Giovanni Savorana

Last Name

Savorana

First Name

Giovanni

ORCID

0000-0002-1082-5642

Show all metadata

Search Results

Publications 1 - 8 of 8

Transport of Pseudomonas aeruginosa in Polymer Solutions
Savorana, Giovanni; Geisel, Steffen; Cen, Tianyu; et al. (2022)
Frontiers in Physics
Bacteria often live surrounded by polymer solutions, such as in animal respiratory, gastrointestinal, and reproductive tracts. In these systems, polymer solutions are often exposed to fluid flow, and their complex rheology can affect the transport of chemical compounds and microorganisms. Recent studies have focused on the effect of polymer solutions on the motility of bacteria in the absence of fluid flow. However, flow can be a game-changer on bacterial transport, as demonstrated by the depletion of motile bacteria from the low-shear regions and trapping in the high-shear regions in simple fluids, even for flows as simple as the Poiseuille one. Despite the relevance of polymer solutions in many bacterial habitats, the effect of their complex rheology on shear-induced trapping and bacterial transport in flow has remained unexplored. Using microfluidic experiments and numerical modeling, we studied how the shear rate and the rheological behavior of Newtonian and non-Newtonian polymer solutions affect the transport of motile, wild-type Pseudomonas aeruginosa in a Poiseuille flow. Our results show that, in Newtonian solutions, an increase in viscosity reduces bacterial depletion in the low-shear regions at the microchannel center, due to a reduction in the bacterial swimming velocity. Conversely, in the non-Newtonian solution, we observed a depletion comparable to the buffer case, despite its zero-shear viscosity being two orders of magnitude higher. In both cases, bacterial swimming and polymer fluid rheology control the magnitude of bacterial depletion and its shear-rate dependence. Our observations underscore the importance of the rheological behavior of the carrier fluid in controlling bacterial transport, in particular, close to surfaces giving rise to velocity gradients, with potential consequences on surface colonization and biofilm formation in many naturally relevant microbial habitats.
The influence of bodily fluid rheology on biofilm formation: Known facts and open questions
Savorana, Giovanni; Di Claudio, Alessia; Rusconi, Roberto; et al. (2025)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Biofilms - microbial communities encased in a self-produced extracellular matrix - pose a significant challenge in clinical settings due to their association with chronic infections and antibiotic resistance. Their formation in the human body is governed by a complex interplay of biological and environmental factors, including the biochemical composition of bodily fluids, fluid dynamics, and cell-cell and cell-surface interactions. Improving therapeutic strategies requires a deeper understanding of how host-specific conditions shape biofilm development. Despite efforts to replicate in vivo conditions, in vitro models are often insufficient for capturing the complex dynamics of biofilm formation within the host. This limitation hinders the translation of experimental findings into clinical applications and slows the development of targeted therapies. In this review, we examine the role of fluid dynamics within the human body, with a particular focus on how the biochemical composition, rheological properties of bodily fluids and local flow conditions influence surface colonization and biofilm formation. We survey the current state of the field and outline key open challenges, intending to inform and inspire the development of next-generation experimental models that more closely reflect physiological reality.
Stress-hardening behaviour of biofilm streamers
Savorana, Giovanni; Redaelli, Tommaso; Truzzolillo, Domenico; et al. (2025)
Nature Communications
Bacteria’s ability to withstand mechanical challenges is enhanced in their biofilm lifestyle, where they are encased in a viscoelastic polymer matrix. Under fluid flow, biofilms can form as streamers – slender filaments tethered to solid surfaces and suspended in the flowing fluid. Streamers thrive in environments subjected to intense hydrodynamic stresses, such as medical devices and water filters, often resulting in catastrophic clogging. Their colonisation success may depend on a highly adaptable mechanical response to varying stress conditions, though the evidence and underlying mechanisms of this adaptation remain elusive. Here, we demonstrate that biofilm streamers exhibit a stress-hardening behaviour, with both differential elastic modulus and effective viscosity increasing linearly with external stress. This stress-hardening is consistent across biofilms with different matrix compositions, formed by various bacterial species, and under diverse growth conditions. We further demonstrate that this mechanical response originates from the properties of extracellular DNA (eDNA) molecules, which constitute the structural backbone of the streamers. In addition, our results identify extracellular RNA (eRNA) as a modulator of the matrix network, contributing to both the structure and rheological properties of the eDNA backbone. Our findings reveal an instantaneous, purely physical mechanism enabling streamers to adapt to hydrodynamic stresses. Given the ubiquity of extracellular nucleic acids (eNA) in biofilms, this discovery prompts a re-evaluation of their functional role in biofilm mechanics, with potential implications for biofilm structural integrity, ecological resilience, and colonisation dynamics.
