Part:BBa_K5034217
PolyP <->Pi, Poly P -> NADP
Contents
Basic Description
This composite part includes the PPK2 gene from Pseudomonas aeruginosa and the NADK gene from Mycobacterium tuberculosis H37Rv. We performed codon optimization on both and expressed in the pBBR1MCS-terminator plasmid together. The PPK2 enzyme facilitates the reversible conversion between inorganic polyphosphate (PolyP) and inorganic phosphate (Pi), and the NADK enzyme converts PolyP to NADP. Importing them separately was successful, thus we intend to proceed with continued optimisation by their combination.The tandem connection of the two enzymes actually promoted the synthesis of NADK, and by maintaining some PolyP reserves, it was able to improve the efficiency of electrical production and improve the phosphorus accumulation capacity of S.oneidensis.
Figure 1: Basic structure of PPK2-NADK
Sequence and Features
Promoter: We use lac promoter in our experiment. There isn't lacI downstream,so it's constitutive promoter for continuous expression.
RBS: Strong ribosome binding site for efficient translation. We use BBa-B0034 which shows the strongest translation in our experiment.
PPK2 Coding Sequence: Encodes the polyphosphate kinase 2 enzyme.
NADK Coding Sequence: Encodes the NAD kinase enzyme.
Terminator: Efficient transcription terminator to ensure proper mRNA processing. We use a double terminator rrnBT1-T7TE(BBa_B0015) in our experiment.
The translational unit is composed of the components above. In this composite part, promotor and terminator is not included.Because the backbone has promotor sequence and terminator sequence.
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Origin
PPK2 Gene: Pseudomonas aeruginosa PAO1 strain.
NADK Gene: Mycobacterium tuberculosis H37Rv strain.
Experimental Characterization and results
Students from dry lab group using mathematical modelling to simulate the introduction of the two enzymes and found an enhancement in the polyphosphate and electroproduction capabilities of S.oneidensis.(Fig.2)
Figure 2: Experimental modelling proves that importing PPK2 and NADK simultaneously is better than importing PPK2 or NADK separately
Figure 3: Plasmid profile of PBBR1mcs-Terminator-PPK2-NADK
Figure 4: Colony PCR to prove that PPK2-NADK plasmid is introduced to S.oneidensis
After successful construction, we transferred it into S.oneidensis and conducted measurements of its electricity production and phosphorus accumulation effects. We found that after transferring into the S.oneidensis, both the electricity production and phosphorus accumulation efficiency were significantly improved compared to the wild type.(Fig.5)
Figure 5: Electricity production capacity and phosphorus accumulation capacity of S.oneidensis with the introduction of PPK2-NADK
Subsequently, we also investigated the reasons for the improvement in electricity generation and phosphorus accumulate efficiency. We found that the levels of ATP and NADH/NAD+ inside the cell were significantly increased(Fig.6), indicating that the metabolic level of S.oneidensis increased, leading to an increase in electricity production and phosphorus accumulation levels.
Figure 6: Levels of ATP and NADH/NAD+ of S.oneidensis with the introduction of PPK2-NADK
Figure 7: Cyclic voltammetry show higher redox activity in the SPPK2-NADK strain
Figure 8: LSV curve indicates lower internal resistance in the MFC cells of the SPPK2-NADK strain
Figure 9: Output power of the PPK2-NADK strain
Chassis and genetic context
We express this gene on Shawanella oneidensis MR-1
Potential Applications
In bioelectrochemical systems, we can utilize PolyP and NADP in microbial fuel cells for further improved electron transfer and energy production.
In fact, based on the results, we make a hardware to demostrate its application.We can use it to collect Pi in the soil and produce electricity to be used by human.(Fig.10)
Figure 10: Hardware about its application
Managing phosphate levels in contaminated environments;
Enhancing phosphate metabolism in engineered microbial systems;
Optimizing phosphate utilization in industrial microbial processes.
Enhancing the performance of bioelectrochemical systems for electricity generation in providing a renewable and sustainable source of electricity, reducing reliance on fossil fuels and contributing to cleaner energy production.
References
1.Mori S, Yamasaki M, Maruyama Y, Momma K, Kawai S, Hashimoto W, Mikami B, Murata K. Crystallographic studies of Mycobacterium tuberculosis polyphosphate/ATP-NAD kinase complexed with NAD. J Biosci Bioeng. 2004;98(5):391-3.
2. Zhang, H., Ishige, K., & Kornberg, A. (2002). A polyphosphate kinase (PPK2) widely conserved in bacteria. Proceedings of the National Academy of Sciences, 99(26), 16678-16683.
3. Neville N, Roberge N, Jia Z. Polyphosphate Kinase 2 (PPK2) Enzymes: Structure, Function, and Roles in Bacterial Physiology and Virulence. Int J Mol Sci. 2022 Jan 8;23(2):670.
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