Abstract
In large areas of the ocean phytoplankton growth is limited by the scarcity of iron (Fe), an essential co-factor for multiple enzymes. Phytoplankton has hence developed strategies to survive under Fe limitation. Here, we characterize the response to Fe limitation of the cyanobacterium Synechococcus sp. PCC7002 acclimated to different Fe concentrations in chemically characterized synthetic seawater. The inorganic Fe concentrations used represent levels of Fe limitation relevant for different domains of the contemporary ocean. Combining physiological and transcriptomic approaches, we provide evidence of the progression of the physiological responses to increasing levels of Fe limitation. Our results showed a rising number of significantly regulated genes and the complexity of the response to increasing Fe limitation. Mild Fe limitation induced up-regulation of genes involved in Fe uptake, while genes involved in photosynthesis and respiration were down-regulated. Strong Fe limitation induced up-regulation of genes involved in energy metabolism and concomitant down-regulation of macronutrients uptake. Severe Fe limitation affected fine metabolic regulation of co-factors expression and activation of anti-oxidative stress responses. Our results suggest that homeostasis under long-term Fe limitation put at play dramatically different mechanisms for oxidative stress mitigation and carbon metabolism than those previously reported under Fe stress. Hence, evidence the importance of acclimation processes on the performance of cyanobacteria under Fe limitation conditions.
Highlights
IntroductionEvolution under the reductive conditions of ancient ocean favored the “luxurious” use of iron (Fe) in chlorophyll a (Chla) and many redox catalysts involved in different metabolic pathways such as respiration, macronutrients assimilation and detoxification of reactive oxygen species (Sunda, 1989; Sunda and Huntsman, 1995; Raven et al, 1999)
Cyanobacteria appeared in the ocean about 3.4 billion years ago
The maximum photosystem II (PSII) photochemical yield (Fv/Fm) did not show significant differences between replete Fe and mild-Felim treatments (0.38 ± 0.01 and 0.36 ± 0.02, respectively), it significantly decreased to 0.31 ± 0.01 and 0.24 ± 0.02 under strong-Felim and severeFelim conditions (Figure 2B)
Summary
Evolution under the reductive conditions of ancient ocean favored the “luxurious” use of iron (Fe) in chlorophyll a (Chla) and many redox catalysts involved in different metabolic pathways such as respiration, macronutrients assimilation and detoxification of reactive oxygen species (Sunda, 1989; Sunda and Huntsman, 1995; Raven et al, 1999). Under the oxygenated conditions of the contemporary ocean the solubility of the thermodynamically stable Fe3+ oxidation state is very low (Martin et al, 1991). Photosynthetic and respiratory electron flow take place in the thylakoid membranes sharing numerous intermediate transporters that account for about 80% of the cellular Fe biological demand (Scherer et al, 1982; Raven, 1990; Campbell et al, 1998).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
