The role of viral energy generators in modern biotechnology

By Kilian Robinson

Renewable energy generation has never been more important, considering climate change and how much more aware humans are of the impacts of carbon dioxide emissions. Consequently, the search for completely renewable energies has been a prominent topic of discussion in modern day energy generation methods. Despite our recent progress in 2020, in which the first 3 months of the year our electricity generation was 47% renewable, there are still major problems in the way of complete reliance on renewable energy; lack of reliable energy on demand, costly infrastructure and environmental impacts to name a few. With 15% of a typical households’ energy going into consumer electrics, experimentation and development with electricity generators using viruses may facilitate the alleviation of some of the power demand and aid the transition to complete renewable power (Ovo energy, 2020),

The M13 virus is a filamentous bacteriophage that contains special properties that allow the generation of electrical currents by something known as the piezoelectric effect. The piezoelectric effect is the induction of an electric charge via the application of mechanical strain (kinetic energy) (Zhang & Hoshino, 2014). The mineral quartz can be used to exemplify this effect due to its crystal-like structure as shown in Figure 1. As you compress the quartz the stress induced into the quartz is converted into electrical energy, and the opposite effect (reverse piezoelectric effect) is seen with the alleviation of compression reducing the voltage formed.

Figure 1 – How the piezoelectric effect yields electrical energy in a block made of a crystalline material and in Quartz (Xie, 2017; Anrophysics, Nd)

A lot of the devices we use day-to-day utilise the piezoelectric effect. A cigarette lighter for example uses a piezoelectric material, in some cases quartz, and this transduces mechanical energy presented by your finger into electrical energy. Once you press the metallic wheel/button, it simultaneously releases butane depressurizing it into its flammable form and produces a small spark via the piezoelectric effect, thus igniting the butane (Pershin, 2019).

We can harness the piezoelectric effect in the M13 bacteriophage to make electricity generators to power household appliances. In fact, the M13 bacteriophage has already been used to produce approximately 6nA of current and 400mV of voltage to power a liquid-crystal display (Lee, 2012). The bacteriophage can be made to exhibit piezoelectric properties due to its coat proteins. To understand how these bacteriophages can be manipulated to produce an electric current we treat the phage as a unit cell. A unit cell is defined as any solid that consists of repeating constituent atoms and contains polar or charged molecules (Woodford, 2020). The M13 bacteriophage of the genus inoviridae, characterised by their filaments, is made of an array of coat proteins.  The major coat protein that encapsulates the phages ssDNA, pVIII, consists of repeating alpha helices, thus satisfying the definitions requirement of a highly ordered repetitive structure. The virus also contains polar amino acids at the poles of the alpha helices as shown in Figure 2.

Figure 2 – Schematic to show the M13 bacteriophage coat protein PVIII, its constituent secondary structure, and amino acid monomers (Chung & Yoo, 2014)

These alpha helices are arranged on a 20°-degree angle to the phage long axis and consequently produce a hexagonal structure as shown in Figure 3. The overlapping of opposite charges produced as a result of the 20°-degree angle produces a net neutral dipole moment which can be altered with mechanical stress. Thus, the virus fulfills all the properties required for piezoelectric stimulation (Lee et al., 2012)

Figure 3 – The M13 bacteriophages pVIII coat (shown in dark blue) arranges itself 20 degrees away from the phage long axis creating a hexagonal shape, with the strength of the piezoelectric effect being increased by a viral film vertically assembled on the right (Park et al., 2020)

Using a technique known as piezoresponse force microscopy (PFM), in which we expose a piezoelectric material to a conductive probe, we can provide a mechanical stress to the bacteriophage and observe the electric current produced. We can use this type of microscopy to investigate the phages piezoelectric properties as shown in Figure 4.

Figure 4 – A schematic of how the conductive probe is applied in PFM. For example, when the probe is applied along the phage axis, net dipole moments are created perpendicular to the phage axis. Conversely, when the probe is applied to the phage body, dipoles in different directions are created (Park et al., 2020)

Perhaps one of the most significant benefits of implementing viral piezoelectric generators is that it is still very much a challenge to source and produce piezoelectric materials. Since the synthesis of such materials requires toxic compounds and harsh conditions, it is not a favoured method of energy generation. Although, viral piezoelectric generators may be hard to produce, they still possess other benefits over artificial synthesis (Lee et al, 2012).

One such advantage  that viral piezoelectric generators have over regular generators is their susceptibility to genetic and biochemical modification. The novel design of the bacteriophage lends itself to modification and this facilitates an increase in their effectiveness (Park et al., 2020). Considering the strength of the piezoelectric effect has a direct correlation to surface charges and dipole moments, by genetic editing of the amino acids on the outer surface of the PVIII protein coat, we can increase the power of viral powered energy systems (Park et al., 2020). Results from an experiment shown in Figure 5, suggest that modifying our bacteriophage will allow us to use them in appliances with a much higher energy demand.

Figure 5 – An experiment investigating the effect of numbers of glutamic acid molecules on the strength of piezoelectric effect as measured by the piezoelectric coefficient. The diagram on the left represents the number of glutamic acid molecules (E) added to the PVIII coat protein, with the gradient of the graph on the right representing piezoelectric coefficient, the higher of which yielding is favourable for more energy demanding appliances.

Despite genetic engineering being a useful tool in enhancing piezoelectric properties, it is limited to the synthesis of the 20 amino acids. A further step to increase the scope of applications is chemical alteration of the coat proteins. Similar to genetic engineering we can add differentially charged groups to the PVIII coat proteins to increase piezoelectric coefficients, with the added benefit here is that we are not limited to 20 amino acids and can add almost any compound we desire. Consequently, we can also use this for other applications as shown in Figure 6. Here we can see that these bacteriophages could be invaluable in the health sector too, as well as a source of renewable energy (Chung & Yoo, 2014).

Figure 6 – (A) is the addition of an alkyne group containing compound and thereby facilitating the addition of an azide molecule to the phage, which allows the phage to act as a biosensor. Furthermore, in (B), the transamination of the bacteriophage with pyridoxzal 5’ phosphate and a fluorophore means it can be used to identify cancer cells via fluorescence microscopy (Carrico, 2012; Chung & Yoo, 2012)

To sum up, the M13 bacteriophage provides a basis for safe and renewable energy generation for household appliances which take up a significant amount of the energy used by a typical household. As it can be genetically and biochemically modified to increase piezoelectric coefficients, this facilitates its use in a wide range of electrical appliances. Additionally, the pVIII coat proteins of the phage can be modified to produce many different forms each of which having significant roles including, but not limited to, cancer imaging and use as a biomarker. The myriad of applications the M13 bacteriophage has the potential to fulfill makes it an invaluable tool, one that should be researched more and brought to the forefront of discussions on renewable energy. 


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