Trabulsiella guamensis is a nonpathogenic enterobacterium that was isolated from a vacuum cleaner on the island of Guam. It has one H2-oxidizing Hyd-2-type hydrogenase (Hyd) and encodes an H2-evolving Hyd that is most similar to the uncharacterized Escherichia coli formate hydrogenlyase (FHL-2Ec) complex. The T. guamensis FHL-2 (FHL-2Tg) complex is predicted to have 5 membrane-integral and between 4 and 5 cytoplasmic subunits. We showed that the FHL-2Tg complex catalyzes the disproportionation of formate to CO2 and H2. FHL-2Tg has activity similar to that of the E. coli FHL-1Ec complex in H2 evolution from formate, but the complex appears to be more labile upon cell lysis. Cloning of the entire 13-kbp FHL-2Tg operon in the heterologous E. coli host has now enabled us to unambiguously prove FHL-2Tg activity, and it allowed us to characterize the FHL-2Tg complex biochemically. Although the formate dehydrogenase (FdhH) gene fdhF is not contained in the operon, the FdhH is part of the complex, and FHL-2Tg 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 H2-oxidizing Hyd-2Tg and the H2-forming FHL-2Tg under these conditions.
IMPORTANCE Biological H2 production presents an attractive alternative for fossil fuels. However, in order to compete with conventional H2 production methods, the process requires our understanding on a molecular level. FHL complexes are efficient H2 producers, and the prototype FHL-1Ec complex in E. coli 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-2Ec complex, allow a first biochemical characterization of T. guamensis’s fermentative metabolism, and establish this enterobacterium as a model organism for FHL-dependent energy conservation.