|Title||Copiotrophic marine bacteria are associated with strong iron-binding ligand production during phytoplankton blooms|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Hogle SL, Bundy RM, Blanton JM, Allen EE, Barbeau KA|
|Journal||Limnology and Oceanography Letters|
Although marine bacteria were identified nearly two decades ago as potential sources for strong iron-binding organic ligands detected in seawater, specific linkages between ligands detected in natural water and the microbial community remain unclear. We compared the production of different classes of iron-binding ligands, dissolved iron and macronutrient concentrations, and phytoplankton and bacterioplankton assemblages in a series of iron amended 6-d incubations. Incubations with high iron additions had near complete macronutrient consumption and higher phytoplankton biomass compared with incubations with low iron additions, but both iron treatments were dominated by diatoms. However, we only detected the strongest ligands in high-iron treatments, and strong iron-binding ligands were generally correlated with an increased abundance of copiotrophic bacteria, particularly Alteromonas strains. Ultimately, these robust correlations suggest a potential linkage between copiotrophic bacteria and strong iron-binding ligand production after iron fertilization events in the marine environment.
We hypothesize that high Fe conditions initially stimulate Fe-limited photoautotrophs, particularly diatoms, but not endemic heterotrophic bacteria due to organic carbon limitation (Kirchman 1990; Church et al. 2000). As the diatom bloom exhausts inorganic nutrients and progresses to senescence, newly released diatom-derived DOM associated with algal senescence stimulates ambient carbon-limited copiotroph bacteria (Seyedsayamdost et al. 2011; Sule and Belas 2013). Because aerobic respiration requires many Fe-containing enzymes (Hogle et al. 2014), rapidly growing copiotrophs may quickly shift to Fe limitation relative to excess algal-derived organic carbon. The most abundant local Fe source in this context would likely be algal-derived metalloproteins, and copiotroph L1 production may function to extract Fe from these algal sources and make it bioavailable to the wider bacterial community. If this phenomenon is widespread it may serve as a significant source of strong organic ligands in marine waters. Strong ligand production by heterotrophic bacteria during early bloom senescence may thus be important for overall iron recycling efficiency in microbial ecosystems and may serve to reduce Fe loss due to particle export in the upper ocean.