Red algae can defeat toxic ‘smart’ dirt

You might have heard of smart bugs – viruses that have mutated and become resistant to ordinary antibiotics. But there is another, less well-known microscopic substance that is dangerous to human health: “smart” dirt. What is it and what is being done to protect the world from these potentially toxic germs?

What is smart dirt?

Smart dirt is made up of germs clinging to the surfaces around us that have become resistant to the chemicals usually used to get rid of them. A big dose of toxic chemicals could kill these bugs, but this poses a risk to the environment.

The accumulation of surface-adhering micro-organisms, such as bacteria and algae, is known as biofouling. The chemical cleaners no longer have an effect in most areas fundamental to human existence, including the water treatment, food and energy industries.

Threat to human life
Biofouling has become the biggest hindrance to developing membrane water treatment plants in South Africa and globally. The filters in these plants can become fouled, lowering water quality and increasing operational costs.

Food security is threatened when irrigation systems get worn out and production lines in industrial settings become plagued by biofouling.

The energy sector, including power utility Eskom, also falls victim to this plague. Cooling water towers are constantly down because of heavy fouling, which reduces heat exchanger efficiency. Repair costs run into the millions and cooling tower lifetimes are severely shortened.

Fortunately, nature has also provided a solution to smart dirt. Researchers have discovered that, on heavily fouled surfaces, the marine red algae Delisea pulchra remains untouched by oceanbacteria and barnacles. A closer look revealed that this marine plant contains substances named furanones that repel bacteria and all other forms of micro-organisms from their surface.

In a research project, these furanones were prepared and tested on laboratory-scale water filters. The furanone-modified water filters not only demonstrated self-cleaning behaviour that repelled bacteria, but also the ability to destroy the bacteria that attempted to stick to the filter surfaces. And because the furanone compound is chemically bound to the material, there is no risk of it leaking into the environment.

Research has shown that the secret to this compound’s effectiveness is that the bugs live together in small communities, referred to as biofilms. They are also in constant communication, and their survival and resistance to certain bug-killing measures rely on this interaction.


The presence of furanone compounds stops communication between the bugs. As a result, their destruction is inevitable. Without a “community feel”, these bugs cannot colonise surfaces. Without attachment, they cannot survive.

This technology opens many possibilities in the fight against surface biofouling. It can eliminate the use of chemical cleaners that are dangerous to the environment and lead to antimicrobial resistance.

Smart dirt may currently be ahead, but the war against biofouling has only just begun.

Nonjabulo Gule is a National Research Foundation and department of science and technology research fellow at Stellenbosch University. This article was first published on The Conversation website.


The Conversation

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Nonjabulo Gule
Nonjabulo Gule works from Stellenbosch University. Post doctoral Research Fellow
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