F-ATPASE AND V-ATPASE IN THE GENUS THERMUS AND RELATED SPECIES

The discovery of a V-type ATPase in the gram-negative bacterium Thermu s thermophilus HB8 [YOKOYA-MA et al., J. Biol. Chem. 265, 21946, 1990) was unexpected, since only eukaryotic endomembranes and archaea were thought to contain this enzyme complex, and horizontal gene transfer w as suggested to explain the finding. We examined membrane-associated A TPases from representatives of several groups of the genus Thermus. Th e enzymes were extracted with chloroform and purified by ion exchange chromatography or native gel electrophoresis. One never Islandic isola te, T. scotoductus SE-1, as well as strain T. filiformis from New Zeal and, possessed F-ATPases, as judged by the typical five subunit compos ition of the F-1-moiety, sensitivity to azide, insensitivity to nitrat e and a strong crossreaction with antibodies against the F-1-ATPase fr om E. coli. In addition, N-terminal amino acid sequencing of the beta subunit from T. scotoductus SE-1 confirmed its homology with beta subu nits from known F-ATPases. In contrast, the same extraction procedure released a V-ATPase from the membranes of T. thermophilus HB27 and T. aquaticus YT-1. The related species Meiothermus (formerly Thermus) chl iarophilus ALT-8 also possessed a V-ATPase. AII V-ATPases examined in this study contained larger major subunits than F-ATPases, crossreacte d with antiserum against subunit A of the V-ATPase from the archaeon H alobacterium saccharovorum, and the N-terminal sequences of their majo r subunits were homologous to those of other V-ATPases. Sequences of t he 16S rRNA gene clearly placed T. scotoductus SE-1, along with other non-pigmented Thermus strains, as a distinct species close to T. aquat icus. Our results suggested that at least two members of the genus, T. scotoductus SE-1 and T. filiformis, contain an F-ATPase, whereas seve ral others possess a V-ATPase. These data could indicate a greater div ersity cti the genus Thermus than was previously thought. Alternativel y, the genus may consist of species where horizontal gene transfer has occurred and others, where it has not.