Anita Sellstedt - Energy Production using Microorganisms

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The aim of our research is to study energy production in microorganisms. We use an integrative approach with a combination of molecular biology, biochemistry and ecophysiology.
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Hydrogen metabolism of Frankia
The nitrogen-fixing filamentous actinobacteria of the genus Frankia form root nodules in symbioses with many woody trees and shrubs. Nitrogen fixation by actinorhizal plants may contribute as much as a quarter of the total biologically fixed nitrogen globally in terrestrial ecosystems each year. In addition, actinorhiza are major sources of new soil nitrogen in many different biomes.
The most important recent achievement in the Frankia research field is undoubtedly the sequencing of three Frankia genomes. We were able to show that there are large differences in the genome sizes. Frankia EANpec1 was found to have the largest genome with 9.0 Megabases (Mb), while Frankia ACN14a had an intermediate size (7.5 Mb) and Frankia HFPCcI3 was the smallest at 5.4 Mb. These numbers were correlated with geographical origin, host plant distribution and repeated sequences, such as IS. Our findings open up a new era in Frankia research, yielding possibilities to explore the molecular biology of Frankia and to utilize its traits, e.g. nitrogen fixation.
An inevitable source of energy-inefficiency in the nitrogen-fixation process is the evolution of hydrogen; as much as 25% of the in vitro electron flow through nitrogenase goes to hydrogen evolution, while in vivo these losses are much higher. Some nitrogen-fixing systems have dealt with this problem of energy loss through an enzyme, called uptake hydrogenase, which is very common in Frankia.


Light micrograph of the bacterium Frankia showing vesicles.	Light micrograph of our isolate of Chalara parvispora

Ethanol production
We are interested in developing ethanol production from cellulose-based biomass. We have shown in a batch fermentation study that a fungal mix could produce 24 gL-1 ethanol using pulp waste as substrate. The fungal mix was able to grow on xylose, hemicellulose and cellulose. In addition, we were able to identify the fungi mix using PCR-amplification of DNA and sequencing as Chalara parvispora and Trametes hirsuta/T. versicolor. In a reconstitution study, the identified fungi were shown to produce equal amounts of ethanol as the fungi mix. In addition, it was shown that C. parvispora could produce ethanol from xylose.
The study shows that refining biomass by ethanol production from pulp waste, a lignocellulose material, can be increased by adding C. parvispora and T. versicolor, which is of great economic significance for energy production.

Svensk sammanfattning

Key publications

DeLuca TH, O Zackrisson, M-C Nilsson, A Sellstedt 2002. Quantifying nitrogen fixation in feather moss carpets. Nature. 419: 917-920.

Mohapatra A, Leul M, Mattsson U, Sellstedt A 2004. A hydrogen-evolving enzyme is present in Frankia R43. FEMS Micro- biol. Lett.236: 235-240

Leul M, Mattsson U, Sellstedt A 2005. Molecular characterization of uptake hydrogenase in Frankia. Biochem. Soc. Trans. 33: 64-66.

Normand, Lapierre, Tisa, Lavire, Alloisio, Cournoyer, Marechal, Pujic, Gogarten,Huang, Mastronunzio, Bickhard, Bassi, Rawnsley, Niemann, Francino, Lapidus, Martinez, Goltsman, Choisne, Schenowitz, Couloux, Demange, Medigue, Cruveiller, Labarre, Rouy, Vallenet, Mullin, Kopp, Wang, Tomkins, Berry, Valverde, Wall, Sellstedt, Tavares Daubi, Benson 2007. Genome structure reflects host biogeography in three plant symbionts Frankia sp. strains. Genome Research, 17, 7-15.

Leul M, Normand P, Sellstedt A 2009. The phylogeni of uptake hydrogenases. Int Microbiol. 12(1):23-28.

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July 2010

Friday, July 30, 2010
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