Spatiotemporal dynamics of growth and death within spherical bacterial colonies

Abstract

Bacterial growth within colonies and biofilms is heterogeneous. Local reduction of growth rates has been associated with tolerance against various antibiotics. However, spatial gradients of growth rates are poorly characterized in threedimensional bacterial colonies. Here, we report two spatially resolved methods for measuring growth rates in bacterial colonies. As bacteria grow and divide, they generate a velocity field that is directly related to the growth rates. We derive profiles of growth rates from the velocity field and show that they are consistent with the profiles obtained by single-cell-counting. Using these methods, we reveal that even small colonies initiated with a few thousand cells of the human pathogen Neisseria gonorrhoeae develop a steep gradient of growth rates within two generations. Furthermore, we show that stringent response decelerates growth inhibition at the colony center. Based on our results, we suggest that aggregation-related growth inhibition can protect gonococci from external stresses even at early biofilm stages.

Collective polarization dynamics in gonococcal colonies

“…In the following, we argue that the observed dynamics is qualitatively and quantitatively different from the radial mass flow caused by cellular proliferation. The growth-related velocity is minimal at the centre of the colony and reaches its maximum at the edge of the colony (32) in contrast to the result shown in Fig. 4c.…”

“…2d). Prior to the formation of the hyperpolarization shell ( t − t switch < 0), colony radii grew exponentially, R * ≈ 1, with an average growth rate λ 0 ≈ 0.6 h −1 in line with previous measurements (32). After shell formation ( t − t switch > 0), the normalized radius R * quickly fell below 1.…”

“…Previously, we showed that within colonies of ∼ 2 - 3 h of age, a characteristic pattern of growth rates forms whereby the rates decrease from the edge of the colony towards its centre (32). We assessed whether growth-inhibition and the onset of collective membrane dynamics are correlated.…”

“…Colony formation protects N. gonorrhoeae against the β-lactam ceftriaxone (31) and the degree of tolerance depends on the physical properties of the colonies (29). Within several hours, a gradient of growth rates develops in these colonies (32), but it is unclear how and at which time scale habitat diversity emerges. Such transitions are expected to occur at some point in the maturation process of the biofilm, and may be linked to cell differentiation and the emergence of sleeper cells (12, 14).…”

Regulating Bacterial Behavior within Hydrogels of Tunable Viscoelasticity

“…During biofilm formation, soil homeostasis, or invasion of biological tissues, microorganisms grow within confined spaces and push against their natural surroundings to accommodate new cells and grow as colony. The resulting compressive forces on the cell population are dependent on the mechanical properties of the local microenvironment, cell–cell and cell–matrix interactions and mechanical instabilities at cellular scale, [ 38 ] and have been shown to influence cell size, [ 39 ] to limit cell growth [ 40 , 41 ] and to delay cell cycle [ 42 ] in studies with microorganisms in synthetic model systems. [ 43 , 44 ] Physical models under discussion consider self‐driven jamming and build‐up of large mechanical pressures as natural principles behind the collective growth and organization of a colony in 3D confinement.…”