Construction of Whole Cell Bacterial Biosensors as an Alternative Environmental Monitoring Technology to Detect Naphthenic Acids in Oil Sands Process-Affected Water

After extraction of bitumen from oil sands deposits,
the oil sand
process-affected water (OSPW) is stored in tailings ponds. Naphthenic
acids (NA) in tailings ponds have been identified as the primary contributor
to toxicity to aquatic life. As an alternative to other analytical
methods, here we identify bacterial genes induced after growth in
naphthenic acids and use synthetic biology approaches to construct
a panel of candidate biosensors for NA detection in water. The main
promoters of interest were the atuAR promoters from
a naphthenic acid degradation operon and upstream TetR regulator,
the marR operon which includes a MarR regulator and
downstream naphthenic acid resistance genes, and a hypothetical gene
with a possible role in fatty acid biology. Promoters were printed
and cloned as transcriptional lux reporter plasmids
that were introduced into a tailings pond-derived Pseudomonas species. All candidate biosensor strains were tested for transcriptional
responses to naphthenic acid mixtures and individual compounds. The
three priority promoters respond in a dose-dependent manner to simple,
acyclic, and complex NA mixtures, and each promoter has unique NA
specificities. The limits of NA detection from the various NA mixtures
ranged between 1.5 and 15 mg/L. The atuA and marR promoters also detected NA in small volumes of OSPW
samples and were induced by extracts of the panel of OSPW samples.
While biosensors have been constructed for other hydrocarbons, here
we describe a biosensor approach that could be employed in environmental
monitoring of naphthenic acids in oil sands mining wastewater.