What Are Phages? And Why Are They So Incredibly Important?

Little microscopic heroes known as phages exist in all parts of nature. They’re so small you can’t see them, but they play a massive role in keeping our planet healthy and balanced. You may have heard of them recently as they gain more attention among scientists and researchers. But what are phages exactly? And why is everyone excited about them?

What are Bacteriophages?

Bacteriophages, or phages for short, are tiny viruses with a big job: they infect and replicate within bacteria. These microscopic warrior viruses are everywhere in nature, making them the most abundant biological agents on Earth. Phages play a crucial role in keeping bacterial populations in check.

Phages exist in your gut (yes, inside you!), in water, in the soil, and in the air. They’re everywhere. And they are a fundamental part of our ecosystem. Although phages are viruses, not all viruses are phages. There are thousands of viruses in our world, many of which are out to harm us. And while we don’t want that and we fight them off, they are simply following their own life path.

Phages are a specific type of virus that attacks bacteria. There’s thousands of good ones and there’s still so much more to discover. The word phage comes from the Greek phagein, which means “to eat.” A good example is the T4 phage, which attacks and kills E.coli bacteria. This particular one is extremely valuable in combating E.coli bacterial infections.

Phages come in all sorts of shapes and sizes, but they all have some things in common. They’re made up of a protein coat that protects their genetic material, which can be either DNA or RNA. Most belong to a group called Caudovirales, which makes up about 95% of all known phages. These have a unique structure that helps them infect bacteria:

• Head (Capsid): This is where the phage’s genetic material is stored.
• Tail: A tube-like structure that helps the phage attach to bacteria.
• Tail Fibers: These act like sensors to find the right bacteria to infect.

One of the most well-studied phages is called T4. It has a head that’s 1150 Å long and 850 Å wide. Its tail is 925 Å long. It also has six long tail fibers that are 1450 Å in length. That’s incredibly tiny – these measurements are in angstroms, ten times smaller than a nanometer!

Phages were once thought to be pests. Some phages cause issues with cheese culturing and alcohol fermentation. Because of this, for a long time, they were dismissed as problematic occurrences that needed to be prevented. Thankfully, science and researchers are giving these little viruses a deeper look. And they’re discovering some pretty amazing things.

How Bacteriophages Infect Bacteria

Phages have a clever way of infecting bacteria. Here’s how they do it:

1. Recognition: The phage uses its tail fibers to find the right bacteria to infect.
2. Attachment: Once it finds a suitable host, the phage attaches to the bacteria’s surface.
3. Injection: The phage then injects its genetic material into the bacteria.
4. Takeover: The phage’s genes take control of the bacteria’s machinery.
5. Replication: The bacteria is forced to make many copies of the phage.

This process is super efficient. A single phage can transform one bacterial cell into a phage-making factory. It produces about 100 new phages before the bacteria bursts open.

Lytic vs Lysogenic Cycles

Phages have two main ways of replicating inside bacteria: the lytic cycle and the lysogenic cycle.

Lytic Cycle:

This is the fast and furious approach. Here’s what happens:

• The phage quickly takes over the bacteria.
• It makes many copies of itself.
• The bacteria bursts open (lyses), releasing new phages.
• These new phages go on to infect other bacteria.

The T4 phage, which infects E. coli bacteria in our intestines, is an excellent example of a lytic phage.

Lysogenic Cycle:

This is more of a sneaky approach:

• The phage’s genetic material becomes part of the bacteria’s DNA.
• The bacteria continue to live and reproduce normally.
• The phage’s genes (now called a prophage) are passed on to new bacteria.
• Under certain conditions, the prophage can become active.
• When activated, it starts the lytic cycle.

The lambda phage, which also infects E. coli, can use both the lytic and lysogenic cycles.

In nature, phages play a crucial role in keeping bacterial populations balanced. They’re like tiny, invisible guardians helping maintain ecosystems’ health everywhere!

