MICROBIAL DECHLORINATION OF 2,3,5,6-TETRACHLOROBIPHENYL UNDER ANAEROBIC CONDITIONS IN THE ABSENCE OF SOIL OR SEDIMENT

Bacterial enrichment cultures developed with Baltimore Harbor (BHR) se diments were found to reductively dechlorinate 2,3,5,6-tetrachlorobiph enyl (2,3,5,6-CB) when incubated in a minimal estuarine medium contain ing short-chain fatty acids under anaerobic conditions with and withou t the addition of sediment. Primary enrichment cultures formed both me ta and ortho dechlorination products from 2,3,5,6-CB, The lag time pre ceding dechlorination decreased from 30 to less than 20 days as the cu ltures were sequentially transferred into estuarine medium containing dried, sterile BH sediment. In addition, only ol-tho dechlorination wa s observed following transfer of the cultures, Sequential transfer int o medium without added sediment also resulted in the development of a strict ortho-dechlorinating culture following a lag of more than 100 d ays. Upon further transfer into the minimal medium without sediment, t he lag time decreased to less than 50 days. At this stage all cultures , regardless of the presence of sediment, would produce 2,3,5-CB and 3 ,5-CB from 2,3,5,6-CB, The strict ortho-dechlorinating activity in the sediment-free cultures has remained stable for more than 1 year throu gh several transfers, These results reveal that the classical microbia l enrichment technique using a minimal medium with a single polychlori nated biphenyl (PCB) congener selected for ortho dechlorination of 2,3 ,5,6-CB. Furthermore, this is the first report of sustained anaerobic PCB dechlorination in the complete absence of soil or sediment.