%0 Journal Article
%T Energy metabolism of Heliobacterium modesticaldum during phototrophic and chemotrophic growth
%A Kuo-Hsiang Tang
%A Hai Yue
%A Robert E Blankenship
%J BMC Microbiology
%D 2010
%I BioMed Central
%R 10.1186/1471-2180-10-150
%X We present the first experimental evidence that D-ribose, D-fructose and D-glucose can be photoassimilated by H. modesticaldum as sole carbon sources in newly developed defined growth medium. Also, we confirm two non-autotrophic CO2-fixation pathways utilized by H. modesticaldum: reactions catalyzed by pyruvate:ferredoxin oxidoreductase and phosphoenolpyruvate carboxykinase, and report acetate excretion during phototrophic and chemotrophic growth. Further, genes responsible for pyruvate fermentation, which provides reducing power for nitrogen assimilation, carbon metabolism and hydrogen production, are either active or up-regulated during chemotrophic growth. The discovery of ferredoxin-NADP+ oxidoreductase (FNR) activity in cell extracts provides the reducing power required for carbon and nitrogen metabolisms. Moreover, we show that photosynthetic pigments are produced by H. modesticaldum during the chemotrophic growth, and demonstrate that H. modesticaldum performs nitrogen fixation during both phototrophic and chemotrophic growth.Collectively, this report represents the first comprehensive studies for energy metabolism in heliobacteria, which have the simplest known photosynthetic machinery among the entire photosynthetic organisms. Additionally, our studies provide new and essential insights, as well as broaden current knowledge, on the energy metabolism of the thermophilic phototrophic bacterium H. modesticaldum during phototrophic and chemotrophic growth.Several features characterize the physiological and metabolic aspects of phototrophic heliobacteria [1-5]: (a) They are the only known phototrophs that belong to the gram-positive bacterial phylum Firmicutes, and as is typical of members of this group, which includes species of Bacillus and Clostridium, heliobacteria can form heat resistant endospores; (b) They produce the unique pigment bacteriochlorophyll g (BChl g); (c) They produce 81-hydroxy-chlorophyll a with a farnesol tail (81-OH-Chl aF), which serves
%U http://www.biomedcentral.com/1471-2180/10/150