Cooperation in a fluid swarm of fuel-free micro-swimmers

While motile bacteria display rich dynamics in dense colonies, the phoretic nature of artificial micro-swimmers restricts their activity when crowded. Here we introduce a new class of synthetic micro-swimmers that are driven solely by light. By coupling a light absorbing particle to a fluid droplet we produce a colloidal chimera that transforms optical power into propulsive thermo-capillary action. The swimmers’ internal drive allows them to operate for a long duration (days) and remain active when crowded, forming a high density fluid phase. We find that above a critical concentration, swimmers form a long lived crowded state that displays internal dynamics. When passive particles are introduced, the dense swimmer phase can re-arrange to spontaneously corral the passive particles. We derive a geometrical, depletion-like condition for corralling by identifying the role the passive particles play in controlling the effective concentration of the micro-swimmers.

Separation and enrichment of sodium-motile bacteria using cost-effective microfluidics

Many motile bacteria are propelled by the rotation of flagellar filaments. This rotation is driven by a membrane protein known as the stator-complex, which drives the rotor of the bacterial flagellar motor. Torque generation is powered in most cases by proton transit through the stator complex, with the next most common ionic power source being sodium. Synthetic chimeric stators which combine sodium- and proton-powered stators have enabled the interrogation of sodium-stators in species that are typically proton-powered, such as the sodium powered PomA-PotB stator complex in E. coli. Much is known about the signalling cascades that respond to attractant and govern switching bias as an end-product of chemotaxis, however less is known about how energetics and chemotaxis interact to affect the colonisation of environmental niches where ion concentrations and compositions may vary. Here we designed a fluidics system at low cost for rapid prototyping to separate motile and non-motile populations of bacteria. We measure separation efficiencies at varying ionic concentrations and confirm using fluorescence that our device can deliver eight-fold enrichment of the motile proportion of a mixed population of motile and non-motile species. Furthermore, our results show that we can select bacteria from reservoirs where sodium is not initially present. Overall, this technique can be used to implement long-term selection from liquid culture for directed evolution approaches to investigate the adaptation of motility in bacterial ecosystems.

Isolation of Probiotic Bacteria from Macrobrachium rosenbergii and Their Antagonistic Efficacy against Pathogenic Bacteria

The probiotic bacteria isolated from prawn, Macrobrachium rosenbergii was studied for their morphological and biochemical characteristics as well as their antagonistic efficacy against pathogenic bacteria. A total of three probiotic bacteria viz. White Colour Bacteria (WCB), Red Colour Bacteria (RCB) and Yellow Colour Bacteria (YCB) were isolated from intestine of healthy prawn while three pathogenic bacteria viz. PB1, PB2 and PB3 were isolated from infected antennae and muscles of moribund prawn. Depending on their physical and biochemical features, the probiotic isolates were gram-positive, rod shaped and motile bacteria belonging to Bacillus spp. and the pathogenic bacteria were also identified as gram-negative, cocci shaped and motile bacteria fit in Enterococcus spp., Vibrio spp. and Micrococcus spp. The optimum culture conditions of all isolates were at pH 7.0 and 37°C temperature. Results on the antibiogram profile of pathogenic bacteria revealed that majority of the isolates were sensitive (43.58%) or intermediate (30.76%) against thirteen antibiotics. The probiotic bacterial antagonistic activities were tested against Enterococcus, Vibrio and Micrococcus spp.by cross-streak method. The results indicate that the strain of YCB showed inhibitory effects against Enterococcus spp. (5 mm), Vibrio spp. (5 mm) and Micrococcus spp. (3 mm). Similarly, WCB showed inhibitory effects against Enterococcus spp. (4 mm), Vibrio spp. (3 mm) and Micrococcus spp. (4 mm). RCB strains showed inhibition against Micrococcus spp. (3 mm) only, but not against Enterococcus spp. and Vibrio spp. Based on the results, it can be concluded that the isolated probiotic bacteria could be a good candidate to consider for further studies to control the pathogenic bacteria in prawn culture.

Sessile bacterium unlocks ability of surface motility through mutualistic interspecies interaction

In addition to their common planktonic lifestyle, bacteria frequently live in surface-associated habitats. Surface motility is essential for exploring these habitats for food sources. However, many bacteria are found on surfaces, even though they lack features required for migrating along surfaces. How these canonical non-motile bacteria adapt to the environmental fluctuations on surfaces remains unknown. Recently, several cases of interspecies interaction were reported that induce surface motility of non-motile bacteria either by using ‘hitchhiking’ strategies or through ‘social spreading’ mechanisms. Here, we report a previously unknown mechanism for interaction-dependent surface motility of the canonical non-motile bacterium, Dietzia sp. DQ12-45-1b, which is induced by interaction with a dimorphic prosthecate bacterium, Glycocaulis alkaliphilus 6B-8T. Dietzia cells exhibits “sliding”-like motility in an area where the strain Glycocaulis cells was pre-colonized with a sufficient density. Furthermore, we show that biosurfactants play a critical role in inducing the surface motility of Dietzia cells. Our analysis also demonstrates that Dietzia degrade n-alkanes and provide Glycocaulis with the resulting metabolites for survival, which in turn enabled directional migration of Dietzia towards nutrients in the environment. Such interaction-dependent migration was also found between Dietzia and Glycocaulis strains isolated from other habitats, suggesting that this mutualistic relationship ubiquitously occurs in natural environments. In conclusion, we propose a novel model for such a ‘win-win’ strategy, whereby non-motile bacteria pay metabolites to dimorphic prosthecate bacteria in return for migrating to reach environments otherwise inaccessible. We propose that this mechanism represents a common strategy for canonically non-motile bacteria living on a surface.ImportanceCell motility provides a selective advantage for bacteria searching for nutrients. While a large body of evidence exists for how motile bacteria migrate on surface by virtue of different ways of motility, fewer studies concerned about how canonical non-motile bacteria adapted to those surface-associated habitats. Recent reports have proposed that interactions with other bacteria trigger the movement of those sessile bacteria. However, these interactions are limited to ‘hitchhiking’ or ‘social spreading’ modes. Here, we characterized a previously unknown interaction mode between Dietzia and Glycocaulis.This interaction differs from previously described modes, thus advance our limited understanding of how sessile bacteria move on surfaces. We propose that this interaction mode represents a ‘win-win’ strategy for both strains, and this mode might be widely distributed across diverse environments. These novel insights should greatly assist in understanding the mechanisms responsible for the cellular interplay between microbes in complex microbiomes.

Flower-like patterns in multi-species bacterial colonies

Diverse interactions among species within bacterial colonies lead to intricate spatiotemporal dynamics, which can affect their growth and survival. Here, we describe the emergence of complex structures in a colony grown from mixtures of motile and non-motile bacterial species on a soft agar surface. Time-lapse imaging shows that non-motile bacteria 'hitchhike' on the motile bacteria as the latter migrate outward. The non-motile bacteria accumulate at the boundary of the colony and trigger an instability that leaves behind striking flower-like patterns. The mechanism of the front instability governing this pattern formation is elucidated by a mathematical model for the frictional motion of the colony interface, with friction depending on the local concentration of the non-motile species. A more elaborate two-dimensional phase-field model that explicitly accounts for the interplay between growth, mechanical stress from the motile species, and friction provided by the non-motile species, fully reproduces the observed flower-like patterns.