Copolymers enhance selective bacterial community colonization for potential root zone applications

Vy T H Pham,David E Mainwaring,Boon K Tan,Falko Mathes,Vi Khanh Truong,Daniel V Murphy,Pandiyan Murugaraj

doi:10.1038/s41598-017-16253-0

Abstract

Managing the impact of anthropogenic and climate induced stress on plant growth remains a challenge. Here we show that polymeric hydrogels, which maintain their hydrous state, can be designed to exploit functional interactions with soil microorganisms. This microbial enhancement may mitigate biotic and abiotic stresses limiting productivity. The presence of mannan chains within synthetic polyacrylic acid (PAA) enhanced the dynamics and selectivity of bacterial ingress in model microbial systems and soil microcosms. Pseudomonas fluorescens exhibiting high mannan binding adhesins showed higher ingress and localised microcolonies throughout the polymeric network. In contrast, ingress of Bacillus subtilis, lacking adhesins, was unaltered by mannan showing motility comparable to bulk liquids. Incubation within microcosms of an agricultural soil yielded hydrogel populations significantly increased from the corresponding soil. Bacterial diversity was markedly higher in mannan containing hydrogels compared to both control polymer and soil, indicating enhanced selectivity towards microbial families that contain plant beneficial species. Here we propose functional polymers applied to the potential root zone which can positively influence rhizobacteria colonization and potentially plant growth as a new approach to stress tolerance.

Highlights

Microbial interactions with polymeric hydrogels play a pivotal role in biomaterials, cell encapsulates and inoculants, while the interactions with biological hydrogels represent a key component of bacterial pathogenicity[1,2,3,4]
The hydrodynamics of microorganism swimming in both the liquid state and across hydrated surfaces has gained research prominence[6,13], motility at the microscale where only viscous drag is available for propulsion[14]
Incorporation of the mannan chains as a grafted copolymer yields a hydrogel suggesting a similar mesoporous microstructure to synthetic PAA26,28, the cell size of polyacrylic acid (PAA)-manngraft was on average ~50% smaller (Fig. 1B,C)

Summary

Introduction

Microbial interactions with polymeric hydrogels play a pivotal role in biomaterials, cell encapsulates and inoculants, while the interactions with biological hydrogels represent a key component of bacterial pathogenicity[1,2,3,4]. Mannan grafting significantly decreases the rigidity of the gel network as seen by the yield stress at comparable degrees of swelling (Q) as well as reducing the corresponding storage (G’) and viscous (G”) moduli, reflecting the reduced crosslink density between PAA chains, both of which have implications for overall bacterial population dynamics[16] (Supplementary Fig. 2).

Results

Conclusion