Marine microbes are the heart of ocean ecosystems, but it has been almost impossible to study them in their natural environment.

Microbial interactions have traditionally been using traditional oceanographic instruments that collect large volumes of seawater (tens of litres), which has resulted in a disconnect between the scales at which these interactions take place and the scale at which humans are able to understand them.

To overcome these limitations a unique collaboration between engineers and microbiologists in America, Australia and Switzerland has developed a new device that gives microbial ecologists the ability to directly investigate microbial behaviour in their natural environment.

Known as the “In Situ Chemotaxis Assay” (ISCA), the device exploits recent advances in microfabrication and microfluidic techniques.

“Until now there has really been no way to probe the behaviour of marine microbes towards certain chemicals in situ,” says University of Technology Sydney (UTS) marine microbiologist Dr Jean-Baptiste Raina.

Just as some people might be drawn by the smell of food or perfumes, microbes are attracted by specific chemicals.

“This behaviour is called chemotaxis and it is important because seawater isn’t homogeneous, the microscale world that microbes inhabit is incredibly patchy, with a number of processes leading to nutrient hotspots and it’s in these microenvironments where all the microbial action takes place” Dr Raina says.

MIT Engineer Ben Lambert says; “With the ISCA we are really opening the door to being able to interrogate this behaviour in the natural environment. Our initial findings have already shown that chemotaxis does take place among marine microbes and this validates many years of laboratory experiments and hypotheses put forth about this behaviour in the ocean”.

The ISCA is one of the first experimental devices that combines micro-engineering with genomic and chemical analyses in the natural environment.

The single-use, credit-card-sized device is made of inert materials and consists of microlitre reservoirs that can be filled with different chemicals which diffuse into surrounding seawater after deployment.

Microbes can respond to a specific chemical by using chemotaxis to swim into the well. The researchers then retrieve the reservoir content and count how many microbes respond to a given chemical, while also determining their identity and function.

Professor Roman Stocker, who pioneered environmental microfluidic technology, said that the device capitalises on rapid advances in 3D-printing and is designed to be robust, easy to make and easy to use.

“This means it will be accessible to a broad user base and doesn’t require extensive training. This is a critical aspect of the design if we hope to have strong adoption by scientists across fields,” he said.

In fact, because the ISCA bridges the gap between aquatic chemistry and microbiology with direct in situ observations, it could be of substantial interest to the broader scientific community.

“The ISCA is an innovative tool that will help to re-shape our perception of microbial processes in a range of aquatic habitats,” Associate Professor Justin Seymour (UTS) says.

“We think that its application will help to answer fundamental questions in microbial oceanography, while it will also potentially be very useful in various other settings including water quality monitoring and prospecting for organisms that may facilitate bioremediation efforts.”

Information on recent tests is available here.