Ten years ago, researchers at Aarhus University, Denmark, reported the discovery of centimeter-long cable bacteria, that live by conducting an electric current from one end to the other. Now the researchers document that a few cells operate with extremely high oxygen consumption while the rest of the cells process food and grow without oxygen. An outstanding way of life.

       We humans need food and oxygen to live. Now, imagine if oxygen was to be found only at the mountain top and food only in the valley. That's what the world looks like for cable bacteria, which live in the bottom of seas and lakes. For them, oxygen is available only at the very surface of the bottom, whereas the food is buried centimeters down.

Biowires

       Lars Peter Nielsen, head of Center for Electromicrobiology, Aarhus University, Denmark said "While other organisms try to solve the problem by moving oxygen and food up and down, cable bacteria have developed electric wires. When consuming food they produce electrons and send them through the biowires to the surface for reduction of oxygen from the overlying water".

       A cable bacterium consists of many cells in line. It can grow centimeters long, the cells encased in a common coat wherein the wires stretch.

Image: Microscope image of cable bacteria reaching one end out for oxygen. The deformed oxygen front is seen as a milky line consisting of smaller bacteria attracted to the interface with the lower oxygen free layer.

Image Credit: Stefano Scilipoti.

       The researchers placed cable bacteria in a small, transparent chamber. In the middle, the bacteria had access to oxygen-free mud stuffed with food, while oxygen diffused in from the edges. Right where the intruding oxygen was depleted, numerous unicellular bacteria formed a distinct front. In that specific position they fought to capture food and oxygen from either side simultaneously.

Less than 10% of the cells are breathing

       Stefano Scilipoti, Ph.D. student at Center for Electromicrobiology, Aarhus University and the primary discoverer has watched how single cable bacteria placed themselves across the front with one end into the zone with oxygen under the microscope. He watched how one single cable bacterium could distort the front made by unicellular, swimming bacteria. The cable bacterium respired so much oxygen that the unicellular bacteria had to move closer to the edge of the chamber to sustain the oxygen supply needed for their respiration. The cable bacterium could just dip a few cells in oxygen, and the magnitude of the distortion in laboratory jargon called bump allowed them to calculate how much oxygen was being consumed.

The cable bacterial machinery

       The ancestors of cable bacteria lived without any oxygen. Anaerobic bacteria, as you call them. For these bacteria, oxygen is toxic and prolonged exposures eventually lead them to death. With the evolution of electric connection to oxygen however, cable bacteria can explore the strength of breathing with oxygen without exposing many cells to oxygen stress, thus getting the best of oxygen (more energy) and avoiding the rest (damage to the cells).

       At Center for Electromicrobiology, the pursuit to unravel the special mechanisms that enable this unique electric form of life continues. The study is published in Science Advances.

Image: In the laboratory, cable bacteria were placed in a little, transparent chamber. In the middle, the bacteria had access to oxygen-free mud stuffed with food, while oxygen diffused in from the edges.

Image Credit: Maria Blach Nielsen

The battle against hard-to-treat fungal infections

       Systemic fungal infections are much rarer than other illnesses, but they are potentially deadly, with limited options for treatment. In fact, fungi are becoming increasingly resistant to the few drugs that are available, and infections are growing more common. A cover story in Chemical & Engineering News, the weekly newsmagazine of the American Chemical Society, details how scientists are working to improve our antifungal arsenal.

       At present, there are only four types of antifungal drugs approved by the U.S. Food and Drug Administration (FDA), and some infections are resistant to those drugs, making surgery the only option for treatment, writes Senior Correspondent Bethany Halford. Fungi can be found almost everywhere, but only a few hundred species are able to infect humans, and most people's immune systems can fight them off. However, people with compromised immune systems (for instance, cancer patients being treated with certain chemotherapies) are at a higher risk for developing fungal infections. The FDA has not approved a drug from a new antifungal class in 20 years, and the ones available all have downsides, including drug resistance and kidney toxicity. This dearth of treatments has doctors concerned that the problem will only get worse as time goes on.

Image: Conidiophores with conidia of the microscopic fungi Aspergillus oryzae under light microscope.

Image Credit: Yulianna.x / Wikimedia / CC BY-SA 4.0

       Creating a new antifungal drug is challenging because of the biological similarities between humans and fungi. Many molecules that are harmful to fungi are also harmful to people. Experts say that exploiting the differences between humans and fungi is key to developing new treatments; for example, fungal cells have walls, but human cells do not. In addition to developing new treatments, pharmaceutical researchers are working to improve established antifungal drugs to make them more potent and have fewer side effects. Although scientists and doctors are hopeful that new antifungals will be approved, establishing clinical trials has proven challenging because most of the people who get fungal infections are already very sick. However, the COVID-19 pandemic could change how pharmaceutical companies think about therapies for infectious diseases, prioritizing them in the future.

Source: www.phys.org