The power of microbial life for the transformation towards a sustainable planet: key messages from the 2024 IUMS Congress in Florence, the city of the Renaissance.

The 2024 International Union of Microbiological Societies Congress was held in Florence, the city of Renaissance. The theme was to increase the awareness of the power of microbial life, recognizing that it can lead the transformation towards a sustainable planet. The meeting gathered over 1400 experts from more than 90 countries and focused on the transformative potential of microbiology in addressing global challenges and aligning microbial science with the Sustainable Development Goals.

Roadmap for animate matter.

Humanity has long sought inspiration from nature to innovate materials and devices. As science advances, nature-inspired materials are becoming part of our lives. Animate materials, characterized by their activity, adaptability, and autonomy, emulate properties of living systems.

The 2025 motile active matter roadmap.

Activity and autonomous motion are fundamental aspects of many living and engineering systems. Here, the scale of biological agents covers a wide range, from nanomotors, cytoskeleton, and cells, to insects, fish, birds, and people. Inspired by biological active systems, various types of autonomous synthetic nano- and micromachines have been designed, which provide the basis for multifunctional, highly responsive, intelligent active materials.

Light-driven synchronization of optogenetic clocks.

Synthetic genetic oscillators can serve as internal clocks within engineered cells to program periodic expression. However, cell-to-cell variability introduces a dispersion in the characteristics of these clocks that drives the population to complete desynchronization. Here, we introduce the optorepressilator, an optically controllable genetic clock that combines the repressilator, a three-node synthetic network in , with an optogenetic module enabling to reset, delay, or advance its phase using optical inputs.

Dynamic Gene Expression Mitigates Mutational Escape in Lysis-Driven Bacteria Cancer Therapy.

Engineered bacteria have the potential to deliver therapeutic payloads directly to tumors, with synthetic biology enabling precise control over therapeutic release in space and time. However, it remains unclear how to optimize therapeutic bacteria for durable colonization and sustained payload release. Here, we characterize nonpathogenic expressing the bacterial toxin Perfringolysin O (PFO) and dynamic strategies that optimize therapeutic efficacy.

Multiple temperatures and melting of a colloidal active crystal.

Thermal fluctuations constantly excite all relaxation modes in an equilibrium crystal. As the temperature rises, these fluctuations promote the formation of defects and eventually melting. In active solids, the self-propulsion of "atomic" units provides an additional source of non-equilibrium fluctuations whose effect on the melting scenario is still largely unexplored.

Colloidal transport by light induced gradients of active pressure.

Active fluids, like all other fluids, exert mechanical pressure on confining walls. Unlike equilibrium, this pressure is generally not a function of the fluid state in the bulk and displays some peculiar properties. For example, when activity is not uniform, fluid regions with different activity may exert different pressures on the container walls but they can coexist side by side in mechanical equilibrium.

A microfluidic method for passive trapping of sperms in microstructures.

Sperm motility is a prerequisite for male fertility. Enhancing the concentration of motile sperms in assisted reproductive technologies - for human and animal reproduction - is typically achieved through aggressive methods such as centrifugation. Here, we propose a passive technique for the amplification of motile sperm concentration, with no externally imposed forces or flows.

Rectification and confinement of photokinetic bacteria in an optical feedback loop.

Active particles can self-propel by exploiting locally available energy resources. When powered by light, these resources can be distributed with high resolution allowing spatio-temporal modulation of motility. Here we show that the random walks of light-driven bacteria are rectified when they swim in a structured light field that is obtained by a simple geometric transformation of a previous system snapshot.

A virtual reality interface for the immersive manipulation of live microscopic systems.

For more than three centuries we have been watching and studying microscopic phenomena behind a microscope. We discovered that cells live in a physical environment whose predominant factors are no longer those of our scale and for which we lack a direct experience and consequently a deep intuition. Here we demonstrate a new instrument which, by integrating holographic and virtual reality technologies, allows the user to be completely immersed in a dynamic virtual world which is a simultaneous replica of a real system under the microscope.

A transition to stable one-dimensional swimming enhances E. coli motility through narrow channels.

Living organisms often display adaptive strategies that allow them to move efficiently even in strong confinement. With one single degree of freedom, the angle of a rotating bundle of flagella, bacteria provide one of the simplest examples of locomotion in the living world. Here we show that a purely physical mechanism, depending on a hydrodynamic stability condition, is responsible for a confinement induced transition between two swimming states in E.

Brownian fluctuations and hydrodynamics of a microhelix near a solid wall.

We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation.

