Molecular phylogenetic analysis of sulfate-reducing bacteria from deep sediment layers of the tropical West Pacific warm pool

The diversity of sulfate-reducing bacteria (SRB) from deep layers of deep-sea sediments [more than 2 m bsf (below seafloor)] of two sites (W01-3 and WP01-4) in a tropical West Pacific warm pool region was characterized by using molecular phylogenetic analysis. The results of culture-independent samples demonstrated that the dominant clones from both sites were related to Gram-positive spore forming genus, Desulfotomaculum, which accounted for 36.8% of all the sequencing clones from Site WP01-3 and 62.8% from Site WP01-4. However, the other SRB group which was generally reported to be predominant in the deep-sea sediments of other regions,δ-subclass of the proteobacteria was found to be in very low percentages. Therefore, it could be speculated that there existed a unique chemical environment in the deep-sea sediment of this warm pool region. When comparing the Desulfotomaculum sp. related sequences from both sites, it was revealed that though the Desulfotomaculum-like sequences from Site WP01-3 were more diverse than those from Site WP01-4, all these sequences from both sites showed high similarity and formed a new phylogenetically homogeneous cluster in the Desulfotomaculum genus which had never been reported before. Successful enrichment of SRB was only achieved from samples of Site WP01-4 and the sequence analysis of culture-dependent samples further confirmed the dominance of Desulfotomaculum genus. But Desulfotomaculum-related sequences from culture-dependent and culture-independent samples belonged to two different clusters respectively. This difference showed the choice of cultivation to the microorganisms.