Characterization of the central metabolic pathways in Thermoanaerobacter sp. strain X514 via isotopomer-assisted metabolite analysis.
Thermoanaerobacter sp. strain X514 has great potential in biotechnology due to its capacity to ferment a range of C(5) and C(6) sugars to ethanol and other metabolites under thermophilic conditions. This study investigated the central metabolism of strain X514 via (13)C-labeled tracer experiments using either glucose or pyruvate as both carbon and energy sources. X514 grew on minimal medium and thus contains complete biosynthesis pathways for all macromolecule building blocks. Based on genome annotation and isotopic analysis of amino acids, three observations can be obtained about the central metabolic pathways in X514. First, the oxidative pentose phosphate pathway in X514 is not functional, and the tricarboxylic acid cycle is incomplete under fermentative growth conditions. Second, X514 contains (Re)-type citrate synthase activity, although no gene homologous to the recently characterized (Re)-type citrate synthase of Clostridium kluyveri was found. Third, the isoleucine in X514 is derived from acetyl coenzyme A and pyruvate via the citramalate pathway rather than being synthesized from threonine via threonine ammonia-lyase. The functionality of the citramalate synthase gene (cimA [Teth514_1204]) has been confirmed by enzymatic activity assays, while the presence of intracellular citramalate has been detected by mass spectrometry. This study demonstrates the merits of combining (13)C-assisted metabolite analysis, enzyme assays, and metabolite detection not only to examine genome sequence annotations but also to discover novel enzyme activities.
Feng
Xueyang
X
Department of Energy, Environmental and Chemical Engineering, Washington University, St. Louis, MO 63130, USA.
Mouttaki
Housna
H
Lin
Lu
L
Huang
Rick
R
Wu
Bing
B
Hemme
Christopher L
CL
He
Zhili
Z
Zhang
Baichen
B
Hicks
Leslie M
LM
Xu
Jian
J
Zhou
Jizhong
J
Tang
Yinjie J
YJ
D000596:Amino Acids / Q000378:metabolism; D053898:Biosynthetic Pathways; D002247:Carbon Isotopes / Q000378:metabolism; D002952:Citric Acid Cycle; D016678:Genome; D005947:Glucose / Q000378:metabolism; D055442:Metabolome; D010427:Pentose Phosphate Pathway; D011773:Pyruvates / Q000378:metabolism; D046968:Thermoanaerobacter / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
D000596:Amino Acids; D002247:Carbon Isotopes; D011773:Pyruvates; D005947:Glucose