Hydration-controlled bacterial motility and dispersal on surfaces

Area of Science:

• Microbiology
• Biophysics
• Environmental Science

Background:

• Flagellar motility is crucial for microbial dispersal in aquatic environments.
• Its role in variably hydrated habitats like unsaturated soils is less understood.
• Soil habitats present unique challenges due to water dynamics and porous surfaces.

Purpose of the Study:

• To quantify the impact of hydration status on the spatial dynamics of Pseudomonas putida KT2440.
• To investigate the role of flagellar motility in bacterial colonization of rough porous surfaces under varying moisture conditions.
• To develop a biophysical model predicting bacterial movement based on hydration and surface properties.

Main Methods:

• Experimental system mimicking unsaturated soil aquatic habitats.
• Comparison of flagellated Pseudomonas putida KT2440 with its nonflagellated mutant.
• Quantification of bacterial spatial dynamics across a range of water potentials.
• Development and application of a biophysical model and a roughness network model.

Main Results:

• Flagellar motility sharply decreased at water potentials between 0 and -2 kPa.
• Motility nearly ceased in liquid films thinner than 1.5 micrometers.
• Bacteria demonstrated rapid resumption of motility upon periodic hydration increases.
• Model predictions aligned well with experimental observations, identifying viscous and capillary forces as key inhibitors.

Conclusions:

• Flagellar motility in soil bacteria is restricted to very wet conditions.
• Transient periods of favorable hydration allow for rapid surface colonization, potentially offsetting flagellar costs.
• This adaptability explains the presence of flagellated prokaryotes in partially saturated environments like soil surfaces.
• The findings highlight the importance of water dynamics in microbial ecology and soil science.