MbnB: the core Mbn biosynthesis gene. (A) MUSCLE alignment of MbnB, including both domains. Residues are colored following the Taylor color scheme , with intensity modified by a conservation color increment of 30%. Truncated metagenomic sequences are not shown in this alignment. (B) Phylogenetic tree (constructed in MEGA 5.0 as described in the Methods section) based on a MUSCLE alignment of all MbnB sequences, not including truncated metagenomic sequences. Gamma distribution parameter 1.5823.