a, Phylogenetic analysis of group-4 [NiFe] hydrogenases in Asgard archaea. The unrooted maximum-likelihood phylogenetic tree was built from an alignment of 425 sequences that included 110 sequences of Asgard archaea, with 308 amino acid positions. b, Phylogenetic analysis of group-3 [NiFe] hydrogenases in Asgard archaea. The unrooted maximum-likelihood phylogenetic tree was built from an alignment of 813 sequences that included 335 sequences of Asgard archaea, with 331 amino acid positions. c, Phylogenetic analysis of group-1 [NiFe] hydrogenases in the Asgard archaea. The unrooted maximum-likelihood phylogenetic tree was built from an alignment of 541 sequences that included 2 sequences of Wukongarchaeota, with 376 amino acid positions.