Identification of Vibrio natriegens uvrA and uvrB genes and analysis of gene regulation using transcriptional reporter plasmids

Redesign of ultrasensitive and robust RecA gene circuit to sense DNA damage

SOS box of the recA promoter, PVRecA from Vibrio natriegens was characterized, cloned and expressed in a probiotic strain E. coli Nissle 1917. This promoter was then rationally engineered according to predicted interactions between LexA repressor and PVRecA . The redesigned PVRecA-AT promoter showed a sensitive and robust response to DNA damage induced by UV and genotoxic compounds. Rational design of PVRecA coupled to an amplification gene circuit increased circuit output amplitude 4.3-fold in response to a DNA damaging compound mitomycin C. A TetR-based negative feedback loop was added to the PVRecA-AT amplifier to achieve a robust SOS system, resistant to environmental fluctuations in parameters including pH, temperature, oxygen and nutrient conditions. We found that E. coli Nissle 1917 with optimized PVRecA-AT adapted to UV exposure and increased SOS response 128-fold over 40 h cultivation in turbidostat mini-reactor. We also showed the potential of this PVRecA-AT system as an optogenetic actuator, which can be controlled spatially through UV radiation. We demonstrated that the optimized SOS responding gene circuits were able to detect carcinogenic biomarker molecules with clinically relevant concentrations. The ultrasensitive SOS gene circuits in probiotic E. coli Nissle 1917 would be potentially useful for bacterial diagnosis.

Construction of a bioreporter by heterogeneously expressing a Vibrio natriegens recA::luxCDABE fusion in Escherichia coli, and genotoxicity assessments of petrochemical-contaminated groundwater in northern China

Here, we constructed an Escherichia coli recA::luxCDABE bioreporter for genotoxicity assessments. The recA promoter was cloned from the marine bacterium Vibrio natriegens. This bioreporter showed a dose-response relationship following induction by mitomycin C, and other pollutants or environmental samples could be calculated as mitomycin C equivalents, which provided a way to quantitatively compare the genotoxicities of different environmental samples. This bioreporter was used to evaluate the genotoxicity under a wide range of external environmental conditions, like temperatures ranging from 15 °C to 42 °C, pH between 4.0 and 9.0, and salinity ranging from 0% to 3%. This successfully extended its application from the laboratory to the field, and allowed the bioreporter to assess the genotoxicity and bioavailability of genotoxins in various environmental media, including surface water, groundwater, seawater, and soil matrix. Expression of V. natriegens recA in E. coli indicated a LexA-like regulator in V. natriegens, and the putative SOS box of V. natriegens recA was similar to that of E. coli. The genotoxicities of groundwater samples from a petrochemical-contaminated site in northern China were evaluated by this bioreporter assay, and the genotoxic levels were in accordance with contamination levels obtained by chemical analyses.

The application of a carrier-based bioremediation strategy for marine oil spills

The application of recycled marine materials to develop sustainable remediation technologies in marine environment was assessed. The remediation strategy consisted of a shell carrier mounted bacterial consortium composed of hydrocarbonoclastic strains enriched with nutrients (Bioaug SC). Pilot scale studies (5000 l) were used to examine the ability of Bioaug-SC to degrade weathered crude oil (10 g l(-1); initially 315,000±44,000 mg l(-1)) and assess the impacts of the introduction and biodegradation of oil. Total petroleum hydrocarbon mass was effectively reduced by 53.3 (±5.75)% to 147,000 (±21,000) mg l(-1) within 27 weeks. 16S rDNA bacterial community profiling using Denaturant Gradient Gel Electrophoresis revealed that cyanobacteria and Proteobacteria dominated the microbial community. Aquatic toxicity assessment was conducted by ecotoxicity assays using brine shrimp hatchability, Microtox and Phaeodactylum tricornutum. This study revealed the importance of combining ecotoxicity assays with oil chemistry analysis to ensure safe remediation methods are developed.

Carrier mounted bacterial consortium facilitates oil remediation in the marine environment

Marine oil pollution can result in the persistent presence of weathered oil. Currently, removal of weathered oil is reliant on chemical dispersants and physical removal, causing further disruption. In contrast few studies have examined the potential of an environmentally sustainable method using a hydrocarbon degrading microbial community attached to a carrier. Here, we used a tank mesocosm system (50 l) to follow the degradation of weathered oil (10 g l(-1)) using a bacterial consortium mobilised onto different carrier materials (alginate or shell grit). GCMS analysis demonstrated that the extent of hydrocarbon degradation was dependent upon the carrier material. Augmentation of shell grit with nutrients and exogenous hydrocarbon degraders resulted in 75±14% removal of >C32 hydrocarbons after 12 weeks compared to 20±14% for the alginate carrier. This study demonstrated the effectiveness of a biostimulated and bioaugmented carrier material to degrade marine weathered oil.