ANALYSIS OF MICROBIAL COMMUNITY STRUCTURE AND FUNCTION OF A LABORATORY SCALE ENHANCED BIOLOGICAL PHOSPHATE REMOVAL REACTOR

The reductive dechlorination (RD) of tetrachloroethene (PCE) to vinyl chloride (VC) and, to a lesser extent, to ethene (ETH) by an anaerobic microbial community has been investigated by studying the processes and kinetics of the main physiological components of the consortium. Molecular hydrogen, produced by methanol-utilizing acetogens, was the electron donor for the PCE RD to VC and ETH without forming any appreciable amount of other chlorinated intermediates and in the near absence of methanogenic activity. The microbial community structure of the consortium was investigated by preparing a 16S rDNA clone library and by fluorescence in situ hybridisation (FISH). The PCR primers used in the clone library allowed the harvest of 16S rDNA from both bacterial and archaeal members in the community. A total of 616 clones was screened by restriction fragment length polymorphism (RFLP) analysis of the clone inserts followed by the sequencing of RFLP group representatives and phylogenetic analysis. The clone library contained sequences mostly from hitherto undescribed bacteria. No sequences similar to those of the known RD bacteria like Dehalococcoides ethenogenes or Dehalobacter restrictus were found in the clone library and none of these bacteria were present in the RD consortium according to FISH. Almost all clones fell into six previously described phyla of the bacterial domain with the majority (56.6%) being deep branching members of the Spirochaetes phylum. Other clones were in the Firmicutes phylum (18.5%), the Chloroflexi phylum (16.4%), the Bacteroidetes phylum (6.3%), the Synergistes genus (1.1%), and a lineage which could not be affiliated with existing phyla (1.1%). No archaeal clones were found in the clone library. Due to the phylogenetic novelty of the microbial community with regard to previously cultured microorganisms, no specific microbial component(s) could be hypothetically affiliated with the RD phenotype. The predominance of Spirochaetes in the microbial consortium, the main group revealed by clone library analysis, was confirmed by FISH using a purposely developed probe