impacts the processing of sinking particulate organic carbon in this region. In this study, we explore siderophore production and uptake throughout the water column at Station ALOHA to examine how the microbial community adapts and responds to changing iron and carbon availability on seasonal timescales.