Dissection of the Hydrogen Metabolism of the EnterobacteriumTrabulsiella guamensis: Identification of a Formate-Dependent and Essential Formate Hydrogenlyase Complex Exhibiting Phylogenetic Similarity to Complex I

Trabulsiella guamensis is a non-pathogenic enterobacterium that was isolated from a vacuum cleaner on the island of Guam. It has one H 2 -oxidizing Hyd-2-type hydrogenase (Hyd), and encodes a H 2 -evolving Hyd that is most similar to the uncharacterized Escherichia coli formate hydrogenlyase (FHL-2 Ec ) complex. The FHL-2 Tg complex is predicted to have 5 membrane-integral and between 4-5 cytoplasmic subunits. We could show that FHL-2 Tg complex catalyses the disproportionation of formate to CO 2 and H 2 . FHL-2 Tg has an activity similar to the E. coli FHL-1 Ec complex in H 2 -evolution from formate, but the complex appears more labile upon cell lysis. Cloning of the entire 13 kbp FHL-2 Tg operon in the heterologous E. coli host has now enabled us to prove FHL-2 Tg activity unambiguously and allowed us to characterize the FHL-2 Tg complex biochemically. Although the formate dehydrogenase (FdhH) gene fdhF is not encoded in the operon, the FdhH is part of the complex and FHL-2 Tg activity was dependent on the presence of E. coli FdhH. Also, in contrast to E. coli, T. guamensis can ferment the alternative carbon source cellobiose, and we further investigated the participation of both the H 2 -oxidizing Hyd-2 Tg and the H 2 -forming FHL-2 Tg under these conditions. Importance Biological H 2 -production presents an attractive alternative for fossil fuels. But in order to compete with conventional H 2 -production methods, the process requires our understanding on the molecular level. FHL complexes are efficient H 2 -producers and the prototype FHL-1 Ec complex in E. coli is well studied. This paper presents the first biochemical characterisation of an FHL-2-type complex. The data presented here will enable us to solve the long-standing mystery of the FHL-2 Ec complex, allow a first biochemical characterisation of T. guamensis ’s fermentative metabolism and establish this enterobacterium as model organism for FHL-dependent energy conservation.