Researchers discover connection between electrical properties and lifestyle of bacteria

The electrical potential across the bacterial cell envelope indicates when the bacteria no longer function as individual cells but as a collective. Researchers at the Institute for Biological Physics at the University of Cologne have discovered this connection between electrical properties and the lifestyle of bacteria. Although bacteria are unicellular organisms, they form spatially structured communities, the so-called biofilms. Within biofilms, bacteria behave as a collective and can better protect themselves against external stress such as antibiotics.

Until now, it was largely unknown how the transition from a single bacterium to such a complex community works. The researchers examined how the electrical properties of bacteria change during biofilm formation and discovered characteristic patterns of electrical potential that evolve in space and time. These patterns were correlated with the development of new habitats with varying degrees of tolerance to antibiotics. The researchers describe their findings in the article ‘Collective polarization dynamics in bacterial colonies means the emergence of distinct subpopulations’ in the Journal PLOS Biology.

Individual bacteria build up an electrical potential across their envelope (the membrane) and thus become electrically polarized. For the cell, this polarization is an important source of energy for respiration, nutrient uptake, and toxin export. Recent methodological advances have allowed researchers to examine the dynamics of membrane potential at the level of individual bacterial cells. These studies revealed that the membrane potential of individual cells fluctuates independently of their neighboring cells.

How does the potential change during biofilm development and what environmental factors influence the potential? How is the potential related to the growth behavior of cells and their tolerance to antibiotics? These questions have now been raised by a team of researchers from the Institute for Biological Physics led by Professor Berenike Maier. They examined the early stages of biofilm formation of Neisseria gonorrhoeae (also known as gonococcus), the causative agent of gonorrhea, one of the most common sexually transmitted diseases, which can cause ectopic pregnancies and infertility. Within a few minutes, gonococci self-assemble into spherical colonies comprising thousands of bacteria.

Using advanced light microscopy and image analysis, we can measure the dynamics of individual cell membrane potential in these colonies. The potential is not correlated within fresh bacterial colonies. When the colony reaches a critical size, we observe something completely unexpected: all the cells in the center suddenly increase their potential; They hyperpolarize.”

Dr. Marc Hennes, first author

Eventually, a shell of hyperpolarized cells occurs in the center of the colony and travels through the colony. Behind this shell, the potential in the center is less. Researchers have interpreted this phenomenon of spatiotemporally correlated polarization patterns as the transition to collective behavior, indicative of biofilm formation. A combination of computer simulations and wet lab experiments showed strong evidence that this polarization pattern is related to a change in oxygen availability. This pattern exists because the cells in the center use up oxygen faster than diffusion replenishes it.

Therefore, an important question was whether the pattern of membrane polarization correlated with the well-known functional heterogeneity of biofilms. In fact, the bacteria slowed down their growth rate after they had gone through the hyperpolarization process, while the growth rate of the bacteria residing on the surface of the colony remained high. In addition, the bacteria in the center of the colony showed more tolerance to antibiotics. Increased tolerance to antibiotics is an acute medical problem when treating biofilms. The molecular mechanisms of tolerance are the subject of a project funded by the UoC’s Center for Molecular Medicine in Cologne.

The future goal is to better understand the molecular mechanisms underlying the formation of polarization patterns and their relationship with antibiotic tolerance. This research will be carried out within a new priority program funded by the German Research Foundation (Deutsche Forschungsgemeinschaft).

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Magazine reference:

Hennes, M., et al. (2023) The dynamics of collective polarization in bacterial colonies means the appearance of different subpopulations. PLOS Biology. doi.org/10.1371/journal.pbio.3001960.

Source: news.google.com