Micro-scale water potential gradients visualized in soil around plant root tips using microbiosensors

Area of Science:

• Soil science
• Microbiology
• Environmental science

Background:

• Soil water potential is crucial for soil microbial communities.
• Empirical measurement of soil water potential at millimetre scales has been challenging.

Purpose of the Study:

• To develop and validate microbial biosensors for measuring soil water potential at millimetre spatial scales.
• To assess the utility of these biosensors in non-sterile soil environments, particularly in the rhizosphere.

Main Methods:

• Engineered microbial biosensors (Pantoea agglomerans and Pseudomonas putida) with a proU-GFP reporter system were used.
• Green fluorescent protein (GFP) production was correlated with total water potential.
• Controlled liquid culture experiments and non-sterile soil experiments in the rhizosphere of Zea mays were conducted.

Main Results:

• The microbial biosensors produced GFP proportionally to total water potential in non-sterile soil.
• Microbiosensor growth rates and osmolytes did not affect GFP output relative to water potential.
• Pantoea agglomerans' GFP levels were influenced by available carbon sources.
• Biosensors detected significantly more negative soil water potentials with increasing distance from plant roots.

Conclusions:

• Microbial biosensors offer a novel method for empirically measuring soil water potential gradients at millimetre scales.
• These biosensors can provide valuable insights into water dynamics and microbial interactions in the soil-rhizosphere continuum.
• The findings support the hypothesis of water potential gradients developing around plant roots due to transpiration.