Iron limitation of microbial phosphorus acquisition in the tropical North Atlantic

Abstract

In certain regions of the predominantly nitrogen limited ocean, microbes can become co-limited by phosphorus. Within such regions, a proportion of the dissolved organic phosphorus pool can be accessed by microbes employing a variety of alkaline phosphatase (APase) enzymes. In contrast to the PhoA family of APases that utilize zinc as a cofactor, the recent discovery of iron as a cofactor in the more widespread PhoX and PhoD implies the potential for a biochemically dependant interplay between oceanic zinc, iron and phosphorus cycles. Here we demonstrate enhanced natural community APase activity following iron amendment within the low zinc and moderately low iron Western North Atlantic. In contrast we find no evidence for trace metal limitation of APase activity beneath the Saharan dust plume in the Eastern Atlantic. Such intermittent iron limitation of microbial phosphorus acquisition provides an additional facet in the argument for iron controlling the coupling between oceanic nitrogen and phosphorus cycles.

Transcriptional patterns identify resource controls on the diazotrophTrichodesmiumin the Atlantic and Pacific oceans

“…Regardless, these data suggest a switch between Fe-and Zn-rich metalloenzymes for DOP hydrolysis consistent with climatological patterns in Fe geochemistry of the NASG and NPSG. Fe and Zn limitation of community AP activity had been previously shown using data from bulk AP activity assays, where AP increased after Fe or Zn additions in different ocean regions [33,80]. This is most likely driven by shifts in the PhoA and PhoX expression ratios, as observed here for Trichodesmium, but not all marine bacteria carry both PhoX and PhoA like Trichodesmium.…”

“…For instance, access to the DOP pool might be limited by Fe bioavailability, because PhoX, the most widely distributed type of AP among marine bacteria [30], requires Fe as a metal cofactor [31,32]. In fact, whole-water field incubations with added Fe in low Fe regions showed an enhancement of AP activity [33]. Such potential interactions and adaptations further exacerbate the complexities surrounding the identification and modeling of the geochemical drivers of N 2 fixation.…”

Temporal Variability in the Nutrient Biogeochemistry of the Surface North Atlantic: 15 Years of Ship of Opportunity Data

“…Unfortunately, we did not have the capacity for trace metal clean sampling within the experiments performed on the cruise. However, previous work within the region (Browning et al, ; Moore et al, , ) performed using trace metal clean techniques and with and without the addition of iron indicates that bulk community production and biomass accumulation (chlorophyll) are insensitive to iron availability within the region.…”

Assessing Phytoplankton Nutritional Status and Potential Impact of Wet Deposition in Seasonally Oligotrophic Waters of the Mid‐Atlantic Bight

“…• Table S1 Correspondence to: P. N. Sedwick, psedwick@odu. There is also good reason to consider the atmospheric deposition of phosphorus (P) and iron (Fe), which have been implicated as limiting (Fe) or colimiting (Fe, P) to primary production in the North Atlantic Ocean Browning, Achterberg, Yong, et al, 2017;Moore et al, 2008Moore et al, , 2013Paerl et al, 1999;Wu et al, 2000). The molar ratio of inorganic N to soluble reactive P in aerosols and rainwater is generally higher than the Redfield ratio (Baker et al, 2003(Baker et al, , 2010Zamora et al, 2013), such that atmospheric deposition to nutrient-depleted waters may potentially result in a secondary limitation of phytoplankton growth due to P deficiency (Fanning, 1989;Moore et al, 2008Moore et al, , 2013Wu et al, 2000).…”