Skip to 0 minutes and 10 secondsIn this step, I am in one of the microbiology teaching labs with Professor Simon Andrews to discuss his research on how bacterial pathogens gain vital nutrients from human hosts. So Simon, you're a microbiologist based here at the University of Reading. And I believe your work focuses on virulence in various bacteria. So could you give me an idea, or explain to me a little bit about why bacteria cause infection in a host, and how they actually survive there? Bacteria live in what you could describe as a highly competitive world. They evolve very rapidly, they grow very rapidly. So they have to be extremely fit in order to survive in their environment.

Skip to 0 minutes and 57 secondsAnd so their main requirement is to obtain food in order to grow, grow, grow. And for a bacterial pathogen, we are nothing other than another food source. So they use us as an environmental niche to occupy-- to colonise. So they're not necessarily victimising us, they're just trying to survive, so they're trying to live off us-- using us as a source of nutrients, essentially. So that's the sort of the basis of pathogenicity. We're an opportunity for invasion and colonisation. Just another niche, like any other niche. So that's essentially what's going on, I guess with pathogenicity. It's just that of course that process causes us a great deal of harm, causes us disease, and can be lethal if it goes unchecked.

Skip to 1 minute and 41 secondsOne key nutrient that virtual organisms require is iron. And that's the one nutrient that our defence systems tries to withdraw from bacterial invaders. So our innate immunity in part involves restricting iron availability. It's a crucial part of our defence against disease. And specialist bacteria, which are able to act as pathogens successfully often have on board within their cells, systems which are designed to acquire iron-- not from the general environment, but specifically from the host. So they will target host iron sources. And these systems would be useless in the environment, but extremely useful inside a human host where those iron sources-- those human host iron sources are available. Are there specific names for the systems that bacteria use to acquire iron?

Skip to 2 minutes and 33 secondsYes. One of the common types of system is called a siderophore. And this is a small molecule, it's a collator. It's secreted by most bacteria, many fungi as well-- some plants, also secrete siderophore-like molecules. And these have extremely high affinity for iron, and they can actually scavenge iron from minerals that can solubilize iron from all sorts of sources-- including from host tissues. And we have a defence system against those siderophores. We have a protein which is released only upon infection as part of our acute phase response. This is a response to infection. And a molecule is produced called lipocalin.

Skip to 3 minutes and 13 secondsAnd this lipocalin has the-- it appears to have the sole purpose of actually binding siderophores, these iron-collating molecules that bacteria produce. And then those siderophores become pretty useless inside the human host. Some of the best siderophores known to man-- the strongest collators known to man are siderophores. And yet those siderophores, which are secreted by certain pathogens, are useless. Or, next to useless. They're not very effective, simply because we have protein in our bloodstream, which is targeting that siderophore and removing it from circulation. But bacteria have a further mechanism to overcome our defences. So one of the things that they can do is they can take the siderophore and they can modify it.

Skip to 3 minutes and 57 secondsThey can add an extra chemical group to it. And then, this molecule that we produce to collate the siderophore doesn't see that molecule. And that molecule then escapes our defence system, and then becomes extremely effective. So salmonella produces a modified siderophore. If not for that modification, that siderophore would be useless. And that modification seems-- the only real purpose that we know of that modification is to avoid our defence systems. So we're in a kind of almost like an arms race. We're trying to develop systems to thwart the bacteria. Bacteria are then countering in order to thwart our defence systems.

Skip to 4 minutes and 37 secondsAlmost no matter what we do, the bacteria evolves so rapidly, they've always got some way of overcoming any defence system that we put in place. So we're always one step behind the evolutionary arms race, simply because bacteria evolve so rapidly, and we evolve so slowly. Could you give us some examples of maybe some research-- ongoing research in your lab at the moment, which is furthering progress along these lines? Yes. One of the things we're looking at is what happens in the human intestine-- what happens in the gut. We're interested in what happens if you vary the iron regime in the diet. If you have a high iron regime or a low iron regime. How does that change the gut microbiota?

Skip to 5 minutes and 18 secondsAnd is any such change beneficial, or is it detrimental? Can you control human health to a degree, simply by adjusting the iron regime in the diet, in a way that favours the beneficial gut microbiota and disfavors that harmful gut microbiota? Thank you, Simon, for your time today. It's been great talking to you about how bacteria acquire iron from their hosts. And I wish you all the luck in your future research. Thank you.

Meet Professor Simon Andrews

Throughout this course you’ll meet a range of experts from the School of Biological Sciences at The University of Reading and hear about their current research.

In this video I join Professor Simon Andrews, a medical microbiologist, in one of our teaching labs. Simon’s research focuses on the ways in which bacteria obtain iron from their environment, and in particular the battle for iron inside a human host. I ask Simon how these bacteria set about acquiring this vital nutrient and what tactics their human hosts use to defend themselves against such attacks.

In humans, iron plays an essential role partly because it is a component of the oxygen-carrying molecule haemoglobin in red blood cells.

Bacteria don’t have blood or haemoglobin, so why do they need iron? Share your thoughts in the comment area below.


Note: If you’ve turned on the subtitles for the videos in the course, you may have noticed that the scientific (binomial) names for species are not in italics. Unfortunately the sub-titling software doesn’t include an option for italics, but we have correctly formatted the names in the accompanying transcripts.

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This video is from the free online course:

Small and Mighty: Introduction to Microbiology

University of Reading