Microbial aerobic degradation of highly chlorinated pollutants in liquid media since 1967: A review of taxonomy and degradation efficiencies

Persistent organic pollutants (POPs) are resistant to biological degradation, resulting in long-term ecological impacts. Numerous geographically diverse studies have isolated microbial strains from soils, sediments and sludges, with abilities to aerobically transform chlorinated POPs in liquid media. However, there remains little evidence that such isolates represent efficient POP degradation phylotypes, making it difficult to identify suitable targets for bioengineering efforts. With a focus on chlorinated POPs, we assessed the taxonomic diversity of soil-isolated culturable bacteria and fungi globally, and their POP degradation efficiencies in liquid culture. The Web of Science database was queried, yielding 321 observations of aerobic POP-transformation in cultures involving 14 different POPs. These observations were derived from 163 bacterial or fungal isolates across 78 studies conducted globally. Transformation efficiencies (% POP decrease per day) were adjusted for assay temperature and normalised. The taxonomic distribution of microbial isolates globally resembled a narrow, but likely stochastic subset of soil microorganisms. When water solubilities, octanol-water constants, vapour pressure and microbial transformation efficiencies in percent of POP reduction per day in liquid media were collated and normalised, no taxonomic marker for POP transformation efficiencies were found. The findings suggested that microbial transformation of chlorinated POPs was not associated with specific taxonomic lineages. However, certain strains across different microbial classes have evolved traits to metabolise specific POPs, particularly those with relatively high water solubility, and thus exhibit high transformation efficiencies. The stochastic taxonomic association with degradation efficiency suggested that any soil may have the potential for artificial community selection to enhance POP degradation.<p></p>