Effects of Facilitated Bacterial Dispersal on the Degradation and Emission of a Desorbing Contaminant.

The quantitative relationship between a compound's availability for biological removal and ecotoxicity is a key issue for retrospective risk assessment and remediation approaches. Here, we investigated the impact of facilitated bacterial dispersal at a model soil-atmosphere interface on the release, degradation, and outgassing of a semivolatile contaminant. We designed a laboratory microcosm with passive dosing of phenanthrene (PHE) to a model soil-atmosphere interface (agar surface) in the presence and absence of glass fibers known to facilitate the dispersal of PHE-degrading Pseudomonas fluorescens LP6a. We observed that glass fibers (used as a model to mimic a fungal hyphal network) resulted in (i) increased bacterial surface coverage, (ii) effective degradation of matrix-bound PHE, and (iii) substantially reduced PHE emission to locations beyond the contamination zone even at low bacterial surface coverage. Our data suggest that bacterial dispersal networks such as mycelia promote the optimized spatial arrangement of microbial populations to allow for effective contaminant degradation and reduction of potential hazard to organisms beyond a contaminated zone.

Effects of predation and dispersal on bacterial abundance and contaminant biodegradation.

Research into the biodegradation of soil contaminants has rarely addressed the consequences of predator-prey interactions. Here, we investigated the joint effect of predation and dispersal networks on contaminant degradation by linking spatial abundances of degrader (Pseudomonas fluorescens LP6a) and predator (Bdellovibrio bacteriovorus) bacteria to the degradation of the major soil contaminant phenanthrene (PHE). We used a laboratory microcosm with a PHE passive dosing system and a glass fiber network to facilitate bacterial dispersal. Different predator-to-prey ratios and spatial arrangements of prey and predator inoculation were used to study predation pressure effects on PHE degradation. We observed that predation resulted in (i) enhanced PHE-degradation at low predator counts (PC) compared to controls lacking predation, (ii) reduced PHE-degradation at elevated PC relative to low PC, and (iii) significant effects of the spatial arrangement of prey and predator inoculation on PHE degradation. Our data suggest that predation facilitated by dispersal networks (such as fungal mycelia) may support the build-up of an effective bacterial biomass and, hence, contaminant biodegradation in heterogeneous systems such as soil.

Catch me if you can: dispersal and foraging of Bdellovibrio bacteriovorus 109J along mycelia.

To cope with heterogeneous environments and resource distributions, filamentous fungi have evolved a spatially extensive growth enabling their hyphae to penetrate air-water interfaces and pass through air-filled pores. Such mycelia are also known to act as dispersal networks for the mobilisation of bacteria ('fungal highways') and connection of microbial microhabitats. Hitherto, however, nothing is known about the effect of mycelia-based dispersal on interactions between bacterial predators and their prey and concomitant effects on biomass formation. We here hypothesise that mycelia enable the contact between predators and their prey and shape a prey's population. We investigated the impact of predation by Bdellovibrio bacteriovorus 109J on the growth of its potential prey Pseudomonas fluorescens LP6a in the presence of mycelia. Our data give evidence that hyphae increase the accessibility of the prey to B. bacteriovorus 109J and, hence, allow for efficient foraging and shaping of prey populations not seen in the absence of mycelia. To test our hypothesis tailored microbial landscapes were used for better reduction of emerging properties in complex systems. Our data suggest that mycelia have substantial influence on prey-predator relationship and hereby may promote the structure of prey and predator populations and, hence, may be a determinant for biomass formation in heterogeneous environments.