Bacterial survival in microscopic surface wetness.

Maor Grinberg,Shifra Steinberg,Nadav Kashtan,Tomer Orevi

doi:10.7554/elife.48508

Abstract

Plant leaves constitute a huge microbial habitat of global importance. How microorganisms survive the dry daytime on leaves and avoid desiccation is not well understood. There is evidence that microscopic surface wetness in the form of thin films and micrometer-sized droplets, invisible to the naked eye, persists on leaves during daytime due to deliquescence - the absorption of water until dissolution - of hygroscopic aerosols. Here, we study how such microscopic wetness affects cell survival. We show that, on surfaces drying under moderate humidity, stable microdroplets form around bacterial aggregates due to capillary pinning and deliquescence. Notably, droplet-size increases with aggregate-size, and cell survival is higher the larger the droplet. This phenomenon was observed for 13 bacterial species, two of which - Pseudomonas fluorescens and P. putida - were studied in depth. Microdroplet formation around aggregates is likely key to bacterial survival in a variety of unsaturated microbial habitats, including leaf surfaces.

Highlights

The phyllosphere – the aerial parts of plants – is a vast microbial habitat that is home to diverse microbial communities (Lindow and Brandl, 2003; Lindow and Leveau, 2002; Vorholt, 2012; Vacher et al, 2016; Leveau, 2015; Bringel and CouAce, 2015)
We constructed a simple experimental system, accessible to microscopy, that enables studying the interplay between bacterial surface colonization, cell survival, and microscopic wetness on artificial surfaces
We studied in depth two model bacterial strains – Pseudomonas fluorescens A506 and P. putida KT2440

Summary

Introduction

The phyllosphere – the aerial parts of plants – is a vast microbial habitat that is home to diverse microbial communities (Lindow and Brandl, 2003; Lindow and Leveau, 2002; Vorholt, 2012; Vacher et al, 2016; Leveau, 2015; Bringel and CouAce, 2015). While leaf surfaces may appear to be completely dry during the day, there is increasing evidence that they are frequently covered by thin liquid films or micrometer-sized droplets that are invisible to the naked eye (Burkhardt and Hunsche, 2013; Burkhardt and Eiden, 1994; Burkhardt et al, 2001) (Figure 1A). This microscopic wetness results, in large part, from the deliquescence of hygroscopic particles that absorb moisture until they dissolve in the absorbed water and form a solution. The phenomenon of deliquescence-associated microscopic surface wetness is under-studied, and little is known about its impact on microbial ecology of the phyllosphere and on its contribution to desiccation avoidance and cell survival during the dry daytime

Methods

Results

Conclusion