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The purpose of this work was to determine the extent of microbial metabolic potential for polychlorinated biphenyls (PCBs) in soils that have had no previous exposure to this class of xenobiotic pollutants. Soil and sediment samples of distinct characteristics from six sites in Germany were used to inoculate PCB oil (Aroclor 1242) microdroplets. All samples yielded multispecies biofilms, as revealed by single-strand conformation polymorphism (SSCP) analyses of polymerase chain reaction (PCR) analysis of 16S rRNA genes, and sequence analysis of the main amplicons. Microbes representing 20 different operational taxonomic units (OTUs) were identified in the biofilms, but only a few were common to all biofilms, namely those closely related to Aquabacterium sp., Caulobacter sp., Imtechium assamiensis, Nevskia ramosa, Parvibaculum lavamentivorans and Burkholderia sp. The PCB biofilm communities were always distinct from control biofilms developing from the same samples in the absence of PCB. All PCB droplet-grown biofilms degraded multiple PCB congeners but differed in the congener spectra they degraded. These findings reveal that microbial potential to degrade PCBs is widespread in soils that have not been subjected to PCB contamination, and that this potential is characteristic of consortia of very diverse phylogenetic composition.

Soil contaminated with polychlorinated biphenyls (PCB) was used as an inoculum to grow a complex biofilm community on PCB oil (Aroclor 1242) on a substratum (Permanox). The biofilm was monitored for 31 days by confocal laser scanning microscopy, community fingerprinting using single-strand conformational polymorphism (SSCP), amplicons of the 16S rRNA genes, and chemical analyses of the PCB congeners. SSCP analysis of the young biofilm revealed a rather diverse microbial community with species of the genera Herbaspirillum and Bradyrhizobium as dominant members. The biofilm developing on the PCB droplets displayed pronounced stages of PCB degradation and biofilm development not described before from pure-culture experiments. The first step was the colonization of the substratum while the PCB oil was hardly populated. When a certain density of bacteria was reached on the Permanox, the PCB was colonized, but soon the degradation of the congeners was markedly reduced and many cells were damaged, as seen by LIVE/DEAD staining. Finally, the biofilm formed aggregates and invaded the PCB oil, showing lower numbers of damaged cells than before and a dramatic increase in PCB degradation. This sequence of biofilm formation is understood as a maturation process prior to PCB oil colonization. This is followed by a thin biofilm on the PCB droplet, an aggregation process forming pockets in the PCB, and finally an invasion of the biofilm into the PCB oil. Only the mature biofilm showed degradation of pentachlorinated PCB congeners, which may be reductively dechlorinated and the resulting trichlorobiphenyls then aerobically metabolized.

The active bacteria of a biofilm community grown directly on polychlorinated biphenyl (PCB) droplets were analyzed by 16S rRNA fingerprinting, identified by their 16S rRNA gene sequences and fatty acid profiling, and compared with isolates from the biofilm. Although, the multi-species biofilm degraded di- and trichlorinated PCB-congeners these substrates were not attacked by its individual isolated members, which suggests that a metabolic network is responsible for PCB degradation in the biofilm. The community metabolized [U-13C]-2,2'-dichlorobiphenyl incorporating the label into certain phospholipid fatty acids matching those found in Burkholderia species. In contrast, abundant biofilm community members, like Methylobacterium species, did not incorporate the label. These results provide prima faciae evidence for Burkholderia species as the main degraders of PCBs in this type of aerobic soils.

Recent advances in the degradation of polychlorinated biphenyls (PCBs) have focussed on the use of experimental enrichment cultures to obtain PCB-degrading communities, and the use of culture-independent approaches to characterize natural and experimental PCB-degrading communities and to identify the key members in this process. PCB-degrading communities can be surprisingly diverse. Novel types of composite bacteria-mineral biofilm communities have been described. Community metabolism of PCBs may lead to the formation of protoanemonin, a dead-end product in some instances but, in others, a seemingly productive intermediate. Analysis of isotope fractionation and preferred enantiomer degradation has provided new information on degradation of PCBs in anaerobic settings. The first defined community capable of dehalorespiration of PCBs has been described, and important community members identified. Here, we provide an overview of the current knowledge of aerobic and anaerobic degradation of PCBs in microbial consortia and in the environment, including novel approaches to determine in situ PCB degradation.

A moorland soil site polluted with PCB showed a high diversity of metabolically active bacteria. Beside frequent types of 16S rRNA sequences similar to those of the species of Sphingomonas and the Acidobacterium phylum an unusual high number of sequences from the genus Burkholderia were found. Burkholderia was also the main genus in isolates enriched on biphenyl or various chlorobenzoates. In microcosm experiments sterilized surfaces exposed to PCB polluted soil always showed the presence of clay aggregates formed by bacteria attached to the substratum. The bacteria use the PCB loaded clay colloids as transport medium for the water insoluble substrate to get access to the carbon source. This is a novel mechanism of how bacteria deal with hydrophobic substrates. [ABSTRACT FROM AUTHOR]

The presumptive metabolically active members of a bacterial community in a moorland soil in Germany, highly polluted with polychlorinated biphenyls (PCBs), were identified by sequencing of cloned reverse transcription–polymerase chain reaction (RT–PCR) amplification products of 16S rRNA generated from total RNA extracts. Analysis of the 16S rRNA clone library revealed a considerable diversity of metabolically active bacteria in the soil, despite the acidic pH and high concentrations of PCBs. Cloned sequence types clustered within the Proteobacteria (34% alpha-, 33% beta- and 7% gamma-subclasses), the Holophaga –Acidobacterium phylum (14%), the Actinobacteria (6.5%) and the Planctomycetales (2%). Three cloned sequence types were not affiliated to any described phylogenetic group. An unusual feature of this soil was the abundance of sequence types within the beta-subclass of the Proteobacteria , most of which were similar to the 16S rRNA gene sequences of species from only two genera, Burkholderia and Variovorax . Three other numerous 16S rRNA sequence types were similar to the sequences of Sphingomonas species, members of the Rhodopila globiformis group and Acidobacterium capsulatum . Some of the sequence types retrieved were similar to the 16S rRNA sequences of bacterial isolates able to degrade a variety of organic pollutants, including PCBs. As the PCB contamination is the major source of measurable carbon in this soil, some of the 16S rRNA sequence types detected and presumed to represent the metabolically active members of the community indicate the organisms likely to be involved, directly or indirectly, in the utilization of the PCBs as carbon and energy sources. [ABSTRACT FROM AUTHOR]