Development of silicon nanostructure capturing moments of conversation 

between microorganisms

Real-time observation of signal transduction between microorganisms through highly precise microbial observation method using light and heat

The results from Professor Hong-Gyu Park’s group were published in Science Advances, a renowned international academic journal.

▲ Professor Hong-Gyu Park of the Department of Physics, College of Science.

Microorganisms may float individually but they may form a colony in the shape of a biofilm as they are gathered on a specific surface.

That is because a colony has advantages in communication between individual microorganisms when responding to changes in the external environment, such as lack of nutrients, a drastic change in temperature, and physical stimuli. A system that enables real-time observation of the microbial group actions was developed.

The National Research Foundation of Korea (President: Jung-Hye Roe) reported that the international joint research team including Professor Hong-Gyu Park from Korea University (corresponding author), Professor Kyoung-Ho Kim from Chungbuk National University (first author), and Bozhi Tian from the University of Chicago developed a method to precisely observe the group actions of microorganisms by using light and heat.

The conventional method was to apply a mechanical stimulus or add a chemical to an entire microbial colony, not a specific individual microorganism, and then infer the results of signal transduction through the analysis of the transcriptome or the composition of the culture solution. However, this method can give information about only the change of the general trend that is found several hours after the application of a stimulus.

To instantaneously capture the change of the microbial action caused by a stimulus, the research team invented a real-time method that enables one to precisely apply a thermal stimulus to a specific microorganism (even to a specific part of an individual microorganism) and observe the response based on the fluorescence. The team fabricated a nanostructure of silicon, which is known as a biocompatible material with mature manufacturing technologies, to instantaneously generate heat by using a laser.

The research team found that the instantaneous heat generation at a silicon nanowire by laser pulses caused the formation of a bacterial colony around the heat-emitting nanowire. The team also observed that a concentric calcium ion wave was generated with the initially heated bacterial cell at the center. The wave was propagated even to a neighboring bacterial cell about 26 μm away. Calcium ions are well known as an important medium in various biophysical reactions for cell growth, differentiation and survival.

The signaling of the thermal stimulus, which resulted in the formation of a colony and the signal transduction between the cells (calcium ion wave), was also observed in a disk-shaped (circular) silicon structure. A heat transfer simulation conducted in the study verified that a drastic spatial gradient of the temperature caused the generation of the calcium ion wave in the bacterial colony.

The study has provided a rapid and precise method of observing a live microbial colony. The method may increase the understanding of microbial adaptability to an environment. The research project was supported by the Basic Research in Science & Engineering Program (Young Researcher Program and Research Leader Program). The results of the study were published in Science Advances, a renowned international academic journal, on February 14.

*Title of Article: Structured silicon for revealing transient and integrated signal transductions in microbial systems

*Authors: Professor Kyoung-Ho Kim (first author from Chungbuk National University), Doctor Xiang Gao (first author from the University of Chicago), Professor Hong-Gyu Park (corresponding author from Korea University), and Bozhi Tian (corresponding author from the University of Chicago)

[Figures]

(Figure 1) Precise stimulation of microbial colony using light and heat

A schematic diagram showing the application of a strong laser to a part of the fabricated silicon nanowire for instantaneous heat generation and the gathering of bacterial cells near to the nanowire (left); and a microscopic image of the gathered bacterial cells (right). Images provided by Professor Kyoung-Ho Kim from Chungbuk National University

(Figure 2) Biofilm formation and temperature gradient

Microscopic images showing the biofilms formed in various patterns (top, biofilms shown in light green) and the temperature gradients around the microplates acquired by the heat transfer simulation (bottom). Images provided by Professor Kyoung-Ho Kim from Chungbuk National University