Researchers control biofilm formation using optical traps

Biofilms – slimy layers formed when bacteria stick to each other on a surface – allow bacteria to protect themselves from extreme environments and even escape antibiotics. In a new study, researchers have shown that laser light in the form of optical traps can be used to control the formation of biofilms. The results could allow scientists to exploit these microbial layers for various bioengineering applications.

“Producing microscopic components typically requires a highly technical manufacturing process, but we found that optical tweezers can be used to precisely control the position of individual bacteria or groups of bacteria,” said Anna Bezryadina, head of research team from California State University Northridge. “This allows us to influence the growth patterns of bacterial structures at a microscopic level with high precision.”

In the magazine Express Biomedical Optics, the researchers report their experiments using optical traps to regulate bacterial aggregation and biofilm development. They found that different types of lasers could be used to stimulate and suppress biofilm growth.

“We can even create a kind of bacterial Lego block that can be moved, stuck and destroyed as needed,” Bezryadina said. “This work could lead to new types of biodegradable materials or a new generation of biofilm-based biosensors, for example.”

Using Light to Control Bacterial Growth

Most biofilm research has focused on mechanical, chemical, and biological approaches to suppress and control biofilms. Although scientists have shown that synthetic and chemical approaches can be used to activate and control biofilms and transform them into specific spatial structures, Bezryadina and his team wanted to know if optical methods could be used to control biofilm dynamics. Achieving this required an interdisciplinary team with expertise in advanced optical technology and microbiology.

The researchers experimented with Bacillus subtilis, a non-pathogenic bacteria that naturally forms biofilms. They used a nutrient-poor environment hostile to B. subtilis to encourage the bacteria to form a biofilm. After obtaining small clusters of biofilms, they conducted optical trapping experiments using either a 473 nm blue laser or a near-infrared Ti:sapphire laser that could be tuned from 700 to 1,000 nm.

They found that using a laser emitting at a wavelength of 820 nm to 830 nm allowed prolonged optical trapping of biofilm clusters while minimizing significant photodamage. However, using a 473 nm laser – a wavelength strongly absorbed by bacteria – caused the cells to rupture and the biofilm clumps to disintegrate. They also observed that the ideal bacterial groups for optical manipulation consisted of three to 15 cells.

Make patterns

When the researchers studied bacteria dynamics and biofilm formation using optical tweezers at a wavelength of 820 nm for an hour, they found that bacterial clumps clustered near optically trapped clumps. , adhered to the surface and began to form a microcolony. They could also move optically trapped bacterial groups in the sample to a specific position, which could be useful for building structures from bacteria. The NIR laser does not appear to disrupt biofilm formation for bacterial clumps exposed to the highly focused NIR laser, implying that NIR wavelengths between 800 nm and 850 nm could be used for extended periods for optical trapping , manipulation and pattern formation. of bacterial clusters.

“Despite the seemingly uncontrolled formation of bacterial biofilm in nature, our work showed that bacterial biofilm formation can be influenced by light,” Bezryadina said. “This paper represents the first step in a long-term project to create microscopic building materials from readily available resources such as bacteria. In future studies, we plan to use what we discovered to develop a process for building structures from bacterial Lego blocks.”

Overall, the experiments revealed some flexibility in the exact growth conditions, cluster sizes, and wavelengths needed to manipulate biofilms. The researchers say it might also be possible to use their methodology with other types of biofilm-forming microorganisms.