Document Detail

Coassimilation of organic substrates via the autotrophic 3-hydroxypropionate bi-cycle in Chloroflexus aurantiacus.
MedLine Citation:
PMID:  21764971     Owner:  NLM     Status:  MEDLINE    
Chloroflexus aurantiacus is a facultative autotrophic green nonsulfur bacterium that grows phototrophically in thermal springs and forms microbial mats with cyanobacteria. Cyanobacteria produce glycolate during the day (photorespiration) and excrete fermentation products at night. C. aurantiacus uses the 3-hydroxypropionate bi-cycle for autotrophic carbon fixation. This pathway was thought to be also suited for the coassimilation of various organic substrates such as glycolate, acetate, propionate, 3-hydroxypropionate, lactate, butyrate, or succinate. To test this possibility, we added these compounds at a 5 mM concentration to autotrophically pregrown cells. Although the provided amounts of H(2) and CO(2) allowed continuing photoautotrophic growth, cells immediately consumed most substrates at rates equaling the rate of autotrophic carbon fixation. Using [(14)C]acetate, half of the labeled organic carbon was incorporated into cell mass. Our data suggest that C. aurantiacus uses the 3-hydroxypropionate bi-cycle, together with the glyoxylate cycle, to channel organic substrates into the central carbon metabolism. Enzyme activities of the 3-hydroxypropionate bi-cycle were marginally affected when cells were grown heterotrophically with such organic substrates. The 3-hydroxypropionate bi-cycle in Chloroflexi is unique and was likely fostered in an environment in which traces of organic compounds can be coassimilated. Other bacteria living under oligotrophic conditions acquired genes of a rudimentary 3-hydroxypropionate bi-cycle, possibly for the same purpose. Examples are Chloroherpeton thalassium, Erythrobacter sp. strain NAP-1, Nitrococcus mobilis, and marine gammaproteobacteria of the OM60/NOR5 clade such as Congregibacter litoralis.
Jan Zarzycki; Georg Fuchs
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2011-07-15
Journal Detail:
Title:  Applied and environmental microbiology     Volume:  77     ISSN:  1098-5336     ISO Abbreviation:  Appl. Environ. Microbiol.     Publication Date:  2011 Sep 
Date Detail:
Created Date:  2011-08-25     Completed Date:  2011-12-13     Revised Date:  2013-06-28    
Medline Journal Info:
Nlm Unique ID:  7605801     Medline TA:  Appl Environ Microbiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  6181-8     Citation Subset:  IM    
Mikrobiologie, Fakultät für Biologie, Schänzlestraße 1, D-79104 Freiburg, Germany.
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MeSH Terms
Autotrophic Processes*
Carbon / metabolism*
Carbon Radioisotopes / metabolism
Chloroflexus / growth & development,  metabolism*
Culture Media / chemistry
Hydrogen / metabolism
Metabolic Networks and Pathways
Organic Chemicals / metabolism*
Staining and Labeling / methods
Reg. No./Substance:
0/Carbon Radioisotopes; 0/Culture Media; 0/Organic Chemicals; 1333-74-0/Hydrogen; 7440-44-0/Carbon

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