Iron–Nutrient Interactions within Phytoplankton

Abstract

Iron limits photosynthetic activity in up to one third of the world’s oceans and in many fresh water environments. When studying the effects of Fe limitation on phytoplankton or their adaptation to low Fe environments, we must take into account the numerous cellular processes within which this micronutrient plays a central role. Due to its flexible redox chemistry, Fe is indispensable in enzymatic catalysis and electron transfer reactions and is therefore closely linked to the acquisition, assimilation and utilization of essential resources. Iron limitation will therefore influence a wide range of metabolic pathways within phytoplankton, most prominently photosynthesis. In this review, we map out four well-studied interactions between Fe and essential resources: nitrogen, manganese, copper and light. Data was compiled from both field and laboratory studies to shed light on larger scale questions such as the connection between metabolic pathways and ambient iron levels and the biogeographical distribution of phytoplankton species.

Physiological responses of the freshwater N2‐fixing cyanobacterium Raphidiopsis raciborskii to Fe and N availabilities

“…The 55 Fe uptake rates of R. raciborskii in the presence of light determined in this study are 3.4-27.2 folds higher than those (0.33-2.65 amolÁcell −1 Áh −1 ) for M. aeruginosa (Fujii et al, 2011a(Fujii et al, , 2014b. This comparison indicates that the diazotrophic R. raciborskii possesses a significantly higher Fe uptake rate per unit cell than the non-diazotrophic cyanobacterium M. aeruginosa, which is in accord with their relatively higher Fe requirements for the maintenance of metabolism and growth (Dutkiewicz et al, 2012(Dutkiewicz et al, , 2014Schoffman et al, 2016). These results suggest a superior competency in iron uptake of R. raciborskii, at least for the CS-506 and CS-509 strains, over the most common bloomforming non-diazotrophic cyanobacteria (e.g.…”

“…Given that N 2 -fixation by the R. raciborskii strains occurs in both light and dark phases, it is likely that Fe uptake and concurrent or subsequent nitrogenase activation of R. raciborskii occurs, for the most part, during the daylight hours in natural waters. This comparison indicates that the diazotrophic R. raciborskii possesses a significantly higher Fe uptake rate per unit cell than the non-diazotrophic cyanobacterium M. aeruginosa, which is in accord with their relatively higher Fe requirements for the maintenance of metabolism and growth (Dutkiewicz et al, 2012(Dutkiewicz et al, , 2014Schoffman et al, 2016). This comparison indicates that the diazotrophic R. raciborskii possesses a significantly higher Fe uptake rate per unit cell than the non-diazotrophic cyanobacterium M. aeruginosa, which is in accord with their relatively higher Fe requirements for the maintenance of metabolism and growth (Dutkiewicz et al, 2012(Dutkiewicz et al, , 2014Schoffman et al, 2016).…”

“…This metalloenzyme is composed of two component proteins, namely dinitrogenase (an Fe-X protein where X represents Fe, Mo or V) and dinitrogenase reductase (an Fe protein) (Yang et al, 2017). Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015). Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015).…”

“…Nitrogenase synthesis requires a large amount of Fe [25-39 atoms of Fe per nitrogenase molecule (Postgate, 1998) with 236 μmol of Fe bound to nitrogenase per mol of cellular carbon (Whittaker et al, 2011)]. Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015). For example, N 2 -fixation rates of the marine diazotrophic cyanobacterium Trichodesmium increased from 0.07 to 0.5 mmol-NÁmol-C −1 Áh −1 on Fe supplementation from 4 nM to 4 μM (Berman-Frank et al, 2007).…”

Trace metal availability affects greenhouse gas emissions and microbial functional group abundance in freshwater wetland sediments

“…In methanotrophs oxidizing CH 4 to methanol (CH 3 OH), the switch 91 between a Cu-dependent pMMO or Fe-dependent soluble MMO is regulated by the environmental 92 availability of each metal (Murrell et al, 2000;Bollinger Jr, 2010). 93 94 Despite the great progress in understanding metal ecotoxicity and metalloenzyme biochemistry, our 95 knowledge of how trace metal availability affects microbial activity in the environment is generally limited to 96 selected processes (e.g., NH 4 + /NO 3 and CO 2 assimilation) in aquatic ecosystems (Twining et al, 2007;Glass et 97 al., 2012;Moore et al, 2013;Romero et al, 2013;Schoffman et al, 2016). A broader understanding of how 98 metal availability regulates microbial processes, especially in soils and sediments, is necessary if we are to 99 fully appreciate environmental controls on ecosystem C and N cycling.…”