Genomic and metagenomic characterization of halophilic microorganisms with insights into the bioremediation of produced water

Abstract

Produced water is an extremely toxic environmental wastewater source derived from oil-production. Produced water is typically a highly saline waste water containing a litany of hydrocarbon and heavy metal pollution. It is very cost ineffective to remediate and return this water to the natural sources it was obtained from prior to oil-production. We have metagenomically characterized a halophilic mixed culture (KWT) and identified the most abundant organism to be an Arhodomonas sp. Within the metagenome, we successfully identified a large assortment of genes theoretically responsible for BTEX degradation belonging to the Arhodomonas sp. Using this KWT culture (and another microbial enrichment Rozel), a complete removal of BTEX in raw produced water from Payne county was achieved. Degradation capability was rescued in extremely toxic produced water from Grant county via a wastewater dilution strategy. In addition to the above mixed culture characterization, we were able to successfully isolate an organism with a 99% 16S rRNA similarity to a novel organism, Modicisalibacter tunisiensis. Modicisalibacter sp. Wilcox genome encodes an assortment of genes responsible for a variety of different hydrocarbon degradation including aromatic ring compounds (BTEX and benzoate), aliphatic compounds (hexadecane, decane, eicosane) as well as biphenyls. We functionally confirmed the degradation of BTEX, benzoate, and hexadecane. We saw an optimum BTEX degradation rate in 1M NaCl concentrations but also noted complete BTEX degradation in 4M NaCl, granted over a 72-day period. Modicisalibacter sp. Wilcox was also capable of degrading BTEX natively in produced water from Payne county. Modicisalibacter sp. Wilcox genome encodes genes responsible for the first step of nitrate-reduction suggesting its ability to respire nitrate anaerobically. Interestingly, under nitrate-reducing conditions, Modicisalibacter sp. Wilcox seems to be able to oxidize and degrade only ethyl benzene in a mixture of BTEX. As the sole carbon source, Modicisalibacter sp. Wilcox was able to degrade ethyl benzene completely in 5 days. More work needs to be done to quantify the amounts of nitrate used in ethyl benzene oxidation under anaerobic conditions.