A microfluidic platform for characterizing the structure and rheology of biofilm streamers
Savorana, Giovanni; Słomka, Jonasz; Stocker, Roman; et al. (2022)
Soft Matter
Biofilm formation is the most successful survival strategy for bacterial communities. In the biofilm lifestyle, bacteria embed themselves in a self-secreted matrix of extracellular polymeric substances (EPS), which acts as a shield against mechanical and chemical insults. When ambient flow is present, this viscoelastic scaffold can take a streamlined shape, forming biofilm filaments suspended in flow, called streamers. Streamers significantly disrupt the fluid flow by causing rapid clogging and affect transport in aquatic environments. Despite their relevance, the structural and rheological characterization of biofilm streamers is still at an early stage. In this work, we present a microfluidic platform that allows the reproducible growth of biofilm streamers in controlled physico-chemical conditions and the characterization of their biochemical composition, morphology, and rheology in situ. We employed isolated micropillars as nucleation sites for the growth of single biofilm streamers under the continuous flow of a diluted bacterial suspension. By combining fluorescent staining of the EPS components and epifluorescence microscopy, we were able to characterize the biochemical composition and morphology of the streamers. Additionally, we optimized a protocol to perform hydrodynamic stress tests in situ, by inducing controlled variations of the fluid shear stress exerted on the streamers by the flow. Thus, the reproducibility of the formation process and the testing protocol make it possible to perform several consistent experimental replicates that provide statistically significant information. By allowing the systematic investigation of the role of biochemical composition on the structure and rheology of streamers, this platform will advance our understanding of biofilm formation.
Genotoxic stress stimulates eDNA release via explosive cell lysis and thereby promotes streamer formation of Burkholderia cenocepacia H111 cultured in a microfluidic device
Heredia-Ponce, Zaira; Secchi, Eleonora; Toyofuku, Masanori; et al. (2023)
npj Biofilms and Microbiomes
DNA is a component of biofilms, but the triggers of DNA release during biofilm formation and how DNA contributes to biofilm development are poorly investigated. One key mechanism involved in DNA release is explosive cell lysis, which is a consequence of prophage induction. In this article, the role of explosive cell lysis in biofilm formation was investigated in the opportunistic human pathogen Burkholderia cenocepacia H111 (H111). Biofilm streamers, flow-suspended biofilm filaments, were used as a biofilm model in this study, as DNA is an essential component of their matrix. H111 contains three prophages on chromosome 1 of its genome, and the involvement of each prophage in causing explosive cell lysis of the host and subsequent DNA and membrane vesicle (MV) release, as well as their contribution to streamer formation, were studied in the presence and absence of genotoxic stress. The results show that two of the three prophages of H111 encode functional lytic prophages that can be induced by genotoxic stress and their activation causes DNA and MVs release by explosive cell lysis. Furthermore, it is shown that the released DNA enables the strain to develop biofilm streamers, and streamer formation can be enhanced by genotoxic stress. Overall, this study demonstrates the involvement of prophages in streamer formation and uncovers an often-overlooked problem with the use of antibiotics that trigger the bacterial SOS response for the treatment of bacterial infections.
Magnetic cilia carpets with programmable metachronal waves
Gu, Hongri; Boehler, Quentin; Cui, Haoyang; et al. (2020)
Nature Communications
Metachronal waves commonly exist in natural cilia carpets. These emergent phenomena, which originate from phase differences between neighbouring self-beating cilia, are essential for biological transport processes including locomotion, liquid pumping, feeding, and cell delivery. However, studies of such complex active systems are limited, particularly from the experimental side. Here we report magnetically actuated, soft, artificial cilia carpets. By stretching and folding onto curved templates, programmable magnetization patterns can be encoded into artificial cilia carpets, which exhibit metachronal waves in dynamic magnetic fields. We have tested both the transport capabilities in a fluid environment and the locomotion capabilities on a solid surface. This robotic system provides a highly customizable experimental platform that not only assists in understanding fundamental rules of natural cilia carpets, but also paves a path to cilia-inspired soft robots for future biomedical applications.
The structural role of bacterial eDNA in the formation of biofilm streamers
Secchi, Eleonora; Savorana, Giovanni; Vitale, Alessandra; et al. (2022)
Proceedings of the National Academy of Sciences of the United States of America
SignificanceStreamers, filamentous bacterial biofilms formed in flowing systems, are ubiquitous in natural and artificial environments, where they cause clogging of devices and spreading of infections. Despite their impact, little is known about the nature and properties of streamers and their response to fluid flow. Here, we uncover the specific contribution of bacterial secreted extracellular DNA and exopolysaccharide Pel, two important components in Pseudomonas aeruginosa biofilms, to the formation and the mechanical properties of the streamers. We then show how this knowledge can be used to control biofilm streamer formation, both to inhibit or to promote it.
