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Deciphering the Coexistence: Unraveling Bacterial Biofilm Formation

Work done in the lab of Dr. Pushpita Ghosh at the Indian Institute of Science Education and Research, Thiruvananthapuram.

About author

Palash Bera
Palash Ber

Mr. Palash Bera is a doctoral student at the Tata Institute of Fundamental Research, Hyderabad, under the guidance of Dr. Jagannath Mondal and Dr. Pushpita Ghosh. He completed his Bachelor’s degree in Physics from Ramakrishna Mission Vivekananda Centenary College, Kolkata, and a Master’s degree in Physics from Jawaharlal Nehru University, New Delhi. Palash has a keen interest in interdisciplinary research, and his work mainly focuses on using computer simulations and bio-physical modeling to understand the in vitro and in vivo dynamics of bacteria and bacterial cytoplasmic organelles. Besides academics, he enjoys playing badminton and cricket, as well as cooking, listening to songs, and watching movies.

Interview

How would you explain your research outcomes to the non-scientific community?

Bacteria play an essential role in different ecosystems. Even though they are small, bacteria exhibit very complex dynamics in their lifestyle. They can self-organize into various collective phases in response to their surroundings. Among the numerous types and varieties of bacteria, self-propelled rod-shaped bacteria exhibit fascinating and diverse spatiotemporal phenomena. They use their flagella to move around, search for new resources and interact with each other and their environment. They can form dynamic clusters and move collectively, known as swarming.

Depending on the environmental conditions, some species of bacteria can produce extracellular polymeric substances (EPS), essential in determining the structural and mechanical properties of the growing colony. EPS exhibits various properties, behaving like a sticky substance that binds individual bacterial cells together or acting as nonadsorbing to the surface of bacteria promoting repulsion between cells and EPS. In sticky EPS, bacteria form cellular aggregates trapped in a self-produced EPS.

Bacteria usually self-organize into a multicellular community known as a biofilm. Biophysical factors, including mechanical interactions, growth-induced stress, and motility-mediated dispersal, influence how motile bacteria transform into biofilm-like structures. However, the exact interplay among these factors is yet to be elusive.

Using computer simulations, we developed a particle-based biophysical model of rod-like bacteria in self-produced EPS. This simple biophysical model helps us to understand the spatiotemporal dynamics and different coexisting phases of a growing and expanding bacterial colony.

In brief, each rod-like motile bacterial cell can grow by consuming the local nutrient from the medium. Once the cell reaches a particular size, it will likely split into two daughter cells. Additionally, depending on the local nutrient availability, each cell can secrete EPS to its nearby region, which is sticky. This approach ensures that our simulated growing colony closely mimics an experimental setup. In our model, every agent interacts repulsively with one another, except for cells and EPS, which have an attractive interaction within a certain cutoff distance, reflecting the sticky properties of EPS. Moreover, they exhibit over-damped dynamics, indicating the medium’s highly viscous nature.

Using this model, we observed that when sticky EPS is present in the growth medium, the microcolony develops a coexistence of both motile and sessile aggregates, rendering the early stage of biofilm formation. The nutrient-dependent heterogeneous EPS production and the interplay between the growth and dispersion of the cells determine the fate of the multicellular growing colony. To conclude, our findings provide a significant understanding of biofilm morphogenesis and the coexistence of various phases.

Figures (a), (b), and (c) represent different time snapshots of a growing bacterial colony. As time evolves, the bacteria grow and divide by consuming nutrients from the medium. They also secrete extracellular polymeric substances (EPS) particles depending on the local nutrient concentration (Figure (b)). The properties of the EPS determine the fate and morphology of the colony. In the presence of sticky EPS, the colony transitions from motile to sessile aggregates, with the cells in the periphery exhibiting active movement (Figure (c)). However, this transformation is dynamic and continues to occur over time.
Figures (a), (b), and (c) represent different time snapshots of a growing bacterial colony. As time evolves, the bacteria grow and divide by consuming nutrients from the medium. They also secrete extracellular polymeric substances (EPS) particles depending on the local nutrient concentration (Figure (b)). The properties of the EPS determine the fate and morphology of the colony. In the presence of sticky EPS, the colony transitions from motile to sessile aggregates, with the cells in the periphery exhibiting active movement (Figure (c)). However, this transformation is dynamic and continues to occur over time.

How do these findings contribute to your research area?

The exact biophysical mechanisms of the coexistence of motile and sessile aggregates in a developing biofilm are still not fully understood. Our work aims to shed light on the underlying complex mechanism. We observed that the interplay of the mechanical interactions among the components, cell motility, and characteristic property of EPS are the key ingredients that provide such a coexisting phase during biofilm morphogenesis. Moreover, our findings open up the possibility of designing experiments that can verify these predictions.

“Our findings provide a significant understanding of biofilm morphogenesis and the coexistence of various phases”

What was the exciting moment during your research?

There were several exciting moments during our research. The most prominent was when our modeling approach successfully predicted the dynamic transition of motile to non-mobile phases within the expanding colony. Furthermore, our control studies using the same model provided significant experimental validation for our predictions, which was also an exciting aspect of our research.

What do you hope to do next?

In this study, we focused on investigating the impact of sticky EPS on the formation of biofilms. In the future, we plan to explore the role of nonadsorbing EPS in the transition from mobile to sessile aggregates. Additionally, the interplay between the effects of motility and depletion could lead to novel and exciting findings. Finally, our ambitious future plan is to model and explore the spatiotemporal dynamics of a growing three-dimensional biofilm in the presence of a mixture of different characteristic EPS in growing media.

Where do you seek scientific inspiration from?

In my scientific journey, various individuals have inspired me at different stages. My mentors, Dr. Pushpita Ghosh and Dr. Jagannath Mondal, strongly motivate and encourage me to pursue innovative research. Their guidance and mentorship help me to tackle various scientific questions critically and adequately. Over and above, scientific literature and collaborations have also been a great source of inspiration for me.

How do you intend to help Indian science improve?

I am passionate about working on interdisciplinary research by asking more relevant questions. By working towards finding innovative solutions to these questions, I believe that we can make a valuable contribution to improving Indian science. In addition, I think that explaining the importance of science to the general audience through some outreach events can play a significant role in stimulating curiosity about science among students at an early stage and prime the Indian scientific endeavor.

Reference

Palash Bera, Abdul Wasim, and Pushpita Ghosh. A mechanistic understanding of microcolony morphogenesis: coexistence of mobile and sessile aggregates.Soft Matter, 19:1034–1045, 2023

https://pubs.rsc.org/en/content/articlelanding/2023/SM/D2SM01365G

Copy Editor: Nivedita Kamath

 

For interview related queries, write to us at interview.biopatrika@gmail.com

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