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Novel assay to assess permissiveness of a soil microbial community toward receipt of mobile genetic elements.

ABSTRACT: There is a wealth of evidence indicating that mobile genetic elements can spread in natural microbial communities. However, little is known regarding the fraction of the community that actually engages in this behavior. Here we report on a new approach to quantify the fraction of a bacterial community that is able to receive and maintain an exogenous conjugal plasmid termed community permissiveness. Conjugal transfer of a broad-host-range plasmid labeled with a zygotically inducible green fluorescent protein (RP4::gfp) from a donor strain (Pseudomonas putida) to a soil bacterial suspension was examined. The mixture of cells was incubated on membrane filters supported by different solid media. Plasmid transfer was scored by in situ visualization of green fluorescent transconjugant microcolonies, and host range was determined by traditional plating or microcolony isolation by using a micromanipulator. Among the conditions tested, the highest plasmid transfer incidence (approximately 1 transfer per 10(4) soil bacteria) was measured after 48 h of incubation on either a 10% soil extract or a 10-fold diluted R2A medium. Stereomicroscopy combined with image analysis allowed easy examination and enumeration of green fluorescent microcolonies. In all experiments, however, stereomicroscopy consistently underestimated the number of conjugation events (approximately 10-fold) in comparison to confocal laser scanning microscopy. The plasmid host range was broad and included bacteria belonging to the Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria classes of proteobacteria. The isolation of transconjugant microcolonies by micromanipulation greatly extended the estimated plasmid host range among soil bacteria. The new approach can be applied to examine the permissiveness of various communities toward receipt of different mobile elements.

SUBMITTER: Musovic S

PROVIDER: S-EPMC2901734 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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Novel assay to assess permissiveness of a soil microbial community toward receipt of mobile genetic elements.

Musovic Sanin S Dechesne Arnaud A Sørensen Jan J Smets Barth F BF

Applied and environmental microbiology 20100528 14

There is a wealth of evidence indicating that mobile genetic elements can spread in natural microbial communities. However, little is known regarding the fraction of the community that actually engages in this behavior. Here we report on a new approach to quantify the fraction of a bacterial community that is able to receive and maintain an exogenous conjugal plasmid termed community permissiveness. Conjugal transfer of a broad-host-range plasmid labeled with a zygotically inducible green fluore ...[more]

PMID: 20511430

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Project description:Bacteriophages ("phages") are hypothesized to be key drivers of bacterial population dynamics, driving microbial community composition, but empirical support for this is mixed. One reason why phages may have a less-than-expected impact on community composition is that many different phages and other mobile genetic elements (MGEs) interact with each bacterium. For instance, the same phage may have higher or lower costs to different bacterial strains or species. Assuming that resistance or susceptibility to MGE infection is not consistent across all MGEs, a simple prediction is that the net effect of MGEs on each bacterial taxon may converge with an increasing number of interactions with different MGEs. We formalized this prediction using in silico population dynamics simulations and then carried out experiments using three bacterial species, one generalist conjugative plasmid, and three species-specific phages. While the presence of only phages or only the plasmid altered community structure, these differential effects on community structure canceled out when both were together. The effects of MGEs were largely indirect and could not be explained by simple pairwise bipartite interactions (i.e., between each MGE and each bacterial species). Our results suggest that the effects of MGEs may be overestimated by studies that focus on a single MGE and not on interactions among multiple MGEs. IMPORTANCE While bacteriophages ("phages") are often cited as some of the key drivers of microbial diversity, evidence for this is greatly mixed. We demonstrate, in silico and experimentally, that the impact of phages, an example of a mobile genetic element (MGE), on community structure can diminish with increasing MGE diversity. This is because MGEs can have diverse effects on host fitness, and therefore as diversity increases, their individual effects cancel out, returning communities back to an MGE-free state. In addition, interactions in mixed-species and MGE communities could not be predicted from simple pairwise interactions, highlighting the difficulty in generalizing a MGE's effect from pairwise studies.

Dataset Information

Novel assay to assess permissiveness of a soil microbial community toward receipt of mobile genetic elements.

Publications

Novel assay to assess permissiveness of a soil microbial community toward receipt of mobile genetic elements.

Similar Datasets

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