Distance tree of proteobacterial clones from Guaymas sediment cores A and C, based on near-complete 16S rDNA sequences. Bootstrap values (in percent) are based on 1,000 replicates each (distance and parsimony) and are shown for branches with more than 50% bootstrap support. For the major phylogenetic divisions, the numbers of core A and core C clones are given in that order. For multiple near-identical clones (>99% identity), the number of multiples is given after the GenBank number of a representative clone. Some sequence types occurred in several sediment layers: Guaymas clone A1 B030 was found three times in the 0- to 1-cm layer of core A and one time in the 1- to 2-cm layer of core A, Guaymas clone A2 B043 was found one time in the 0- to 1-cm layer of core A and five times in the 1- to 2-cm layer of core A, and Guaymas clone A2 B004 was found three times in the 0- to 1-cm layer of core A and three times in the 1- to 2-cm layer of core A.