Discovery of a bacterium, with distinctive dioxygenase, that is responsible for in situ biodegradation in contaminated sediment

Microorganisms maintain the biosphere by catalyzing biogeochemical processes, including biodegradation of organic chemical pollutants. Yet seldom have the responsible agents and their respective genes been identified. Here we used field-based stable isotopic probing (SIP) to discover a group of bacteria responsible for in situ metabolism of an environmental pollutant, naphthalene. We released ¹³C-labeled naphthalene in a contaminated study site to trace the flow of pollutant carbon into the naturally occurring microbial community. Using GC/MS, molecular biology, and classical microbiological techniques we documented ¹³CO₂ evolution (2.3% of the dose in 8 h), created a library of 16S rRNA gene clones from ¹³C labeled sediment DNA, identified a taxonomic cluster (92 of 95 clones) from the microbial community involved in metabolism of the added naphthalene, and isolated a previously undescribed bacterium (strain CJ2) from site sediment whose 16S rRNA gene matched that of the dominant member (48%) of the clone library. Strain CJ2 is a β proteobacterium closely related to Polaromonas vacuolata. Moreover, strain CJ2 hosts the sequence of a naphthalene dioxygenase gene, prevalent in site sediment, detected before only in environmental DNA. This investigative strategy may have general application for elucidating the bases of many biogeochemical processes, hence for advancing knowledge and management of ecological and industrial systems that rely on microorganisms.