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

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