“It is a rare sight,” said Professor Mathias Middelboe about his photo, which won second place in the DNRF’s Photo Competition 2023.
“Like all other organisms, bacteria are also infected by viruses, and the picture shows an infected bacterium right at the moment when these viruses have reproduced themselves inside the cell, and the cell bursts. So the bacterium is caught right at the moment it is killed. The image of the exploding cell was taken with an electron microscope and has been enlarged 80,000 times. I have spent many hours looking down into an electron microscope, and I have taken a lot of electron microscopy pictures, but it is very rare to capture this exact moment – the actual climax of the infection.”
Professor Middelboe is a marine biologist and researcher in marine viruses, which are the most numerous biological units in the ocean. In every milliliter of seawater, there are around 10 million viruses. And within the last 15-20 years, it has been shown that viruses play a major and important role because they influence a wide range of processes in the marine environment.
“We are interested in understanding the importance of viruses in the ocean. Like all other organisms, bacteria are infected by viruses,” Middelboe explained.
“When a cell full of viruses bursts, some of the organic matter built into the bacteria is released. And because that process takes place millions of times a day in every liter of seawater, it plays a big role in the entire metabolism and recycling of organic matter and nutrients, and it affects the global carbon cycle. A virus that has infected a bacterium can also pick up some of the bacteria’s genes, which then spread to other bacteria when the cell dies. And in this way, viruses also contribute to the diversity and evolution of the microbial community in the ocean and can make other bacteria more adaptable.”
The viral component is an inspiration for new scientific angles
Research on viruses is a relatively new discipline within marine biology. And according to Middelboe, this has really turned our understanding of what regulates circulation and degradation and the role of bacteria in the ocean upside down.
“The first article in this area was published around 1989-90. It was suddenly discovered that viruses were a very important and numerous component of aquatic systems. And now there are many research groups around the world working on this issue,” said Middelboe and continued:
“Back then, I was writing my Ph.D. thesis, and I also took an interest in viruses. I wanted to examine what happens when a cell breaks because it has a viral infection. What happens when the cell content comes out of these bacteria and becomes food for other bacteria? That is, how does the process contribute to the carbon and nitrogen cycle in the ocean? And no one else was really investigating that at this point. I got hooked and have been going down that path ever since. Today, it is a huge research area within microbial biology, especially in the ocean. But the processes are just as important in soils and lakes, etc. And today there is also a growing interest in looking at the role of viruses in our own intestinal system.”
Can viruses become the future alternative to antibiotics?
Middelboe’s research area draws attention because there is a huge need to develop alternatives to antibiotics.
“The viruses we’re looking at are very specific; they only infect certain bacteria. So unlike antibiotics, which usually kill everything, in the future you may be able to use the virus in very targeted disease control, in other words, to kill disease-causing bacteria.”
Middelboe works primarily with fish diseases in fish farming, but there are also other groups in the world that, for example, work with viral control of diseases in humans, poultry, or cattle.
“My research is primarily about gaining a basic understanding of the role of viruses in the ocean. Overall, we need to understand how, for example, climate change will affect the interaction between viruses and bacteria and the effect on the global substance cycle. But it is also important to get a deep understanding of the interaction between viruses and bacteria when it comes to the replication part of our research: If you are going to use specific viruses to kill disease-causing bacteria, you need to know what resistance mechanisms the bacteria have to these viruses. And then there’s all this stuff about how viruses work if we add them to fish food and they get into a fish’s stomach, or we add them to a biofilter to clean the water of disease-causing bacteria. And we also need to investigate whether, for example, you can continue to use the same viruses, or whether they become ineffective at some point, so you need to find or develop something else. And last but not least, we need to learn more about how the virus infects the bacterium: how fast it goes, how long the effect lasts, etc.
I actually believe that in the long term, we can develop a useful product for the aquaculture industry that can be an alternative to antibiotics, but it will take a few more years before we have optimized the technology and before we know how effectively it works.”
In his right element
Middelboe spends much of his time in the Marine Biological Section at the University of Copenhagen in Elsinore, which also houses the Øresund Aquarium.
“We cover marine biology very broadly here. From deep-sea research to microbes and viruses to fish and algae; we are professors, post-docs, students, and zookeepers. All the many different things that go on here are inspiring and motivating,” said Middelboe. “And in addition, there is a lot of outside collaboration with researchers who have other specialties and expertise: We often run into things not covered by our expertise. That’s how collaborations come about, and we get in touch with people who know other methods or have different approaches to a problem. In this way, things develop,” he concluded. To the question of what really motivates him in his research, he answered:
“I am really driven by a curiosity to understand these extremely complicated connections in marine ecosystems. The more we dive into it, the more complicated it turns out to be. I find that exciting.”
Mathias Middelboe is affiliated with the DNRF Center for Hadal Research, which works to understand the role of viruses in the deep sea, with a special focus on how they affect the substance cycle and contribute to shaping the microbial communities in these extreme environments.
Read more about Mathias Middelboe’s research