Deep in the mud: How biofilms behave on the inside

Significance 

Recent technological advances have revolutionized biofilms for syntrophic consortium of microorganisms. However, these microbial cells are attached to surfaces with growing colonies embedding themselves in extracellular polymeric substances (EPS). The EPS is made up of water, polysaccharides, lipids, proteins, extracellular DNA and lysis products, that together form boundary layers. Previous studies have shown that EPS operate as a protective layer against biotic and abiotic conditions such as temperature fluctuation, drought and also antibiotics. In a faster changing word, biofilms have gained high value in industrial applications. In particular, due to their self-immobilizing nature, biofilms have been employed for simplifying downstream processing and making biotechnological processes easier and more efficient. It is noteworthy to mention that a mature biofilm consists of dense cell clusters in an extracellular matrix, grooves and channels.

Recent reports in the emerging field of biofilms have shown that the concentration gradient in the biofilms is distributed in the cell by diffusion in mass transport. Specifically, this was observed when the biofilm: Lactococcus lactis (L. lactis), was grown in custom-made flow-cells and diffusion constants was recorded across the height of the biofilms. Moreover, recent research has revealed that biofilms portray different diffusional behavior with regard to flow rate and pH variations. Overall, diffusion in biofilms is still vaguely understood. As such, there is an urgent need to resolve this variance. On this account, University of Kaiserslautern in Germany researchers: Jonas Chodorski (graduate student), Dr. Jan Hauth, Dr. Dorina Strieth, Dr. Andreas Wirsen and Professor Roland Ulber employed a recently developed model for assessing diffusion constants via the FRAP method to generate diffusion profiles for undisturbed, growing biofilms of L. lactis under different cultivation conditions. Their work is currently published in the research journal Engineering in life Sciences.

The research team goal was to develop an accurate model describing how diffusion in biofilms of a given species work in order to better assess cultivation conditions, such as time on trial-and-error approaches.

In this scenario, the authors found out that at a higher flow rate, the biofilm exhibited slower diffusion compared to the reference cultivation at lower flow rate. Additionally, the researchers noted that the biofilm exhibited faster growth and little differences in diffusion compared to the reference cultivation in increasing pH. Moreover, their analysis pointed out new insights whereby external factors affect the structure and density of biofilms.

In summary, the study presented a novel approach coined with the aim of developing a model for assessing diffusion constants via the FRAP methods to generate diffusion profiles for undisturbed, growing biofilms of L. lactis under different cultivation conditions. Surprisingly, it was discovered that a diffusion profile of a living, growing and undisturbed biofilm inside a flow cell can be generated. In a statement to Advances in Engineering, the lead author, Professor Roland Ulber, explained through their work, it is now possible to generate diffusion profiles of biofilms which can help researchers to better comprehend biofilms, as well as their process conditions.

Deep in the mud: How biofilms behave on the inside - Advances in Engineering
FIGURE LEGNED: FRAP measurements of an L. lactis biofilm, Leica SP5 II CLSM, Objective: 63×0.9, Fluorescent dye: Sodium-Fluorescein.
Center: Diffusion rate (m x s^-2) plotted against discrete time points (cultivation time continuous mode). Orange – Diffusion rates inside of biofilm, Blue – Diffusion rates in water control. Pos 1-3 denote the respective positions on the sample with Pos1 being the most upstream and Pos3 being the most downstream position.
Rim: Time series of FRAP measurement as general flowchart. 5 frames bleaching (frame time 0.195 s), rapid recovery. Unlike with dextran conjugated fluorescein this dye seems to adsorb to the cells themselves. It was still possible to determine diffusion constants, however, due to aforementioned circumstances recovery recording and assessment of constants was not as precisely possible as with the dextran conjugated dye. After bleaching and full recovery the same spot could be bleached again.

Reference

Jonas Chodorski, Jan Hauth, Dorina Strieth, Andreas Wirsen, Roland Ulber. Diffusion profiles in L. lactis biofilms under different Conditions. Engineering in Life Sciences 2021; volume 21: page 29–36.

Go To Engineering in Life Sciences

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