Invariance properties of bacterial random walks in complex structures.

Motile cells often explore natural environments characterized by a high degree of structural complexity. Moreover cell motility is also intrinsically noisy due to spontaneous random reorientations and speed fluctuations. This interplay of internal and external noise sources gives rise to a complex dynamical behavior that can be strongly sensitive to details and hard to model quantitatively.

3D dynamics of bacteria wall entrapment at a water-air interface.

Swimming bacteria can be trapped for prolonged times at the surface of an impenetrable boundary. The subsequent surface confined motility is found to be very sensitive to the physico-chemical properties of the interfaces which determine the boundary conditions for the flow. The quantitative understanding of this complex dynamics requires detailed and systematic experimental data to validate theoretical models for both flagellar propulsion and interfacial dynamics.

An optical reaction micro-turbine.

To any energy flow there is an associated flow of momentum, so that recoil forces arise every time an object absorbs or deflects incoming energy. This same principle governs the operation of macroscopic turbines as well as that of microscopic turbines that use light as the working fluid. However, a controlled and precise redistribution of optical energy is not easy to achieve at the micron scale resulting in a low efficiency of power to torque conversion.

Dynamic density shaping of photokinetic .

Many motile microorganisms react to environmental light cues with a variety of motility responses guiding cells towards better conditions for survival and growth. The use of spatial light modulators could help to elucidate the mechanisms of photo-movements while, at the same time, providing an efficient strategy to achieve spatial and temporal control of cell concentration. Here we demonstrate that millions of bacteria, genetically modified to swim smoothly with a light controllable speed, can be arranged into complex and reconfigurable density patterns using a digital light projector.

Microrheology of DNA hydrogel gelling and melting on cooling.

We present systematic characterisation by means of dynamic light scattering and particle tracking techniques of the viscosity and of the linear viscoelastic moduli, G'(ω) and G''(ω), for two different DNA hydrogels. These thermoreversible systems are composed of tetravalent DNA-made nanostars whose sticky sequence is designed to provide controlled interparticle bonding. While the first system forms a gel on cooling, the second one has been programmed to behave as a re-entrant gel, turning again to a fluid solution at low temperature.

Currents and flux-inversion in photokinetic active particles.

Many active particles, both of biological and synthetic origin, can have a light controllable propulsion speed, a property that in biology is commonly referred to as photokinesis. Here we investigate directed transport of photokinetic particles by traveling light patterns. We find general expressions for the current in the cases where the motility wave, induced by light, shifts very slowly or very quickly.

Memory-less response and violation of the fluctuation-dissipation theorem in colloids suspended in an active bath.

We investigate experimentally and numerically the stochastic dynamics and the time-dependent response of colloids subject to a small external perturbation in a dense bath of motile E. coli bacteria. The external field is a magnetic field acting on a superparamagnetic microbead suspended in an active medium.

Light controlled 3D micromotors powered by bacteria.

Self-propelled bacteria can be integrated into synthetic micromachines and act as biological propellers. So far, proposed designs suffer from low reproducibility, large noise levels or lack of tunability. Here we demonstrate that fast, reliable and tunable bio-hybrid micromotors can be obtained by the self-assembly of synthetic structures with genetically engineered biological propellers.

Shape and Displacement Fluctuations in Soft Vesicles Filled by Active Particles.

We investigate numerically the dynamics of shape and displacement fluctuations of two-dimensional flexible vesicles filled with active particles. At low concentration most of the active particles accumulate at the boundary of the vesicle where positive particle number fluctuations are amplified by trapping, leading to the formation of pinched spots of high density, curvature and pressure. At high concentration the active particles cover the vesicle boundary almost uniformly, resulting in fairly homogeneous pressure and curvature, and nearly circular vesicle shape.

Active dynamics of colloidal particles in time-varying laser speckle patterns.

Colloidal particles immersed in a dynamic speckle pattern experience an optical force that fluctuates both in space and time. The resulting dynamics presents many interesting analogies with a broad class of non-equilibrium systems like: active colloids, self propelled microorganisms, transport in dynamical intracellular environments. Here we show that the use of a spatial light modulator allows to generate light fields that fluctuate with controllable space and time correlations and a prescribed average intensity profile.

Velocity distribution in active particles systems.

We derive an analytic expression for the distribution of velocities of multiple interacting active particles which we test by numerical simulations. In clear contrast with equilibrium we find that the velocities are coupled to positions. Our model shows that, even for two particles only, the individual velocities display a variance depending on the interparticle separation and the emergence of correlations between the velocities of the particles.