Influence of matrix composition and ambient flow conditions on the properties of biofilm streamers
Savorana, Giovanni (2024)
Bacteria are among the most successful organisms on Earth. Their success comes from a wide range of resources they can deploy to face the environment when it turns hostile. One of the most powerful resources is the secretion of extracellular polymeric substances (EPS), which can self-assemble and give rise to biofilms, communities of cells embedded in a protective EPS matrix. Biofilms are ubiquitous and difficult to eradicate, largely due to their viscoelastic mechanical properties: they elastically respond to quick mechanical stimuli, preserving their structure, but can also adapt and dissipate persistent mechanical stresses through viscous deformation. Biofilm viscoelasticity is determined by matrix composition and microstructure. These can be strongly affected by the interaction with the surrounding microenvironment, which often enhance the fitness of biofilms to their specific habitat. Ambient flow is a common feature of moist microbial habitats and plays a crucial role in biofilm development and dissemination. One of the best examples is the formation of biofilm streamers, slender biofilm filaments that self-assemble into a streamlined shape in the presence of flow. Streamers have one or both ends tethered to a solid surface, with the rest of the filament suspended in the flowing fluid. Their viscoelastic properties allow them to withstand flow fluctuations and extend far from their tethering surfaces, bridging gaps between obstacles and walls, and accelerating bacterial colonization. Streamers can develop in soil-like porous media, water filters and medical stents and cause rapid clogging of their habitat. Despite the need to predict and control streamer formation, how matrix composition and ambient flow influence their development and properties is still poorly understood, mainly due to the lack of a platform and framework for systematic studies. The first goal of this thesis was to develop a microfluidic platform to grow biofilm streamers in a reproducible way, and to characterize their composition, morphology and viscoelasticity in situ. In this platform, isolated pillars in straight microfluidic channels act as nucleation sites for biofilm streamers, under the continuous flow of a diluted bacterial suspension. Streamers grow tethered to the pillars, parallel to the direction of flow, increasing in length and radius over time. The full optical access of the microfluidic platform allows the characterization of the biochemical composition and morphology of the streamers through light microscopy, combined with the fluorescent staining of the EPS matrix components. Additionally, we optimized a technique to perform hydrodynamic stress tests in situ by inducing controlled variations of the axial stress exerted by flow on the streamers. The reproducibility of the formation process and the characterization protocol allowed us to investigate the influence of matrix composition and ambient flow on the properties of biofilm streamers. Here, we investigated the role of matrix composition in streamers formed by Pseudomonas aeruginosa PA14. The EPS produced by PA14 mainly include extracellular DNA (eDNA) and a polysaccharide called Pel. By using mutants for Pel production, we discovered that eDNA is the only structural component required for streamer formation, while Pel affects streamer morphology and viscoelasticity. In particular, Pel contributes to increasing the matrix elastic modulus and viscosity, thus the overall mechanical strength of biofilm streamers. We then used the microfluidic platform to investigate the role of ambient flow in determining the properties of biofilm streamers. When flowing PA14 suspensions at different flow velocities, we observed differences in the kinematics of streamer formation: the stronger the flow, the slower the length increase. However, we did not observe any significant adaptation of streamer biochemical composition and viscoelasticity to ambient flow. Instead, we discovered that the elastic modulus and viscosity of biofilm streamers are proportional to the axial stress they are subjected to. Our experiments show that such changes are due to an instantaneous stress-hardening effect, which functions as an intrinsic, purely mechanical adaptation mechanism of the streamer matrix to external loads. Experiments with Pel mutants showed that stress-hardening is independent of polysaccharide abundance in the matrix, suggesting it may be an emergent property of the eDNA scaffold of the streamers. We generalized our findings to other bacterial species, suggesting that stress-hardening may be a widespread behavior of the biofilm matrix. The above experiments on biofilms in flow were conducted in simple aqueous culture media. However, natural bacterial habitats often involve complex fluids, such as those found in animal hosts and soil. In such habitats, the interaction of bacteria and biofilms with flow still awaits to be explored. As an outlook for future research, we conclude this thesis with a first investigation of the interaction between shear flow and bacterial motility in polymer solutions. In water, shear-motility interactions can enhance surface colonization and promote biofilm formation: we showed that this effect can be significantly altered in polymer fluids that affect cell motility and the hydrodynamic environment.

Publications 1 - 8 of 8

Giovanni Savorana

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results