The microbes with the Midas touch

Purple bacteria are not fussy eaters. Whether carbon, electrons, or light, these ancient organisms consume whatever they can to stay alive. 

Their diverse appetite comes from an unusual ability. These microbes can radically alter their metabolisms depending on the physical conditions around them.

These metabolic chameleons could be game-changers for the circular economy, helping us turn all kinds of waste into valuable compounds without the need for expensive inputs.

Here’s the low-down on how purple bacteria could unlock cost-effective and sustainable waste management.

A green Midas touch

In the famous Greek legend, King Midas of Phrygia gained the power to turn whatever he touched into gold. Eventually, he transformed everything around him – including his daughter – into a precious metal that he could neither eat, drink, nor love. 

The legend is a cautionary tale of greed. Yet in the real world, the ability to turn ordinary waste into valuable resources could offer humanity a more optimistic takeaway, such as the power of biology to solve planetary problems.

Globally, the economics of industry still favour virgin resource extraction and toxic landfilling over sustainable resource recovery. This will remain the case for as long as circular waste management is costlier than discarding materials or simply generating new resources. 

Part of the answer to building a circular economy will be developing cost-effective biotechnologies to recover value from waste. 

Researchers believe that purple bacteria could have a big role to play in this. 

The microbial all-rounder

Purple bacteria were among some of the first life forms on earth. Over billions of years, they have evolved remarkable capabilities.

One of the things that make them unique is that they are multi-talented. They can make a diverse range of speciality and commodity chemicals, which is why many researchers believe they could become lynchpins of the circular economy. 

The range of chemicals they are able to synthesise and recover is so wide that purple bacteria can produce goods for almost every biobased market out there, from biofuels to beauty. 

Protein, polyhydroxybutyrate (PHB), carotenoids, coenzyme Q10 and hydrogen are some of the things they can produce – all high-value chemicals with markets in cosmetics, nutraceuticals, and foodtech. Which particular byproducts they make depends on the physical conditions around them.

Purple bacteria can also recover valuable chemicals from their surroundings. Carbon (a biomaterial and biofuels building block), nitrogen (plant fertiliser) and hydrogen (a form of energy) are just some of the resources that purple bacteria can accumulate in their bodies from the outside. Once concentrated like this, the chemicals can be harvested, purified, and re-used.  

A metabolic chameleon

Apart from the diversity of their products, purple bacteria hold commercial appeal for their hardiness. Many enzymes and bacteria conventionally used in biomanufacturing need special conditions to survive, like carefully prepared synthetic media. This raises production costs significantly. 

Purple phototrophic bacteria, however, are not so picky about their environments. They can live among heavy metals and other toxic contaminants, and even inhabit seawater. Some purple bacteria can grow when carbon and light sources are limited. 

Few living things could survive such a wide range of environments. Purple bacteria can do so because they switch between different metabolic pathways depending on the conditions around them. 

Certain species of purple bacteria can extract energy from wildly different sources if circumstances force them to, including electrons, light photons, organic carbon (like most animals), or non-organic carbon (like plants).

The ability to shift between radically different ways of making energy is what makes these bacteria so special. These metabolic chameleons are the ultimate opportunists of the microbial world, making them prime candidates as waste upcyclers. 

The microbes with the Midas touch

The metabolic morphing abilities of purple bacteria make them well-suited to converting non-uniform feedstocks, like wastewater, into high quality chemicals.

Wastewater is generally costly to purify and upcycle. It is the opposite of a high-quality industrial feedstock. Rather than a consistent raw material, it is a chaotic and often toxic mix of untreated chemicals, at different concentrations.

The flipside of this is that wastewater is often some of the most resource-rich feedstocks out there. Everything from potential plant nutrients to raw materials can be found inside it, albeit at dilute or unpredictable concentrations. 

The main barrier to recovering and selling on valuable wastewater residues is finding methods that can pick them out efficiently. Purple bacteria could be one of the best ways to do this, thanks to a biology that can rapidly adapt to changing chemical conditions. 

The most active research into purple bacteria biotech is happening in the EU, where scientists and industry have been proving it can work in full-scale industrial systems. 

EU’s landmark purple bacteria demos

All this is good in theory, but can these processes operate at scale? In the EU, ongoing trials suggest they can be.

Since 2019, the bloc has mounted two projects to test purple bacteria waste upcycling systems: Deep Purple and Post Purple. 

The EU’s already-completed Deep Purple project proved purple bacteria can upcycle wastewater on an industrial scale. The microbes were used to extract cellulose and other industrial resources from municipal solid waste at two demonstration wastewater treatment plants and a biogas facility in Spain. 

Now, a follow-on project called Post Purple launched this year is setting up purple bacteria-based urban biorefinery. This new project aims to valorise two very different kinds of wastestreams: ordinary solid garbage as well as domestic wastewater. 

The keystone tech being tested by Post Purple are innovative photobioreactors. Inside them, the purple bacteria mine nitrogen, phosphorus, and carbon from the two combined wastestreams.

Post Purple is looking at producing higher-value chemicals than the ones extracted for Deep Purple. Now, the purple bacteria are meant to siphon off nutrients that can be made into carotenoids, omega 3 fatty acids and coenzyme Q10, compounds used across pharma, nutraceuticals, and beauty.

A bacteria for the climate 

When it comes to microbial multi-tasking, purple bacteria reigns supreme. The waste recovery systems being tested by the EU reflect that. 

Both Deep Purple and Post Purple constructed systems that manufacture multiple high-value products simultaneously, maximising revenue from a single, abundant feedstock. 

It also offers various environmental pay-offs. As well as waste management and the development of sustainable manufacturing, the Post Purple project is closely tied to EU climate ambitions. 

On top of recovering nutrients, the purple bacteria in the Post Purple system also captures nitrous oxide from waste. Nitrous oxide, as well as methane, are potent greenhouse gases released by waste.

This highlights how wastestreams do not just pose a pollution risk to water and soil – they are also drivers of global heating. Figuring out ways to capture and use waste-related greenhouse gases like methane will be vital to meeting EU emissions targets. 

As well as direct capture of emissions, the Post Purple system also reduces greenhouse emissions more indirectly.  helping avoid virgin fertiliser production. By getting purple bacteria to recover nitrogen from the waste, it can displace demand for virgin nitrogen fertiliser, which is carbon intensive to manufacture. 

Beyond wastewater

Microorganisms are already widely used in the bioeconomy. Countless startups already deploy E. Coli, bacillus, microalgae, and species of cyanobacteria to make biofuels and biochemicals. 

By comparison, purple bacteria is still an emerging living biotechnology. Only a few startups are moving towards commercialisation. Until recently, researchers didn’t even have the genetic tools and genome data needed to study their properties. 

Now, things are changing as evidence on their efficacy mounts. Wastewater treatment and valorisation is where researchers believe these microbes could have the most impact. When we begin to see the major investments, this is where funds are likely to be targeted.

However, wastewater conversion is just one area where purple bacteria could find uses. One of the only startups commercialising purple bacteria IP today is Japan’s Symbiobe, which makes premium aquaculture feed out of their biomass.  

The company claims its product is more sustainable than standard feeds because it needs so few inputs to grow. The company cultivates its purple bacteria in seawater – a medium it is just as happy to inhabit as toxic sludge.  

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