Dissertation Abstract
The role of heterotrophic bacteria in the coupling of iron and carbon cycles in the ocean
Fourquez, Marion A 2012 marion.fourquez-utas.edu.au
Biological oceanography, University Pierre and Marie Curie (France), 315 pp.
Iron is a physiological requirement for life; however in oceanic environments its bioavailability for microorganisms is low. Due to the scarcity of iron phytoplankton, and more specifically photosynthesis and related biogeochemical processes (e.g. carbon dioxide uptake) are limited in large regions of the global ocean. In this context, processes controlled by heterotrophic bacteria could play two parts: firstly, they can compete with phytoplankton for access to iron. Then, the effects of Fe-deficiency on their metabolism may also impact the carbon cycle.
The metabolic response of two strains of Alteromonas macleodii, isolated from contrasting marine environments (coastal and oceanic), was investigated. Iron limitation leads to a decrease in respiration and significant changes in expression of several key enzymes associated with carbon catabolism, specifically those involved the citric acid cycle and glycolysis. The study shows strain-specific responses to iron limitation. Growth rate of the oceanic strain was less sensitive to low iron concentrations compared to those of the coastal strain.
The study provides new insights into how heterotrophic bacteria acclimatize to low iron concentrations. Thus, by altering carbon metabolism and energy acquisition of heterotrophic bacteria, Fe may affect cycling of carbon in certain oceanic regions.
Heterotrophic bacteria have evolved several strategies to access various chemical forms of iron. However, due to the absence of a suitable method, the ability of different bacterial groups to incorporate iron has remained largely uncharacterized. In order identify marine bacterial assemblages actively incorporating iron, microautoradiography combined with CARD-FISH was developed using 55Fe as the radioisotope. Initial application of this technique highlights its potential and shows the major contribution of Gammaproteobacteria, including Alteromonas genus, to iron incorporation in both NW Mediterranean Sea and Southern Ocean.
In the Southern Ocean bacterial iron demand was measured during the KEOPS2 cruise. At the beginning of the spring bloom, bacteria competed strongly with pico-nanoplankton for iron. Iron incorporation by bacteria was 20 times higher when pico-nanoplankton was removed from the experiments. In addition iron incorporation by heterotrophic bacteria was positively correlated with primary production. The results suggest that the availability of dissolved organic carbon is a crucial parameter for bacterial iron demand and could indirectly influence trophic relationships.
Overall, this study sheds new light on the role of heterotrophic bacteria in the coupling of iron and carbon cycles at both single cell and ecosystem scales.
The metabolic response of two strains of Alteromonas macleodii, isolated from contrasting marine environments (coastal and oceanic), was investigated. Iron limitation leads to a decrease in respiration and significant changes in expression of several key enzymes associated with carbon catabolism, specifically those involved the citric acid cycle and glycolysis. The study shows strain-specific responses to iron limitation. Growth rate of the oceanic strain was less sensitive to low iron concentrations compared to those of the coastal strain.
The study provides new insights into how heterotrophic bacteria acclimatize to low iron concentrations. Thus, by altering carbon metabolism and energy acquisition of heterotrophic bacteria, Fe may affect cycling of carbon in certain oceanic regions.
Heterotrophic bacteria have evolved several strategies to access various chemical forms of iron. However, due to the absence of a suitable method, the ability of different bacterial groups to incorporate iron has remained largely uncharacterized. In order identify marine bacterial assemblages actively incorporating iron, microautoradiography combined with CARD-FISH was developed using 55Fe as the radioisotope. Initial application of this technique highlights its potential and shows the major contribution of Gammaproteobacteria, including Alteromonas genus, to iron incorporation in both NW Mediterranean Sea and Southern Ocean.
In the Southern Ocean bacterial iron demand was measured during the KEOPS2 cruise. At the beginning of the spring bloom, bacteria competed strongly with pico-nanoplankton for iron. Iron incorporation by bacteria was 20 times higher when pico-nanoplankton was removed from the experiments. In addition iron incorporation by heterotrophic bacteria was positively correlated with primary production. The results suggest that the availability of dissolved organic carbon is a crucial parameter for bacterial iron demand and could indirectly influence trophic relationships.
Overall, this study sheds new light on the role of heterotrophic bacteria in the coupling of iron and carbon cycles at both single cell and ecosystem scales.