Metallophores associated with Trichodesmium erythraeum colonies from the Gulf of Aqaba

Abstract

Colonies of the marine diazotroph Trichodesmium host a complex microbial population. We show that colony consortia produce metallophores that likely influence the bioavailability of the trace nutrient iron within the colony microenvironment.

Mineral iron dissolution in Trichodesmium colonies: The role of O2 and pH microenvironments

“…Since ferrihydrite is not internalized directly by Trichodesmium (Rubin et al ), the surplus uptake over abiotic dissolution implies that Trichodesmium biologically enhanced ferrihydrite dissolution, in a process that may involve reductive and/or ligand‐promoted dissolution, in agreement with previous reports by Basu and Shaked (). Production of iron‐binding ligands (siderophores) by the Trichodesmium consortium was recently documented in the Gulf of Eilat (Gledhill et al ) and shown to increase ferrihydrite bioavailability by promoting its dissolution (Basu et al ). To specifically test for microenvironment effects on ligand‐promoted dissolution, four of the uptake experiments were conducted in the presence of the iron‐binding ligand DFB (March 27 th till March 29 th ; Fig.…”

Investigation of Siderophore-Promoted and Reductive Dissolution of Dust in Marine Microenvironments Such as Trichodesmium Colonies

“…Moreover, recent incubation studies with natural Trichodesmium colonies from the Gulf of Aqaba measured production of 50 pM to 1.2 nM -during 1-2 days, presumably synthesized by the bacteria associated with the colonies (Basu et al, 2019;Gledhill et al, 2019). Considering the colony numbers in the incubation and a colony volume of 0.25 µl, these concentrations correspond to a maximum of 0.8 µM ferrioxamines in the colony's microenvironment.…”

“…Furthermore, dissolved Fe(II), released by biologic reduction, may have a longer life-time within the colony microenvironment than in solution, due to photochemical processes and to the fact that the pH and oxygen levels within Trichodesmium colony decrease during the night (Eichner et al, 2019a,b). Furthermore, Gledhill et al (2019) have shown that Trichodesmium colonies from the Gulf of Aqaba secrete a mixture of 18 Fe-binding metallophores. The simultaneous activity of different siderophores, combined with the colony's reducing power, may act synergistically and result in faster dissolution of dust-Fe.…”

“…Maintaining the enzymatic machinery required for nitrogen fixation raises Trichodesmium's Fe requirements, resulting in cellular Fe quotas that exceed other oceanic phytoplankton by ∼10-fold (Berman-Frank et al, 2001;Kustka et al, 2003;Nuester et al, 2012). Accumulating research indicates that Trichodesmium is especially adapted to utilize dust as a source of Fe (Rueter et al, 1992;Tovar-Sanchez et al, 2006;Rubin et al, 2011;Langlois et al, 2012;Basu and Shaked, 2018;Polyviou et al, 2018;Basu et al, 2019;Eichner et al, 2019a,b;Gledhill et al, 2019;Kessler et al, 2019). Trichodesmium employs different strategies to overcome the physical constraints on dust-Fe acquisition: dust sinking to depth and loss of attached particles.…”

“…Siderophores enhance Fe dissolution rates by forming a surface complex with Fe atoms exposed at the mineral surface, facilitating the breaking of the bonds with the mineral lattice and carrying the Fe into solution as Fe(III)-siderophore complexes (Kraemer et al, 2005). In a recent study, our group showed that heterotrophic bacteria, naturally residing in Trichodesmium colonies, secrete the ferrioxamine siderophores B (DFOB), E, and G (Gledhill et al, 2019). Furthermore, the secretion of the siderophores was found to be stimulated by dust inputs, suggestive of a mutualistic pathway for increasing the supply of Fe from dust (Basu et al, 2019).…”