Some bacteria use tiny biological needles to make us sick!

By Danny Ward

There are many bacteria all around us, some are beneficial while others can cause disease. The way in which different bacteria cause disease are varied. Some bacteria use a certain infection mechanism known as the type III secretion system which functions just like a tiny biological needle.

Very few people have heard of the type III secretion system and far fewer still are aware that it is a way in which certain bacteria are able to cause disease. It’s a fascinating and complex system, which we still don’t fully understand and so, there is still much research to be done.

The type III secretion system consists of a needle complex connected to a basal body complex which spans the bacterial membrane. This system is dynamic in the sense that the needle can contract and extend as necessary to facilitate infection. This dynamic movement combined with a translocon protein located at the end of the needle allows for penetration into a target’s cellular membrane.

Located at the base of the system is an ATPase enzyme. This is a protein which acts like a motor, driving the entire system. The ATPase breaks down ATP, one of the rawest forms of energy in living things. This allows for proteins to be secreted out of the needle and into the target host. These secreted proteins are ‘effector’ proteins that change the host cell to make conditions more favourable for bacterial colonisation. An example role of an effector protein is one which will suppress the immune system of the host which would otherwise seek out and destroy the infecting bacteria.

One type of bacteria which uses a type III secretion system for establishing infection is Pseudomonas. This is a species of bacteria which presents itself as a large issue in healthcare and agriculture. Pseudomonas aeruginosa is a prominent hospital-acquired infection which can quickly become aggressively resistant to antibiotics. This puts infected patients at high risk and also becomes expensive for the healthcare provider to treat.  Pseudomonas syringae poses as a plant pathogen that puts crops and food security at risk. The variety of plant species which P. syringae can infect is vast. One example is black speck disease of tomatoes – caused by P. syringae it can easily ruin entire crop harvests.

About the author
I am a molecular microbiology PhD student at The John Innes Centre and the University of East Anglia in Norwich, England.  I am interested in how Pseudomonas is able to control its type III secretion system and my research area of focus lies with the ATPase protein which allows the system to function. We think that a cellular signalling molecule called cyclic-di-GMP, or CdG for short, may bind to this ATPase which in turn regulates bacterial virulence. CdG has been shown to have numerous regulatory roles in bacteria, particularly so in Pseudomonas. As part of my PhD, I spend most of my time in the laboratory conducting experiments in order to better understand this potential type III regulation system with CdG.

It is important we understand how bacteria can cause infection using systems like the type III secretion system, and how they regulate these systems so that we can better develop control measures to stop these micro-organisms in future. By understanding the complex infection systems and their regulation mechanisms, we can use this knowledge to our advantage by producing molecules to target and hijack these systems to control them. This will in turn help to prevent or treat bacterial infection.

This PhD is being funded by “the UKRI Biotechnology and Biological Sciences Research Council Norwich Research Park Biosciences Doctoral Training Partnership”. This article was written by Danny Ward, a molecular microbiology PhD student from Norwich, England. Learn more about the author at or @DannyJamesWard on Twitter and Instagram.

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