What are the factors to be considered in propagation of bacteria?
Answers
Explanation:
Abstract
How motile bacteria move near a surface is a problem of fundamental biophysical interest and is key to the emergence of several phenomena of biological, ecological and medical relevance, including biofilm formation. Solid boundaries can strongly influence a cell’s propulsion mechanism, thus leading many flagellated bacteria to describe long circular trajectories stably entrapped by the surface. Experimental studies on near-surface bacterial motility have, however, neglected the fact that real environments have typical microstructures varying on the scale of the cells’ motion. Here, we show that micro-obstacles influence the propagation of peritrichously flagellated bacteria on a flat surface in a non-monotonic way. Instead of hindering it, an optimal, relatively low obstacle density can significantly enhance cells’ propagation on surfaces due to individual forward-scattering events. This finding provides insight on the emerging dynamics of chiral active matter in complex environments and inspires possible routes to control microbial ecology in natural habitats.
Introduction
Microorganisms live in natural environments that present, to different extents, physical, chemical and biological complexity1,2. This heterogeneity influences all aspects of microbial life and ecology in a wide range of habitats, from marine ecosytems3 to biological hosts4. For example, flow and surface topology can trigger or disrupt quorum sensing in bacterial communities5,6,7 as can shape dynamics of microbial competition in biofilms8. To enhance their fitness within such complexity, several bacterial species, e.g. Escherichia coli bacteria9, are motile, which is key in promoting many biologically relevant processes, such as the formation of colonies and biofilms on surfaces1,2,10. Justified by fundamental biophysical curiosity as well as by the ecological and medical relevance of biofilms11,12,13, significant research effort has, therefore, been devoted to elucidate the dynamics of bacterial near-surface swimming. We now know that, due to hydrodynamic interactions14,15,16, several flagellated bacteria tend to describe circular trajectories when swimming near surfaces13,17,18,19,20,21,22. The interaction with a physical boundary can also lead to escape times that are much longer than the typical reorientation times for bulk swimming23,24,25,26, thus resulting in long stable trajectories on surfaces that can eventually promote cell adhesion14,27,28,29,30. Surprisingly, even though natural bacterial habitats present characteristic features that vary on a spatial scale comparable to that of the cells’ motion7,8, experimental studies of near-surface swimming have mainly focused on smooth surfaces devoid of this natural complexity. Nonetheless, for far-from-equilibrium self-propelling particles, such as motile bacteria, both individual and collective motion dynamics can depend on environmental factors in non-intuitive ways, as recently shown for microscopic non-chiral active particles numerically31,32,33,34,35 and experimentally36,37. Moreover, in environments densely packed with periodic patterns of obstacles, turning angle distributions of bacterial cells change from bulk swimming and their trajectories can be efficiently guided along open channels in the lattice38,39.