Phylogenetic characterization of several para- and meta-PCB dechlorinatingClostridium species: 16s rDNA sequence analyses

The genus Clostridium has more than 127 species, grouped according to their morphology and functions. Nine Clostridium species were identified based o n their ability to dechlorinate meta- and para-PCB (polychlorinated bipheny l) contaminated sediments. The phylogenetic relatedness of these PCB-degrad ing Clostridium species was studied using ribosomal RNA genes. The diversit y of small-subunit rRNA genes associated with the domain bacteria was exami ned using defined operational taxonomic units (OTUs) in samples from PCB co ntaminated sediments from Lake Medinah, New York. The RFLP (restrict;ion fr agment length polymorphism) of the OTVs was measured. OTUs B (105 clones), A (33 clones) and C (45 clones) accounted for 75% of all the 16S rDNA clone s expressing anaerobic para- and meta-PCB dechlorinating activity. In this report we describe complete 16S rDNA sequences of OTU-A and OTU-B, and part ial rDNA sequences of OTUs C-J. The OTU-B and OTU-I form a phylogenetically related cluster, closely affiliated with Clostridium hydroxybenzoicum stra ins. OTUs A, C, D, G, H and J also belong to the genus Clostridium, but the y represent separate species. OTU-E, a close affiliate to Bacteroides forsy nthus, is a meta-PCB dechlorinator. The Cl. hydroxybenzoicum strains (OTU-B ) are primarily para-PCB dechlorinators and are the most common. Some less prevalent OTUs (-E, -G, -H and -I), are also mostly para-PCB dechlorinators . Other Clostridium species such as Cl. beijerinckii (OTU-A), Cl, intestina lis (OTU-D) and Cl. thermolacticum (OTU-J) are primarily meta-PCB dechlorin ators. Cl. paraputrificum (OTU-C) and Cl. cellulosi (OTU-F), were less prev alent in the total consortium, but they could dechlorinate both para- and m eta-PCB. Although a few less prevalent Clostridium species can degrade both para- and meta-PCBs, this study confirms that para- and meta-PCB dechlorin ating species are generally phylogenetically different.