Extracellular polymers physically connect individual cells to a grid (right)
Source: Biotechnical Faculty of the University of Ljubljana
Publish Date: 26.10.2017
Category: Interdisciplinary research, Our contribution to sustainable development goals
Sustainable development goals: 15 Life on land (Indicators)
A fundamental scientific discovery by researchers at the University of Ljubljana enables a new understanding of bacterial co-operation, communication and the impact of bacteria on the environment.
A group of researchers from the University of Ljubljana discovered mechanical connections between bacteria that were previously considered non-existent. The pioneering researchers observed that cells in the suspension connect to an invisible grid, following the motion of the optically trapped bacteria. Behind the visible bacterial structure, an invisible network of intercellular links is hidden, which represents the previously unwitnessed fabric of the ecosystem.
From the definition of plankton in 1887, researchers were convinced that the movement of bacteria was primarily determined by the flow of surrounding water, where the cells do not have interconnections and move freely, independently of one another. Researchers at the University of Ljubljana have recently proved that this is not the case. “Physical connections between bacterial cells are present in the planktonic form, but they cannot be detected using standard microscopic techniques. While individual cells can be seen and counted in diluted bacterial suspensions, their connections can only be demonstrated with an active disorder of one or more cells that are interconnected,” said the leader of the group of researchers Prof. Dr. David Stopar from the Biotechnical Faculty of the University of Ljubljana. To confirm this, the researchers used an optical tweezer and were the first to observe that cells in the suspension connect to an invisible grid, following the motion of the optically trapped bacteria. Behind the visible bacterial structure, an invisible network of intercellular links is hidden, which represents previously invisible fabric of the ecosystem.
The research showed that mechanical connections were present even at low densities of bacteria, which is in sharp contrast with the currently accepted model that bacterial networking only occurs at high densities, when switching to the so-called biofilm. “Molecular connections that allow initial association of bacteria are different from those found in biofilms. Nucleic acids are very important; because of their high elasticity and the ability to form complex origami, they allow self-assembly of the ecosystem fabric. Once the network is composed, it can easily be inserted into new environments. Therefore, in addition to a cell with a graft, we also transfer its local environment as an inseparable unit,” explains Stopar.
According to the results of the research, bacteria are capable of producing well-connected microbial tissues over long distances (more than 100 μm). This is surprising, says Stopar, because so far it has been assumed that single-celled organisms in suspension are unrelated to one another. He further emphasises that multicellular association has always been a sign of a higher level of development, reserved for multicellular organisms. The work of the researchers is not yet complete. The discovery of a weak viscoelastic extracellular bacterial network has raised additional questions about the action of bacteria in suspensions; at the same time, it allows the resolution of some basic microbiological problems associated with intracellular bacterial cell communication and their resistance to antimicrobial substances.
Researchers of the University of Ljubljana have found that bacteria are not as isolated as it seemed. The results of this research changes our perception of bacteria as isolated solitary cells, which associate only occasionally under poor conditions. This fundamental scientific discovery enables a new understanding of bacterial co-operation, communication and their impact on the environment. The existence of mechanical connections between cells in rare bacterial suspensions was first described in the August issue of the journal Nature Communications.
Researchers from three University of Ljubljana Members were involved in the research:
- Dr. David Stopar, Biotechnical Faculty
- Simon Sretenović, Biotechnical Faculty
- Prof. Dr. Iztok Dogša, Biotechnical Faculty
- Dr. Rok Kostanjšek, Biotechnical Faculty
- Dr. Igor Poberaj, Faculty of Mathematics and Physics
- Biljana Stojković, Medical Faculty
Bacillus subtilis trapped in extracellular DNA in suspension (left); extracellular polymers physically connect individual cells to a grid (right). Photos: archive of Biotechnical Faculty of the University of Ljubljana