Siderophores as an iron source for Prochlorococcus in deep chlorophyll maximum layers of the oligotrophic ocean

Abstract

Prochlorococcus is one of the most abundant photosynthesizing organisms in the oligotrophic oceans. Gene content variation among Prochlorococcus populations in separate ocean basins often mirrors the selective pressures imposed by the region's distinct biogeochemistry. By pairing genomic datasets with trace metal concentrations from across the global ocean, we show that the genomic capacity for siderophore-mediated iron uptake is widespread in low-light adapted Prochlorococcus populations from iron-depleted regions of the oligotrophic Pacific and S. Atlantic oceans: Prochlorococcus siderophore consumers were absent in the N. Atlantic ocean (higher iron flux) but constituted up to half of all Prochlorococcus genomes from metagenomes in the N. Pacific (lower iron flux). Prochlorococcus siderophore consumers, like many other bacteria with this trait, also lack siderophore biosynthesis genes indicating that they scavenge exogenous siderophores from seawater. Statistical modeling suggests that the capacity for siderophore uptake is endemic to remote ocean regions where atmospheric iron fluxes are the smallest, particularly at deep chlorophyll maximum and primary nitrite maximum layers. We argue that abundant siderophore consumers at these two common oceanographic features could be a symptom of wider community iron stress, consistent with prior hypotheses. Our results provide a clear example of iron as a selective force driving the evolution of Prochlorococcus.

Simultaneous acclimation to nitrogen and iron scarcity in open ocean cyanobacteria revealed by sparse tensor decomposition of metatranscriptomes

“…S6). Rather, at these latitudes the Prochlorococcus community was dominated by the LLI and LLVII clades, the former noteworthy for a high frequency of genes involved in iron acquisition via siderophore uptake (53). In the transition zone (TZ) between the subtropical and subarctic gyres, expression of both the nitrogen and iron acclimation clusters was elevated in both Prochlorococcus and Synechococcus populations (Fig.…”

Competitive Interactions Between Microbial Siderophores and Humic-Like Binding Sites in European Shelf Sea Waters

“…Iron is an essential micronutrient for pyhtoplankton growth, but its low solubility in oxygenated water results in sub nanomolar concentrations (Liu and Millero, 2002) which limit productivity in approximately 30-40% of the surface ocean (Boyd and Ellwood, 2010;Hutchins and Boyd, 2016). Siderophores are secondary metabolites produced by bacteria and fungi in order to acquire iron (Hider and Kong, 2010) and are thought to make up a component of the dissolved iron pool in seawater, likely influencing iron bioavailability to marine microbes (Shaked and Lis, 2012;Hogle et al, 2021). More than forty siderophores from marine bacteria have been characterised (Vraspir and Butler, 2009) and four groups of these siderophores, ferrioxamines, amphibactins, synechobactins and petrobactins have been shown to occur in open ocean surface waters (Mawji et al, 2008;Boiteau et al, 2016;Velasquez et al, 2016;Bundy et al, 2018;Manck et al, 2021).…”