Horizontal Gene Transfer

Phages are also super important because they can move genes from one bacterium to another. This is called horizontal gene transfer, and it’s a big deal in the world of microbes. There are a few ways this can happen:

• Generalized transduction: This is when a phage accidentally packages bits of bacterial DNA instead of its own. When it infects a new bacterium, it can pass along these genes.
• Specialized transduction: This happens with lysogenic phages. When they leave a bacterium, they might take some of the bacterial genes with them.
• Lateral transduction: This is a really cool way that phages move large chunks of bacterial DNA. It occurs in bacteria like Staphylococcus aureus. It can move genes 1000 times more often than other types of transduction.

Through these methods, phages can help bacteria share various useful genes. These include genes that help them resist antibiotics. They may also help them adapt to new environments. Phages have a big impact on the diversity of microbial communities. They can change which bacteria are most common in an ecosystem. And they can help maintain a balance between different species.

In one cool experiment, scientists added a phage that targets a specific type of bacteria to a mix of different bacterial species. They found that the phage drastically changed the community structure. The targeted bacteria almost disappeared, while another species became the most common. This shows how phages can shake things up in the microbial world. They can also help maintain diversity by preventing any one species from taking over. They do this by targeting the most abundant bacteria, which gives other species a chance to grow.

The relationship between phages and bacteria is super complex. Sometimes it’s like a predator-prey relationship, with phages hunting bacteria. Other times, it is more of a partnership, with phages and bacteria helping each other out.

Phages vs Bacteria Medicinal Uses

Phages are incredibly specific about which bacteria they infect. This makes them potentially useful for medical treatments. They can target harmful bacteria without hurting helpful ones. Scientists are looking into using them as an alternative to antibiotics. This is particularly for bacteria that have become resistant to traditional treatments.

These tiny helpful viruses present an exciting alternative for treating bacterial infections, especially those caused by multi-drug resistant (MDR) bacteria. Phage therapy has a long history. It dates back over 100 years. Felix d’Herelle, a French-Canadian microbiologist, first discovered and named them bacteriophages in 1917.

In the early days, phages were used to combat various bacterial infections, from typhoid fever to cholera. Phage therapy fell out of favor in the West with the advent of antibiotics. However, it continued to be used in Eastern Europe and the former Soviet Union. The United States and other Western countries heavily relied (and still rely) on antibiotics. In hindsight, this reliance was not a great idea. Thankfully, western countries are now revisiting phage therapy and realizing the great potential this old but new therapy has.

Some exciting applications of phage therapy include:

• Treating lung infections in cystic fibrosis patients
• Combating urinary tract infections
• Addressing skin infections caused by various bacteria

One of the most promising aspects of phage therapy is its specificity. Unlike antibiotics, which can affect both harmful and beneficial bacteria, phages target only specific bacterial species. This precision makes phage therapy an attractive option. The infection can be treated without disrupting the body’s natural microbiome.

However, it’s important to note that not all phages are suitable for therapy. Lytic phages are preferred as they infect and burst the host cell, effectively killing the bacterium.

Phages and Food Safety

Phages have shown great potential in enhancing food safety by targeting harmful bacteria in our food supply. Each year, foodborne hazards cause a staggering number of deaths. These hazards are predominantly bacterial. They are responsible for 420,000 deaths and an estimated 600 million cases of foodborne infections globally. Phages offer a natural and effective solution to this problem.

In countries like Canada, Israel, and the USA, phages are already being used in food processing to target serious human pathogens such as:

• Listeria monocytogenes
• Salmonella serotypes
• Escherichia coli O157:H7

One interesting application is the use of phages to treat meats. Studies have shown that phage treatment can extend the shelf life of products like pork and beef steaks. However, the effectiveness of phage treatment can vary. A lot depends on the food’s texture and the specific phage-host interactions.

Phages and the Environment

Phages aren’t just valuable for medicine and food safety. They also have important environmental applications. One of the most exciting uses of phages in the environment is as indicators of water quality.

Phages can serve as:

• Fecal indicators
• Microbial water quality bioindicators
• Early warning systems for sewage contamination
• Efficiency markers for water or wastewater treatment

Phages are particularly useful in this context because they can persist in the environment longer than traditional bacterial indicators. They’re also more resistant to sludge treatments, especially when adsorbed to surfaces. In wastewater treatment systems, phages can be used to remove human and animal pathogenic bacteria. Their lytic capacity makes them useful for cleaning wastewater and improving environmental safety.

FAQs