Different glycolytic pathways for glucose and fructose in the halophilic archaeon Halococcus saccharolyticus.
The glucose and fructose degradation pathways were analyzed in the halophilic archaeon Halococcus saccharolyticus by 13C-NMR labeling studies in growing cultures, comparative enzyme measurements and cell suspension experiments. H. saccharolyticus grown on complex media containing glucose or fructose specifically 13C-labeled at C1 and C3, formed acetate and small amounts of lactate. The 13C-labeling patterns, analyzed by 1H- and 13C-NMR, indicated that glucose was degraded via an Entner-Doudoroff (ED) type pathway (100%), whereas fructose was degraded almost completely via an Embden-Meyerhof (EM) type pathway (96%) and only to a small extent (4%) via an ED pathway. Glucose-grown and fructose-grown cells contained all the enzyme activities of the modified versions of the ED and EM pathways recently proposed for halophilic archaea. Glucose-grown cells showed increased activities of the ED enzymes gluconate dehydratase and 2-keto-3-deoxy-gluconate kinase, whereas fructose-grown cells contained higher activities of the key enzymes of a modified EM pathway, ketohexokinase and fructose-1-phosphate kinase. During growth of H. saccharolyticus on media containing both glucose and fructose, diauxic growth kinetics were observed. After complete consumption of glucose, fructose was degraded after a lag phase, in which fructose-1-phosphate kinase activity increased. Suspensions of glucose-grown cells consumed initially only glucose rather than fructose, those of fructose-grown cells degraded fructose rather than glucose. Upon longer incubation times, glucose- and fructose-grown cells also metabolized the alternate hexoses. The data indicate that, in the archaeon H. saccharolyticus, the isomeric hexoses glucose and fructose are degraded via inducible, functionally separated glycolytic pathways: glucose via a modified ED pathway, and fructose via a modified EM pathway.
Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität Kiel, Germany.
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U
Johnsen
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M
Selig
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KB
Xavier
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Santos
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Schönheit
D001673:Biodegradation, Environmental; D005631:Fructokinases / Q000378:metabolism; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis; D019625:Halococcus / Q000254:growth & development / Q000378:metabolism*; D006836:Hydro-Lyases / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010732:Phosphofructokinase-1 / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism
D005632:Fructose; D005631:Fructokinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D010732:Phosphofructokinase-1; C021475:ketohexokinase; C021471:2-keto-3-deoxygluconokinase; C068652:1-phosphofructokinase; D006836:Hydro-Lyases; C020576:gluconate dehydratase; D005947:Glucose