![]() ![]() Repeat three more times, once for each protist species and each with an initial population of 20. Record observations about the time the population grows, the change in population size, and type of population growth. Select ‘Go’ to observe the population grow over time. Add the default amount of 200 bacteria into the petri dish. You can download your graph using the buttons in the top right corner above the graph. Clicking on ‘Go’ a second time stops the simulation, and clicking on ‘Setup’ resets the simulation. Take some time to familiarize yourself with the model before beginning the exercise. The volume and light level of the microcosm can be adjusted in the simulation. When ‘Go’ is clicked on the individuals reproduce, feed or die. You can add a specified amount of each microbe, and watch them move about the dish. Microcosm Model is used to simulate the population growth in Escherichia coli (bacteria), Paramecium aurelia (protists), Paramecium bursaria (protists) and Didinium nasutum (protists) Procedure: The model opens to a virtual petri dish, which is initially filled with sterile nutrient broth."Biofilms will grow and be very sturdy, sometimes in places that we don't want them, whether that's in patients with disease that are immunocompromised, or in water treatment plants, or on the hulls of ships.INVESTIGATION: POPULATION DYNAMICS Materials Needed: "We're motivated to study them because they intersect with the human world," says Asp. "Bacterial organisms, by biomass, are the most predominant life form on the earth," says Patteson, acknowledging this overlap in interest with Welch, from whose lab they procured the strains of bacteria. We don't exactly know why in the case of the biofilms, but it makes sense that they're able to exert more force and move faster." "It makes sense, in a way," says Patteson, "if you tried to climb a sticky wall instead of a slippery wall, you could exert more force on it. Indeed, by mapping the stress, the team was able to show how biofilms exert more pressure on a stiff surface than on a softer one. Unlike with the less controllable agar, Patteson's team can now make calculations to measure the forces that the biofilms are putting on the gels. "We study mechanics and soft matter systems, so we have equations that describe how something deforms under certain amounts of stress," says Patteson. "We typically think of biofilms as really slow-growing things, but if they're on something soft, they can actually disrupt it." This has implications for disease it means that tissue damage during and following infection might not just be caused by reactions of the body's immune system, but from the bacteria exerting strain on it.īesides design and manipulation of the gels, Patteson and Asp apply physics to biology in the ways that they process the images, measure the boundaries of the biofilms, and calculate how quickly the boundaries expand. "One of the things we found is that when a biofilm grows out, it's actually strong enough to exert force on the substrate," Patteson continues. To the right, a mathematical model of an elastic solid is used to calculate the stress exerted by the bacteria. The left image depicts how each small part of the hydrogel moved based on the movement of embedded fluorescent beads. "We're able to probe how much deformation the gel undergoes under a certain amount of strain," says Patteson. Instead, Patteson's team synthesized transparent gel substrates that could be tuned to a specific stiffness, that would allow them to take time-lapse videos of bacterial colonies growing on them. "Are they sensing the solid part or the fluid part?" she asks. ![]() "We call it a complex material because it is a solid but has properties like a fluid." This mixture of properties, she explains, means that teasing out exactly which aspects make the bacteria behave a certain way more difficult. "It's a substance popular in culinary applications because it makes things gelatinous and adds texture," says Patteson. In the past, scientists investigating this question typically grew the colonies on gels made from agar, an extract of red algae. Patteson and her team wanted to investigate what makes a biofilm-or a colony of microorganisms that bond together-grow and flourish on some kinds of surfaces but not others. In a paper published by PNAS Nexus, a new journal from Oxford Academic, she and graduate student Merrill Asp, along with the collaboration of Professor Roy Welch of the biology department, describe the surprising findings from their recent work with bacterial colonies, that has potential to help shape further understanding of all living systems and improve outcomes in medicine and health. ![]()
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