The megaplasmids of both species include a complete nitrate reductase operon (narGHJIK). T. oshimai JL-2 possesses two nitrate/nitrite transporters (narK1 and narK2), which is similar to T. thermophilus HB8 (6), whereas T. thermophilus JL-18 possesses a single copy of narK. Genes encoding nitrite reductase (nirS and nirK in T. oshimai JL-2 and nirS in T. thermophilus JL-18) and nitric oxide reductase (norB and norC) were also identified in close proximity to the narGHIJK operon in the megaplasmids of both T. thermophilus JL-18 and T. oshimai JL-2. However, nitrous oxide reductase (nos) genes, which are needed for the conversion of nitrous oxide to dinitrogen, are absent, concurrent with the incomplete denitrification phenotype of these strains and the high flux of nitrous oxide reported at Great Boiling Spring (2). Both megaplasmids also possess genes encoding a DNA repair system that is proposed to impart thermophily in T. thermophilus HB8 and HB27 (5). A sox gene cluster that includes a sulfite dehydrogenase gene (soxCD) essential for the chemotrophic growth of Paracoccus pantotrophus (7) was identified in T. oshimai JL-2 and T. thermophilus JL-18 chromosomes, suggesting that these organisms can carry out sulfur oxidation.