Journal of Biotechnology 56 (1997) 135–142 Enzymatic evidence for an involvement of pyruvate dehydrogenase in the anaerobic glycerol metabolism of Klebsiella pneumoniae Kirsten Menzel, An-Ping Zeng *, Wolf-Dieter Deckwer GBF-Gesellschaft fu ¨r Biotechnologische Forschung, Biochemical Engineering Diision, M ascheroder W eg 1, D -38 124 Braunschweig, Germany Received 21 August 1996; received in revised form 27 May 1997; accepted 28 May 1997 Abstract Stoichiometric analysis of pathways involved in anaerobic bioconversion of glycerol by Klebsiella pneumoniae revealed that enzyme(s) in addition to pyruvate formate-lyase (PFL) must be involved in pyruvate decarboxylation. In this work, enzymatic evidence is presented that confirmed a simultaneous involvement of pyruvate dehydrogenase complex (PDH) and excluded the presence of pyruvate:ferredoxin oxidoreductase in this anaerobic bioprocess. The in vitro PDH activity of cell extract from continuous culture was found to be strongly affected by the substrate (glycerol) concentration in medium and cell growth rate (dilution rate). It increases with increasing glycerol concentration and correlates well with the specific substrate uptake rate at different dilution rates in a kind of saturation function. At a similar substrate uptake rate, it decreases with cell growth rate. The in vitro activity of PDH is much higher than its in vivo activity calculated from the pathway stoichiometry but comparable to the calculated in vivo activity of PFL. © 1997 Elsevier Science B.V. Keywords: Klebsiella pneumoniae ; Pyruvate dehydrogenase; Pyruvate formate-lyase; Glycerol fermentation; 1,3- propanediol 1. Introduction Glycerol is an interesting substrate for biologi- cal conversion because of its availability from renewable resources and the ability of several microorganisms to use glycerol as a sole carbon and energy source (Lin, 1976). For example, mi- croorganisms of the genera Klebsiella, Clostridium and Citrobacter can anaerobically convert glycerol into the industrially appealing product 1,3- propanediol (PD) (Lin, 1976; Hohmann et al., *Corresponding author. Tel.: +49 531 6181188; fax: +49 531 6181111; e-mail: AZE@GBF-Braunschweig.de 0168-1656/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0168-1656(97)00110-7