Researchers have found that bacteria form colonies in three dimensions in rough crystal-like shapes.
Bacterial colonies often grow in streaks on petri dishes in laboratories, but no one has understood how the colonies organize themselves into three-dimensional (3-D) environments, like the tissues and cells in human bodies or in soils and sediments in the environment. , to now. This knowledge could be important for advancing environmental and therapeutic research.
A Princeton University team has now developed a method for keeping bacteria in 3-D environments. As the bacteria grow, their colonies constantly form attractive rough shapes that resemble a branched head of cabbage, far more complex than the one seen in the petri dish.
“Since bacteria were discovered over 300 years ago, most lab research has studied them in test tubes or petri dishes,” said Sujit Datta, assistant professor of chemistry and biology at Princeton and author of the older study. This is a result of curiosity rather than a lack of practical limitations. “If you want to look at bacteria growing in tissues or soil, they’re opaque, and you can’t see what the colony is doing. It was really a challenge.
Datta’s research group discovered this behavior using an experimental framework that allows them to make previously unheard-of observations of bacterial colonies in their natural, three-dimensional state. Unexpectedly, scientists discovered that the growth of wild colonies was consistently similar to other natural phenomena such as the growth of crystals or frost spread on a windowpane.
“These types of rough, branching shapes are ubiquitous in nature, but typically in the context of growing or growing non-living systems,” says Datta. “What we found is that in 3-D growing, bacterial colonies exhibit a very similar process, despite the fact that these are collectives of living organisms.”
This new explanation of how bacterial colonies evolved in three dimensions was recently published in the journal Journal of the Academy of Sciences. Datta and colleagues hope that their findings will aid a wide range of bacterial growth research, from the creation of effective antimicrobials to pharmaceutical, medical and environmental research, as well as methods that harness bacteria for industrial use.
“On a fundamental level, we are excited that this work will reveal surprising links between the evolution of form and function in biological systems and the study of inanimate growth processes in material science and statistical physics. But also, we think that this new view of when and where cells grow in 3D will be of interest to anyone in growth bacterial treatment, such as in environmental, industrial and biomedical applications,” said Datta.
Over several years, Datta’s research team has developed a system that allows the analysis of phenomena that occur in opaque settings, such as fluid flows through the earth. The team uses specially designed hydrogels that absorb water, similar to those found in gel and contact lenses, as matrices for 3-D bacterial growth. Unlike those common versions of hydrogels, Datta’s materials are made of large hydrogel balls that are easily deformed by bacteria, allowing the free passage of oxygen and nutrients that support bacterial growth and are transparent to light.
“It’s like a ball pit where each ball is a hydrogel. They’re tiny, so you can’t see them,” said Datta. The research team calibrated the makeup of the hydrogel to mimic the structure of soil or tissue. to be checked
“When bacterial colonies grow in the hydrogel matrix, they can easily arrange spheres around them to avoid capture,” he said. “It’s about putting your arm down in the ball pit. If you pull through, the balls will arrange themselves around your arm.
The researchers did experiments with four different species of bacteria (including one that helps generate the bitter taste of kombucha) to see how it grew in three dimensions.
“We changed the cell types, the nutrient conditions, the properties of the hydrogel,” said Datta. The researchers saw the same growth patterns in both rough-edged cases. “We systematically changed all the parameters, but this seems to be a general phenomenon.”
Datta said two factors seemed to make the cabbage grow on the surface of the colony. First, bacteria with access to high levels of nutrients or oxygen will grow and reproduce faster than those in a less abundant environment. Even the most uniform environments have uneven food density, and these variations on the surface of the colony cause spots to fall forward or backward. Repeated in three dimensions, this causes bacteria to colonize and form bumps and nodules as certain subgroups of bacteria grow faster than their neighbors.
Second, the researchers observed that in three-dimensional growth, only bacteria near the surface of the colony grew and divided. The bacteria, pressed into the medium of the colony, seemed to languish in a dormant state. Because the bacteria did not grow and divide internally, the outer surface was not subject to pressure that would allow it to spread evenly. Its expansion, however, is driven mainly by the growth of the very edge of the colony. And growth at the margin is subject to nutrient variations, which later results in rough, uneven growth.
“If the growth was uniform and there was no difference between the bacteria inside the colony and the periphery, like filling a vesicle, said Alejandro Martinez-Calvo, a postdoctoral researcher at Princeton and the first author of the paper. “The performance of the interior would fill all the disturbances in the periphery.”
To explain why this pressure did not occur, the researchers added a fluorescent tag to proteins that become active in the cells when the bacteria grow. Fluorescent proteins illuminate when the bacteria are active and remain dark when they are not. Researchers observing the colonies of bacteria saw that the edge of the colony was bright green, while the core remained dark.
“The colony essentially organizes itself into a core and a shell, which are very different,” said Datta.
Datta said the theory is that the bacteria at the edges of the colony concentrate most of the nutrients and oxygen, leaving little for the bacteria inside.
“We think they’re sleepy because they’re hungry,” Datta said, although he cautioned that further research is needed to explore this.
Datta said experiments and mathematical models used by the researchers found that there is an upper limit to the bumps that are formed on colony surfaces. The bumpy surface arises from random variations of oxygen and nutrients in the environment, but it also tends to be random within certain limits.
“The plant has a higher limit of how much it can grow – the size of a flower if we compare it to cabbage,” he said. “He was able to predict it from mathematics, and it seems to be an inevitable feature of large colonies growing in 3D.”
Since bacterial growth has been shown to follow a similar pattern to crystal growth and other well-measured phenomena in inanimate materials, Datta said the researchers could adapt mathematical models to reflect bacterial growth. He said future research will be needed to better understand the mechanisms behind growth, the implications of crude growth forms for colony functioning, and applying the same lessons to other areas of interest.
“Ultimately, this work gives us more tools to understand and ultimately control how bacteria grow in nature,” he said.
Report: “Morphological instability and roughness of bacterial colonies growing in 3D” Alejandro Martínez-Calvo, Tapomoy Bhattacharjee, R. Kōnane Bay, Hao Nghi Luu, Anna M. Hancock, Ned S. Wingreen and Sujit S. Datta, October 18, 2022; Journal of the Academy of Sciences.
The study was funded by the National Science Foundation, the New Jersey Health Foundation, the National Institutes of Health, The Eric and Wendy Schmidt Fund for Transformative Technologies, the Pew Biomedical Scholars Fund, and the Humanities Frontiers Program.
#Years #Research #Princeton #Scientists #Solve #Bacterial #Mystery