Bacterial biofilms, which are sticky assemblies of microbes, can develop concentric rings containing cells with different biological features.
January 6 2022
Bacterial biofilms contain a level of structural organization that we thought was unique to plants and animals.
Biofilms, which are sticky masses of microorganisms such as bacteria and fungi, have long been thought to be biologically simple, having nothing more than a rudimentary level of structural organization. This contrasts with many multicellular organisms, including animals, where cells can grow into different shapes at different times and places during the body’s development to produce complex and diverse biological structures.
Now, Gürol Süel of the University of California, San Diego, and colleagues have discovered that bacterial biofilms are less simple than we thought. The researchers found that biofilms form ring-like structures as they grow and consume nutrients in their environment. With nutrient supply diminishing, some cells essentially freeze over time in terms of the way they function, washed away by a wave of nutrient depletion. This is known as the “clock and wave interface”, and was previously only seen in animals and plants.
Süel and colleagues made this discovery during an experiment exploring the response of a Bacillus subtilis Biofilm for starvation of bio-nitrogen. This usually causes the bacterial cells to change and become more flexible in an adaptive state called ovulation.
But rather than all cells in biofilms adapting in the same way, the researchers can demonstrate that stress-reducing genes produced by biofilms cause only some cells to adapt, resulting in the formation of concentric rings through the nearly circular biofilm. This tree-ring-like structure corresponds to a “clock and wavefront” mechanism (see image above).
“If we only think of [biofilms] “Like balls of bacterial cells, even if they’re of one kind, we’re wrong,” Sowell says. “They are very organized, and they are organized in a very non-trivial way. This organization seems to remind us of what vertebrates and plants did during evolution, so there must be a connection there.”
Although the research was focused solely on observing patterns, Sewell suggests that the patterning could be biofilms that diversify their flexible cells in an effort to increase their chances of survival.
While biofilms have proven to be more complex in recent years, being capable of forms of long-range memory and communication, the discovery of complex structures could challenge the supposed gap between simple unicellular organisms and complex multicellular organisms.
“This debate will be revived with this study,” says Tanmay Bharat of the University of Oxford. “From an evolutionary cell biology perspective, it would be interesting to study where the differences lie. What distinguishes a true multicellular organism?”
Biofilms are also responsible for a wide range of natural phenomena, both good and bad. They can be used to filter water and prevent corrosion, but they are also the main cause of clinical infections, as well as being highly corrosive in some scenarios. Understanding the true basic structure of these bacterial membranes can change the ways they are used and mitigated.
“You can’t assume that one method or one chemical agent is enough to do the job, because biofilms are such a complex community,” Sowell says.
Journal reference: cell, DOI: 10.1016 / j.cell.2021.12.001
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